Palo Alto, California

Palo Alto ( -LSB- ˌpæloʊ_ˈæltoʊ -RSB- ; -LSB- ˈpalo ˈalto -RSB- ; from palo , literally `` stick '' , colloquially `` tree '' , and alto `` tall '' ; meaning : `` tall tree '' ) is a charter city located in the northwest corner of Santa Clara County , California , in the San Francisco Bay Area of the United States . The city shares its borders with East Palo Alto , Mountain View , Los Altos , Los Altos Hills , Stanford , Portola Valley , and Menlo Park . It is named after a coast redwood tree called El Palo Alto .   Palo Alto was established by Leland Stanford Sr. when he founded Stanford University , following the death of his son , Leland Stanford Jr. . The city includes portions of Stanford and is headquarters to a number of high-technology companies , including Hewlett-Packard ( HP ) , Space Systems/Loral , VMware , Tesla Motors , Ford Research and Innovation Center , PARC , IDEO , Skype , Palantir Technologies , and Houzz . It has also served as an incubator to several other high-technology companies such as Google , Facebook , Logitech , Intuit , Pinterest , and PayPal .   As of the 2010 census , the city 's total resident population is 64,403 . Palo Alto is one of the most expensive cities in the United States and its residents are amongst the highest educated in the country .


Pandemic

A pandemic ( from Greek πᾶν pan `` all '' and δῆμος demos `` people '' ) is an epidemic of infectious disease that has spread through human populations across a large region ; for instance multiple continents , or even worldwide . A widespread endemic disease that is stable in terms of how many people are getting sick from it is not a pandemic . Further , flu pandemics generally exclude recurrences of seasonal flu . Throughout history , there have been a number of pandemics , such as smallpox and tuberculosis . One of the most devastating pandemics was the Black Death , killing over 75 million people in 1350 . The most recent pandemics include the HIV pandemic as well as the 1918 and 2009 H1N1 pandemics .


Parinacota (volcano)

Parinacota ( in Hispanicized spelling ) , Parina Quta or Parinaquta is a dormant stratovolcano on the border of Chile and Bolivia . Together with Pomerape it forms the Nevados de Payachata volcanic chain . Part of the Central Volcanic Zone of the Andes , its summit reaches an elevation of 6380 m above sea level . The symmetrical cone is capped off by a summit crater with widths of 1 km or 500 m. Farther down on the southern slopes lie three parasitic centres known as the Ajata cones . These cones have generated lava flows . The volcano overlies a platform formed by lava domes and andesitic lava flows .   The volcano started growing during the Pleistocene and formed a large cone . At some point between the Pleistocene and the Holocene , the western flank of the volcano collapsed , generating a giant landslide that spread west and formed a large , hummocky landslide deposit . The avalanche crossed and dammed a previously existing drainage , impounding or enlarging Lake Chungará ; numerous other lakes now forming the headwaters of the Rio Lauca sprung up within the deposit . Volcanic activity rebuilt the cone after the collapse , cancelling out the collapse scar .   Parinacota had numerous effusive and explosive eruptions during the Holocene , the latest about 200 years ago . While there are no recorded eruptions , legends of the local Aymara people imply that they may have witnessed one eruption .   Renewed activity at Parinacota is possible in the future , although the relatively low population density in the region acts to limit the amount of damage that could occur . Some towns and a regional highway between Bolivia and Chile are potentially exposed to the effects of a new eruption .


Paris

Paris ( French pronunciation : -LSB- pɑʁi -RSB- , -LSB- paʁi -RSB- ) is the capital and most populous city of France . It has an area of 105 km2 and a population of 2,229,621 in 2013 within its administrative limits . The city is both a commune and department and forms the centre and headquarters of the Île-de-France , or Paris Region , which has an area of 12,012 km2 and a population in 2016 of 12,142,802 , comprising roughly 18 percent of the population of France . By the 17th century , Paris was one of Europe 's major centres of finance , commerce , fashion , science , and the arts , and it retains that position still today . The Paris Region had a GDP of $ 624 billion ( US $ 687 billion ) in 2012 , accounting for 30.0 percent of the GDP of France and ranking it as one of the wealthiest regions in Europe .   The City of Paris is but the core of a built-up area that extends well beyond its administrative limits . Commonly referred to as the agglomération Parisienne , and statistically as a unité urbaine ( a measure of urban area ) , the agglomeration has a 2013 population of 10,601,122 , which makes it the largest in the European Union . City-influenced commuter activity reaches well beyond even this in a statistical aire urbaine de Paris ( a measure of metropolitan area ) , that had a 2013 population of 12,405,426 , a number one-fifth the population of France , and one that makes it , after London , the second largest metropolitan area in the European Union . Although joined in a single urban tissue , Paris ' lack of administrative and economic cohesion with its suburbs has been a longstanding problem , but a 2016 ` Metropole of Grand Paris ' economic and environmental initiative covering an 814 km2 area and a population of 7 million , exists since 2016 .   The city is also a major rail , highway , and air-transport hub served by two international airports : Paris-Charles de Gaulle ( the second busiest airport in Europe after London Heathrow Airport with 63.8 million passengers in 2014 ) and Paris-Orly . Opened in 1900 , the city 's subway system , the Paris Métro , serves 5.23 million passengers daily . It is the second busiest metro system in Europe after Moscow Metro . Notably , Paris Gare du Nord is the busiest railway station in the world outside of Japan , with 262 millions passengers in 2015 .   Paris has many important cultural institutions : its Louvre museum is the most visited in the world ; its Musée d'Orsay is noted for its collection of French Impressionist art , and its Pompidou-center Musée National d'Art Moderne has the largest collection of modern and contemporary art in Europe . The central area of the city along the Seine River is classified as a UNESCO Heritage Site and includes many notable monuments , including Notre Dame Cathedral , the Sainte-Chapelle , the former Universal Exposition Grand Palais , Petit Palais and Eiffel Tower , and the Basilica of Sacré-Cœur in Montmartre . In 2015 , Paris received 22.2 million visitors , making it one of the world 's top tourist destinations .   The association football club Paris Saint-Germain and the rugby union club Stade Français are based in Paris . The 80,000-seat Stade de France , built for the 1998 FIFA World Cup , is located just north of Paris in the neighbouring commune of Saint-Denis . Paris hosts the annual French Open Grand Slam tennis tournament on the red clay of Roland Garros . Paris hosted the 1900 and 1924 Summer Olympics and is bidding to host the 2024 Summer Olympics . The 1938 and 1998 FIFA World Cups , the 2007 Rugby World Cup , and the 1960 , 1984 , and 2016 UEFA European Championships were also held in the city , and every July , the Tour de France bicycle race finishes in the city .


Paris Agreement

The Paris Agreement ( Accord de Paris ) is an agreement within the United Nations Framework Convention on Climate Change ( UNFCCC ) dealing with greenhouse gas emissions mitigation , adaptation and finance starting in the year 2020 . The language of the agreement was negotiated by representatives of 195 countries at the 21st Conference of the Parties of the UNFCCC in Paris and adopted by consensus on 12 December 2015 . It was opened for signature on 22 April 2016 ( Earth Day ) at a ceremony in New York . As of May 2017 , 195 UNFCCC members have signed the treaty , 147 of which have ratified it . After several European Union states ratified the agreement in October 2016 , there were enough countries that had ratified the agreement that produce enough of the world 's greenhouse gases for the agreement to enter into force . The agreement went into effect on 4 November 2016 .   The head of the Paris Conference , France 's foreign minister Laurent Fabius , said this `` ambitious and balanced '' plan is a `` historic turning point '' in the goal of reducing global warming .   One year on , the ratification of the Paris Agreement was celebrated by the Mayor of Paris Anne Hidalgo by illuminating the Eiffel Tower and the Arc de Triomphe , Paris ' most iconic monuments , in green .


Particulates

Atmospheric particulate matter -- also known as particulate matter ( PM ) or particulates -- are microscopic solid or liquid matter suspended in the Earth 's atmosphere . The term aerosol commonly refers to the particulate/air mixture , as opposed to the particulate matter alone . Sources of particulate matter can be man-made or natural . They have impacts on climate and precipitation that adversely affect human health .   Subtypes of atmospheric particulate matter include suspended particulate matter ( SPM ) , thoracic and respirable particles , inhalable coarse particles , which are -LSB- coarse -RSB- particles with a diameter between 2.5 and 10 micrometers ( μm ) ( PM10 ) , fine particles with a diameter of 2.5 μm or less ( PM2 .5 ) , ultrafine particles , and soot   The IARC and WHO designate airborne particulates a Group 1 carcinogen . Particulates are the deadliest form of air pollution due to their ability to penetrate deep into the lungs and blood streams unfiltered , causing permanent DNA mutations , heart attacks , and premature death . In 2013 , a study involving 312,944 people in nine European countries revealed that there was no safe level of particulates and that for every increase of 10 μg / m3 in PM10 , the lung cancer rate rose 22 % . The smaller PM2 .5 were particularly deadly , with a 36 % increase in lung cancer per 10 μg / m3 as it can penetrate deeper into the lungs .


Passive solar building design

In passive solar building design , windows , walls , and floors are made to collect , store , and distribute solar energy in the form of heat in the winter and reject solar heat in the summer . This is called passive solar design because , unlike active solar heating systems , it does not involve the use of mechanical and electrical devices .   The key to design a passive solar building is to best take advantage of the local climate performing an accurate site analysis . Elements to be considered include window placement and size , and glazing type , thermal insulation , thermal mass , and shading . Passive solar design techniques can be applied most easily to new buildings , but existing buildings can be adapted or `` retrofitted '' .


Past sea level

Global or eustatic sea level has fluctuated significantly over the Earth 's history . The main factors affecting sea level are the amount and volume of available water and the shape and volume of the ocean basins . The primary influences on water volume are the temperature of the seawater , which affects density , and the amounts of water retained in other reservoirs like rivers , aquifers , lakes , glaciers , polar ice caps and sea ice . Over geological timescales , changes in the shape of the oceanic basins and in land/sea distribution affect sea level . In addition to eustatic changes , local changes in sea level are caused by tectonic uplift and subsidence .   Over geologic time sea level has fluctuated by hundreds of meters . Today 's interglacial level is near historic highs and is 130 meters above the low level reached during the Last Glacial Maximum 19,000 -- 20,000 years ago .   Observational and modeling studies of mass loss from glaciers and ice caps indicate a contribution to sea-level rise of 0.2 to 0.4 mm/yr averaged over the 20th century . Over this last million years , whereas it was higher most of the time before then , sea level was lower than today .


Patrick Michaels

Patrick J. ( `` Pat '' ) Michaels ( born February 15 , 1950 ) is an American climatologist . Michaels is a senior fellow in environmental studies at the Cato Institute . Until 2007 he was research professor of environmental sciences at the University of Virginia , where he had worked from 1980 .   A self-described skeptic on the issue of global warming , he is a past president of the American Association of State Climatologists . He has written a number of books and papers on climate change , including Sound and Fury : The Science and Politics of Global Warming ( 1992 ) , The Satanic Gases ( 2000 ) , and Meltdown : The Predictable Distortion of Global Warming by Scientists , Politicians , and the Media ( 2004 ) . He 's also the co-author of Climate of Extremes : Global Warming Science They Do n't Want You to Know ( 2009 ) . Michaels ' viewpoint , as argued in a 2002 article in the journal Climate Research , is that the planet will see `` a warming range of 1.3 -- 3.0 ° C , with a central value of 1.9 ° C '' for the 1990 to 2100 period ( an analysis far smaller than the IPCC 's average predictions ) .


Paul Samuelson

Paul Anthony Samuelson ( May 15 , 1915 -- December 13 , 2009 ) was an American economist and the first American to win the Nobel Memorial Prize in Economic Sciences . The Swedish Royal Academies stated , when awarding the prize in 1970 , that he `` has done more than any other contemporary economist to raise the level of scientific analysis in economic theory '' . Economic historian Randall E. Parker calls him the `` Father of Modern Economics '' , and The New York Times considered him to be the `` foremost academic economist of the 20th century '' .   Samuelson was likely the most influential economist of the later 20th century . In 1996 , when he was awarded the National Medal of Science , considered America 's top science honor , President Bill Clinton commended Samuelson for his `` fundamental contributions to economic science '' for over 60 years . Samuelson considered Mathematics to be the natural language for economists and contributed significantly to the mathematical foundations of economics with his book Foundations of Economic Analysis . He was author of the best-selling economics textbook of all time : Economics : An Introductory Analysis , first published in 1948 . It was the second American textbook to explain the principles of Keynesian economics and how to think about economics , and the first one to be successful , and is now in its 19th edition , having sold nearly 4 million copies in 40 languages , including Russian , French , Greek , Slovak , Chinese , Portuguese , German , Spanish , Polish , Japanese , Czech , Vietnamese , Hungarian , Indonesian , Swedish , Croatian , Dutch , Turkish , Hebrew , Italian , and Arabic . James Poterba , former head of MIT 's Department of Economics , noted that by his book , Samuelson `` leaves an immense legacy , as a researcher and a teacher , as one of the giants on whose shoulders every contemporary economist stands '' .   He entered the University of Chicago at age 16 , during the depths of the Great Depression , and received his PhD in economics from Harvard . After graduating , he became an assistant professor of economics at Massachusetts Institute of Technology ( MIT ) when he was 25 years of age and a full professor at age 32 . In 1966 , he was named Institute Professor , MIT 's highest faculty honor . He spent his career at MIT where he was instrumental in turning its Department of Economics into a world-renowned institution by attracting other noted economists to join the faculty , including Robert M. Solow , Franco Modigliani , Robert C. Merton , Joseph E. Stiglitz , and Paul Krugman , all of whom went on to win Nobel Prizes .   He served as an advisor to Presidents John F. Kennedy and Lyndon B. Johnson , and was a consultant to the United States Treasury , the Bureau of the Budget and the President 's Council of Economic Advisers . Samuelson wrote a weekly column for Newsweek magazine along with Chicago School economist Milton Friedman , where they represented opposing sides : Samuelson , as a self described `` Cafeteria Keynesian '' , took the Keynesian perspective but adapted it accepting what he felt was good . By contrast Friedman represented the monetarist perspective . Samuelson died on December 13 , 2009 , at the age of 94 .


Pavel Banya

Pavel Banya is a small town in Stara Zagora Province , South-central Bulgaria , located between the towns of Kalofer and Kazanlak . It is the administrative centre of the homonymous Pavel Banya Municipality . As of December 2009 , the town has a population of 2,918 inhabitants . The place is famous for its mineral springs .


Peak oil

Peak oil , an event based on M. King Hubbert 's theory , is the point in time when the maximum rate of extraction of petroleum is reached , after which it is expected to enter terminal decline . Peak oil theory is based on the observed rise , peak , fall , and depletion of aggregate production rate in oil fields over time . It is often confused with oil depletion ; however , peak oil is the point of maximum production , while depletion refers to a period of falling reserves and supply .   Some observers , such as petroleum industry experts Kenneth S. Deffeyes and Matthew Simmons , predict negative global economy implications following a post-peak production decline and subsequent oil price increase because of the high dependence of most modern industrial transport , agricultural , and industrial systems on the low cost and high availability of oil . Predictions vary greatly as to what exactly these negative effects would be .   Oil production forecasts on which predictions of peak oil are based are often made within a range which includes optimistic ( higher production ) and pessimistic ( lower production ) scenarios . Optimistic estimations of peak production forecast the global decline will begin after 2020 , and assume major investments in alternatives will occur before a crisis , without requiring major changes in the lifestyle of heavily oil-consuming nations . Pessimistic predictions of future oil production made after 2007 stated either that the peak had already occurred , that oil production was on the cusp of the peak , or that it would occur shortly .   Hubbert 's original prediction that US peak oil would be in about 1970 seemed accurate for a time , as US average annual production peaked in 1970 at 9.6 million barrels per day . However , the successful application of massive hydraulic fracturing to additional tight reservoirs caused US production to rebound , challenging the inevitability of post-peak decline for the US oil production . In addition , Hubbert 's original predictions for world peak oil production proved premature .


Pearson correlation coefficient

In statistics , the Pearson correlation coefficient ( PCC , pronounced -LSB- ˈpɪərsən -RSB- ) , also referred to as the Pearson 's r , Pearson product-moment correlation coefficient ( PPMCC ) or bivariate correlation , is a measure of the linear correlation between two variables X and Y . It has a value between +1 and − 1 , where 1 is total positive linear correlation , 0 is no linear correlation , and − 1 is total negative linear correlation . It is widely used in the sciences . It was developed by Karl Pearson from a related idea introduced by Francis Galton in the 1880s .


Peat

Peat ( -LSB- piːt -RSB- ) , also called turf ( -LSB- tɜːrf -RSB- ) , is an accumulation of partially decayed vegetation or organic matter that is unique to natural areas called peatlands , bogs , mires , moors , or muskegs . The peatland ecosystem is the most efficient carbon sink on the planet because peatland plants capture the CO2 which is naturally released from the peat ; this maintains an equilibrium . In natural peatlands , the `` annual rate of biomass production is greater than the rate of decomposition '' , but it takes `` thousands of years for peatlands to develop the deposits of , which is the average depth of the boreal -LSB- northern -RSB- peatlands '' . Sphagnum moss ( peat moss ) is one of the most common components in peat , although many other plants can contribute . Soils that contain mostly peat are known as histosols . Peat forms in wetland conditions , where flooding obstructs flows of oxygen from the atmosphere . This slows rates of decomposition .   Peatlands , particularly bogs , are the most important source of peat . That said , other less common wetland types , including fens , pocosins , and peat swamp forests , also deposit peat . Landscapes covered in peat are home to specific kinds of plants including Sphagnum moss , ericaceous shrubs , and sedges ( see bog for more information on this aspect of peat ) . Because organic matter accumulates over thousands of years , peat deposits also provide records of past vegetation and climates stored in plant remains like pollen . This allows humans to reconstruct past environments and study changes in human land use .   Peat is harvested as an important source of fuel in certain parts of the world . By volume , there are about 4 e12m3 of peat in the world , covering a total of around 2 % of the global land area ( about 3 e6km2 ) , containing about 8 billion terajoules of energy . Over time , the formation of peat is often the first step in the geological formation of other fossil fuels such as coal , particularly low-grade coal such as lignite .


Peer review

Peer review is the evaluation of work by one or more people of similar competence to the producers of the work ( peers ) . It constitutes a form of self-regulation by qualified members of a profession within the relevant field . Peer review methods are employed to maintain standards of quality , improve performance , and provide credibility . In academia , scholarly peer review is often used to determine an academic paper 's suitability for publication . Peer review can be categorized by the type of activity and by the field or profession in which the activity occurs , e.g. , medical peer review .


Percentage

In mathematics , a percentage is a number or ratio expressed as a fraction of 100 . It is often denoted using the percent sign , '' % '' , or the abbreviations `` pct . '' , `` pct '' ; sometimes the abbreviation `` pc '' is also used . A percentage is a dimensionless number ( pure number ) .


Perceptual control theory

Perceptual control theory ( PCT ) is a model of behavior based on the principles of negative feedback , but differing in important respects from engineering control theory . Results of PCT experiments have demonstrated that an organism controls neither its own behavior , nor external environmental variables , but rather its own perceptions of those variables . Actions are not controlled , they are varied so as to cancel the effects that unpredictable environmental disturbances would otherwise have on controlled perceptions . According to the standard catch-phrase of the field , `` behavior is the control of perception . '' PCT demonstrates circular causation in a negative feedback loop closed through the environment . This fundamentally contradicts the classical notion of linear causation of behavior by stimuli , in which environmental stimuli are thought to cause behavioral responses , mediated ( according to cognitive psychology ) by intervening cognitive processes .   Numerous computer simulations of specific behavioral situations demonstrate its efficacy , with extremely high correlations to observational data ( 0.95 or better ) , which are vanishingly rare in the so-called ` soft ' sciences . While the adoption of PCT in the scientific community has not been widespread , it has been applied not only in experimental psychology and neuroscience , but also in sociology , linguistics , and a number of other fields , and has led to a method of psychotherapy called the method of levels .


Perennial plant

A perennial plant or simply perennial is a plant that lives for more than two years . The term ( per - #Prefix + - ennial #Suffix , `` through the years '' ) is often used to differentiate a plant from shorter-lived annuals and biennials . The term is also widely used to distinguish plants with little or no woody growth from trees and shrubs , which are also technically perennials .   Perennials , especially small flowering plants , that grow and bloom over the spring and summer , die back every autumn and winter , and then return in the spring from their rootstock , are known as herbaceous perennials or Herbaceous plants . However , depending on the rigors of local climate , a plant that is a perennial in its native habitat , or in a milder garden , may be treated by a gardener as an annual and planted out every year , from seed , from cuttings or from divisions . Tomato vines , for example , live several years in their natural tropical/subtropical habitat but are grown as annuals in temperate regions because they do n't survive the winter .   There is also a class of evergreen , or non-herbaceous , perennials , including plants like Bergenia which retain a mantle of leaves throughout the year . An intermediate class of plants is known as subshrubs , which retain a vestigial woody structure in winter , e.g. Penstemon . The local climate may dictate whether plants are treated as shrubs or perennials . For instance , many varieties of Fuchsia are shrubs in warm regions , but in colder temperate climates may be cut to the ground every year as a result of winter frosts .   The symbol for a perennial plant , based on Species Plantarum by Linnaeus , is , which is also the astronomical symbol for the planet Jupiter .


Permafrost

In geology , permafrost is ground , including rock or ( cryotic ) soil , at or below the freezing point of water 0 C for two or more years . Most permafrost is located in high latitudes ( in and around the Arctic and Antarctic regions ) , but alpine permafrost may exist at high altitudes in much lower latitudes . Ground ice is not always present , as may be in the case of nonporous bedrock , but it frequently occurs and it may be in amounts exceeding the potential hydraulic saturation of the ground material . Permafrost accounts for 0.022 % of total water on earth and exists in 24 % of exposed land in the Northern Hemisphere . It also occurs subsea on the continental shelves of the continents surrounding the Arctic Ocean , portions of which were exposed during the last glacial period , with global weather implications .   A global temperature rise of 1.5 C-change above current levels would be enough to start the thawing of permafrost in Siberia , according to one group of scientists .


Permafrost carbon cycle

The Permafrost Carbon Cycle is a sub-cycle of the larger global carbon cycle . Permafrost is defined as subsurface material that remains below 0o C ( 32o F ) for at least two consecutive years . Because permafrost soils remain frozen for long periods of time , they store large amounts of carbon and other nutrients within their frozen framework during that time . Permafrost represents a large carbon reservoir that is seldom considered when determining global terrestrial carbon reservoirs . Recent and ongoing scientific research however , is changing this view .   The permafrost carbon cycle ( Arctic Carbon Cycle ) deals with the transfer of carbon from permafrost soils to terrestrial vegetation and microbes , to the atmosphere , back to vegetation , and finally back to permafrost soils through burial and sedimentation due to cryogenic processes . Some of this carbon is transferred to the ocean and other portions of the globe through the global carbon cycle . The cycle includes the exchange of carbon dioxide and methane between terrestrial components and the atmosphere , as well as the transfer of carbon between land and water as methane , dissolved organic carbon , dissolved inorganic carbon , particulate inorganic carbon and particulate organic carbon .


Permian

The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period million years ago ( Mya ) , to the beginning of the Triassic Period 252.2 Mya . It is the last period of the Paleozoic Era ; the following Triassic Period belongs to the Mesozoic Era . The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison , who named it after the city of Perm .   The Permian witnessed the diversification of the early amniotes into the ancestral groups of the mammals , turtles , lepidosaurs , and archosaurs . The world at the time was dominated by two continents known as Pangaea and Siberia , surrounded by a global ocean called Panthalassa . The Carboniferous rainforest collapse left behind vast regions of desert within the continental interior . Amniotes , who could better cope with these drier conditions , rose to dominance in place of their amphibian ancestors .   The Permian ( along with the Paleozoic ) ended with the Permian -- Triassic extinction event , the largest mass extinction in Earth 's history , in which nearly 90 % of marine species and 70 % of terrestrial species died out . It would take well into the Triassic for life to recover from this catastrophe . Recovery from the Permian-Triassic extinction event was protracted ; on land , ecosystems took 30 million years to recover .


Permian–Triassic extinction event

The Permian -- Triassic ( P -- Tr or P -- T ) extinction event , colloquially known as the Great Dying , the End-Permian Extinction or the Great Permian Extinction , occurred about 252 Ma ( million years ) ago , forming the boundary between the Permian and Triassic geologic periods , as well as the Paleozoic and Mesozoic eras . It is the Earth 's most severe known extinction event , with up to 96 % of all marine species and 70 % of terrestrial vertebrate species becoming extinct . It is the only known mass extinction of insects . Some 57 % of all families and 83 % of all genera became extinct . Because so much biodiversity was lost , the recovery of life on Earth took significantly longer than after any other extinction event , possibly up to 10 million years . Studies in Bear Lake County near the Idaho city of Paris showed a quick and dynamic rebound in a marine ecosystem , illustrating the remarkable resiliency of life .   There is evidence for one to three distinct pulses , or phases , of extinction . Suggested mechanisms for the latter include one or more large meteor impact events , massive volcanism such as that of the Siberian Traps , and the ensuing coal or gas fires and explosions , and a runaway greenhouse effect triggered by sudden release of methane from the sea floor due to methane clathrate dissociation or methane-producing microbes known as methanogens ; possible contributing gradual changes include sea-level change , increasing anoxia , increasing aridity , and a shift in ocean circulation driven by climate change .


Perth

Perth is the capital and largest city of the Australian state of Western Australia . It is the fourth-most populous city in Australia , with an estimated population of 2.06 million living in Greater Perth . Perth is part of the South West Land Division of Western Australia , with the majority of the metropolitan area located on the Swan Coastal Plain , a narrow strip between the Indian Ocean and the Darling Scarp . The first areas settled were on the Swan River , with the city 's central business district and port ( Fremantle ) both located on its shores .   Perth was founded by Captain James Stirling in 1829 as the administrative centre of the Swan River Colony . It gained city status ( currently vested in the smaller City of Perth ) in 1856 , and was promoted to the status of a Lord Mayorality in 1929 . The city is named after Perth , Scotland , due to the influence of Sir George Murray , Member of Parliament for Perthshire and Secretary of State for War and the Colonies . The city 's population increased substantially as a result of the Western Australian gold rushes in the late 19th century . During Australia 's involvement in World War II , Fremantle served as a base for submarines operating in the Pacific Theatre , and a US Navy Catalina flying boat fleet was based at Matilda Bay . An influx of immigrants after the war , predominantly from Britain , Greece , Italy and Yugoslavia , led to rapid population growth . This was followed by a surge in economic activity flowing from several mining booms in the late 20th and early 21st centuries that saw Perth become the regional headquarters for a number of large mining operations located around the state .   As part of Perth 's role as the capital of Western Australia , the state 's Parliament and Supreme Court are located within the city , as is Government House , the residence of the Governor of Western Australia . Perth came seventh in the Economist Intelligence Unit 's August 2016 list of the world 's most liveable cities , and was classified by the Globalization and World Cities Research Network in 2010 as a world city .   Perth is divided into 30 local government areas and 250 suburbs , stretching from Two Rocks in the north to Singleton in the south , and east inland to The Lake . Outside of the main CBD , important urban centres within Perth include Armadale , Fremantle , Joondalup , Midland , and Rockingham . Most of those were originally established as separate settlements , and retained a distinct identity after being subsumed into the wider metropolitan area . Mandurah , Western Australia 's second-largest city , has in recent years formed a conurbation with Perth along the coast , though for most purposes it is still considered a separate city .


Petroleum

Petroleum ( from petra #Greek : `` rock '' + oleum #Latin : `` oil '' . ) is a naturally occurring , yellow-to-black liquid found in geological formations beneath the Earth 's surface , which is commonly refined into various types of fuels . Components of petroleum are separated using a technique called fractional distillation .   It consists of hydrocarbons of various molecular weights and other organic compounds . The name petroleum covers both naturally occurring unprocessed crude oil and petroleum products that are made up of refined crude oil . A fossil fuel , petroleum is formed when large quantities of dead organisms , usually zooplankton and algae , are buried underneath sedimentary rock and subjected to both intense heat and pressure .   Petroleum has mostly been recovered by oil drilling ( natural petroleum springs are rare ) . Drilling is carried out after studies of structural geology ( at the reservoir scale ) , sedimentary basin analysis , and reservoir characterization ( mainly in terms of the porosity and permeability of geologic reservoir structures ) have been completed . It is refined and separated , most easily by distillation , into a large number of consumer products , from gasoline ( petrol ) and kerosene to asphalt and chemical reagents used to make plastics and pharmaceuticals . Petroleum is used in manufacturing a wide variety of materials , and it is estimated that the world consumes about 95 million barrels each day .   Concern over the depletion of the earth 's finite reserves of oil , and the effect this would have on a society dependent on it , is a concept known as peak oil . The use of fossil fuels , such as petroleum , will have a negative impact on Earth 's biosphere , damaging ecosystems through events such as oil spills and releasing a range of pollutants into the air including ground-level ozone and sulfur dioxide from sulfur impurities in fossil fuels . The burning of fossil fuels plays the major role in the current episode of global warming .


Phalodi

Phalodi is a city and a municipality in Jodhpur district in the Indian state of Rajasthan . It is the headquarters for Phalodi tehsil . Phalodi is also called the `` salt city '' due to the concentration of a large number of salt industries located in the area . Phalodi is in the buffer zone of Thar Desert and often subject to extreme temperature conditions due to arid climate . It holds the record for the highest verified temperature recorded in India at 52 degrees Celsius ( 123.8 ° F ) on 20 May 2016 .


Phanerozoic

The Phanerozoic Eon ( British English Phanærozoic ) is the current geologic eon in the geologic time scale , and the one during which abundant animal and plant life has existed . It covers million years to the present , and began with the Cambrian Period when diverse hard-shelled animals first appeared . Its name was derived from the Ancient Greek words φανερός ( phanerós ) and ζωή ( zōḗ ) , meaning visible life , since it was once believed that life began in the Cambrian , the first period of this eon . The time before the Phanerozoic , called the Precambrian supereon , is now divided into the Hadean , Archaean and Proterozoic eons .   The time span of the Phanerozoic starts with the rapid emergence of a number of animal phyla ; the evolution of those phyla into diverse forms ; the emergence and development of complex plants ; the evolution of fish ; the emergence of insects and tetrapods ; and the development of modern fauna . Land plant life appeared in the early Phanerozoic eon . During this time span , tectonic forces caused the continents to move and eventually collect into a single landmass known as Pangaea , which then separated into the current continental landmasses .


Phase-out of incandescent light bulbs

Governments around the world have passed measures to phase out incandescent light bulbs for general lighting in favor of more energy-efficient lighting alternatives . Phase-out regulations effectively ban the manufacture , importation or sale of incandescent light bulbs for general lighting . The regulations would allow sale of future versions of incandescent bulbs if they are sufficiently energy efficient .   Brazil and Venezuela started the controversial phase-out in 2005 , and the European Union , Switzerland , and Australia started to phase them out in 2009 . Likewise , other nations are implementing new energy standards or have scheduled phase-outs : Argentina , and Russia in 2012 , and the United States , Canada , Mexico , Malaysia and South Korea in 2014 .   Objections to replacement of incandescent lamps for general lighting mainly include the higher purchasing cost of alternative light bulbs . To mitigate the effects of these concerns , various programs have been put in place ranging from subsidies for lamps to improved standards for measurement of performance and for labelling products . Manufacturers develop fluorescent lamps with reduced mercury content compared to original designs , and recycling programs are intended to prevent mercury release . New lamp types offer improved starting characteristics , and dimmable types are available .


Phenology

Phenology is the study of periodic plant and animal life cycle events and how these are influenced by seasonal and interannual variations in climate , as well as habitat factors ( such as elevation ) . The word , coined by the Belgian botanist Charles Morren around 1849 , is derived from the Greek φαίνω ( phainō ) , `` to show , to bring to light , make to appear '' + λόγος ( logos ) , amongst others `` study , discourse , reasoning '' and indicates that phenology has been principally concerned with the dates of first occurrence of biological events in their annual cycle . Examples include the date of emergence of leaves and flowers , the first flight of butterflies and the first appearance of migratory birds , the date of leaf colouring and fall in deciduous trees , the dates of egg-laying of birds and amphibia , or the timing of the developmental cycles of temperate-zone honey bee colonies . In the scientific literature on ecology , the term is used more generally to indicate the time frame for any seasonal biological phenomena , including the dates of last appearance ( e.g. , the seasonal phenology of a species may be from April through September ) .   Because many such phenomena are very sensitive to small variations in climate , especially to temperature , phenological records can be a useful proxy for temperature in historical climatology , especially in the study of climate change and global warming . For example , viticultural records of grape harvests in Europe have been used to reconstruct a record of summer growing season temperatures going back more than 500 years .  In addition to providing a longer historical baseline than instrumental measurements , phenological observations provide high temporal resolution of ongoing changes related to global warming .


Phenotype

A phenotype is the composite of an organism 's observable characteristics or traits , such as its morphology , development , biochemical or physiological properties , behavior , and products of behavior ( such as a bird 's nest ) . A phenotype results from the expression of an organism 's genetic code , its genotype , as well as the influence of environmental factors and the interactions between the two . When two or more clearly different phenotypes exist in the same population of a species , the species is called polymorphic . A well-documented polymorphism is Labrador Retriever coloring ; while the coat color depends on many genes , it is clearly seen in the environment as yellow , black and brown .   This genotype-phenotype distinction was proposed by Wilhelm Johannsen in 1911 to make clear the difference between an organism 's heredity and what that heredity produces . The distinction is similar to that proposed by August Weismann , who distinguished between germ plasm ( heredity ) and somatic cells ( the body ) . The genotype-phenotype distinction should not be confused with Francis Crick 's central dogma of molecular biology , which is a statement about the directionality of molecular sequential information flowing from DNA to protein , and not the reverse .   Richard Dawkins in 1978 and then again in his 1982 book The Extended Phenotype suggested that bird nests and other built structures such as caddis fly larvae cases and beaver dams can be considered as `` extended phenotypes '' .


Phil Jones (climatologist)

Philip Douglas Jones ( born April 22 , 1952 ) retired from his positions as the Director of the Climatic Research Unit ( CRU ) and as a Professor in the School of Environmental Sciences at the University of East Anglia ( UEA ) at the end of 2016 . Jones was replaced as CRU director by Tim Osborn and has taken up a position as a Professorial Fellow at the UEA from January 2017 .   His research interests include instrumental climate change , palaeoclimatology , detection of climate change and the extension of riverflow records in the UK . He has also published papers on the temperature record of the past 1000 years .   He is known for maintaining a time series of the instrumental temperature record . This work was featured prominently in both the 2001 and 2007 IPCC reports , where he was a contributing author to Chapter 12 , Detection of Climate Change and Attribution of Causes , of the Third Assessment Report and a Coordinating Lead Author of Chapter 3 , Observations : Surface and Atmospheric Climate Change , of the AR4 .


Philadelphia

Philadelphia ( -LSB- ˌfɪləˈdɛlfi.ə -RSB- ) is the largest city in the Commonwealth of Pennsylvania and the sixth-most populous city in the United States , with an estimated population of 1,567,872 and more than 6 million in the seventh-largest metropolitan statistical area , . Philadelphia is the economic and cultural anchor of the Delaware Valleya region located in the Northeastern United States at the confluence of the Delaware and Schuylkill Rivers with 7.2 million people residing in the eighth-largest combined statistical area in the United States .   In 1682 , William Penn , an English Quaker , founded the city to serve as capital of the Pennsylvania Colony . Philadelphia played an instrumental role in the American Revolution as a meeting place for the Founding Fathers of the United States , who signed the Declaration of Independence in 1776 and the Constitution in 1787 . Several other key Philadelphia events during the Revolution include the First and Second Continental Congress , the preservation of the Liberty Bell , the Battle of Germantown , the Siege of Fort Mifflin , and the Philadelphia Convention . Philadelphia was one of the nation 's capitals in the Revolutionary War , and served as temporary U.S. capital while Washington , D.C. , was under construction . In the 19th century , Philadelphia became a major industrial center and railroad hub that grew from an influx of European immigrants . The majority of European immigrants have come from Ireland , Italy and Germany -- the three largest reported ancestry groups in the city . The city became a prime destination for African Americans during the Great Migration of the 20th century , as well as Puerto Ricans , surpassing two million occupants by 1950 .   The area 's many universities and colleges make Philadelphia a top international study destination , as the city has evolved into an educational and economic hub . With a gross domestic product of $ 388 billion , Philadelphia ranks ninth among world cities and fourth in the nation . Philadelphia is the center of economic activity in Pennsylvania and is home to seven Fortune 1000 companies . The Philadelphia skyline is growing , with a market of almost 81,900 commercial properties in 2016 including several nationally prominent skyscrapers . The city is known for its arts , culture , and rich history , attracting over 41 million domestic tourists alone in 2015 . Philadelphia has more outdoor sculptures and murals than any other American city . Fairmount Park , when combined with the adjacent Wissahickon Valley Park in the same watershed , is one of the largest contiguous urban park areas in the United States . The 67 National Historic Landmarks in the city helped account for the $ 10 billion generated by tourism . Philadelphia is the birthplace of the United States Marine Corps , and is also the home of many U.S. firsts , including the first library ( 1731 ) , first hospital ( 1751 ) and medical school ( 1765 ) , first Capital ( 1777 ) , first stock exchange ( 1790 ) , first zoo ( 1874 ) , and first business school ( 1881 ) . Philadelphia is the only World Heritage City in the United States .


Philippines

The Philippines ( -LSB- ˈfɪlᵻpiːnz -RSB- Pilipinas -LSB- ˌpɪlɪˈpinɐs -RSB- ) , officially the Republic of the Philippines ( -LSB- Republika ng Pilipinas , links = no -RSB- ) , is a sovereign island country in Southeast Asia situated in the western Pacific Ocean . It consists of about 7,641 islands that are categorized broadly under three main geographical divisions from north to south : Luzon , Visayas , and Mindanao . The capital city of the Philippines is Manila and the most populous city is Quezon City , both part of Metro Manila . Bounded by the South China Sea on the west , the Philippine Sea on the east and the Celebes Sea on the southwest , the Philippines shares maritime borders with Taiwan to the north , Vietnam to the west , Palau to the east and Malaysia and Indonesia to the south .   The Philippines ' location on the Pacific Ring of Fire and close to the equator makes the Philippines prone to earthquakes and typhoons , but also endows it with abundant natural resources and some of the world 's greatest biodiversity . The Philippines has an area of 300000 km2 , and a population of approximately 100 million . It is the eighth-most populated country in Asia and the 12th most populated country in the world . , approximately 10 million additional Filipinos lived overseas , comprising one of the world 's largest diasporas . Multiple ethnicities and cultures are found throughout the islands . In prehistoric times , Negritos were some of the archipelago 's earliest inhabitants . They were followed by successive waves of Austronesian peoples . Exchanges with Chinese , Malay , Indian , and Islamic nations occurred . Then , various competing maritime states were established under the rule of Datus , Rajahs , Sultans or Lakans .   The arrival of Ferdinand Magellan in Homonhon , Eastern Samar in 1521 marked the beginning of Hispanic colonization . In 1543 , Spanish explorer Ruy López de Villalobos named the archipelago Las Islas Filipinas in honor of Philip II of Spain . With the arrival of Miguel López de Legazpi from Mexico City , in 1565 , the first Hispanic settlement in the archipelago was established . The Philippines became part of the Spanish Empire for more than 300 years . This resulted in Roman Catholicism becoming the dominant religion . During this time , Manila became the western hub of the trans-Pacific trade connecting Asia with Acapulco in the Americas using Manila galleons .   As the 19th century gave way to the 20th , there followed in quick succession the Philippine Revolution , which spawned the short-lived First Philippine Republic , followed by the bloody Philippine -- American War of conquest by US military force . Aside from the period of Japanese occupation , the United States retained sovereignty over the islands until after World War II , when the Philippines was recognized as an independent nation . Since then , the Philippines has often had a tumultuous experience with democracy , which included the overthrow of a dictatorship by a non-violent revolution .   It is a founding member of the United Nations , World Trade Organization , Association of Southeast Asian Nations , the Asia-Pacific Economic Cooperation forum , and the East Asia Summit . It also hosts the headquarters of the Asian Development Bank . The Philippines is considered to be an emerging market and a newly industrialized country , which has an economy transitioning from being one based on agriculture to one based more on services and manufacturing . It is one of the only two predominantly Christian nations in Southeast Asia , the other being East Timor .


Philosophical skepticism

For a general discussion of skepticism , see Skepticism .  Philosophical skepticism ( UK spelling scepticism ; from Greek σκέψις skepsis '' , `` inquiry '' ) is both a philosophical school of thought and a method that questions the possibility of certainty in knowledge . It is generally agreed that knowledge requires justification . It is not enough to have a true belief : one must also have good reasons for that belief . Skeptics claim that it is not possible to have an adequate justification .   Skepticism is not a single position but covers a range of different positions . In the ancient world there were two main skeptical traditions . Academic skepticism took the dogmatic position that knowledge was not possible ; Pyrrhonian skeptics refused to take a dogmatic position on any issue -- including skepticism . Radical skepticism ends in the paradoxical claim that one can not know anything -- including that one can not know about knowing anything .   Skepticism can be classified according to its scope . Local skepticism involves being skeptical about particular areas of knowledge , e.g. moral skepticism , skepticism about the external world , or skepticism about other minds , whereas global skepticism is skeptical about the possibility of any knowledge at all .   Skepticism can also be classified according to its method . In the Western tradition there are two basic approaches to skepticism . Cartesian skepticism -- named somewhat misleadingly after René Descartes , who was not a skeptic but used some traditional skeptical arguments in his Meditations to help establish his rationalist approach to knowledge -- attempts to show that any proposed knowledge claim can be doubted . Agrippan skepticism focuses on the process of justification rather than the possibility of doubt . According to this view there are three ways in which one might attempt to justify a claim but none of them are adequate : one can keep on providing further justification but this leads to an infinite regress ; one can stop at a dogmatic assertion ; or one can argue in circular reasoning , never reaching a viable conclusion .   Philosophical skepticism is distinguished from methodological skepticism in that philosophical skepticism is an approach that questions the possibility of certainty in knowledge , whereas methodological skepticism is an approach that subjects all knowledge claims to scrutiny with the goal of sorting out true from false claims .


Philosophy of geography

Philosophy of geography is that subfield of philosophy which deals with epistemological , metaphysical , and axiological issues in geography , with geographic methodology in general , and with more broadly related issues such as the perception and representation of space and place .


Photosynthesis

Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that can later be released to fuel the organisms ' activities ( energy transformation ) . This chemical energy is stored in carbohydrate molecules , such as sugars , which are synthesized from carbon dioxide and water -- hence the name photosynthesis , from the Greek φῶς , phōs , `` light '' , and σύνθεσις , synthesis , `` putting together '' . In most cases , oxygen is also released as a waste product . Most plants , most algae , and cyanobacteria perform photosynthesis ; such organisms are called photoautotrophs . Photosynthesis is largely responsible for producing and maintaining the oxygen content of the Earth 's atmosphere , and supplies all of the organic compounds and most of the energy necessary for life on Earth .   Although photosynthesis is performed differently by different species , the process always begins when energy from light is absorbed by proteins called reaction centres that contain green chlorophyll pigments . In plants , these proteins are held inside organelles called chloroplasts , which are most abundant in leaf cells , while in bacteria they are embedded in the plasma membrane . In these light-dependent reactions , some energy is used to strip electrons from suitable substances , such as water , producing oxygen gas . The hydrogen freed by the splitting of water is used in the creation of two further compounds that act as an immediate energy storage means : reduced nicotinamide adenine dinucleotide phosphate ( NADPH ) and adenosine triphosphate ( ATP ) , the `` energy currency '' of cells .   In plants , algae and cyanobacteria , long-term energy storage in the form of sugars is produced by a subsequent sequence of reactions called the Calvin cycle ; some bacteria use different mechanisms , such as the reverse Krebs cycle , to achieve the same end . In the Calvin cycle , atmospheric carbon dioxide is incorporated into already existing organic carbon compounds , such as ribulose bisphosphate ( RuBP ) . Using the ATP and NADPH produced by the light-dependent reactions , the resulting compounds are then reduced and removed to form further carbohydrates , such as glucose .   The first photosynthetic organisms probably evolved early in the evolutionary history of life and most likely used reducing agents such as hydrogen or hydrogen sulfide , rather than water , as sources of electrons . Cyanobacteria appeared later ; the excess oxygen they produced contributed directly to the oxygenation of the Earth , which rendered the evolution of complex life possible . Today , the average rate of energy capture by photosynthesis globally is approximately 130 terawatts , which is about three times the current power consumption of human civilization .  Photosynthetic organisms also convert around 100 -- 115 thousand million metric tonnes of carbon into biomass per year .


Photovoltaics

Photovoltaics ( PV ) is a term which covers the conversion of light into electricity using semiconducting materials that exhibit the photovoltaic effect , a phenomenon studied in physics , photochemistry , and electrochemistry .   A typical photovoltaic system employs solar panels , each comprising a number of solar cells , which generate electrical power . PV installations may be ground-mounted , rooftop mounted or wall mounted . The mount may be fixed , or use a solar tracker to follow the sun across the sky .   Solar PV has specific advantages as an energy source : its operation generates no pollution and no greenhouse gas emissions once installed , it shows simple scalability in respect of power needs and silicon has large availability in the Earth 's crust .   PV systems have the major disadvantage that the power output is dependent on direct sunlight , so about 10-25 % is lost if a tracking system is not used , since the cell will not be directly facing the sun at all times . Dust , clouds , and other things in the atmosphere also diminish the power output . Another main issue is the concentration of the production in the hours corresponding to main insolation , which do n't usually match the peaks in demand in human activity cycles . Unless current societal patterns of consumption and electrical networks mutually adjust to this scenario , electricity still needs to be made up by other power sources , usually hydrocarbon .   Photovoltaic systems have long been used in specialized applications , and standalone and grid-connected PV systems have been in use since the 1990s . They were first mass-produced in 2000 , when German environmentalists and the Eurosolar organization got government funding for a ten thousand roof program .   Advances in technology and increased manufacturing scale have in any case reduced the cost , increased the reliability , and increased the efficiency of photovoltaic installations .  Net metering and financial incentives , such as preferential feed-in tariffs for solar-generated electricity , have supported solar PV installations in many countries . More than 100 countries now use solar PV .   After hydro and wind powers , PV is the third renewable energy source in terms of globally capacity . In 2014 , worldwide installed PV capacity increased to 177 gigawatts ( GW ) , which is two percent of global electricity demand . China , followed by Japan and the United States , is the fastest growing market , while Germany remains the world 's largest producer , with solar PV providing seven percent of annual domestic electricity consumption . With current technology ( as of 2013 ) , photovoltaics recoups the energy needed to manufacture them in 1.5 years in Southern Europe and 2.5 years in Northern Europe .


Physical impacts of climate change

This article is about the physical impacts of climate change . For some of these physical impacts , their effect on social and economic systems are also described .   This article refers to reports produced by the IPCC . In their usage , `` climate change '' refers to a change in the state of the climate that can be identified by changes in the mean and/or variability of its properties , and that persists for extended periods , typically decades or longer ( IPCC , 2007d :30 ) . The climate change referred to may be due to natural causes and/or the result of human activity .


Physics

Physics ( from -LSB- φυσική , phusikḗ ( epistḗmē ) , knowledge of nature -RSB- , from φύσις phúsis `` nature '' ) is the natural science that involves the study of matter and its motion and behavior through space and time , along with related concepts such as energy and force . One of the most fundamental scientific disciplines , the main goal of physics is to understand how the universe behaves .   Physics is one of the oldest academic disciplines , perhaps the oldest through its inclusion of astronomy . Over the last two millennia , physics was a part of natural philosophy along with chemistry , biology , and certain branches of mathematics , but during the scientific revolution in the 17th century , the natural sciences emerged as unique research programs in their own right . Physics intersects with many interdisciplinary areas of research , such as biophysics and quantum chemistry , and the boundaries of physics are not rigidly defined . New ideas in physics often explain the fundamental mechanisms of other sciences while opening new avenues of research in areas such as mathematics and philosophy .   Physics also makes significant contributions through advances in new technologies that arise from theoretical breakthroughs . For example , advances in the understanding of electromagnetism or nuclear physics led directly to the development of new products that have dramatically transformed modern-day society , such as television , computers , domestic appliances , and nuclear weapons ; advances in thermodynamics led to the development of industrialization , and advances in mechanics inspired the development of calculus .   The United Nations named 2005 the World Year of Physics .


Pine Island Glacier

Pine Island Glacier ( PIG ) is a large ice stream glacier , and the fastest melting glacier in Antarctica , responsible for about 25 % of Antarctica 's ice loss . The glacier ice streams flow west-northwest along the south side of the Hudson Mountains into Pine Island Bay , Amundsen Sea , Antarctica . It was mapped by the United States Geological Survey ( USGS ) from surveys and United States Navy ( USN ) air photos , 1960 -- 66 , and named by the Advisory Committee on Antarctic Names ( US-ACAN ) in association with Pine Island Bay .   The area drained by Pine Island Glacier comprises about 10 % of the West Antarctic Ice Sheet . Satellite measurements have shown that the Pine Island Glacier Basin has a greater net contribution of ice to the sea than any other ice drainage basin in the world and this has increased due to recent acceleration of the ice stream .   The ice stream is extremely remote , with the nearest continually occupied research station at Rothera , nearly 1300 km away . The area is not claimed by any nations and the Antarctic Treaty prohibits any new claims while it is in force .


Planck temperature

Planck temperature , denoted by TP , is the unit of temperature in the system of natural units known as Planck units .   It serves as the defining unit of the Planck temperature scale . In this scale the magnitude of the Planck temperature is equal to 1 , while that of absolute zero is 0 .  Other temperatures can be converted to Planck temperature units . For example , 0 ° C = 273.15 K = 1.9279 × 10 − 30TP .   In SI units , the Planck temperature is about 1.417 × 1032 kelvin ( equivalently , degrees Celsius , since the difference is trivially small at this scale ) , or 2.55 × 1032 degrees Fahrenheit or Rankine .


Planet

A planet is an astronomical body orbiting a star or stellar remnant that  is massive enough to be rounded by its own gravity ,  is not massive enough to cause thermonuclear fusion , and  has cleared its neighbouring region of planetesimals.This definition is drawn from two separate IAU declarations ; a formal definition agreed by the IAU in 2006 , and an informal working definition established by the IAU in 2001/2003 for objects outside of the Solar System . The official 2006 definition applies only to the Solar System , whereas the 2003 definition applies to planets around other stars . The extrasolar planet issue was deemed too complex to resolve at the 2006 IAU conference .  The term planet is ancient , with ties to history , astrology , science , mythology , and religion . Several planets in the Solar System can be seen with the naked eye . These were regarded by many early cultures as divine , or as emissaries of deities . As scientific knowledge advanced , human perception of the planets changed , incorporating a number of disparate objects . In 2006 , the International Astronomical Union ( IAU ) officially adopted a resolution defining planets within the Solar System . This definition is controversial because it excludes many objects of planetary mass based on where or what they orbit . Although eight of the planetary bodies discovered before 1950 remain `` planets '' under the modern definition , some celestial bodies , such as Ceres , Pallas , Juno and Vesta ( each an object in the solar asteroid belt ) , and Pluto ( the first trans-Neptunian object discovered ) , that were once considered planets by the scientific community , are no longer viewed as such .   The planets were thought by Ptolemy to orbit Earth in deferent and epicycle motions . Although the idea that the planets orbited the Sun had been suggested many times , it was not until the 17th century that this view was supported by evidence from the first telescopic astronomical observations , performed by Galileo Galilei . At about the same time , by careful analysis of pre-telescopic observation data collected by Tycho Brahe , Johannes Kepler found the planets ' orbits were not circular but elliptical . As observational tools improved , astronomers saw that , like Earth , the planets rotated around tilted axes , and some shared such features as ice caps and seasons . Since the dawn of the Space Age , close observation by space probes has found that Earth and the other planets share characteristics such as volcanism , hurricanes , tectonics , and even hydrology .   Planets are generally divided into two main types : large low-density giant planets , and smaller rocky terrestrials . Under IAU definitions , there are eight planets in the Solar System . In order of increasing distance from the Sun , they are the four terrestrials , Mercury , Venus , Earth , and Mars , then the four giant planets , Jupiter , Saturn , Uranus , and Neptune . Six of the planets are orbited by one or more natural satellites .   Several thousands of planets around other stars ( `` extrasolar planets '' or `` exoplanets '' ) have been discovered in the Milky Way . As of , known extrasolar planets in planetary systems ( including multiple planetary systems ) , ranging in size from just above the size of the Moon to gas giants about twice as large as Jupiter have been discovered , out of which more than 100 planets are the same size as Earth , nine of which are at the same relative distance from their star as Earth from the Sun , i.e. in the habitable zone . On December 20 , 2011 , the Kepler Space Telescope team reported the discovery of the first Earth-sized extrasolar planets , Kepler-20e and Kepler-20f , orbiting a Sun-like star , Kepler-20 . A 2012 study , analyzing gravitational microlensing data , estimates an average of at least 1.6 bound planets for every star in the Milky Way .  Around one in five Sun-like stars is thought to have an Earth-sized planet in its habitable zone .


Planetary boundaries

Planetary boundaries is the central concept in an Earth system framework proposed by a group of Earth system and environmental scientists led by Johan Rockström from the Stockholm Resilience Centre and Will Steffen from the Australian National University . In 2009 , the group proposed a framework of `` planetary boundaries '' designed to define a `` safe operating space for humanity '' for the international community , including governments at all levels , international organizations , civil society , the scientific community and the private sector , as a precondition for sustainable development . This framework is based on scientific research that indicates that since the Industrial Revolution , human actions have gradually become the main driver of global environmental change . The scientists assert that once human activity has passed certain thresholds or tipping points , defined as `` planetary boundaries '' , there is a risk of `` irreversible and abrupt environmental change '' . The group identified nine Earth system processes which have boundaries that , to the extent that they are not crossed , mark the safe zone for the planet . However , because of human activities some of these dangerous boundaries have already been crossed , while others are in imminent danger of being crossed .   Rockström and Steffen collaborated with 26 leading academics , including Nobel laureate Paul Crutzen , Goddard Institute for Space Studies climate scientist James Hansen and the German Chancellor 's chief climate adviser Hans Joachim Schellnhuber . The group identified nine `` planetary life support systems '' essential for human survival , and attempted to quantify just how far seven of these systems have been pushed already . They then estimated how much further we can go before our own survival is threatened ; beyond these boundaries there is a risk of `` irreversible and abrupt environmental change '' which could make Earth less habitable . Estimates indicate that three of these boundaries -- climate change , biodiversity loss , and the biogeochemical flow boundary -- appear to have been crossed . The boundaries are `` rough , first estimates only , surrounded by large uncertainties and knowledge gaps '' that interact in ways that are complex and not well understood . Boundaries can help identify where there is room and define a `` safe space for human development '' , which is an improvement on approaches which aim at just minimizing human impacts on the planet . The 2009 report was presented to the General Assembly of the Club of Rome in Amsterdam . An edited summary of the report was subsequently published as the featured article in a special edition of Nature . Nature also published critical commentary from leading academics they invited to comment on each of the seven planetary boundaries which had been quantified , including comments from Nobel laureate Mario J. Molina and biologist Cristián Samper . In 2015 , a second paper was published in Science updating the Planetary Boundaries concept . The findings were presented at the World Economic Forum in Davos , January 2015 .


Planetary habitability

Planetary habitability is the measure of a planet 's or a natural satellite 's potential to have habitable environments hospitable to life . Habitable environments do not need to contain life . Life may develop directly on a planet or satellite or be transferred to it from another body , a hypothetical process known as panspermia . As the existence of life beyond Earth is unknown , planetary habitability is largely an extrapolation of conditions on Earth and the characteristics of the Sun and Solar System which appear favorable to life 's flourishing -- in particular those factors that have sustained complex , multicellular organisms and not just simpler , unicellular creatures . Research and theory in this regard is a component of planetary science and the emerging discipline of astrobiology .   An absolute requirement for life is an energy source , and the notion of planetary habitability implies that many other geophysical , geochemical , and astrophysical criteria must be met before an astronomical body can support life . In its astrobiology roadmap , NASA has defined the principal habitability criteria as `` extended regions of liquid water , conditions favorable for the assembly of complex organic molecules , and energy sources to sustain metabolism '' .   In determining the habitability potential of a body , studies focus on its bulk composition , orbital properties , atmosphere , and potential chemical interactions . Stellar characteristics of importance include mass and luminosity , stable variability , and high metallicity . Rocky , wet terrestrial-type planets and moons with the potential for Earth-like chemistry are a primary focus of astrobiological research , although more speculative habitability theories occasionally examine alternative biochemistries and other types of astronomical bodies .   The idea that planets beyond Earth might host life is an ancient one , though historically it was framed by philosophy as much as physical science.This article is an analysis of planetary habitability from the perspective of contemporary physical science . A historical viewpoint on the possibility of habitable planets can be found at Beliefs in extraterrestrial life and Cosmic pluralism . For a discussion of the probability of alien life see the Drake equation and Fermi paradox . Habitable planets are also a staple of fiction ; see Planets in science fiction . The late 20th century saw two breakthroughs in the field . The observation and robotic spacecraft exploration of other planets and moons within the Solar System has provided critical information on defining habitability criteria and allowed for substantial geophysical comparisons between the Earth and other bodies . The discovery of extrasolar planets , beginning in the early 1990s and accelerating thereafter , has provided further information for the study of possible extraterrestrial life . These findings confirm that the Sun is not unique among stars in hosting planets and expands the habitability research horizon beyond the Solar System .   The chemistry of life may have begun shortly after the Big Bang , 13.8 billion years ago , during a habitable epoch when the Universe was only 10 -- 17 million years old . According to the panspermia hypothesis , microscopic life -- distributed by meteoroids , asteroids and other small Solar System bodies -- may exist throughout the Universe . Nonetheless , Earth is the only place in the Universe known to harbor life . Estimates of habitable zones around other stars , along with the discovery of hundreds of extrasolar planets and new insights into the extreme habitats here on Earth , suggest that there may be many more habitable places in the Universe than considered possible until very recently . On 4 November 2013 , astronomers reported , based on Kepler space mission data , that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs within the Milky Way . 11 billion of these estimated planets may be orbiting Sun-like stars . The nearest such planet may be 12 light-years away , according to the scientists .


Planetary nebula

A planetary nebula , often abbreviated as PN or plural PNe , is a kind of emission nebula consisting of an expanding , glowing shell of ionized gas ejected from old red giant stars late in their lives . The word `` nebula '' is Latin for mist or cloud , and the term `` planetary nebula '' is a misnomer that originated in the 1780s with astronomer William Herschel because when viewed through his telescope , these objects resemble the rounded shapes of planets . Herschel 's name for these objects was popularly adopted and has not been changed . They are a relatively short-lived phenomenon , lasting a few tens of thousands of years , compared to a typical stellar lifetime of several billion years .   A mechanism for formation of most planetary nebulae is thought to be the following : at the end of the star 's life , during the red-giant phase , the outer layers of the star are expelled by strong stellar winds . After most of the red giant 's atmosphere is dissipated , the ultraviolet radiation of the hot luminous core , called a planetary nebula nucleus ( PNN ) , ionizes the outer layers earlier ejected from the star . Absorbed ultraviolet light energises the shell of nebulous gas around the central star , causing it to appear as a brightly coloured planetary nebula .   Planetary nebulae likely play a crucial role in the chemical evolution of the Milky Way by expelling elements to the interstellar medium from stars where those elements were created . Planetary nebulae are also observed in more distant galaxies , yielding useful information about their chemical abundances .   Starting from the 1990s , Hubble Space Telescope images have revealed many planetary nebulae to have extremely complex and varied morphologies . About one-fifth are roughly spherical , but the majority are not spherically symmetric . The mechanisms that produce such a wide variety of shapes and features are not yet well understood , but binary central stars , stellar winds and magnetic fields may play a role .


Plant

Plants are mainly multicellular , predominantly photosynthetic eukaryotes of the kingdom Plantae .   The term is today generally limited to the green plants , which form an unranked clade Viridiplantae ( Latin for `` green plants '' ) . This includes the flowering plants , conifers and other gymnosperms , ferns , clubmosses , hornworts , liverworts , mosses and the green algae , and excludes the red and brown algae . Historically , plants formed one of two kingdoms covering all living things that were not animals , and both algae and fungi were treated as plants ; however all current definitions of `` plant '' exclude the fungi and some algae , as well as the prokaryotes ( the archaea and bacteria ) .   Green plants have cell walls containing cellulose and obtain most of their energy from sunlight via photosynthesis by primary chloroplasts , derived from endosymbiosis with cyanobacteria . Their chloroplasts contain chlorophylls a and b , which gives them their green color . Some plants are parasitic and have lost the ability to produce normal amounts of chlorophyll or to photosynthesize . Plants are characterized by sexual reproduction and alternation of generations , although asexual reproduction is also common .   There are about 300 -- 315 thousand species of plants , of which the great majority , some 260 -- 290 thousand , are seed plants ( see the table below ) . Green plants provide most of the world 's molecular oxygen and are the basis of most of Earth 's ecologies , especially on land . Plants that produce grains , fruits and vegetables form humankind 's basic foodstuffs , and have been domesticated for millennia . Plants play many roles in culture . They are used as ornaments and , until recently and in great variety , they have served as the source of most medicines and drugs . The scientific study of plants is known as botany , a branch of biology .


Plate tectonics

Plate tectonics ( from the Late Latin tectonicus , from the τεκτονικός `` pertaining to building '' ) is a scientific theory describing the large-scale motion of 7 large plates and the movements of a larger number of smaller plates of the Earth 's lithosphere , over the last hundreds of millions of years . The theoretical model builds on the concept of continental drift , an idea developed during the first few decades of the 20th century . The geoscientific community accepted plate-tectonic theory after seafloor spreading was validated in the late 1950s and early 1960s .   The lithosphere , which is the rigid outermost shell of a planet ( the crust and upper mantle ) , is broken up into tectonic plates . The Earth 's lithosphere is composed of seven or eight major plates ( depending on how they are defined ) and many minor plates . Where the plates meet , their relative motion determines the type of boundary : convergent , divergent , or transform . Earthquakes , volcanic activity , mountain-building , and oceanic trench formation occur along these plate boundaries . The relative movement of the plates typically ranges from zero to 100 mm annually .   Tectonic plates are composed of oceanic lithosphere and thicker continental lithosphere , each topped by its own kind of crust . Along convergent boundaries , subduction carries plates into the mantle ; the material lost is roughly balanced by the formation of new ( oceanic ) crust along divergent margins by seafloor spreading . In this way , the total surface of the lithosphere remains the same . This prediction of plate tectonics is also referred to as the conveyor belt principle . Earlier theories , since disproven , proposed gradual shrinking ( contraction ) or gradual expansion of the globe .   Tectonic plates are able to move because the Earth 's lithosphere has greater mechanical strength than the underlying asthenosphere . Lateral density variations in the mantle result in convection . Plate movement is thought to be driven by a combination of the motion of the seafloor away from the spreading ridge ( due to variations in topography and density of the crust , which result in differences in gravitational forces ) and drag , with downward suction , at the subduction zones . Another explanation lies in the different forces generated by tidal forces of the Sun and Moon . The relative importance of each of these factors and their relationship to each other is unclear , and still the subject of much debate .


Pleistocene

The Pleistocene ( -LSB- pronˈplaɪstəˌsiːn , _ - toʊ - -RSB- , often colloquially referred to as the Ice Age ) is the geological epoch which lasted from about 2,588,000 to 11,700 years ago , spanning the world 's most recent period of repeated glaciations . The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology .   The Pleistocene is the first epoch of the Quaternary Period or sixth epoch of the Cenozoic Era . In the ICS timescale , the Pleistocene is divided into four stages or ages , the Gelasian , Calabrian , Ionian and Tarantian . All of these stages were defined in southern Europe . In addition to this international subdivision , various regional subdivisions are often used .   Before a change finally confirmed in 2009 by the International Union of Geological Sciences , the time boundary between the Pleistocene and the preceding Pliocene was regarded as being at 1.806 million years Before Present ( BP ) , as opposed to the currently accepted 2.588 million years BP : publications from the preceding years may use either definition of the period .


Pluto

Pluto ( minor-planet designation : 134340 Pluto ) is a dwarf planet in the Kuiper belt , a ring of bodies beyond Neptune . It was the first Kuiper belt object to be discovered .   Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun . After 1992 , its planethood was questioned following the discovery of several objects of similar size in the Kuiper belt . In 2005 , Eris , a dwarf planet in the scattered disc which is 27 % more massive than Pluto , was discovered . This led the International Astronomical Union ( IAU ) to define the term `` planet '' formally in 2006 , during their 26th General Assembly . That definition excluded Pluto and reclassified it as a dwarf planet .   Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun . It is the largest known trans-Neptunian object by volume but is less massive than Eris . Like other Kuiper belt objects , Pluto is primarily made of ice and rock and is relatively small -- about one-sixth the mass of the Moon and one-third its volume . It has a moderately eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU ( 4.4 -- 7.4 billion km ) from the Sun . This means that Pluto periodically comes closer to the Sun than Neptune , but a stable orbital resonance with Neptune prevents them from colliding . Light from the Sun takes about 5.5 hours to reach Pluto at its average distance ( 39.5 AU ) .   Pluto has five known moons : Charon ( the largest , with a diameter just over half that of Pluto ) , Styx , Nix , Kerberos , and Hydra . Pluto and Charon are sometimes considered a binary system because the barycenter of their orbits does not lie within either body .   On July 14 , 2015 , the New Horizons spacecraft became the first spacecraft to fly by Pluto . During its brief flyby , New Horizons made detailed measurements and observations of Pluto and its moons . In September 2016 , astronomers announced that the reddish-brown cap of the north pole of Charon is composed of tholins , organic macromolecules that may be ingredients for the emergence of life , and produced from methane , nitrogen and other gases released from the atmosphere of Pluto and transferred about 19,000 km to the orbiting moon .


Podlaskie Voivodeship

This is an article about a present administrative unit of Poland . For historical units , see History of Podlaskie Voivodeship .   Podlaskie Voivodeship or Podlasie Province ( Województwo podlaskie , -LSB- woje ` wuctfo-pod ` laskJe -RSB- ) is a voivodeship ( province ) in northeastern Poland . It borders on Masovian Voivodeship to the west , Warmian-Masurian Voivodeship to the northwest , Lublin Voivodeship to the south , the Belarusian Voblasts of Grodno and Brest to the east , the Lithuanian Counties of Alytus and Marijampolė to the northeast , and the Kaliningrad Oblast of Russia to the north .   The capital of Podlasie Province is Białystok . The province was created on 1 January 1999 , pursuant to the Polish local government reforms adopted in 1998 , from the former Białystok and Łomża Voivodeships and the eastern half of the former Suwałki Voivodeship


Point Henry smelter

The Point Henry aluminium smelter was located near Geelong , Victoria in the suburb of Moolap prior to its closure in 2014 . The smelter had a production capacity of 185,000 tonnes of aluminium a year . It was operated by Alcoa World Alumina and Chemicals Australia , a joint venture between Alcoa ( 60 % ) and Alumina Limited ( 39.25 % ) . Alumina was brought in by ship and unloaded at a dedicated pier , and approximately half of this finished aluminium was sold to the neighbouring Alcoa Australia Rolled Products plant , where aluminium was rolled into sheet for can manufacture . The remainder of the aluminium was despatched by road as ingots . Around 1000 people were employed at the Point Henry plant .   Construction of the smelter at Point Henry commenced in 1960 by the Cavalier Construction Company . Smelting commenced in 1962 , with full production commencing on 4 April 1963 . The initial electricity supply to the smelter was a 220 kV transmission lines from the Geelong Terminal Station direct to the smelter . When production started , the maximum power demand of the smelter was 39.76 Megawatts ( MW ) . By June 1964 it was 68.38 MW , and by October 76.6 MW -- more than the entire Geelong region 's demand . In November the following year it was 78.88 MW , February 1967 79.84 MW , and 140 MW by 1969 . On 20 March 1969 Alcoa 's own brown coal-fired Anglesea Power Station was brought on line . With 150 MW capacity , the power station was connected to the smelter by around 30 kilometres of high-voltage transmission lines , and was used to augment the supply from the Victorian electrical grid .   The power demand of the smelter was 360 MW for a 185,000 tonne annual production capacity in 2014 , of which approximately 40 per cent was met by the Anglesea power station . The Point Henry smelter , along with the smelter at Portland , used 18 to 25 per cent of Victoria 's electricity production during the 2000s . In March 2010 it was announced that the operators of Loy Yang A power station ( Loy Yang Power ) had signed a contract with the smelter operators for the supply of electricity to power aluminium smelters at Portland and Point Henry until 2036 , the existing power contracts expiring in 2014 .


Polar amplification

Polar amplification is the phenomenon that any change in the net radiation balance ( for example greenhouse intensification ) tends to produce a larger change in temperature near the poles than the planetary average . On a planet with an atmosphere that can restrict longwave radiation to space ( a greenhouse effect ) , surface temperatures will be warmer than a simple planetary equilibrium temperature calculation would predict . Where the atmosphere or an extensive ocean is able to convect heat polewards , the poles will be warmer and equatorial regions cooler than their local net radiation balances would predict .   In the extreme , the planet Venus is thought to have experienced a very large increase in greenhouse effect over its lifetime , so much so that its poles have warmed sufficiently to render its surface temperature effectively isothermal ( no difference between poles and equator ) . On Earth , water vapor and trace gasses provide a lesser greenhouse effect , and the atmosphere and extensive oceans provide efficient poleward heat transport . Both palaeoclimate changes and recent global warming changes have exhibited strong polar amplification , as described below .


Polar bear

The polar bear ( ursus #Latin maritimus #Latin ) is a carnivorous bear whose native range lies largely within the Arctic Circle , encompassing the Arctic Ocean , its surrounding seas and surrounding land masses . It is a large bear , approximately the same size as the omnivorous Kodiak bear ( Ursus arctos middendorffi ) . A boar ( adult male ) weighs around 350 -- , while a sow ( adult female ) is about half that size . Although it is the sister species of the brown bear , it has evolved to occupy a narrower ecological niche , with many body characteristics adapted for cold temperatures , for moving across snow , ice and open water , and for hunting seals , which make up most of its diet . Although most polar bears are born on land , they spend most of their time on the sea ice . Their scientific name means `` maritime bear '' and derives from this fact . Polar bears hunt their preferred food of seals from the edge of sea ice , often living off fat reserves when no sea ice is present . Because of their dependence on the sea ice , polar bears are classified as marine mammals ; an alternative basis for classification as marine mammals is that they depend on the ocean as their main food source .   Because of expected habitat loss caused by climate change , the polar bear is classified as a vulnerable species , and at least three of the nineteen polar bear subpopulations are currently in decline . For decades , large-scale hunting raised international concern for the future of the species , but populations rebounded after controls and quotas began to take effect . For thousands of years , the polar bear has been a key figure in the material , spiritual , and cultural life of circumpolar peoples , and polar bears remain important in their cultures .


Polar ice cap

A polar ice cap or polar cap is a high-latitude region of a planet , dwarf planet , or natural satellite that is covered in ice .   There are no requirements with respect to size or composition for a body of ice to be termed a polar ice cap , nor any geological requirement for it to be over land ; only that it must be a body of solid phase matter in the polar region . This causes the term `` polar ice cap '' to be something of a misnomer , as the term ice cap itself is applied more narrowly to bodies that are over land , and cover less than 50,000 km ² : larger bodies are referred to as ice sheets .   The composition of the ice will vary . For example , Earth 's polar caps are mainly water ice , whereas Mars 's polar ice caps are a mixture of solid carbon dioxide and water ice .   Polar ice caps form because high-latitude regions receive less energy in the form of solar radiation from the Sun than equatorial regions , resulting in lower surface temperatures .   Earth 's polar caps have changed dramatically over the last 12,000 years . Seasonal variations of the ice caps takes place due to varied solar energy absorption as the planet or moon revolves around the Sun . Additionally , in geologic time scales , the ice caps may grow or shrink due to climate variation .


Polar regions of Earth

The polar regions of Earth , also known as Earth 's frigid zones , are the regions of Earth surrounding its geographical poles ( the North and South Poles ) . These regions are dominated by Earth 's polar ice caps , the northern resting on the Arctic Ocean and the southern on the continent of Antarctica .


Polar vortex

A polar vortex is an upper level low-pressure area lying near the Earth 's pole . There are two polar vortices in the Earth 's atmosphere , which overlie the North , and South Poles . Each polar vortex is a persistent , large-scale , low pressure zone that rotates counter-clockwise at the North Pole ( called a cyclone ) , and clockwise at the South Pole . The bases of the two polar vortices are located in the middle and upper troposphere and extend into the stratosphere . Beneath that lies a large mass of cold , dense arctic air . The vortices weaken and strengthen from year to year . When the vortex of the arctic is strong it is well defined , there is a single vortex and the arctic air is well contained ; when weaker , which it generally is , it will break into two or more vortices ; when very weak , the flow of arctic air becomes more disorganized and masses of cold arctic air can push equatorward , bringing with it a rapid and sharp temperature drop . The interface between the cold dry air mass of the pole and the warm moist air mass further south defines the location of the polar front . The polar front is centered , roughly at 60 ° latitude . A polar vortex strengthens in the winter and weakens in the summer due to its dependence on the temperature difference between the equator and the poles . The vortices span less than 1,000 kilometers ( 620 miles ) in diameter within which they rotate counter-clockwise in the Northern Hemisphere , and in a clockwise fashion in the Southern Hemisphere . As with other cyclones , their rotation is driven by the Coriolis effect .   When the polar vortex is strong , there is a single vortex with a jet stream that is `` well constrained '' near the polar front . When the northern vortex weakens , it separates into two or more vortices , the strongest of which are near Baffin Island , Canada and the other over northeast Siberia . The Antarctic vortex of the Southern Hemisphere is a single low pressure zone that is found near the edge of the Ross ice shelf near 160 west longitude . When the polar vortex is strong , the mid-latitude Westerlies ( winds at the surface level between 30 ° and 60 ° latitude from the west ) increase in strength and are persistent . When the polar vortex is weak , high pressure zones of the mid latitudes may push poleward , moving the polar vortex , jet stream , and polar front equatorward . The jet stream is seen to `` buckle '' and deviate south . This rapidly brings cold dry air into contact with the warm , moist air of the mid latitudes , resulting in a rapid and dramatic change of weather known as a `` cold snap '' .   Ozone depletion occurs within the polar vortices -- particularly over the Southern Hemisphere -- reaching a maximum depletion in the spring .


Political positions of Paul Ryan

The political positions of Paul Ryan , since 1999 the U.S. Representative from Wisconsin 's 1st congressional district and currently the 54th Speaker of the United States House of Representatives , are conservative and Republican with a focus on fiscal policy . Ryan was Chairman of the House Budget Committee from 2011 to 2015 and of Ways and Means in 2015 . Ryan was the Republican nominee for vice president as the running mate of Mitt Romney in the 2012 presidential election .   Ryan supports eliminating the capital gains tax , the corporate income tax , the estate tax , and the Alternative Minimum Tax .  In 1999 Ryan supported the Gramm -- Leach -- Bliley Act , which repealed some financial regulation of banks from the Glass -- Steagall Act of 1933 . During the economic recovery from the Great Recession of the late 2000s , Ryan supported the Troubled Asset Relief Program ( TARP ) , which authorized the Treasury to purchase toxic assets from banks and other financial institutions , and the auto industry bailout ; Ryan opposed the Credit CARD Act of 2009 , which expanded consumer protections regarding credit card plans , and the Dodd -- Frank Wall Street Reform and Consumer Protection Act , which strengthened financial regulation .   Ryan believes federal poverty reduction programs are ineffective and supports cuts to welfare , child care , Pell Grants , food stamps , and other federal assistance programs . Ryan supports the privatization of social security and Medicare and block granting Medicaid to the states . Ryan supported the Medicare Part D prescription drug benefit , and opposes the Patient Protection and Affordable Care Act ( ACA ) , also known as `` Obamacare '' , and supports its repeal .   Ryan is pro-life and opposes abortion rights . Ryan opposed the Lilly Ledbetter Fair Pay Act of 2009 , which bolstered women 's rights to equal pay for equal work . Ryan supports civil unions and opposes same-sex marriage . Ryan supports school vouchers , and supported the No Child Left Behind Act in 2001 and its repeal in 2015 . Ryan is unsure , and believes climate scientists are unsure , of the impact of human activity on climate change . Ryan supports tax incentives for the petroleum industry and opposes them for renewable energy . Ryan supports gun rights and opposes stricter gun control . Ryan supported the wars in Iraq and Afghanistan .


Politics of global warming

The complex politics of global warming results from numerous cofactors arising from the global economy 's interdependence on carbon dioxide emitting hydrocarbon energy sources and because carbon dioxide is directly implicated in global warming -- making global warming a non-traditional environmental challenge .


Pollution

Pollution is the introduction of contaminants into the natural environment that cause adverse change . Pollution can take the form of chemical substances or energy , such as noise , heat or light . Pollutants , the components of pollution , can be either foreign substances/energies or naturally occurring contaminants . Pollution is often classed as point source or nonpoint source pollution .


Population density

Population density ( in agriculture : standing stock and standing crop ) is a measurement of population per unit area or unit volume ; it is a quantity of type number density . It is frequently applied to living organisms , and most of the time to humans . It is a key geographical term .


Population genetics

Population genetics is a subfield of genetics that deals with genetic differences within and between populations , and is a part of evolutionary biology . Studies in this branch of biology examine such phenomena as adaptation , speciation , and population structure .   Population genetics was a vital ingredient in the emergence of the modern evolutionary synthesis . Its primary founders were Sewall Wright , J. B. S. Haldane and Ronald Fisher , who also laid the foundations for the related discipline of quantitative genetics . Traditionally a highly mathematical discipline , modern population genetics encompasses theoretical , lab , and field work . Population genetic models are used both for statistical inference from DNA sequence data and for proof/disproof of concept .   What sets population genetics apart today from newer , more phenotypic approaches to modelling evolution , such as evolutionary game theory and adaptive dynamics , is its emphasis on genetic phenomena as dominance , epistasis , and the degree to which genetic recombination breaks up linkage disequilibrium . This makes it appropriate for comparison to population genomics data .