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1 Eastern Boundary Upwelling Systems (Benguela Current, Canary Current, California Current, and Humboldt Current); {Box 5.3} |
Figure TS.5 | b |
TS.3 Polar Regions |
This chapter assesses the state of physical, biological and social |
knowledge concerning the Arctic and Antarctic ocean and cryosphere, |
how they are affected by climate change, and how they will evolve |
in future. Concurrently, it assesses the local, regional and global consequences and impacts of individual and interacting polar system changes, and it assesses response options to reduce risk and build resilience in the polar regions. Key findings are: |
The polar regions are losing ice, and their oceans are changing |
rapidly. The consequences of this polar transition extend to |
the whole planet, and are affecting people in multiple ways.Arctic surface air temperature has likely increased by more |
than double the global average over the last two decades, with |
feedbacks from loss of sea ice and snow cover contributing to the amplified warming. For each of the five years since the IPCC |
5th Asesssment Report (AR5) (2014–2018), Arctic annual surface air temperature exceeded that of any year since 1900. During the winters (January to March) of 2016 and 2018, surface temperatures in the central Arctic were 6ºC above the 1981–2010 average, contributing to unprecedented regional sea ice absence. These trends and extremes provide medium evidence with high agreement of the |
contemporary coupled atmosphere-cryosphere system moving well |
outside the 20th century envelope. {Box 3.1, 3.2.1.1} |
52Technical Summary |
TSThe Arctic and Southern Oceans are continuing to remove |
carbon dioxide from the atmosphere and to acidify (high |
confidence ). There is medium confidence that the amount of CO 2 |
drawn into the Southern Ocean from the atmosphere has experienced significant decadal variations since the 1980s. Rates of calcification (by which marine organisms form hard skeletons and shells) declined in the Southern Ocean by 3.9 ± 1.3% between 1998 and 2014. In the Arctic Ocean, the area corrosive to organisms that form shells and skeletons using the mineral aragonite expanded between the 1990s and 2010, with instances of extreme aragonite undersaturation. {3.2.1.2.4} |
Both polar oceans have continued to warm in recent years, |
with the Southern Ocean being disproportionately and |
increasingly important in global ocean heat increase ( high |
confidence ). Over large sectors of the seasonally ice-free Arctic, |
summer upper mixed layer temperatures increased at around 0.5ºC per decade during 1982–2017, primarily associated with increased absorbed solar radiation accompanying sea ice loss, and the inflow of ocean heat from lower latitude increased since the 2000s (high |
confidence ). During 1970–2017, the Southern Ocean south of 30ºS |
accounted for 35–43% of the global ocean heat gain in the upper |
2000 m ( high confidence ), despite occupying ~25% of the global |
ocean area. In recent years (2005–2017), the Southern Ocean was |
responsible for an increased proportion of the global ocean heat increase (45–62%) ( high confidence ). {3.2.1.2.1, Figure TS.5} |
Climate-induced changes in seasonal sea ice extent and |
thickness and ocean stratification are altering marine primary |
production ( high confidence ), with impacts on ecosystems |
(medium confidence ). Changes in the timing, duration and intensity |
of primary production have occurred in both polar oceans, with |
marked regional or local variability ( high confidence ). In the Antarctic, |
such changes have been associated with locally-rapid environmental |
change, including retreating glaciers and sea ice change ( medium |
confidence ). In the Arctic, changes in primary production have |
affected regional species composition, spatial distribution, and |
abundance of many marine species, impacting ecosystem structure |
(medium confidence ). {3.2.1, 3.2.3, 3.2.4} |
In both polar regions, climate-induced changes in ocean |
and sea ice, together with human introduction of non-native |
species, have expanded the range of temperate species and |
contracted the range of polar fish and ice-associated species |
(high confidence ). Commercially and ecologically important fish |
stocks like Atlantic cod, haddock and mackerel have expanded their |
spatial distributions northwards many hundreds of kilometres, and |
increased their abundance. In some Arctic areas, such expansions have |
affected the whole fish community, leading to higher competition and |
predation on smaller sized fish species, while some commercial fisheries |
have benefited. There has been a southward shift in the distribution of Antarctic krill in the South Atlantic, the main area for the krill fishery (medium confidence ). These changes are altering biodiversity in polar |
marine ecosystems ( medium confidence ). {3.2.3, Box 3.4} |
Arctic sea ice extent continues to decline in all months of |
the year ( very high confidence ); the strongest reductions in |
September ( very likely –12.8 ± 2.3% per decade; 1979 –2018) are unprecedented in at least 1000 years ( medium confidence ). |
Arctic sea ice has thinned, concurrent with a shift to younger ice: since 1979, the areal proportion of thick ice at least 5 years old has declined by approximately 90% (very high confidence ). Approximately |
half the observed sea ice loss is attributable to increased atmospheric |
greenhouse gas concentrations (medium confidence ). Changes in Arctic |
sea ice have potential to influence mid-latitude weather on timescales |
of weeks to months ( low to medium confidence ). {3.2.1.1, Box 3.2} |
It is |
very likely that Antarctic sea ice cover exhibits no |
significant trend over the period of satellite observations |
(1979 –2018). While the drivers of historical decadal variability are |
known with medium confidence, there is currently limited evidence |
and low agreement concerning causes of the strong recent decrease |
(2016–2018), and low confidence in the ability of current-generation |
climate models to reproduce and explain the observations. {3.2.1.1} |
Shipping activity during the Arctic summer increased over the |
past two decades in regions for which there is information, |
concurrent with reductions in sea ice extent ( high confidence ). |
Transit times across the Northern Sea Route have shortened due |
to lighter ice conditions, and while long-term, pan-Arctic datasets |
are incomplete, the distance travelled by ships in Arctic Canada |
nearly tripled during 1990–2015 ( high confidence ). Greater levels |
of Arctic ship-based transportation and tourism have socioeconomic |
and political implications for global trade, northern nations, and |
economies linked to traditional shipping corridors; they will also |
exacerbate region specific risks for marine ecosystems and coastal |
communities if further action to develop and adequately implement |
regulations does not keep pace with increased shipping ( high |
confidence ). {3.2.1.1, 3.2.4.2, 3.2.4.3, 3.4.3.3.2, 3.5.2.7} |
Permafrost temperatures have increased to record high levels |
(very high confidence ), but there is medium evidence and low |
agreement that this warming is currently causing northern |
permafrost regions to release additional methane and |
carbon dioxide. During 2007–2016, continuous-zone permafrost |
temperatures in the Arctic and Antarctic increased by 0.39 ± 0.15ºC |
and 0.37 ± 0.10ºC respectively. Arctic and boreal permafrost region |
soils contain 1460–1600 Gt organic carbon ( medium confidence ). |
Changes in permafrost influence global climate through emissions of |
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