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will markedly accelerate due to positive feedback
processes not currently accommodated in model
projections (5).
Photo courtesy of Uwe Hermann
­
IV. “Drivers” of Climate Change
and Their Effects on Florida’s
Ocean and Coastal Resources
E F F ECT : Increases in Ocean Acidification
As levels of carbon dioxide in ocean waters increase, the oceans become more acidic. The average pH of
the ocean has been approximately 8.3 units. A downward change in any pH value means an increase in acidity.
A change of as little as 0.1 pH unit can have a large impact on organisms living in the sea because it repre
sents a 30 percent increase in acidity.
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IV
W H A T W E K N O W :
• The average pH of the world’s oceans has
fallen by 0.1 pH unit since 1750 because of
the uptake of carbon dioxide created by human
activities (24).
• Marine organisms with calcium carbonate
shells or skeletons, such as corals, clams, and
some plankton at the base of the food chain,
can be adversely affected by decreases in pH
and carbonate saturation state (5, 26). A
higher carbonate saturation state favors the precipitation of calcium carbonate, a mineral in
their shells, while a lower state supports its dissolution into the water.
• Ocean chemistry is changing at least 100 times
more rapidly today than at any time during the
650,000 years prior to the industrial era (22).
W H A T I S P R O B A B L E :
• An additional decrease in pH is under way (25,
27).
• With decreases in the pH of seawater, which is a
measure of its relative acidity, some marine plants
may show increases in production until a particular
threshold is met, and then will decline.
• Some marine organisms will not be able to tolerate
the predicted decreases in pH in the ocean.
• Carbonate sediment dissolution will accelerate as
pH decreases (28).
W H A T I S P O S S I B L E :
• The average pH of the world’s oceans may decrease by as much as 0.1 to 0.4 pH units over the
next 90 years (29).
• Ocean acidification may lead to shifts in marine
ecosystem structure and dynamics that can alter the
biological production and export of organic carbon
and calcium carbonate from the ocean surface
(29).
• Important fisheries habitats, such as coral reefs, will
markedly decline or disappear (22, 27).
Photo courtesy of Paige Gill — Florida Keys NMS
­
IV. “Drivers” of Climate Change
and Their Effects on Florida’s
Ocean and Coastal Resources
DR IVE R : Increasing Air Temperature and Water Vapor
Water vapor, the most abundant greenhouse gas, is an important factor causing uncertainty in climate prediction
models. As air temperature increases, its capacity to hold water vapor increases. However, clouds may have a
cooling or heating effect, and cloud processes are one of the largest sources of uncertainty in climate change pro
jections. Our inability to correctly characterize the effects of water vapor greatly complicates climate forecasts.
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IV
W H A T W E K N O W :
• Mean global atmospheric temperature has
increased by more than 1.1 degrees Fahrenheit (0.6 degrees Celsius) since 1901 (5).
• Since the 1980s, the atmospheric column
average water vapor concentration has
increased by 1.2 percent (5).
W H A T I S P R O B A B L E :
• Coastal air temperature observations around Florida
since the 1830s do not show any statistically significant trend (30).
• Air temperature in south Florida may increase
because of changes in land use and land cover,
such as urbanization and the reduction of wetlands
(31, 32).
• Global average air temperatures are projected to increase by 2.5 to 10.4 degrees Fahrenheit (1.4 and
5.8 degrees Celsius) by 2100 (5).
W H A T I S P O S S I B L E :
• Florida may begin to experience increasing air
temperatures.
­
IV. “Drivers” of Climate Change
and Their Effects on Florida’s
Ocean and Coastal Resources
E F F ECT : Altered Rainfall and Runoff Patterns
Rainfall over the Florida peninsula depends on the winds (e.g., sea breezes), especially in the summer, and on
hurricanes and tropical storms. Rainfall variations are highly cyclical (33). Climate change, land use, and other
factors may result in greater variations in observed patterns, conflicting trends, and regional differences within
the state. Distinguishing Florida specific rainfall and runoff trends from future global trends is a critical research
need.
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IV
W H A T W E K N O W :
• Annual rainfall in Florida is affected by tropical
storms and variability over decades, such as the
Atlantic Multidecadal Oscillation or the El NiñoSouthern Oscillation warming phenomenon in
the Pacific Ocean (33, 34, 35).
• Summer rainfall varies over periods of a few
decades (36).