Environmental Engineering Reference
In-Depth Information
beginning to use small amounts of alternative energy sources, but it will
be at least fi fty years before they form the major part of their energy use.
And it is apparent that nations wanting to industrialize rapidly, such as
China and India, may continue to increase their use of fossil fuels even
further into the future.
Many feedback loops affect global warming, and the strength of each
of them is changing with time. There are as yet no quantitative data to
determine the effect of each one on global warming. As noted earlier,
increasing water vapor in the air creates a positive feedback loop, rein-
forcing global warming. The warmer the air is, the more water vapor it
can hold. Given the amount of temperature increase that is likely to occur
in the lower atmosphere, the air will be not be able to hold more than
about 4 percent of water vapor.
The water vapor increases the rate at which ice is lost from the
sea, and decreasing the amount of sea ice creates an additional posi-
tive feedback loop. Ice refl ects away a large portion of incoming
sunlight, whereas the darker open ocean absorbs 80 percent more
radiation. This is the main reason that the infl uence of warming is
more pronounced at high northern latitudes than in temperate or
tropical regions.
But there is also a negative feedback to the loss of sea ice. Water
absorbs much of the carbon dioxide gas humans emit, so exposing more
water permits additional absorption of carbon dioxide and decreases the
warming effect of carbon dioxide emissions. From a high of 5.7 million
square miles in 1950, the annual average extent of arctic sea ice has
decreased to 4.2 million square miles.
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Arctic summer ice is currently
receding by an average of approximately 8 percent per decade, a pace
that has been steadily quickening since 2001. Ice-free summers in the
Arctic Ocean may occur within ten to twenty years. Winter sea ice is
also decreasing in aerial extent.
The mass of ice-free water over most of the globe absorbs at least half
of the carbon dioxide humans produce. But recent studies have revealed
that the ocean is absorbing less carbon dioxide than it was in 1997. This
is to be expected because warm water cannot hold as much gas as cooler
water can. So here is an additional positive feedback loop. Warmer air
drives carbon dioxide from the ocean into the air, and additional carbon
dioxide in the air increases global warming and causes carbon dioxide
to escape from the water.
Clouds are made of water, and as water in the atmosphere is increas-
ing, global cloudiness must also be increasing. Increased cloudiness
