Environmental Engineering Reference
In-Depth Information
Africa, and Sahel (between the Sahara Desert and the more fertile lands in the
South) and parts of Southern Asia. There is evidence of increased cyclone activity,
mainly in the North Atlantic. The increase in strong precipitation events is consist-
ent with global warming and with the higher atmospheric concentration of water
vapor. Intense and longer droughts have been more frequent since the 1970s, par-
ticularly in the tropics and subtropics. Also, associated with droughts are the alter-
ations in ocean temperatures and wind standards and an increase in mountain de-
frosting.
Some of the increase in the number of extreme events is probably due to sig-
nificant improvements in information access and to population growth. Extreme
events are relatively rare and occur only 5% or less of the time. They are identified
on the basis of the event's occurrence over time. On the basis of this definition the
number of earthquakes per year has been approximately constant since 1960, but
the number of cyclones has increased some 50% and the number of floods has in-
creased 100% since 1995.
According to the IPCC modeling assessment, between 1999 and 2099, the average
temperature of the planet will increase by 0.3°°C to 6.4°°C, the sea level will rise
between 0.18 and 0.59 m, and the ocean pH will be reduced between 0.14 and 0.35.
The models also predict that warming will be greater on land than on
oceans—and higher in the northern latitudes; perennial snow and ice will decrease;
heat waves and strong precipitation will increase; cyclones will be more intense;
extratropical storms will move toward the poles; and ocean currents will decrease
by about 25%, altering the Gulf Stream—the consequence of which will be harsher
winters in Western Europe.
Therefore, to stabilize the CO
2
concentrations in the atmosphere at 450 ppm, we
will need to reduce emissions from fossil fuels by more than 50%. This will require
a considerable effort.
Past and future CO
2
emissions caused by human activities will keep contribut-
ing to global warming and the increase in ocean levels for more than a millennium,
owing to the time scale necessary to remove these gases from the atmosphere.
