Environmental Engineering Reference
In-Depth Information
also has the world's highest per capita CO
2
emissions,
followed by Australia, Canada, and the Netherlands.
In its 2001 report, the IPCC listed a number of
findings indicating that is it
very likely
(90-99% proba-
bility) that the troposphere is getting warmer (Fig-
ure 16-2, bottom right).
First,
the 20th century was the hottest century in
the past 1,000 years (Figure 16-2, bottom left).
Second,
since 1861 the average global temperature
of the troposphere near the earth's surface has risen
0.6°C (1.1°F) over the entire globe (Figure 16-2, bottom
right) and about 0.8°C (1.4°F) over the continents.
Most of this increase has taken place since 1980.
Third,
the 16 warmest years on record have oc-
curred since 1980 and the 10 warmest years have oc-
curred since 1990.
Fourth,
glaciers and floating sea ice in some parts
of the world are melting and shrinking (Figure 16-6,
p. 372). This process exposes darker and less reflective
surfaces of water and land, resulting in a warmer tro-
posphere. As more ice melts, the troposphere can be-
come warmer, which melts more ice and increases the
tropospheric temperature even more. According to a
2004 study by nearly 300 scientists, the Arctic “is now
experiencing some of the most rapid and severe cli-
mate change on Earth.” The study concluded that the
accelerated melting of Greenland's ice sheets will
cause sea levels to rise around the world.
Fifth,
warmer temperatures in Alaska and in other
parts of the Arctic are melting permafrost. This is re-
leasing large amounts of CO
2
and CH
4
into the tropos-
phere, which can accelerate tropospheric warming.
Sixth,
sea levels are rising. During the last century,
the world's average sea level rose by 0.1-0.2 meters
(4-8 inches), mostly because of runoff from melting
land-based ice and because of the expansion of ocean
water as its temperature increases.
410
360
310
260
1800
1900
2000
2100
Year
Carbon dioxide (CO
2
)
2.4
1.8
1.2
0.6
1800
1900
2000
2100
Year
Methane (CH
4
)
320
310
300
290
260
1800
1900
2000
2100
Examine how four major greenhouse gases have increased
in recent decades and find out why at Environmental
ScienceNow.
Year
Nitrous oxide (N
2
O)
Active Figure 16-5
Science:
Increases in average
concentrations of three greenhouse gases—carbon dioxide,
methane, and nitrous oxide—in the troposphere between
1860 and 2004. The fluctuations in the CO
2
curve reflect sea-
sonal changes in photosynthetic activity that cause small differ-
ences between summer and winter concentrations of CO
2
.
See an animation based on this figure and take a short quiz on
the concept.
(Data from Intergovernmental Panel on Climate
Change, National Center for Atmospheric Research, and World
Resources Institute)
Science: The Scientific Consensus
about Future Climate Change
Most climate scientists agree that human activities
have influenced recent climate changes and will lead to
further significant climate change during this century.
To project the effects of increases in greenhouse gases
on average global temperature, scientists develop
complex
mathematical models
of interactions among the
earth's sunlight, clouds, landmasses, oceans and ocean
currents, ice, and the atmospheric concentration of
gases like carbon dioxide and sulfur dioxide. Then
they run the models on supercomputers and use the
results to forecast future changes in the earth's average
ter of CO
2
—producing almost one-fourth of the annual
global emissions of this gas. It is followed by the Euro-
pean Union (12%), China (11%), Russia (7%), Japan
(5%), and India (5%). China's emissions are expected
to surpass U.S. emissions by 2025. The United States
