Geoscience Reference
In-Depth Information
occurred in the Great Lakes region, where the annual
length of the growing season increased by about 1
week in the 1990s.
Although some “environmental benefits” may take
place in a warmer world, the data suggest that many
negative results will probably occur. One of these neg-
ative effects is a rising sea level, which would result
from increased melting of polar ice caps and thermal
expansion of water. According to current predictions,
sea level will rise 15 cm to 90 cm (5.11 in. to 35.4 in.)
by 2100, which will place 92 million people around
the globe within the risk of coastal flooding. This issue
will be discussed in more detail in Chapter 19.
Another potential negative factor is that climate
change may promote the spread of insect-borne dis-
eases such as malaria. Climate boundaries may also
shift, making some regions drier while others become
wetter. This boundary shift may cause significant displacement
of human populations due to changes in agricultural patterns.
Still another potential change is that climate variability may
be enhanced, with a higher frequency of extreme events such
as snowstorms, rainstorms, and intense spells of hot and cold
weather. Data suggest that these kinds of extreme events have
been occurring more frequently since 1980. Although it is dif-
ficult to link any individual event to human causes, a number of
scientists believe that the searing temperatures and associated
drought in the U.S. heartland during the summer of 2012 were
related in part to ongoing climate change. Similar patterns have
been seen elsewhere on Earth.
Because it appears that global warming really is occurring
and that many negative consequences will likely result, world
leaders have made efforts to control greenhouse emissions. The
first truly global effort occurred at the 1992 Earth Summit in
Brazil, where 150 nations signed a treaty that limited the emis-
sions of greenhouse gases. A subsequent, more comprehensive,
global treaty was proposed in 1997 at Kyoto, Japan. The result-
ing
Kyoto Protocol
called for the 38 leading industrial nations,
including the United States, nations of the European Union, and
Japan, to reduce greenhouse emissions to 5% to 8% below 1990
levels. These reductions could be accomplished either through
Figure 9.30 Predicted climate change by the 2050s.
This
map shows the projected change in global average surface tem-
perature from the late 20th century (1971-2000 mean) to the mid-
dle 21st century. The map is based on IPCC scenario A1B that
assumes concentrations of atmospheric CO2 will rise to a little
over 600 ppm by the 2050s.
melt and thus less radiation is reflected to space, which, in turn,
results in even more warming. In contrast, the ultimate negative
feedback is that melting ice caps cause warm-water currents
such as the Gulf Stream to stop flowing as far north because of
the rapid influx of cold water at high latitudes. Some models
suggest that Earth might suddenly shift into another ice age if
this feedback occurs. Fortunately, neither the ultimate positive
nor negative feedback is considered likely.
Although the response of the Earth's future climate to
feedbacks is uncertain, the fact is that the IPCC and the vast
majority of publishing climatologists believe that warming
will continue for the next few generations. Some argue that no
major environmental consequence will happen—that, in fact,
a warmer world might be a good thing. Those who live in the
northern tier of states in the United States, for example, might
find some warming a welcome respite from the usually harsh
winters that occur there. A potential benefit may have already
The Greenhouse Effect and Global Climate Change
The issue of ongoing and future climate change is complex
and can be seen more clearly in animation. To do so, open
the animation
The Greenhouse Effect and Global Climate
Change
. This module demonstrates how greenhouse gases
such as carbon dioxide trap longwave radiation emitted by
Earth. It subsequently walks you through the logic behind cli-
mate change science. The last part of the module is an excel-
lent visualization of average global temperatures since the late
19th century and what they are projected to be in one scenario
by 2100. It is impressive. After you complete the exercise, be
sure to answer the questions at the end to ensure you under-
stand this concept.
