The concern with increasing carbon dioxide in the atmosphere is that it will lead to
— indeed is leading to — an excess of a good thing, warming of the global atmosphere.
This is the now well known greenhouse effect, which may not become as dire as some
experts predict, but which has a real possibility of becoming the worst environmental
problem so far created by humans.
Is Earth warming? Sophisticated computer models predict that it is backed by
evidence from increasingly accurate temperature records over more than 100 years.
Especially accurate temperature measurements taken by satellite show that the 1980s
were the warmest decade on record globally. But this record decade was followed by
the 1990s, which were warmer still. The 48 contiguous states of the U.S. had an average
temperature of 3.6 ̊C for the 1999-2000 winter, the warmest winter on record, and records
of 3.1 ̊C and 3.2 ̊C were set for the winters of 1997-1998 and 1998-1999, respectively.
In New England and the Northern Plains, the first freezes and the first snowfalls were
the latest on record during the 1999-2000 winter. February, 2000, was notable for setting
record high temperatures in the northern regions of the contiguous 48 states. Both the
first freeze and first snowfall came later than ever in colder regions of the 48 states,
including New England and the Northern Plains. Numerous places across the northern
tier of states set high temperature records during February, 2000. Continuing the trend,
the spring of 2000 was the warmest on record in the 48 contiguous states of the U.S.
Unfortunately, for those counting on the greenhouse effect to lower fuel bills, November
and December of 2000-2001 turned out to be the coldest on record in the 48 contiguous
states of the U.S.!
Gases other than carbon dioxide may be involved in greenhouse warming. These
include chlorofluorocarbons and N 2 O. The one most likely to cause a problem is methane,
CH 4 , which has increased from estimated pre-industrial atmospheric levels of 0.70 ppm,
to present values of l.8 ppm. Although these values are much lower than those of carbon
dioxide, each methane molecule is 20–30 times more effective in trapping heat than is
each CO 2 molecule. A number of human activities have contributed to the release of
methane. Part of this is due to leakage of natural gas, which consists of methane, and
from release as a byproduct of petroleum production. Bacteria growing in the absence
of oxygen in municipal refuse landfills, in rice paddies, and in the stomachs of ruminant
animals (cows, sheep, moose) release enormous quantities of methane. Green chemistry
can also be applied to avoid the generation of ultrastable volatile compounds that have
a high greenhouse gas potential. Sulfur hexafluoride, SF 6 , was mentioned as such a gas
in Section 8.8. Also included in this category are completely fluorinated hydrocarbons,
such as CF 4.
Although there could be some benefits of mild global warming, the net effect
would almost certainly be bad, perhaps catastrophic. Climate models predict an average
global temperature increase of 1.5–5 ̊C. That does not sound like much, but it is about
as much again as the temperature increase that occurred from the last ice age until now.
Especially if the warming is toward the high side of the projected range, it would greatly
affect climate and rainfall. The melting of the polar and Greenland ice caps along with
expansion of warmer ocean water would cause sea levels to rise as much as 0.5–1.5
Chap. 8. Air and the Atmosphere 215