Energy and Changes in the Environment - Hydrogen and Fuel Cells: Advances in Transportation and Power - page 68

No matter what is done at this point, global temperatures may
continue to increase in the coming decades although there has been no
major temperature changes measured in the upper atmosphere. There
may be changes in monsoon patterns, ocean currents, or major droughts
which will all be blamed on global warming.
Many activists and environmentalists believe that climate change is
the major threat facing human civilization in the 21st century and that
institutions are doing little to battle the problem.
Climate change has become a burning issue, but given the way
some environmentalists and others exploit it, and the inaccurate record
of past predictions of ecological disaster, skepticism is still a reasonable
position. The hyping of the issue may even have begun to backfire on
environmentalists.
A 2004 Gallup Poll indicated that there was declining public interest
in global warming. Part of this may be the inability of the scientific
community to provide a probability estimate of either a rise in temperature
or the effects of such a rise, either regionally and globally. This tends to
show how limited the present knowledge of the world's climate actually
is. If the basic theory of global warming is correct, then much more work
is needed to provide a true understanding of regional and global climate
change.
During the past millennium the average global temperature was
essentially flat until about 1900, then spiked upward, like the upturned
blade of a hockey stick. Some view this as a clear indication that humans
are warming the globe, but others hold that the climate is undergoing a
natural fluctuation not unlike those in past eras.
One theory is that farming practices started global warming.
Many point to human actions that first began to have a warming effect
on Earth's climate in the past century. But other evidence indicates that
concentrations of carbon dioxide began increasing about 8,000 years ago,
in spite of natural trends indicating they should have been decreasing, and
that methane began to increase in concentration about 3,000 years later. In
the past few decades methane increases seen to be leveling at about 1.7
parts per million in the atmosphere.
In the northern hemisphere, meteorologists measured record-setting
spring and summer temperatures in 2004 and the level of atmospheric
carbon dioxide also reached a record high, averaging 379 parts per million,
a jump from 2003 levels that was much greater than the average annual
increase of 1.8 parts per million recorded over the past decade.