(1) There is strong scientific consensus that the warming is real, (2) the warming is
geographically uneven, and (3) anthropogenic increases of greenhouse gases is
a major contributor to the warming. For the first time in human history there is a
“very high likelihood” that humans have significantly impacted the greenhouse
effect and that all projected greenhouse gasscenarios indicate increases in the
warming effect.
The current time is a relatively warm one in recentEarthhistory. The planet
has not been as warm for 1,300 years and the last time the planet had extended
warmth at the level of the present day,it was 125,000 years ago and sea level
was 6–8 m higher. Earth’s climate was considerably warmer for most of Earth’s
history but those eons are separated from us by the Pleistocene Epoch ice age of
the last couple of million years.
The mechanism for the current globalwarming has been the unintentional
enhancement of the greenhouse effect by a number of human activities. The con-
cern is that the increase of greenhouse gases has increased the atmospheric equi-
librium temperature by causing a greater percentage of the Earth surface and
atmosphere’s longwave emitted energy to be absorbed and then re-emitted by the
atmosphere. Worldwide industrialization and population increase has led to a third
more atmospheric carbon dioxide since the middle of the 1800s. Carbon dioxide is
a greenhouse gas produced by all combustion processes, including the burning of
fossil fuels, so that there are myriad major sources. Other gases such as methane,
nitrous oxides, and chlorofluorocarbons (entirely human-made) have also signifi-
cantly increased; they are trace gases but are far more absorptive of longwave
energy on a per mass basis.
Scientific consensus for the global warming effects has increased and been con-
firmed by virtually all evidence. Perhaps the most publicized warming effect is the
worldwide decrease in the mass and geographic extent of ice on the planet. Satel-
lite and on-site surveys have confirmed that the mass of ice is decreasing at
increasing rates over virtually the entire planet. Even glaciers that have advancing
margins have been shown to exhibit this behavior by the increase of subsurface
meltwater lubricating glacial motion.
The current global warming does not seem to have been extreme in the minds of
most non-scientists. After all, the world mean temperature has been on the order of
three-quarters of a degree Celsius since the mid-1800s. Research does not suggest
the greenhouse effect will increase to the point where human life becomes impos-
sible. Yet, the worry extends far beyond temperatures. The vehicle to convey
global warming scientific knowledge and the bellwether for ferocious criticism
has been the series ofAssessmentreports made by the Intergovernmental Panel
on Climate Change (IPCC). The IPCC is an effort of the World Meteorological
Organization and the Environment Programme of the United Nations. Over a158 Global Warming