the ten warmest years since reliable records have
been kept on a global scale (roughly 1890) by 1999
had occurred after 1980. Temperatures continued
to rise steadily after the 1990’s.
Scientific Consensus and Dissent Though lively
debates in political circles and the news media have
sometimes raised questions about whether human
activity is significantly warming the Earth, scientific
evidence in support of global warming accumulated
steadily during the 1990’s. With the exception of a
minority of contrarians, the human role in a rapid
warming of the Earth has become nearly incontro-
vertible.
At the same time that scientific consensus on the
seriousness of global warming formed during the
1990’s, however, so did resistance to the idea by a
much smaller number of dissenters, some of them
funded in part by major fossil-fuel companies. Gen-
erally, the skeptics believe that warming will be a
balm for humanity. A skeptics’ journal, theWorld Cli-
mate Report, replied to an editorial in the prominent
British medical journalThe Lancetthat asserted that
malaria and other mosquito-borne diseases will
spread into the temperate zones as global tempera-
tures rise. According to the contrarians, malaria’s
spread has very little to do with temperature or hu-
midity and more to do with medical technology and
air conditioning. The contrarians assert that epi-
demics of malaria were common in most of the
United States before the 1950’s. In 1878, 100,000
Americans were infected and one-quarter of them
died.
Impact At stake in the global warming debate is the
way in which humans will produce and use energy
for the foreseeable future. Many scientists believe
that the Earth’s entire energy infrastructure will
have to be changed to avoid a crisis. Scientists who
study the future potential of human-induced warm-
ing also point to several other natural mechanisms
that could cause the pace of climate change to accel-
erate, releasing carbon dioxide and methane from
permafrost. Melting Arctic ice also creates a darker
ocean surface, changing albedo (reflectivity), caus-
ing more heat to be absorbed. The possibility of a
“runaway” greenhouse effect by the year 2050 has
been raised, often with a palatable sense of urgency.
Across Alaska, northern Canada, and Siberia, sci-
entists are finding telltale signs that permafrost is
melting at an accelerated rate. As permafrost melts,
additional carbon dioxide and methane convert
from solid form, stored in the earth, to gas, in the at-
mosphere, retaining more heat. Human contribu-
tions of greenhouse gases are provoking natural pro-
cesses at an alarming rate. The Arctic ice cap melted
steadily during the 1990’s, a trend that continued in
the subsequent decade. Inuit hunters have reported
that enough methane is bubbling out of the Cana-
dian north to light fires. Yellow jacket wasps have
been sighted on the far northern Canadian Arctic,
where the Inuit have no words in their own language
to describe them. In 2006, a manatee, a subtropical
marine animal, was observed swimming in the Hud-
son River near Manhattan Island.
Subsequent Events Using a complex set of feed-
backs (“thermal inertia”), scientists conclude that
humans will feel today’s emissions as heat roughly
half a century from now. In the oceans, the feedback
loop is longer, probably a century and a half, maybe
two. The real debate is not over how much the
oceans may rise from melting ice by the end of this
century (one to three feet, perhaps) but how much
melting will be “in the pipeline” by that time. James
E. Hansen, director of the NASA Goddard Institute
for Space Studies, estimates that thermal inertia by
the year 2100 may guarantee a 25-meter (82-foot)
sea-level rise within two centuries. Such a rise could
put millions of people out of their homes.
Further Reading
Gelbspan, Ross.The Heat Is On: The High Stakes Battle
over Earth’s Threatened Climate. Reading, Mass.: Ad-
dison-Wesley, 1997. A guide to the political battle
over global warming during the 1990’s.
Houghton, John.Global Warming: The Complete Brief-
ing.New York: Cambridge University Press, 1997.
A concise but expert outline of the issue as it
stood in the 1990’s.
Johansen, Bruce E.The Global Warming Desk Reference.
Westport, Conn.: Greenwood Press, 2001. A sum-
mary of the field as it stood at the end of the de-
cade.
Lynas, Mark.High Tide: The Truth About Our Climate
Crisis. New York: Picador, 2004. A travelogue that
illustrates everyday impacts of a changing cli-
mate.
Bruce E. JohansenSee also Agriculture in the United States; Air pol-
lution; Airline industry; Architecture; Biosphere 2;The Nineties in America Global warming debate 375