now hottest it has been
in thousands of years?
(Top Posts - Science - 062206)
Earth 'likely' hottest in 2,000 years
'Warmth is unprecedented for
at least the last 400 years'
June 22, 2006;
Posted: 3:46 p.m. EDT (19:46 GMT)
- - -
(AP) -- It has been 2,000
years and possibly much longer since Earth
has run such a fever.
National Academy of Sciences, reaching
that conclusion in a broad review of scientific
work requested by Congress, reported Thurs-
day that the "recent warmth is unprecedented
for at least the last 400 years and potentially
the last several millennia."
panel of top climate scientists told lawmak-
ers that Earth is heating up and that "human
activities are responsible for much of the
panel looked at how other scientists recon-
structed Earth's temperatures going back thous-
ands of years, before there was data from
modern scientific instruments.
all but the most recent 150 years, the aca-
demy scientists relied on "proxy" evidence from
tree rings, corals, glaciers and ice cores, cave
deposits, ocean and lake sediments, boreholes
and other sources. They also examined indirect
records such as paintings of glaciers in the Alps.
that information gave the panel "a
high level of confidence that the last few dec-
ades of the 20th century were warmer than any
comparable period in the last 400 years," the
the panel agreed that the warming in
the last few decades of the 20th century was
unprecedented over the last 1,000 years,
though relatively warm conditions persisted
around the year 1000, followed by a "Little Ice
Age" from about 1500 to 1850.
scientists said they had less confidence
in the evidence of temperatures before 1600.
But they considered it reliable enough to con-
clude there were sharp spikes in carbon diox-
ide and methane, the two major "greenhouse"
gases blamed for trapping heat in the atmos-
phere, beginning in the 20th century, after re-
maining fairly level for 12,000 years.
1 A.D. and 1850, volcanic eruptions
and solar fluctuations were the main causes
of changes in greenhouse gas levels. But
those temperature changes "were much less
pronounced than the warming due to green-
house gas" levels by pollution since the mid-
19th century, it said.