A 1999 study showed
that humans are altering the climate
have endorsed the contentions findings of a global
warming study that showed humans are drastically
altering the climate. The U.S National Academics
of science said the last few decades of the 20th
century were the warmest for 400 years. It adds
that many parts of the globe were warmer during
the past 25 years than during any comparable period
over the last 1,000 years. But it had less confidence
in more specific claims that the 1990s were the
warmest decade, and 1998 the warmest year.
The new report, published on
Thursday, focused on the "hockey stick"
graph - a reconstruction of average global temperature
over the last 1,000 years that shows a sharp upswing
in the late 20th century. The image was produced
in 1999 by a team led by climate expert Michael
Mann who estimated past temperatures using centuries-old
sediments and tree rings.
It seemed t show the rise in
global temperatures since the industrial revolution.
It became a main factor in the climate change
debate but critics said Dr. Mann's techniques
Thursday's report, prepared
by the National Academics' national research council
said: "The committee found the Mann team's
conclusion that warming in the last few decades
of the 20th century was unprecedented over the
last 1,000 years to be plausible."