A 1999 study showed
that humans are altering the climate
U.S. Scientists 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 were flawed.
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