Earth's Temperature Is Hottest in Centuries
Scientists Blame 'Human  Activities' for Warming Trend
By JOHN HEILPRIN,  AP
WASHINGTON (June 22) -- The Earth is the hottest it has  been in at least 400
years, probably even longer. The National Academy of  Sciences, reaching that
conclusion in a broad review of scientific work  requested by Congress,
reported Thursday that the "recent warmth is  unprecedented for at least the last
400 years and potentially the last several  millennia."
A panel of top climate scientists told lawmakers that the  Earth is heating
up and that "human activities are responsible for much of the  recent warming."
Their 155-page report said average global surface temperatures  in the
Northern Hemisphere rose about 1 degree during the 20th century.
This is shown in boreholes, retreating glaciers and other  evidence found in
nature, said Gerald North, a geosciences professor at Texas  A&M University
who chaired the academy's panel.
The report was requested in November by the chairman of the  House Science
Committee, Rep. Sherwood Boehlert, R-N.Y., to address naysayers  who question
whether global warming is a major threat.
Last year, when the House Energy and Commerce Committee  chairman, Rep. Joe
Barton, R-Texas, launched an investigation of three climate  scientists,
Boehlert said Barton should try to learn from scientists, not  intimidate them.
Boehlert said Thursday the report shows the value of having  scientists
advise Congress.
"There is nothing in this report that should raise any  doubts about the
broad scientific consensus on global climate change," he  said.
Other new research Thursday showed that global warming  produced about half
of the extra hurricane-fueled warmth in the North Atlantic  in 2005, and
natural cycles were a minor factor, according to Kevin Trenberth  and Dennis Shea of
the Commerce Department's National Center for Atmospheric  Research. Their
study is being published by the American Geophysical Union.
The Bush administration has maintained that the threat is  not severe enough
to warrant new pollution controls that the White House says  would have cost 5
million Americans their jobs.
Climate scientists Michael Mann, Raymond Bradley and  Malcolm Hughes had
concluded the Northern Hemisphere was the warmest it has been  in 2,000 years.
Their research was known as the "hockey-stick" graphic because  it compared the
sharp curve of the hockey blade to the recent uptick in  temperatures and the
stick's long shaft to centuries of previous climate  stability.
The National Academy scientists concluded that the  Mann-Bradley-Hughes
research from the late 1990s was "likely" to be true, said  John "Mike" Wallace, an
atmospheric sciences professor at the University of  Washington and a panel
member. The conclusions from the '90s research "are very  close to being right"
and are supported by even more recent data, Wallace  said.
The panel looked at how other scientists reconstructed the  Earth's
temperatures going back thousands of years, before there was data from  modern
scientific instruments.
For all but the most recent 150 years, the academy  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.
Combining that information gave the panel "a high level of  confidence that
the last few decades of the 20th century were warmer than any  comparable
period in the last 400 years," the academy said.
Overall, 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.
The scientists said they had less confidence in the  evidence of temperatures
before 1600. But they considered it reliable enough to  conclude there were
sharp spikes in carbon dioxide and methane, the two major  "greenhouse" gases
blamed for trapping heat in the atmosphere, beginning in the  20th century,
after remaining fairly level for 12,000 years.
Between 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  greenhouse gas" levels
by pollution since the mid-19th century, it said.
The National Academy of Sciences is a private organization  chartered by
Congress to advise the government of scientific matters.
06/22/06 12:40 EDT