USATODAY.com – Study: Earth is hottest now in 2,000 years; humans responsible for much of the warming
By John Heilprin, Associated Press
WASHINGTON — It has been 2,000 years and possibly much longer since the Earth has run such a fever. 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.
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.
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 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. [Full.Article]