Last 25 years warmest on Earth since 1600
The last few decades were the warmest on Earth in
the past 400 years, and may well have been warmer than any comparable period
since the Middle Ages...
The last few decades were the warmest on Earth in the past 400 years, and may well have been warmer than any comparable period since the Middle Ages, U.S. scientists reported on Thursday.
In a new report by the National Research Council, researchers said they were highly confident the mean global surface temperature was higher in the past 25 years than any comparable period during the previous four centuries.
They had less confidence the past quarter-century was hotter than any comparable period in the years from 900 to 1600, but found that plausible. For the years before 900, the scientists said they had very little confidence about what the Earth’s mean surface temperatures were.
The scientists also noted that temperature reconstructions for periods before the Industrial Revolution — when levels of climate-warming greenhouse gases were much lower — supported the notion the current global climate change was caused by human activities, rather than natural variations in climate.
Nothing unexpected in this report; but, I thought I’d post it because it explains how some of this research is formulated. There are folks who wonder how anything could be known before the weather guy started showing up on TV.
Figuring out global temperatures over the past 150 years is relatively simple, since reliable records exist. But for the years and centuries before that, researchers must read clues left by the growth rings on trees, the retreat of glaciers and even old paintings and diaries that document climate.
Such clues are called proxies, and scientists began using them in sophisticated ways in the 1990s to estimate Earth’s surface temperature in past eras.
The council’s report was prompted by a request from the U.S. Congress, spurred by a controversial 1998 report in the journal Nature that used a number of sources, including proxies, to estimate temperatures in the Northern Hemisphere over the last 1,000 years.
One would hope the folks in Congress who made the request — read the report.
Posted: Fri - June 23, 2006 at 09:41 AM