Twentieth century hottest in a long time
Date: 18-Feb-00
Country: UK
The earth's temperature has increased by about one degree Centigrade
(1.8 degrees Fahrenheit) since the 1500s, they said. In the Northern
Hemisphere it was even faster: 1.1C (2F) in the last 500 years and 0.6 C
(1.1F) in the 20th century alone.
"The 20th century was the warmest for the last five, and the one which
was most rapidly changing," Henry Pollack, of the University of
Michigan, said in a statement.
Pollack and his colleague Shaopeng Huang and Po-Yu Shen of the
University of Western Ontario reconstructed past trends in climate
change by using data on sub-surface temperature gathered from holes
drilled into the ground at 616 sites on every continent except
Antarctica.
Their research is published in the latest edition of the science journal
Nature.
Highly sensitive thermometers in the holes show just how much
temperature has changed over the years because signals from surface
temperature travel below the earth and are preserved in rock and soil.
Temperatures of the past 1,000 years are recorded to a depth of 500
metres (yards) down.
"So the upper 500 metres is an archive - a historical record of
temperature changes that have occurred in the last thousand years," said
Pollack
"Like any historical archive, there are of course missing pages, and the
ink has run in a few places. But in principle, if you drill a borehole
anywhere on a continent, you can observe a temperature profile and
reconstruct what has happened at that location," he added.
By averaging the temperatures taken from the boreholes, the researchers
reconstructed a picture of past climates. Pollack and his team had
previously examined data from 358 borehole sites around the globe.
Their findings are consistent with other ways of estimating past
temperature such as studying ice cores, lake sediment and coral growth.
"All the methods generally show a very unusual 20th century, and ours
does, too," Pollack added.
