New study reports heating up of earth's surface
Date: 18-Feb-00
Country: USA
The new study in "Science" magazine supports a National Academy of
Sciences panel that concluded that strong evidence showed an
"undoubtedly real" warming of the Earth's surface.
One of the authors of the new study, research meteorologist Dian Gaffen,
said the contention that the Earth's surface had warmed up appreciably
over the past 20 years was proven in their research.
The Earth's surface was warming up at 0.05 to 0.08 degrees Celsius per
decade, said Gaffen of the National Oceanic and Atmospheric
Administration in Maryland.
The study tries to resolve a major discrepancy in global climate - that
measurements at the Earth's surface suggest a temperature rise but that
satellite measurements indicate the lower troposphere shows little or no
signs of warmup.
This discrepancy in temperature trends cast doubt about how the Earth's
surface could be warming up if the air directly above it had not,
raising questions over whether man-made Greenhouse gases had contributed
to global warming.
Gaffen's group studied data from a series of weather balloons sent aloft
in the Tropics to measure the temperature of the Earth's surface as well
as in the troposphere, the area just above Earth.
"Our results support the contention that the surface has been warming
appreciably in the last 20 years versus the troposphere which does not
show as much warming," she said.
Gaffen's study focused on the tropical belt, the region on the Earth
where the difference between measurements taken by satellites and ground
station measurements is greatest.
Some scientists had argued that data from both satellite and ground
measurements were so different that they could only be wrong, changing
how meteorologists looked at climate change in the decades to come.
"The most important thing is that there has been a debate among policy
circles that satellite data did not show warming and so the surface
could not be warming either," Gaffen said.
Gaffen wrote that both calculations were correct and the discrepancy
arose from variations in how atmospheric temperature decreased with
altitude.
Ben Santer of Lawrence Livermore National Laboratory in California, who
wrote an accompanying paper in "Science", said there were good "physical
reasons" why the Earth's surface was warmer than the troposphere above
the surface.
He cited external factors such as increases in Greenhouse gases, the
number of particles in the air due to combustion, depletion of the Ozone
layer or natural events such as the eruption of Mount Pinatubo in 1991.
Santer said he hoped the study would clarify that the discrepancies
could not be reduced to "sound bytes".
"The bottom line is that the discrepancy between the surface of the
Earth and the lower troposphere seems to be real. Also there are
plausible reasons to explain how we have these different temperatures,"
said Santer.
Commenting on the study, John Christy, professor of Atmospheric Science
at the University of Alabama in Huntsville, said it reinforced the
conclusion that the atmosphere had not warmed as fast in the troposphere
as at the Earth's surface.
"The behaviour of the surface temperatures and the atmosphere over the
past 21 years is at odds with the theories that explain how
human-induced climate changes should occur," said Christy, who
contributed to the research.
He added: "This suggests that what has happened in the past 21 years is
not an example of human-induced climate change."
