SCIENTISTS CLAIM FINAL PROOF OF GLOBAL WARMING
By Mark Henderson
Science Correspondent, The Times, 6 May 2004
POWERFUL evidence for
global warming has been discovered by scientists funded by the US Government,
demolishing the chief argument of sceptics who deny that the phenomenon is real.
A new analysis of
satellite data has revealed that temperatures in a critical part of the
atmosphere are rising much faster than previously thought, strengthening the
scientific consensus that the world is warming at an unnatural rate.
resolves one of the most contentious anomalies in climate science, which has
often been invoked by the Bush Administration to question whether man-made
global warming is happening.
While it is
generally accepted that surface temperatures are increasing by an average of
0.17C (0.31F) per decade, satellites have been unable to detect a parallel
trend in the troposphere — the lowest level of the atmosphere, extending 7.5
miles above the ground, in which most weather occurs.
This lack of
tropospheric warming has long puzzled scientists, as it is predicted by all the
major models of climate change. It has also been seized on by a small but vocal
minority of scientists, who have used it to raise doubts about whether global
temperatures are rising at all. The enigma, however, has been explained by a
team led by Qiang Fu, of the University of Washington in Seattle.
His research reveals
that the troposphere is warming almost precisely as the models predict it
should: by about 0.2C (0.4F) per decade. Satellites have not previously detected
the trend as they have been confused by colder temperatures in the atmospheric
The findings, details
of which are published today in the journal Nature, provide one of the
final pieces of proof that global warming is taking place, and that it is a
Sceptics have often
argued that if temperatures are rising at all, this is down to natural variation
in the climate as the world emerges from a “little Ice Age”. The tropospheric
trend, however, is precisely what scientists would expect to see if man-made
emissions of greenhouse gases were causing it to heat up.
“I think this could
convince not just scientists but the public as well,” Dr Fu said.
Mike Hulme, director of
the Tyndall Centre for Climate Change Research in Norwich, said: “It will become
that much harder for people to claim that the world isn’t warming and that the
warming isn’t caused by greenhouse-gas emissions.”
In their study, the
Washington team examined atmospheric temperature data collected between January
1979 and December 2001 from satellites operated by the US National Atmospheric
and Oceanic Administration.
These satellites used
instruments known as microwave-sounding units to measure microwave radiation
emitted by oxygen molecules, and thus to calculate the temperature.
The raw data for the
troposphere, as measured by the instruments’ channel 2 setting, showed no
pronounced warming trend.
Dr Fu realised,
however, that about a fifth of the signal picked up on channel 2 in fact
originated in the stratosphere — the higher level of the atmosphere between 10km
and 50km above the Earth’s surface. This had skewed the data, as the
stratosphere is known to be cooling rapidly.
“Because of ozone
depletion and the increase of greenhouse gases, the stratosphere is cooling
about five times faster than the troposphere is warming, so the channel 2
measurement by itself provided us with little information on the temperature
trend in the lower atmosphere,” Dr Fu said.
His team then used
measurements from weather balloons and from another channel on the microwave
units to determine precisely how much of the channel 2 signal was coming from
Once this stratospheric
error was eliminated, the remaining data showed that the troposphere had indeed
been warming, by about 0.2C (0.4F) a decade.
“This tells us very
clearly what the lower atmosphere temperature trend is, and the trend is very
similar to what is happening at the surface,” Dr Fu said.
The new tropospheric
data does not suggest that the pace of global warming is increasing or
decreasing. The research was funded by the US Government, through the Department
of Energy, the National Science Foundation and Nasa.
Panel on Climate Change estimates that global temperatures will rise by an
average of between 1.4C and 5.8C by the end of the century.
Dr Hulme said that
while the results further confirm the overwhelming scientific consensus that
man-made global warming is a proven phenomenon, he would be surprised if it were
accepted by critics.
“I’m under no illusions
that it will knock down the critics altogether,” he said. “In some quarters,
people hold almost fundamentalist beliefs that are immune to carefully reasoned
argument. A new paper that seems to take the legs away from one of their
critiques may unfortunately not make much difference to their arguments.
“It is the totality of
the evidence that has convinced the vast majority of experts that the planet is
warming: surface temperature recordings, rises in sea level, retreating
glaciers, shifting species domains.
“The compendium of
evidence from all these different sources means the overwhelming majority of
scientists feel justified in warning society about this.”