Satellite data confirms climate change
Global warming anomaly may succumb to microwave study
By Quirin Schiermeier
This article is from the news section of the journal Nature
Published May 6, 2004
For years, climate researchers have struggled with an
apparent discrepancy in the data on global warming: temperatures
in the lower atmosphere have been rising far slower than
models predict, given how fast the Earths surface
The discrepancy has been central to the arguments of
sceptics about global warming. But according to a study
in this issue of Nature1 it can be explained by interactions
between the troposphere - the first 11 km of the atmosphere
- and the stratosphere above it.
In the study, a team from the University of Washington
at Seattle and the Air Resources Laboratory of the National
Oceanic and Atmospheric Administration (NOAA), based in
Maryland, analysed microwave emissions from the atmosphere.
The emissions were recorded between 1979 and 2001 by NOAAs
polar orbiting satellites. The data can be used to deduce
temperatures in different layers of the atmosphere. And
the study finds that stratospheric cooling, a known effect
of greenhouse gases,appears to account for discrepancies
between temperature trends on the ground and in the troposphere.
The team, led by Qiang Fu, an atmospheric researcher
at the University of Washington, subtracted the impact
of such cooling from data on the stratosphere and performed
a statistical analysis, which found temperature trends
consistent with observed warming on the surface and the
predictions of climate models.
The finding is a stunningly elegant and accurate
method of clarifying global trends, says Kevin Trenberth,
head of the climate analysis section at the National Center
for Atmospheric Research in Boulder,Colorado.
But it does not impress John Christy, director of the
Earth System Science Center at the University of Alabama
in Huntsville, whose work established the inconsistency
between temperature trends on the surface and in the troposphere2.
You cannot eliminate the stratospheric influence
with statistical tools alone, he says. If
you want to know precisely what happens you need physical
measurements. He says that Fu has overcorrected
for the impact of the stratosphere in his analysis.
Other climate scientists welcomed the new findings. This
is the answer - I wish we had recognized it ourselves,
says John Wallace, an atmospheric researcher also at the
University ofWashington, who chaired a 2000 survey on
reconciling global warming discrepancies for the US National
The study should be noted by policymakers who justify
lack of action on global warming by citing scientific
uncertainty, says Wallace. But he is not optimistic about
how many minds will be changed. Single scientific
discoveries have little impact in the political arena,
he says. NOAA officials declined to comment on the political
implications of the study.
The research comes just after a report from the Pew Center
on Global Climate Change predicted that global warming
could shrink the US economy.
But neither economic nor scientific analyses are likely
to affect US climate change policy, says Henry Jacoby,
director of the Massachusetts Institute of Technologys
Joint Program on the Science and Policy of Global Change.
After the Kyoto fiasco, the US administration began
to ask for advice from all sides, he says.But
unfortunately it has never taken the advice it received.
Qiang, F., Johanson, C. M., Warren, S. G. & Seidel,
D. J. Nature, 429, 55 - 57, doi:10.1038/nature02524 (2004).
Science, 247, 1558 - 1662, (1990). |Homepage|