Atmosphere, Not Oceans, Carries Most Heat to the Poles from the Equator
BOULDER —
According to a new data analysis, the atmosphere
redistributes annually as much heat from the tropics to the poles as
would be produced by five million of the world’s biggest power
stations,
generating 1,000 megawatts each. This is far more heat than previously
estimated and much more than the oceans carry poleward. Until now
scientists have been unable to reconcile observations of the
atmosphere and ocean with results from global climate models. The new
study establishes the role of each in total heat transport poleward.
“This new analysis makes the observations more consistent with the
most stable global climate models and gives us confidence that the
models are on target,” says Kevin Trenberth of the National Center
for Atmospheric Research. Trenberth and NCAR colleague Julie Caron
performed the analysis, which was published in a recent issue of the
Journal of Climate, a publication of the American Meteorological
Society. It was selected this month by the journal Science as an
Editor’s Choice of important new findings.
The atmosphere and oceans help to even out the planet’s temperatures
by moving vast amounts of solar heat from the equator toward both
poles, primarily during winter in each hemisphere. Without this
leveling effect, all the high latitudes would be frozen solid while
the tropics would be much warmer and wetter.
Based on a reanalysis of data gathered between February 1985 and
April 1989, the study shows that the atmosphere handles 78% of the
total heat transport in the Northern Hemisphere and 92% in the
Southern Hemisphere at 35 degrees latitude —
where the total poleward
transport in each hemisphere peaks. The ocean carries more heat than
the atmosphere only in the tropics between 0 and 17 degrees north,
according to the study.
In the past, computer models attempting to mimic the Earth’s climate
have required artificial fixes to match real-world observations. Only
recently have NCAR and the United Kingdom’s Hadley Center developed
climate models stable enough to simulate centuries of climate without
these fixes. Their results now nearly match the observations. To
complete the picture, recent results from ocean measurements fit well
with those deduced by Trenberth and Caron from the atmospheric
component and both now add up to the alreadh known total heat
transport.
In the late 1970s the ocean and atmosphere were thought to be
conveying about the same amount of heat globally. Scientists
estimated that the atmosphere was hauling 57% of the heat load, with
oceans bearing a hefty 43% at the 35-degree latitude. As analyses
have improved, estimates have steadily increased the magnitude of
poleward heat transport occurring in the atmospheres of both
hemispheres.
The atmosphere’s role may have been slighted in the past because of a
lack of data over the oceans, where substantial atmospheric heat
transport occurs. Satellites have helped fill that gap. Trenberth and
Caron focused on the 1985-1989 period because it offers reliable top-
of-the-atmosphere radiation data from satellite measurements taken
during the Earth Radiation Budget Experiment.
The new study was based on two data reanalyses, one by the National
Centers for Environmental Prediction and NCAR, the other by the
European Centre for Medium-Range Weather Forecasts. The study was
funded by the National Oceanic and Atmospheric Administration and
NASA. NCAR is managed by the University Corporation for Atmospheric
Research with primary sponsorship by the National Science Foundation.
Contact:
Anatta
UCAR Communications
P.O. Box 3000
Boulder, CO 80307-3000
Telephone: (303) 497-8604
Fax: (303) 497-8610
E-mail:
anatta@ucar.edu
Stephanie Kenitzer
American Meteorological
Society
425-432-2192
kenitzer@dc.ametsoc.org
