Fate of Earth’s
heat-transfer process
captivates scientists
gathering here

By Helen Altonn

About 60 scientists from 10 countries launched a collaborative effort at a meeting in Honolulu to try to understand the Hadley Circulation, the earth's heat distributor.

If they can track changes or variations in the system affecting climate in the past, it may tell them something about climate in the future.

"We're looking at the potential effects of increasing greenhouse gases of carbon dioxide to see how different patterns of circulation may change toward the end of the 21st century," said Henry Diaz, of the National Oceanic and Atmospheric Administration's Climate Diagnostic Center in Boulder, Colo.

Climatologists, meteorologists, computer modelers and paleoclimatologists got together for the first time at a workshop at the East-West Center Nov. 12-15 to discuss the latest research on "The Hadley Circulation: Present, Past and Future."

Diaz said the purpose was "to examine what we know about the Hadley Circulation, one of the fundamental systems of the earth's climate, where heat is exported from the tropics through the high latitudes to maintain the planet's energy balance so the poles don't get too cold and the tropics don't get too hot."

The International Pacific Research Center, which sponsored the gathering, described the Hadley Circulation this way:

"Very warm, moist air near the equator rises high into the atmosphere, losing some of its heat as it moves toward the poles and sinking about 30 degrees latitude.

"It then brings the cooler air back toward the equator as tradewinds, drives the ocean currents and winds, lets off the equator's 'steam' and helps to warm mid-latitudes."

One of the problems in trying to unravel changes in the Hadley Circulation is that only very short records exist of any aspect of atmospheric circulation, said Raymond Bradley, paleoclimatologist at the University of Massachusetts Climate System Research Center.

"Detailed structure of the atmosphere is only well known at best for 50 years," he said.

So, to really understand how the system might have changed over long periods, he said, "proxy records" of climate must be studied, such as tree rings, ice cores, sediments in lakes and stalagmites from caves.

"All these records tell us something about the past climate, that it was warmer, cooler, drier or wetter," he said.

One of the co-organizers of the workshop, Bradley said a meteorology textbook would describe the Hadley Circulation as a simple system, but scientists learned at the meeting that "it's a very complicated story. ...

"We're right at the beginning of this process of trying to understand better the long-term variability of Hadley."

Bradley said more research is needed to study the proxy records or archives of past climate; modeling studies are necessary to put all the records together of the atmosphere and ocean and see how they are working, and observations are important to see how accurate models are in producing observed behavior of the climate system.

"Only when you start to patch all these together, you begin to get a rather crude snapshot of what happened over time."

Bradley said paleoclimatologists are just beginning to explore how the Hadley Circulation may change in the future using models to simulate the past.

International Pacific Research Center

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