NOAA 99-R528
Contact: Jana Goldman


Regions that are already both warm and humid may grow even more so because of global warming, according to climate model projections run by the National Oceanic and Atmospheric Administration.

A study published in the October issue of Climatic Change indicates that substantial increases in the Heat Index (a measure of stress placed on humans by elevated atmospheric temperature and moisture levels) may occur in humid regions of the tropics and sub-tropics. The findings suggest that regions such as the southeastern United States, which are already both warm and humid, will be particularly vulnerable during summer.

The study was written by Thomas Delworth, Jerry Mahlman, and Thomas Knutson, all meteorologists at NOAA's Geophysical Fluid Dynamics Laboratory, Princeton, N.J.

"We found that while summer near-surface air temperature increases are largest over mid-latitude continental interiors such as the Great Plains, differences in ‘moisture-induced stress,' are more closely linked to coastal and oceanic regions, like the southeastern United States," said Delworth.

While the more humid areas have smaller temperature increases, they experience greater heat index effects because of increased moisture in the air. As the moisture content of the air increases, the ability of humans to release heat through perspiration is inhibited, causing discomfort and stress.

"That's why when we evaluate the potential impact of future climate change on human health and comfort, the moisture in the air as well as the surface air temperature must be considered," said Delworth.

In the study, the NOAA scientists used their computer model of the Earth's climate system. Such models, which simulate the interactions among the atmosphere, ocean, land surface and sea ice, are the primary tools used in the study of climate change and make use of the latest generation of supercomputers. The scientists used their model to simulate climate change over the period 1765-2065 by incorporating into the model the effect of increasing greenhouse gases and sulfate particles.

One of NOAA's mission responsibilities is to describe and predict changes in the Earth's environment.

For more information on climate change research, visit the GFDL web site at: