Global Warming Means Drier Summers for Caribbean, Central America

LOS ANGELES, California, April 17, 2006 (ENS) - Global warming will bring a summer drying trend to parts of the Caribbean and Central America by the middle of this century, UCLA atmospheric scientists will report in the April 18 issue of Proceedings of the National Academy of Sciences.

By the end of this century, the researchers predict a decrease in summer rainfall of 20 percent or more in parts of the Caribbean and Central America, said lead author J. David Neelin, UCLA professor of atmospheric and oceanic sciences, a member of UCLA's Institute of Geophysics and Planetary Physics.

St. Croix

Caribbean islands like St. Croix in the U.S. Virgin Islands already experience drought that global warming is likely to exacerbate. (Photo courtesy USDA)
The research is based on an analysis of 10 global climate computer simulations, from the U.S. National Center for Atmospheric Research, the U.S. National Oceanic and Atmospheric Administration's Geophysical Fluid Dynamics Laboratory, and from Australia, Britain, France, Germany and Japan.

The majority of the computer models calls for a substantial decrease in tropical rainfall to occur by 2054, or sooner under some of the models. If the models prove correct, the decreased rainfall would be "a consequence of human-induced global warming," Neelin said.

Drought is already a problem in some of the Caribbean islands, such as the U.S. Virgin Islands where droughts are frequent and severe. Even minor depletions in rainfall affect agriculture and require water rationing.

In Jamaica, residents in communities across the western part of the island are now experiencing a severe water shortage as a result of extended islandwide drought conditions.


Lucea town center in western Jamaica. The island nation suffers from periodic droughts. (Photo courtesy Go-Local Jamaica)
The UCLA findings are likely to be discussed at the Heads of Government meeting of the Caribbean Community, CARICOM, opening Tuesday in Antigua and Barbuda.

"The Caribbean Community has set the highest priority on addressing the many challenges related to climate change and disaster mitigation and management," said Ambassador Lolita Applewhaite, CARICOM deputy secretary general. "We are among the first countries of the world to recognize the growing threat to our vulnerable economies and societies of climate change and the need to adapt to the increasingly severe phenomena."

Applewhaite was speaking April 4, at the signing ceremony of a scientific cooperation agreement with Italy in hydro-meteorological monitoring, natural disaster and early warning.

This agreement will launch a feasibility study, which is intended to provide benchmarks for the establishment of a Caribbean early warning system.

On January 1, the CARICOM countries established a single market, and CARICOM intends to form a single economy by 2008. "Reliable early warning systems, which can inform disaster preparedness and readiness are therefore vital components of our sustainable development," said Applewhaite.

The UCLA study finds that the winter change in rainfall in this region is not dramatic, because summer and winter rains occur by very different climate phenomena.

"The regions in the tropics that get a lot of summer precipitation are going to get more, and the regions that get very little precipitation will get even less, if the models are correct," Neelin said.

"Certain regions in between will get shifted from a moderate amount of precipitation to a low amount," he said. "The bigger the temperature rise, the larger the change in precipitation."

Neelin says the areas most likely to experience the summer drying trend are Cuba, Jamaica and Haiti, Mexico's Yucatan Peninsula, Belize, Guatemala and Honduras.

Concerning global warming, Neelin said, "For years, the vast majority of scientists have felt there is convincing evidence that we are at the beginning stages of human-induced global warming, and the observed global temperature record keeps supporting these predictions. However, there is still uncertainty about the amount of warming that will occur by the end of this century."


UCLA Professor J. David Neelin conducts research on processes that govern tropical precipitation, and year-to-year climate variability. He is writing a textbook for Cambridge University Press on climate modeling and climate change. (Photo courtesy UCLA)
"Precipitation change is much more difficult than temperature change to detect, and requires great precision; the models do not all agree, but the majority of them do," Neelin said.

"A slight error - for example, whether the wind is flowing from a dry region into the convection zone, or whether the wind is blowing past the convection zone without going into it - can cause one model to have a drought in a particular region, while another model does not," he said. "You have to be careful when talking about precipitation; there is natural variability, from year to year and from decade-to-decade."

In addition to analyzing the computer simulations, Neelin and his colleagues analyzed satellite precipitation data available since 1979, and rain gauge measurements since the 1950s. Over the last 50 years, the Caribbean has experienced a trend of decreased summer precipitation, but not a dramatic one, Neelin said. The computer models predict that will be a continuing trend.

"We can't exclude that the precipitation decrease over the last 50 years is part of a natural cycle, unrelated to global warming," Neelin said. "It is plausible that the decrease is due to global warming, but there is not yet a smoking gun that shows that to be the case."

The computer climate simulations also agree on the magnitude of drying trends in other regions within the tropics but disagree on where it will occur. The Caribbean/Central-American region is an example where the models agree reasonably well.

Neelin's research is funded by the National Science Foundation and the National Oceanic and Atmospheric Administration.

Co-authors on the PNAS article are Matthias Münnich, a UCLA researcher in atmospheric and oceanic sciences; Hui Su, a former UCLA researcher now at Caltech's Jet Propulsion Laboratory; Joyce Meyerson, a UCLA researcher in atmospheric and oceanic sciences; and Chris Holloway, a UCLA graduate student in atmospheric and oceanic sciences.