Scientists Predict Future of Weather Extremes

BOULDER, Colorado, October 20, 2006 (ENS) - The planet will face more deadly heat waves, prolonged drought, intense rainstorms and other weather extremes by century's end, U.S. climate researchers said Thursday. The study looks specifically at how weather extremes could change from global warming caused by human emissions of greenhouse gas.

The researchers studied only extreme temperature and precipitation conditions for the future - meaning the very cold and hot days, the dry periods and the heavy downpours.

They used simulations created on supercomputers from nine different climate models for the periods 1980-1999 and 2080-2099.

Recent droughts in the Western United States and Australia may only be precursors of what is to come. (Photo courtesy EC)

Each model simulated the 2080-2099 interval three times, varying the extent to which greenhouse gases accumulate in the atmosphere to account for uncertainty about how fast society may act to reduce greenhouse gas emissions.

For all three scenarios, the models agree the number of extremely warm nights and the length of heat waves will increase significantly over nearly all land areas across the globe. In addition, most areas above about 40 degrees north will see a significant jump in the number of days with heavy precipitation, including the northern tier of U.S. states, Canada, and most of Europe.

The models agree that dry spells could lengthen significantly across the western United States, southern Europe, eastern Brazil, and several other areas. They also predict that the average growing season could increase significantly across most of North America and Eurasia.

Most of these trends are significantly weaker for the lowest-emission scenario than for the moderate and high-emission scenarios, the researchers said, illustrating that cutting greenhouse gas emissions should reduce the risk that the most severe changes will occur.

The models all predicted an upsurge in extreme storms. (Photo courtesy University Corporation for Atmospheric Research)

"It's the extremes, not the averages, that cause the most damage to society and to many ecosystems," said lead author Claudia Tebaldi, a scientist with the National Center for Atmospheric Research. "We now have the first model-based consensus on how the risk of dangerous heat waves, intense rains, and other kinds of extreme weather will change in the next century."

The new study will appear in the December issue of the journal "Climatic Change." It is one of the first studies to draw on the extensive and sophisticated climate modeling that will form the basis of the upcoming Fourth Assessment Report of the Intergovernmental Panel on Climate Change (IPCC). The IPCC's next assessment report will be released early in 2007.

The research comes in the wake of a study by British climate scientists, released earlier this month that found drought could double by century's end because of global warming, threatening the survival of millions of people around the world.

The UK study warned that this estimate may actually be too conservative, as it doe not take into account the potential for carbon feedbacks in the climate system that are likely to accelerate warming across the planet.

It showed that extreme drought could affect 30 percent of the world's land surface, up from the current span of 3 percent. Severe drought will affect 40 percent of the earth's land, up from eight percent, and moderate drought, which currently affects about 25 percent of the world's surface, will rise to 50 percent.

In addition, a report released Thursday by the Christian development agency Tearfund warned that climate change threatens the water supply for millions of people and could create 200 million climate refugees by 2050.