Recent studies by scientists in ICTP's Physics of Weather and Climate group show that weather variability and extreme weather events are likely to increase.

Weather or Not

Jeremy Pal, Filippo Giorgi and Bi Xunqiang

What's the weather going be like today and tomorrow? That's what concerns most people. Few people outside the scientific community worry about what the climate will be like a decade or century from now.
Yet a recent series of events--a deadly heat wave in Europe three summers ago and a series of destructive hurricanes along the Caribbean and the Gulf Coast of North America this past autumn--have increased public awareness that short-term weather patterns and long-term climatic conditions may indeed be related.
The nature of the relationship between weather and climate also lies at the heart of the climate change debate among scientists. Until recently, scientists found it difficult to attribute the rising number of extreme weather events to rising levels of greenhouse gases in the atmosphere. Relying on observational evidence, they simply didn't know if what was happening was cyclical in nature or symptomatic of permanent changes in the climate; nor could they determine, with any confidence, the impact of such changes on a regional scale.
Now, high-powered computer models are enabling scientists to examine more closely the potential relationship between long-term alterations in climate and year-to-year changes in weather--and to do so in ever-smaller geographical areas.
Taking advantage of these more sophisticated modelling tools, ICTP scientists Filippo Giorgi, Bi Xunqiang and Jeremy Pal recently engaged in two research projects that examined future scenarios for climate variability and extreme weather events across virtually all regions of the globe. The findings of Giorgi and Bi were published in Geophysical Research Letters and subsequently reported in Nature's "Research Highlights" section. The findings of Giorgi and Pal (together with their coauthors N.S. Diffenbaugh and R.J. Trapp, assistant professors of earth-atmospheric sciences at Purdue University, USA) were published in the Proceedings of the National Academy of Sciences and subsequently reported in National Geographic News.
Giorgi and Bi's article, relying on 18 different global model simulations covering 26 regions in different parts of the world, indicates that precipitation variability is expected to increase across the globe. Simply put, this means rainfall is expected to become more variable, and that periods of drought and periods of excessive rain will become more frequent. The article by Giorgi, Pal and their coauthors confirms this finding using a computer model that spans the United States. Both articles correspond to other scientific conclusions showing that as the atmosphere becomes warmer, precipitation patterns will become less predictable and more extreme.
And what does all of this mean for you and me? What can people expect the weather to be like as they plan their daily and weekly activities both now and in the future? And perhaps more importantly, what does this mean for farmers seeking to earn a living from the land or resource managers seeking to ensure adequate supplies of safe drinking water for their citizens?
First of all, it is important to note that scientists can never be entirely sure of their findings regardless of how sophisticated their models are. Yet, this much can be said with some degree of scientific confidence. As temperatures warm, year-to-year variabilities in weather and climate are expected to increase. And, as this variability increases, extreme weather events are likely to become more frequent, rendering many economic and social sectors--for instance, agriculture, public health, and ecosystem management--more vulnerable to the whims of nature.
And there's another important point. Because weather and climate variability is expected to be most intense in tropical regions, we can anticipate that a host of countries in the developing world will find themselves most at risk. That makes it more important than ever for developing countries to devise adaptive measures to help them meet the challenges posed by climate change, not just a century from now but today.

For more detailed information about these findings, see F. Giorgi and Bi Xunqiang, "Regional Changes in Surface Climate Interannual Variability for the 21st Century," Geophysical Research Letters 32 (29 October 2005) and N.S. Diffenbaugh, et al., "Fine-Scale Processes Regulate the Response of Extreme Weather Events to Global Climate Change," Proceedings of the National Academy of Sciences 102
(2 November 2005).

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