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Primer: What's New (and What Isn't) in the IPCC's Report on Extreme Weather

The world's leading science panel studied the link between man-made warming and wild weather for the first time. InsideClimate News examines its results.

Nov 22, 2011
Rajenda Pachauri, chair of the Intergovernmental Panel on Climate Change (IPCC),

Record heat waves, drought, floods, thunderstorms, tornado outbreaks—extreme weather battered much of the United States and parts of the world in recent years, causing an unprecedented number of deaths and economic losses.

What role has global warming played, if any?

The answer has implications that go beyond the ideological debate in U.S. politics over climate change. It affects, among other things, the future direction of the 19-year-old U.N. Framework Convention on Climate Change (UNFCCC), the main forum for the global fight to limit warming. To date its priority has been emissions cuts, or "mitigation," to keep climate change in check. But is it too late for that, as some scientists now say? Is it time for "adaptation" (finding ways to live with heat waves, rising seas and flooded coastlines and scarcer water and food supplies) to finally share focus and UNFCCC resources?

Growing scientific evidence indicates that the answer to that question is yes.

Severe weather in the United States and elsewhere has grown more frequent since 1980. Contributing to the shift is the accumulation of heat-trapping carbon dioxide in the air from human activities—though teasing out the exact contribution is tricky. 

As usual with climate science, there are uncertainties and complexities in the data on climate extremes, and skeptics have pounced on the unknowns to exaggerate doubts about the consensus on climate change and to make the case for inaction. To counter those charges, the UN Intergovernmental Panel on Climate Change (IPCC), the world's leading scientific body on global warming, has produced a new report designed especially for the world's politicians that tries for the first time to clarify the link between wild weather and global warming. 

Specifically, the authors of the Special Report for Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation (SREX) wanted to know what the research says about whether greenhouse gas emissions cause extreme weather; who is, and will be, hardest hit by these disasters; and how can governments and organizations lessen the impacts.

In this primer InsideClimate News takes a look at what the IPCC gleaned from its two years of research into these questions.

Has "anthropogenic," or human-caused, climate change already altered the frequency of extreme weather events?

Simply put, yes.

Using observations from papers published in peer-reviewed journals, data from long-term monitoring projects and climate models dating back to 1950, IPCC scientists concluded there has been an overall global increase in the number of warm days and nights, as well as in the length and frequency of heat waves, because of global warming.

Droughts are more frequent and longer, particularly in southern Europe and West Africa, it found. As well, the frequency of days with heavy precipitation is up in some regions (warmer air holds more moisture). Tropical cyclones, the generic term for typhoons and hurricanes, have shifted poleward in recent years; and, as a result, storms have made landfall in areas that previously didn't lie in the tracks of cyclones.

The IPCC said it is "likely"—a 66 percent to 100 percent probability—that the temperature and precipitation trends mentioned above are caused by a rise in greenhouse gas emissions from human activities like burning fossil fuels and deforestation. They are less certain about cyclones because of spotty historical records.

Who has been most affected by these extremes so far?

During the past half century, developed countries were the hardest hit economically from weather- and climate-related disasters, with damages of as much as $200 billion annually, up from a few billion in 1980. The number of deaths linked to these calamities is up, too. More than 95 percent of the deaths recorded occurred in developing countries. The IPCC authors predict these trends will continue throughout the 21st century.

What, specifically, does the IPCC say about what's in the store for the future?

In short, the extreme weather the world experienced in recent years is likely to become the norm.

Temperatures: It's no secret the planet is heating up. Last month, a two-year review of world temperature data by a former climate skeptic at the University of California, Berkeley, confirmed the consensus that the Earth has warmed by roughly 1.6 degrees Fahrenheit over the past 50 years.

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