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Extreme weather: the reality of a warming world

Scientists are starting to link natural disasters to rising greenhouse gases.

Brazil floods Rio
Aerial view of damages in Poco Fundo, an isolated area in the state of Rio de Janeiro, Brazil, Jan. 18, 2011. (Vanderlei Almeida/AFP/Getty Images)

RIO DE JANEIRO, Brazil — In the past year, every continent except Antarctica has seen record-breaking floods. Rains submerged one-fifth of Pakistan, a thousand-year deluge swamped Nashville and storms just north of Rio caused the deadliest landslides Brazil has ever seen.

Southern France and northern Australia had floods, too. Sri Lanka, South Africa, the list goes on.

And while no single weather event can be linked definitively to global climate change, a growing number of scientists say these extreme events represent the face of a warming world.

“Any one of these events is remarkable,” said Jay Gulledge, senior scientist for the Pew Center on Global Climate Change. “But all of this taken together could not happen without the extra heat that’s in the ocean. It defies common sense to overlook that link.”

That link works more or less like this. Concentrations of greenhouse gases are the highest the earth has seen in 15 million years. These gases trap heat, warming both the air and the oceans. Warmer oceans give off more moisture, and a warmer atmosphere can hold more of it in suspension. The more moisture in the air, the more powerful storms tend to grow. When these supercharged weather systems hit land, they don’t just turn into rain or snow, they become cyclones, blizzards and floods.

“There is a lot of tropical moisture in the atmosphere that is getting transported over very long distances and is dropping out in various places around the world in dramatic fashion,” Gulledge said.

Last year tied with 2005 as the warmest on record, according to the U.S. National Oceanic and Atmospheric Administration. And floods in 2010 weren’t the only extremes.

In Russia, 15,000 people died during a record heat wave. Australia suffered its warmest summer on record. Pakistan witnessed its hottest day in history, as did Los Angeles. The U.S. East Coast has struggled under unusually heavy snows for two winters running. The Brazilian Amazon suffered one of the worst droughts in its history. And even as the Brazilian government recovered the bodies of those killed by record storms in the state of Rio de Janeiro, it trucked drinking water to cities in the north blighted by drought.

Weather like this matches the predictions of numerous recent climate studies. In 2007, the Intergovernmental Panel on Climate Change noted that severe droughts and heavy rains were already on the rise in many parts of the world, and linked them to the surge in greenhouse gases. A study published last year by the National Academy of Sciences predicted an increase in heavy rainfall of somewhere between 3 and 10 percent for every Celsius degree of warming. Each additional degree would also cause the amount of area burned by wildfires in North America to double or quadruple, according to the same report.

“If you think it’s bad now — when we’ve had about 0.7 degrees Celsius of warming — wait until we’ve had 3 or 4,” Gulledge said. “There’s absolutely no reason to think it will not continue getting worse and worse and worse.”

Some scientists are starting to worry that natural weather patterns, which played a role in some of the biggest recent flooding, are also showing effects of human-driven climate change. This year’s rainy season in Australia is linked to a phenomenon called a La Nina, which occurs when water in the equatorial region of the Pacific is cooler than normal.

http://www.globalpost.com/dispatch/brazil/110120/climate-change-floods-natural-disasters