In Russia, a record-breaking heat wave along with a record-breaking drought destroyed millions of acres of wheat and sparked wildfires that killed dozens.
In the United States, flooding battered New England, then Tennessee, Arkansas, and Oklahoma, while a record-breaking heat wave baked the entire eastern part of the country.
Scientists have long agreed that a single freak snowstorm or a particularly bad heat wave doesn't tell us much about climate change. But all these weather extremes in the past yearso many examples in so many different parts of the worldare making some climatologists wonder whether global warming is to blame. The collective answer of the scientific community can be boiled down to a single word: probably.
"The climate is changing," says Jay Lawrimore of the National Climatic Data Center in Asheville, N.C. "Extreme events are occurring with greater frequency, and in many cases with greater intensity."
Theory vs. Proof
Climatologists have theorized that a world warming up because of a buildup of greenhouse gases will feature heavier rainstorms in summer, bigger snowstorms in winter, more intense droughts in at least some places, and more record-breaking heat waves. Scientists and government reports say the statistical evidence shows that much of this is starting to happen.
Still, most scientists are reluctant to link specific weather events to climate change, noting that weather was characterized by remarkable variability long before humans began burning fossil fuels and releasing greenhouse gases into the atmosphere.
"If you ask me as a person, do I think the Russian heat wave has to do with climate change, the answer is yes," says Gavin Schmidt, a climate researcher with NASA. "If you ask me as a scientist whether I have proved it, the answer is noat least not yet."
The Earth has warmed by about 1.4 degrees Fahrenheit since the Industrial Revolution, when humans began pumping enormous amounts of carbon dioxide, a heat-trapping greenhouse gas, into the atmosphere. For this January through July, average temperatures were the warmest on record, according to the National Oceanic and Atmospheric Administration.
Climatologists have long theorized that in a warming world, the added heat would cause more record highs and fewer record lows. That seems to be what is happening: In the U.S. these days, about two record highs are being set for every record lowevidence that amid all the random weather variation, the trend is toward a warmer climate.
Climate-change skeptics dispute such statistical arguments, contending that climatologists don't know enough about long-range patterns to draw definitive links between global warming and weather extremes. They cite events like the heat and drought of the 1930swhich contributed to the Dust Bowl, dislocating millions of Americans and eventually changing the country's population structureas evidence that extreme weather is nothing new.
The statistics indicate that the Eastern U.S. may be getting wetter as the arid West dries out further. Places that depend on the runoff from spring snowmelt appear particularly vulnerable to climate change, because higher temperatures are making the snow melt earlier, leaving the ground parched by midsummer.
In general, the research suggests that global warming will worsen climate extremes across much of the planet. As in the U.S., wet areas will get wetter, the scientists say, while dry areas get drier.
What People Think
For a long time, scientists criticized the use of weather as an indicator of climate change. Even environmentalists hesitated to draw any conclusions.
"Weather is our day-to-day experience, while climate is more static, describing a region's typical weather conditions as established over periods of time," explained Adrianna Quintero of the Natural Resources Defense Council, in a blog post last winter.
But scientists seem to be coming around to the idea that recent wild weather may be linked to climate change. And regardless of the facts, the weather seems to be having an impact on the public's perception of global warming.
Consider the evolving perspective of the Russian leadership. Russia has long played a reluctant role in global negotiations over limiting climate change. But this summer's drought and wildfires have changed their tune. "Everyone is talking about climate change now," said President Dmitri Medvedev in August. "Unfortunately, what is happening now in our central regions is evidence of this global climate change, because we have never in our history faced such weather conditions."
(The New York Times Upfront, Vol. 143, September 20, 2010)