Published online 16 February 2011 | Nature 470, 316 (2011) | doi:10.1038/470316a 
 
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 Likelihood of extreme rainfall may have been doubled by rising greenhouse-gas levels. 
 
 The effects of severe weather — such as these floods in Albania — take a huge human and financial toll. REUTERS/A. CELI 
 
 Climate change may be hitting home. Rises in global average temperature are remote from most people's experience, but two studies in this week's Nature1,2 conclude that climate warming is already causing extreme weather events that affect the lives of millions. The research directly links rising greenhouse-gas levels with the growing intensity of rain and snow in the Northern Hemisphere, and the increased risk of flooding in the United Kingdom. 
 
 Insurers will take note, as will those developing policies for adapting to climate change. "This has immense importance not just as a further justification for emissions reduction, but also for adaptation planning," says Michael Oppenheimer, a climate-policy researcher at Princeton University in New Jersey, who was not involved in the studies. 
 
 There is no doubt that humans are altering the climate, but the implications for regional weather are less clear. No computer simulation can conclusively attribute a given snowstorm or flood to global warming. But with a combination of climate models, weather observations and a good dose of probability theory, scientists may be able to determine how climate warming changes the odds. An earlier study3, for example, found that global warming has at least doubled the likelihood of extreme events such as the 2003 European heatwave. 
 
 More-localized weather extremes have been harder to attribute to climate change until now. "Climate models have improved a lot since ten years ago, when we basically couldn't say anything about rainfall," says Gabriele Hegerl, a climate researcher at the University of Edinburgh, UK. In the first of the latest studies1, Hegerl and her colleagues compared data from weather stations in the Northern Hemisphere with precipitation simulations from eight climate models (see page 378). "We can now say with some confidence that the increased rainfall intensity in the latter half of the twentieth century cannot be explained by our estimates of internal climate variability," she says. 
 
 The second study2 links climate change to a specific event: damaging floods in 2000 in England and Wales. By running thousands of high-resolution seasonal forecast simulations with or without the effect of greenhouse gases, Myles Allen of the University of Oxford, UK, and his colleagues found that anthropogenic climate change may have almost doubled the risk of the extremely wet weather that caused the floods (see page 382). The rise in extreme precipitation in some Northern Hemisphere areas has been recognized for more than a decade, but this is the first time that the anthropogenic contribution has been nailed down, says Oppenheimer. The findings mean that Northern Hemisphere countries need to prepare for more of these events in the future. "What has been considered a 1-in-100-years event in a stationary climate may actually occur twice as often in the future," says Allen. 
 
 But he cautions that climate change may not always raise the risk of weather-related damage. In Britain, for example, snow-melt floods may become less likely as the climate warms. And Allen's study leaves a 10% chance that global warming has not affected — or has even decreased — the country's flood risk. 
 
 Similar attribution studies are under way for flood and drought risk in Europe, meltwater availability in the western United States and drought in southern Africa, typical of the research needed to develop effective climate-adaptation policies. "Governments plan to spend some US$100 billion on climate adaptation by 2020, although presently no one has an idea of what is an impact of climate change and what is just bad weather," says Allen. 
 
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 Establishing the links between climate change and weather could also shape climate treaties, he says. "If rich countries are to financially compensate the losers of climate change, as some poorer countries would expect, you'd like to have an objective scientific basis for it." 
 
 The insurance industry has long worried about increased losses resulting from more extreme weather (see 'Fatal floods'), but conclusively pinning the blame on climate change will take more research, says Robert Muir-Wood, chief research officer with RMS, a company headquartered in Newark, California, that constructs risk models for the insurance industry. "This is a key part of our research agenda and insurance companies do accept the premise" that there could be a link, he says. "If there's evidence that risk is changing, then this is something we need to incorporate in our models." 
 
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 An increase in heavy precipitation that has afflicted many countries is at least partly a consequence of human influence on the atmosphere, climate scientists reported in a new study. 
 
 
 
 
 
 
 
 
 
 In the first major paper of its kind, the researchers used elaborate computer programs that simulate the climate to analyze whether the rise in severe rainstorms, heavy snowfalls and similar events could be explained by natural variability in the atmosphere. They found that it could not, and that the increase made sense only when the computers factored in the effects of greenhouse gases released by human activities like the burning of fossil fuels. 
 
 As reflected in previous studies, the likelihood of extreme precipitation on any given day rose by about 7 percent over the last half of the 20th century, at least for the land areas of the Northern Hemisphere for which sufficient figures are available to do an analysis. 
 
 The principal finding of the new study is “that this 7 percent is well outside the bounds of natural variability,” said Francis W. Zwiers, a Canadian climate scientist who took part in the research. The paper is being published in Thursday’s edition of the journal Nature. 
 
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 The paper covers climate trends from 1951 to 1999 and therefore does not include any analysis of last year’s extreme precipitation, including catastrophic floods in Pakistan, China and Australia as well as parts of the United States, including Tennessee, Arkansas and California. However, the paper is likely to bolster a growing sense among climate scientists that events like the 2010 floods will become more common. 
 
 Indeed, an increase of weather extremes has been a fundamental prediction of climate science for decades. Basic physics suggests that as the earth warms, precipitation extremes will become more intense, winter and summer, simply because warmer air can carry more water vapor. Weather statistics confirm that this has begun to happen. 
 
 Scientists have long been reluctant to attribute any specific weather event to global warming, but a handful of papers that do so are beginning to appear in the scientific literature. One such installment is being published on Thursday in Nature as a companion piece to the broader paper. It finds that severe rains that flooded England and Wales in 2000, the wettest autumn since record-keeping began there in 1766, were made substantially more likely by the greenhouse gases released by human activity. 
 
 In that analysis, scientists at the University of Oxford used computer time donated by the public to analyze the climate of Britain in 2000 as it actually existed and to compare that with a hypothetical climate in which the Industrial Revolution never happened and few greenhouse gases were released. 
 
 The computers found that the chances of those memorable floods, which sent geese swimming through city streets, were roughly doubled in a climate with the greenhouse gases. 
 
 That it took a decade to come to that conclusion illustrates one of the major problems of climate science at the moment. Researchers are barraged with questions about weather extremes like the recent winters in Europe and the United States and the heat waves and droughts of last summer. 
 
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 Yet, even when adequate weather statistics are available for an affected region, the scientists need years to run computer analyses of any specific event and calculate whether it was made more or less likely by global warming. 
 
 In a briefing for reporters, a leading climate scientist for the British government, Peter A. Stott, acknowledged a need for more rapid analysis of weather extremes and said that researchers were working to develop this capability. 
 
 The problem is becoming more than theoretical. Billions of dollars have been pledged by rich countries to help poor countries adapt to climate change. 
 
 “Because that money is on the table, it’s suddenly going to be in everybody’s interest to be a victim of climate change,” said Myles R. Allen, a University of Oxford researcher whose group ran the British flood study. “We need urgently to develop the science base to be able to distinguish genuine impacts of climate change from unfortunate consequences of bad weather.” 
 
 The analyses being published on Thursday can be expected to draw fire from climate-change contrarians, who have long scoffed at computer simulations of the climate. They point out that such programs cannot fully capture the complexity of the real world. 
 
 Mainstream scientists acknowledge that point to a degree but contend that the programs are becoming more accurate. They also note that the programs are the only tools available to answer questions about how much humans are influencing the climate. 
 
 “In the future, it won’t be enough for your weather service to predict the weather,” Dr. Allen said. “They’ll have to explain it as well.”
– We may have no one but ourselves—in part—to blame for the heavy rains and floods that have been plaguing everywhere from Nashville to Australia in recent years. Prior studies discovered that the likelihood of experiencing severe precipitation on a given day jumped 7% over the years 1951 to 1999, and a new study, based on elaborate computer modeling, has found that the increase cannot be attributed to natural variability. The computers found that the bump only made sense when mankind's effects on the atmosphere, by way of activities like the burning of fossil fuels, were factored in. A second study, also published in Nature, looked at major flooding in England and Wales during 2000. Using more computer simulations, researchers compared the events of that year to a hypothetical year that existed in a world that saw no Industrial Revolution and the release of few greenhouse gases. The result? The gases basically doubled the chances of those floods occurring. The New York Times notes that the studies are unlikely to change the minds of climate-change contrarians, who feel computer simulations can't capture the full complexity of the real world.