By Henry Fountain / Source: nytimes

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In this era of global warming, when there is extreme weather like the recent heavy rains that led to flooding in Paris and other parts of France and Germany, the question inevitably comes up: Did climate change play a role?

Not too long ago, the immediate response from most climate scientists would be that while it is generally accepted that global warming will lead to more rain because warmer air can hold more moisture, it is difficult to attribute any one event to climate change. A more detailed answer, perhaps with a definitive conclusion, would come months or years later in a paper published in a peer-reviewed journal.

But scientists in Europe have much more rapidly assessed the role of climate change in the European floods, when parts of France got a month’s worth of rain in a few days in late May.

Their conclusion is that climate change made the flooding in France far more likely. But they were unable to draw a conclusion about Germany.

The researchers, from a group called World Weather Attribution that is coordinated by the climate-change research organization Climate Central, used similar approaches to the methods employed by longer peer-reviewed studies. This includes analyzing historical temperatures for the region and running many computer simulations with regional climate models, including some in which it is assumed there is no human-caused climate change.

For an extreme three-day rain event like the one that occurred in France, the scientists’ best estimate was that global warming increased the probability of such a deluge by 80 percent for the Seine River basin (which includes Paris, where the river rose about 20 feet above normal) compared with a world where the climate was not changing.

For the Loire River basin, to the south and west of Paris, the best estimate was a 90 percent greater likelihood. For both regions, the researchers said, they had high confidence that there was at least a 40 percent greater likelihood of a three-day deluge because of climate change.

In Germany, even though the rains were caused by the same meteorological conditions — essentially a zone of low-pressure air that stalled over the region — the rains tended to come in shorter, more intense bursts, said Heidi Cullen, chief scientist at Climate Central.

So in their analysis of Germany, the researchers looked at the likelihood of one-day extreme events, but their analysis found no consistent link to climate change.

The study by the team, which includes scientists from the Royal Netherlands Meteorological Institute, Oxford University and other institutions, will soon be submitted for peer review and eventual publication in a journal. But the group has embraced this rapid-response approach as a way of increasing public awareness of the effects of climate change.

“After every event like this, there’s a lot of speculation in the media about whether climate change is responsible,” Dr. Cullen said. “The scientific community has the responsibility, and the tools, to analyze these things objectively.”

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