Scientists Study Links Between Climate Change and Extreme Weather
cause that heat wave? That hurricane? That drought? examined extreme weather events last year, including drought, floods and storms, to look for signs that climate change was a cause or contributor and found mixed results. The papers are part of a broader effort to recognize the effects of climate change as the world warms, and to tease out those factors from other possible causes of extreme events. Climate change is often discussed in terms of predictions about what may happen in the next 100 years or more as average global temperatures rise. But an emerging field of science is dedicated to discerning whether climate change is already having effects, and what they might be. The set of 32 studies published Thursday examined 28 extreme weather events in 2014; it is the fourth in a series of annual reports, and appears in The Bulletin of the American Meteorological Society. The studies this year are pretty evenly split, about 50-50, for those that did and did not find a role for climate change in the events likelihood or intensity, said Stephanie Herring, lead editor of the report and a National Oceanic and Atmospheric Administration climate scientist, in a news conference. The strength of the climate change signals that we see really varies based on the type of event being looked at. The papers suggest that human-caused climate change greatly increased the likelihood and intensity of heat waves in some regions, including Argentina, Europe, China, the Korean Peninsula, Australia, and the northern Atlantic and Pacific Oceans. The researchers also say that climate change probably had a role in the unusually large number of tropical cyclones that hit Hawaii last year. The scientists, however, did not discern the influence of climate change in every event, nor did they see it playing a consistent role in certain types of events, like drought. According to the papers, which run to nearly 200 pages altogether, some droughts appeared to have more to do with population growth and government policies than rising levels of carbon dioxide and its effects. The researchers, however, did conclude that was made worse by a lack of rainfall linked to climate change. It is by no means a prevailing one-story-fits-all-events type of approach to this, said Martin Hoerling, an editor of the report and a NOAA meteorologist, at the news conference. It does require a specific analysis of each case on its own merit. No strong link was established between climate change and the wildfires last year in the American West, or to the unusually tough Midwestern winter, which was tied more strongly to a pattern of unusual winds in the tropical Pacific. The authors added, however, that even where no link to climate change was detected, The failure to find a human fingerprint could be due to insufficient data or poor models. The authors emphasized that they were not describing direct cause and effect, but an analysis of probabilities based on computer models and other factors. The analysis contains uncertainty, said , an author of the paper on Hawaiian hurricanes and an associate research scholar at Princeton who works at the at NOAA. The analysis by Dr. Murakami and colleagues took into account many factors, including natural variability and phenomena like El Nino, that play roles in hurricane formation. But the signal of human-caused climate change was clearly present in the models, he said, so we still see that global warming increased the probability of tropical cyclones in Hawaii. The efforts to evaluate the effects of climate change are important for planning responses to extreme weather and a changing world, said , an author of one of the studies and chief scientist for , a news and research organization in Princeton, N.J. Communities, businesses and governments affected by extreme events are increasingly asking for objective assessments of the causes, she said. Dr. Cullen also leads the , an international coalition formed to quickly determine climate links to extreme weather events. In some instances, scientists are now able to quantify the relationship between an extreme event and long-term warming trends, rather than consigning the public to reliance on dueling speculations not grounded in science, she said. The meteorological society reports do not sit well with some climate scientists who remain wary of the focus on tying climate change to specific events rather than taking a broader view. , a climate expert at Pennsylvania State University, said the current level of warming of about 1.5 degrees Fahrenheit around the globe (and somewhat more over North America and the Arctic) has fundamentally influenced all meteorological events, not just those that get written up in a study. Dr. Mann said the work and the debate about it were useful. If anything, this particular debate underscores that the question is no longer whether there is an influence of climate change on extreme weather events. The debate is simply over the magnitude and extent of that influence. Nicholas St. Fleur contributed reporting.