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Report links 2012 extreme weather with human-induced climate change

Source: World Resources Institute - Mon, 9 Sep 2013 09:33 AM
Author: C. Forbes Tompkins and James Bradbury, WRI
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Flood waters rise against a historic flood marker near the Murrumbidgee River at Wagga Wagga, about 380km (236 miles) southwest of Sydney, Australia, in this handout picture made available Mar. 8, 2012. REUTERS/New South Wales State Emergency Service/Handout
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Any views expressed in this article are those of the author and not of Thomson Reuters Foundation.

As extreme weather events like wildfires, heat waves, downpours, and droughts continue to make headlines in the United States and around the world, many have wondered what their connection is to climate change. A new report sheds some light, firmly drawing correlations between several extreme weather events in 2012 and human-induced warming.

In a report published last week in the Bulletin of the American Meteorological Society (BAMS), scientists at the National Oceanic and Atmospheric Administration (NOAA), the UK Met Office, and other institutions examine the extent to which manmade climate change influenced 12 extreme weather events that occurred in 2012. The conclusions of yesterday’s report are similar to those of a related, first-of-its-kind study published last year that focused on extreme weather events in 2011.

Three big takeaways reveal troubling insights into how climate change is impacting weather – and what dangers a warmer future may hold:

1) New methods and better data enable scientists to connect the dots between extreme weather and climate change.

It is remarkable and worrisome that human influences are already having a discernible impact on individual extreme weather events. Because of the random nature of weather, it had been assumed until recently that no single event can be attributed to climate change. However, with new research methods and better quality data, scientists are increasingly able to connect the dots between extreme weather events and climate change.

For example, one can quantify the odds of a typical heat wave happening and estimate how much a warmer world would load the dice toward the more frequent occurrence of a similar event. Or, to understand the causes of melting sea-ice or severe drought, researchers can now use sophisticated climate models to help identify – and potentially isolate – various factors that could individually contribute or dynamically interact to influence climate conditions in a particular region.

2) Human influence was detected in several extreme weather events in 2012.

The Arctic sea ice extent reached an observed all-time record low in 2012, mostly due to warmer atmospheric and oceanic temperatures melting the younger, thinner ice. The report determined that natural climate variability alone is “extremely unlikely” for explaining this observed magnitude of melting. The report cites research (Overland and Wang 2013) showing that an extrapolation of recent trends would cause further decline in the extent of summer Arctic sea ice, with the region expected to become largely ice-free during summer months in the coming decades.

Extreme rainfall inundated communities in southeastern Australia in March 2012. While there is still uncertainty on the impact of human-induced warming on extreme precipitation events, the report shows that the likelihood of above-average precipitation over the longer term was determined to have increased due to manmade climate change.

Scientists also studied the impacts of climate change on extreme weather in the United States. For the north-central and northeastern region of the country, the heat wave that resulted in July 2012 being the hottest month on record for the contiguous United States was found to be four times more likely to occur today – as a result of human-induced climate change – than in pre-industrial times.

Additionally, due to sea-level rise, extreme flooding along the mid-Atlantic coast on the scale of Hurricane Sandy’s impact is more than 30 percent more likely to occur today than it would have been roughly half a century ago. Furthermore, if sea levels at Sandy Hook, NJ were to rise by another 1.2 meters, (a scenario projected by the 2013 National Climate Assessment), the flooding level caused by Hurricane Sandy could be expected roughly once every 20 years by the end of the century.

3) Not every extreme event can be measurably attributed to climate change.

The report included several studies of 12 extreme weather and climate events, finding that half of these were unlikely to have been significantly influenced by human-induced climate change. For example, while the U.S. drought of 2012 was exacerbated by accompanying record high temperatures throughout much of the year, researchers did not find a clearly detectable human influence on this historic event. Researchers in this report found that the majority of the 2012 drought was likely attributable to natural variability. Other studies have concluded that regional aspects of the drought - like in the Central Great Plains - were likely the result of a temporary northern shift in weather systems and infrequent thunderstorms, which typically occur in July and August.

As authors of the report point out, just as speeding increases the chance of having a car accident, climate change intensifies the risk of heat waves, droughts, and heavy precipitation. On the other hand, climate change does not always strongly influence every extreme weather event, just as speeding does not cause every car accident. But they can both be significant contributors.

What does the future hold?

In addition to the research findings in this special report, a much broader and growing body of scientific research has shown that several types of extreme events are becoming more frequent and severe. For heat waves, heavy precipitation and coastal flooding, studies show that upward trends are likely caused by human-induced global climate change. Further temperature rise is expected to make matters worse, also bringing more frequent drought, flooding, and more severe tropical storm intensities.

Countries are already experiencing the disastrous impacts of extreme weather events on their communities, their infrastructure, and their economies. The United States alone has experienced 25 extreme weather events since 2011 that each caused more than $1 billion in damages, contributing to the loss of more than 1,000 lives and costing each American family roughly $400 per year. As research shows, the world is likely in for more extreme weather if it stays on its current course. As the costs of climate inaction become clearer, the urgency for shifting toward a low-carbon economy becomes ever-more pressing.

C. Forbes Tompkins and James Bradbury work with the Climate and Energy Program at the World Resources Institute.

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