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Severe Thunderstorms Top the List of Climate Disasters So Far This Year

Spring cold snaps were also costly in the U.S. and Europe.
Lightning strikes during a thunderstorm in Las Vegas, Nevada.

Lightning strikes during a thunderstorm in Las Vegas, Nevada.

The economic costs of natural disasters related to global warming are adding up; some of the largest effects of these catastrophes can be felt in the United States, where politics and policies are not keeping pace with the physical realities of climate change.

During the first half of 2017, a series of extremely powerful thunderstorm outbreaks with damaging hail and tornadoes caused $41 billion of damage in the U.S., according to a new report from Munich Re, a German reinsurance company that tracks and analyzes natural disasters. So far this year there have been six severe, large-scale thunderstorm outbreaks, each causing billions of dollars in losses.

Another analysis by the National Centers for Environmental Information found 2017 marked the first time there were five separate billion-dollar extreme weather events during the first three months of a year, including a crop-killing freeze in the Southeast. Neither of the tallies includes the current drought in North Dakota, which will likely result in a near-total—and very costly—failure of the wheat crop.

For Munich Re, which puts billions of dollars on the line by backing up insurance companies, there's little doubt that the damages from severe thunderstorm outbreaks are linked with global warming, although this year's outbreak in the U.S. may have also been related to the emergence of a pool of extremely warm water off the coast of South America, which also caused deadly flooding in Chile, Peru, and Colombia.

"We think there is a signal out of the atmosphere," says Peter Höppe, a risk analyst with the company and a board member of the Global Climate Forum. "There is proof the atmosphere has become more humid. The water vapor comes from increased sea surface temperatures, which are clearly caused by global warming."

Warmer temperatures and more moisture intensify the convective events, and studies show there has been a long-term increase in the number and severity of storms in both the U.S. and Europe.

"The number of tornadoes observed in the first quarter of 2017 was twice as high as the average for the last 10 years."

"The unusual atmospheric conditions in the U.S.A. in the first half of 2017 provided the perfect conditions for powerful supercell thunderstorms, which frequently bring major hailstorms and tornadoes. The number of tornadoes observed in the first quarter of 2017 was twice as high as the average for the last 10 years," Höppe says.

Kevin Trenberth, a climate scientist with the National Center for Atmospheric Research, says the link to climate change is a clear one.

"With very high sea surface temperatures that have a strong global warming component, these flooding events break records, and cause untold damage," he says.

Thunderstorms in the U.S. were responsible for three of the world's five costliest events in the first half of the year, each causing economic losses of over $2 billion. The total economic loss from these storms amounted to $18.5 billion, of which $13.5 billion was insured. The number of tornadoes in the U.S. in the first quarter of 2017 was twice as high as the average for the years 2005 through 2015.

There are no clear climate-change projections for tornado frequency yet, but the continued rise in temperatures is sure to fuel additional severe weather, and there is ongoing research to try and limit the damage, primarily through better construction materials and techniques that can withstand large hail and strong winds. Höppe says there are now several wind tunnel labs where structures can be tested.

In Europe, one of the most damaging climate-related events was a late April cold snap that caused $1.5 billion in agricultural damage by freezing fruits and vegetables.

"This was an extremely unusual event, both because of its wide geographical spread and the severity of the losses ... largely because plant growth was well advanced thanks to mild temperatures over the preceding weeks," Munich Re reports.

In many parts of Europe, March was record-warm, which spurred early plant growth. And, in general, scientists have documented how the warming climate has caused plants to grow and flower earlier. In Austria, which was hit hard by the April freeze, fruit trees are blooming 10 to 14 weeks earlier than they did in the 1980s, which makes them more susceptible to subsequent cold snaps.

There's not much farmers can do to protect themselves from this type of damage in the short term, other than perhaps setting up warming systems for high-value crops. In the long-term, with a good prospect for more extremes, it could be beneficial to think about diversifying crops to reduce dependency on varieties that are susceptible to the pattern of early heat followed by cold snaps.

According to climate scientist Michael Mann, it's very possible that several of the recent severe and costly extreme weather outbreaks are linked to changes in the jet stream he identified in a recent study. As the Arctic warms up it slows the weather-steering jet stream, "which leads to large persistent meanders in the jet stream associated with persistent weather extremes. We have shown that climate change is increasing the incidence of this phenomenon," he says.