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Seminal Study Finds ‘Climate-Change Footprint’ In North America, ‘Continent With The Largest Increases in Disasters’

“Climate­-driven changes are already evident over the last few decades for severe thunderstorms, for heavy precipitation and flash flood­ing, for hurricane activity, and for heatwave, drought and wild­-fire dynamics in parts of North America.”

So concludes Munich Re, a top reinsurer, in a major new study that, for the first time, links the rapid rise in North American extreme weather catastrophes to manmade climate change.

At the same time non-climatic events (earthquakes, volcanos, tsunamis) have hardly changed, as the figure shows.

Prof. Peter Höppe, who heads Munich Re’s Geo Risks Research unit, said:

“In all likelihood, we have to regard this finding as an initial climate-change footprint in our US loss data from the last four decades. Previously, there had not been such a strong chain of evidence. If the first effects of climate change are already perceptible, all alerts and measures against it have become even more pressing.”

The 274-page study, “Severe weather in North America” draws on “the most comprehensive natural catastrophe database worldwide,” though my favorite part is four words at the bottom of the back jacket:

Precisely.

This study builds on a September 2010 analysis by Munich Re, “Large number of weather extremes as strong indication of climate change,” which concluded:

… it would seem that the only plausible explanation for the rise in weather-related catastrophes is climate change. The view that weather extremes are more frequent and intense due to global warming coincides with the current state of scientific knowledge

At the time Höppe, explained to me what had persuaded him of the causal link:

For me the most convincing piece of evidence that global warming has been contributing already to more and more intense weather related natural catastrophes is the fact that while we find a steep increase in the number of loss relevant weather events (about tripling in the last 30 years) we only find a slight increase in geophysical (earthquake, volcano, tsunami) events, which should not be affected by global warming. If the whole trend we find in weather related disaster should be caused by reporting bias, or socio-demographic or economic developments we would expect to find it similarly for the geophysical events.

And that was before two years of off-the-charts extreme weather catastrophes, particularly in North America (see NOAA Chief 11/11: U.S. Record of a Dozen Billion-Dollar Weather Disasters in One Year Is “a Harbinger of Things to Come”).

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It was also before multiple studies linking the surge in extreme weather to global warming, particularly in North America (see NOAA Bombshell: Warming-Driven Arctic Ice Loss Is Boosting Chance of Extreme U.S. Weather and links therein and below).

The new study finds:

Nowhere in the world is the rising number of natural catastrophes more evident than in North America. The study shows a nearly quintupled number of weather-related loss events in North America for the past three decades, compared with an increase factor of 4 in Asia, 2.5 in Africa, 2 in Europe and 1.5 in South America.

The study draws on a forthcoming journal article on how global warming is driving up “large-scale thunderstorm forcing”:

The results of the study indicate that climatic changes have driven up multi­year aver­ages of thunderstorm-­related normalized losses since 1970 and that anthropogenic climate change, most likely respon­sible for increasing levels of humidity over time, is fully con­sistent with this change.

Here’s a key figure on thunderstorm losses from the Munich Re study, “normalized to the current amount of destructible wealth exposed in the areas hit.” The “normalized annual overall thunderstorm losses displays a clear positive trend, even if the record­breaking year 2011 is ignored”:

No normalization is perfect. After all, while it’s certainly true that socio-­economic factors mainly drive up losses (and so must be accounted by some type of normalization scheme), it’s also true that there are factors typically not accounted for in these kind of analyses that would tend to reduce losses. For instance, building codes are better, and weather forecasting has improved, giving people more warnings of severe storms, and so on.

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The scientific literature is also clear that we can expect an increase in thunderstorm intensity and destructiveness as greenhouse gas concentrations rise (see, for instance, here). And so the Munich Re study concludes:

Based on studies projecting the number of days with high thunderstorm poten­ tial to further increase with climate change, it can be expected that the number of large loss events will continue to rise. This translates into an imperative to take account of increasing losses over time in natural hazard risk management.

After all, we have warmed “only” about 1.4° Fahrenheit in the past century. We are poised to warm more than 5 times that this century. And that means — if we are foolish enough to stay anywhere near our current emissions path — we ain’t seen nothing yet.

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