Territory Affected by Extreme Weather Increased 90 Times Over Past Decade

Zafrir Rinat
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Flooding in Germany, July
Flooding in Germany, JulyCredit: REMKO DE WAAL / AFP
Zafrir Rinat

The amount of territory affected by extreme climate events worldwide was 90 times greater over the last decade than the amount affected by such events between 1950 and 1980, a new study has concluded.

The biggest increase was in the tropics, according to the study, which was published last week in the journal “Climate and Atmospheric Science.”

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The researchers said that about a quarter of the extreme rainfall events over the last decade could be ascribed to the influence of climate change. The average temperature worldwide has risen by a quarter of a degree over the last decade.

The study examined the frequency of events in which the temperature or the amount of rainfall deviated from the monthly average in each of the regions studied. It was conducted by scientists from the University of Madrid, the University of Amsterdam and Germany’s Potsdam Institute for Climate Impact Research.

The scientists chose the period from 1950 to 1980 as their basis for comparison because there is a lot of information about those decades and because it is considered a relatively stable period.

A wildfire in California, last monthCredit: PATRICK T. FALLON / AFP

The study ranked each event on a scale of 1 to 4 based on how much it deviated from the local monthly average, with 4 representing the greatest deviation. It founded that events ranked as a 3 – what the study terms 3-sigma events – affected nine percent of the earth over the last decade. That is 90 times the amount of territory affected by 3-sigma events from 1950 to 1980.

Moreover, there were no 4-sigma events during the control period, whereas over the last decade, 4-sigma events affected three percent of the earth.

One example of a 4-sigma event is the unprecedented heat wave that hit the western parts of Canada and the United States a few months ago. Altogether, the study said, the number of extreme heat events in which previous monthly records were shattered was eight times higher than what would have been expected without the influence of global warming.

Another notable finding was that the number of extreme weather events rose particularly sharply in tropical regions. One reason for this, the researchers said, is the rise in humidity in these regions due to global warming. Each one-degree temperature increase in these regions raises humidity by seven percent, which in turn increases the amount of rain that is likely to fall.

Altogether, the number of extreme rainfall events rose by 30 percent over the last decade compared to 1950-80.

What these findings mean, the researchers said, is that a single decade of global warming is enough to cause a significant rise in the frequency of extreme weather events. Therefore, this trend can be expected to worsen in the coming decade, to the point that it could endanger large numbers of people in several parts of the world, they warned.

“These data show that extremes are now far outside the historical experience. Extreme heat and extreme rainfall are increasing disproportionately,” one of the researchers, Stefan Rahmstorf of the Potsdam Institute, said in a press statement issued by the institute. “Our analysis confirms once again that for the impacts of global heating on us humans, every tenth of a degree matters.”

The latest report by the UN’s Intergovernmental Panel on Climate Change, published two months ago, discussed extreme weather events at length. It said that an increase of half a degree in the earth’s average temperature is enough to cause real changes in the frequency of extreme events.

Last week, America’s National Academy of Sciences published its own report on the need for additional research into the climate crisis. One field in which such research is needed, the report said, is how extreme events affect each other. For instance, heavy rainstorms can cause severe soil erosion in places where trees have been destroyed by a wildfire caused by hotter temperatures.

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