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This is how extreme weather events and climate change are connected

This is how extreme weather events and climate change are connected

It is widely known that weather is not climate. It is also widely known that climate, and therefore climate change, can significantly affect the weather over time — not only with respect to changes in trends in important indicators like temperature and precipitation, but also with respect to the likelihoods and intensities of extreme events.

The correlation between climate and impacts is, however, most often complicated by confounding factors that include all variety of human behaviors; and that is why something called “forensic attribution” is now a growth industry. Benjamin Santer crafted an up-to-date and extensive review of the state of knowledge of forensic attribution even in its formative stages and summarized in a recent op-ed.

In 2021, when an extreme event like the recent flash flooding in western Germany occurs, the question is “How much of the observed extreme intensity can be attributed to climate change?”

As is always the case in climate change, the answer to the question is always “It depends.” But on what? Is there any way to sort out the facts about both change and the rate of change?

It turns out that a scientifically rigorous answer to this question is “Yes.” Since responding to climate change is a risk management problem, the world has accepted that the key to organize our thoughts must focus on the two fundamental components of risk — likelihood and consequence or, in the vernacular, frequency and intensity.

Take, for example, the very recent severe flooding in Western Germany. Three months of rain fell in three hours. Flooding caused enormous damage with nearly 200 deaths and more than 300 missing as of July 20. It was the worst flooding event in more than 50 years — but that means that there had been a similar flooding event in the lifetimes of some residents. It was very unusual to see it repeat in 2021, but it was not statistically difficult to explain.