The weather appears to be getting more intense. In the United States, last month was the hottest June on record, and this past week, The New York Times reported that “the summer of 2021 appears to be on pace to be the [country’s] hottest on record.” Devastating wildfires are blazing through the American West, and globally, while communities in China, Germany, and Belgium are coping with the aftermath of deadly flooding from intense precipitation. What is happening?

Noah Diffenbaugh, a climate scientist and senior fellow at Stanford University, says there’s always natural variation in the weather and the climate, but “we now have clear evidence that global warming is increasing the risk of unprecedented heat.” He also notes that extreme precipitation intensity is “one of the clearest signatures of global warming.” Although the world could still rally to meet the climate crisis and mitigate its effects, Diffenbaugh explains, “We can expect increases in the probability and severity of extreme heat to continue to intensify” in the summers to come.

Graham Vyse: Why is it so hot?

Noah Diffenbaugh: Left on its own, the climate system will vary. It varies day to day, month to month, season to season, and year to year. We get hot years and cool years. We get hot summers and cool summers. We even get heat waves as part of our normal climate. That’s the baseline—and then global warming is occurring against it. The amount of energy in the climate system is increasing as a result of the emission of greenhouse gases into the atmosphere, so in addition to those natural variations in the climate system, we’re also experiencing climate change.

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