June, July, and August were the hottest three-month spanin human history. By the end of summer in the northern hemisphere, more than 110 million people in the United States alone were still living under governmental excessive-heat warnings, as temperatures hit record highs in the country’s Southeast and Southwest. To the north, Canadian wildfires had burned more than 20 million acres, forcing many to evacuate their homes and sending thick, hazardous smoke down through the U.S. Northeast and Midwest.

In the meantime, unprecedented flooding hit India and China. Flooding also killed dozens in Haiti, Pakistan, Nepal, South Korea, Colombia, and the U.S. state of Vermont. A cyclone killed more than 400 in Burma and Bangladesh. And this year marked the first time two tropical storms formed in the Atlantic during the month of June—an early and ominous start to a hurricane season that led recently to devastation from Idalia across Cuba, Mexico, and the U.S. Southeast. Now, with Tropical Storm Daniel making landfall in eastern Libya, thousands are already feared dead. Where is this all going?

Rachel Cleetus is a researcher and the policy director in the Climate and Energy program at the Union of Concerned Scientists, a nonprofit science-advocacy organization founded in 1969 at the Massachusetts Institute of Technology. According to Cleetus, while there’s some natural variation in weather patterns behind this year’s extremes, they’re mostly among the effects of anthropogenic climate change—climate change caused by us. These effects are in the extreme weather taking place all around the world—and also in less visible but no less significant environmental changes, as in rising ocean temperatures, melting ice sheets, and withering rainforests. The increased adoption of renewable-energy sources is encouraging, Cleetus says—but for now, they’re still competing with heavy, sustained investment in fossil fuels; the world is far from meeting the targets its leaders have set for emission reductions; and uncertainty about the extent of “irreversible changes in natural systems” remains high.

Michael Bluhm: How do you understand all this devastating weather?

Rachel Cleetus: We know it’s been amplified this year by the El Niño effect—a regular warming of ocean currents that increases air temperatures and rainfall levels. But the fundamental climate trend the El Niño effect is amplifying is very clear—and very in keeping with what a global scientific consensus has predicted for years now: As heat-trapping emissions increase, mainly from fossil fuels, average temperatures are rising around the world, and a range of transformative effects are accompanying them.

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