“Going someplace far away, we now know, is the biggest single action a private citizen can take to worsen climate change,” the journalist Andy Newman in wrote recently in The New York Times. “One seat on a flight from New York to Los Angeles effectively adds months worth of human-generated carbon emissions to the atmosphere. And yet we fly more and more.”

I certainly have. Since the turn of the millennium, I have amassed approximately 270,000 air miles, equivalent to flying around the planet almost a dozen times over. Based on the correlation between carbon-dioxide output and polar-ice melt established in the 2016 study cited in Newman’s article, this means that my flights alone have accounted for some 90 tons of carbon emissions, enough to melt about 260 square meters of polar sea ice. I have melted a tennis-court-size chunk of the Arctic all on my own.

Ignoring the impact of climate change is no longer an option, because I have seen its impact on four continents. In temperate London, where I live, global warming for now means that I didn’t wear a scarf last winter, and the daffodils opened early. Far more tangible are the symptoms of climate crisis I’ve witnessed abroad: shrinking glaciers in the Andes, record-breaking heat waves in southern Europe, the startling expansion of the Gobi desert. It has also become much harder to ignore the alarming testimonies of the people who live among them. Earlier this year, I received an email from a mountain guide I knew in Malawi. He was asking for help because his house had been washed away after Cyclone Idai barreled through southeastern Africa.