Englander isn’t at all sanguine. The average rate at which sea level is rising around the world, he estimates, has more than tripled over the past three decades, to five millimeters a year from 1.5 millimeters. That may still seem minute, yet as the world learned during the pandemic, exponential increases have a way of hitting hard.

“When something is on a straight line or a smooth curve, you can plot its trajectory,” Englander said. “But sea level, like earthquakes and mudslides, is something that happens irregularly and can change rather quickly and surprise us. The point is, you can no longer predict the future by the recent past.”

Another major wild card is Antarctica, where the average rate of ice mass loss is more than 150 gigatons a year. Shortly after I returned from Greenland, a glacier in West Antarctica called Thwaites, roughly the size of Florida, caught the world’s attention when a study suggested it was, according to a co-author, Robert Larter of the British Antarctic Survey, “holding on today by its fingernails.”

Or was that alarmist? In The Wall Street Journal’s editorial pages, where I used to work, the theoretical physicist Steven Koonin, a former under secretary for science in the Obama administration’s Energy Department, cast doubt on the threat from Thwaites in a voice that could have once been mine. He also thinks the risks associated with Greenland’s melting are less a product of human-induced global warming than of natural cycles in North Atlantic currents and temperatures, which over time have a way of regressing to the mean.

“Much climate reporting today highlights short-term changes when they fit the narrative of a broken climate but then ignores or plays down changes when they don’t, often dismissing them as ‘just weather,’” he wrote in February.

Another climate nonalarmist is Roger Pielke Jr., a professor of environmental studies at the University of Colorado Boulder. I call Pielke a nonalarmist rather than a skeptic because he readily acknowledges that the challenges associated with climate change, including sea-level rise, are real, serious and probably unstoppable, at least for many decades.

But that is also the source of his (relative) optimism. “If we have to have a problem,” he told me when I reached him by phone, “we probably want one with a slow onset that we can see coming. It’s not like an asteroid coming from space.”

Among Pielke’s areas of expertise is the analysis of long-term trends in weather and climate-related disasters. Even as the nominal cost of hurricanes, floods, fires and droughts has grown, the economic impact of these disasters relative to the overall size of the economy continues to fall, a function of better forecasting, infrastructure, planning and responsiveness when disaster strikes — all of which, in turn, are the result of the massive increase in wealth the world has enjoyed in the past century.

“Since the 1940s, the impact of floods as a proportion of U.S. gross domestic product has dropped by 70 percent-plus,” Pielke said. “We see this around the world, across phenomena. The story is that fewer people are dying and we are having less damage proportional to G.D.P.”

A considerable amount of data bears Pielke out. In the 1920s, the estimated average annual death toll from natural catastrophes around the globe averaged more than 500,000 a year. The 1931 China floods alone killed as many as four million people not only through drowning but also by exposure, disease and famine. A more recent example, the 1970 Bhola cyclone, killed as many as half a million people in what is now Bangladesh.

In the 2010s, the annual average death toll was below 50,000 — a tenth of what it was a century ago. Hurricane Ian, among the strongest storms ever to hit Florida, had a death toll of at least 119, a small fraction of the 8,000 believed killed by the Great Galveston hurricane of 1900

Even the poorest countries, while still unacceptably vulnerable, are suffering far fewer human and economic losses to climate-related disasters.

Global warming is real and getting worse, Pielke said, yet still it’s possible that humanity will be able to adapt to, and compensate for, its effects.

The death rate from natural disasters has fallen globally

Average number of deaths per 100,000 people, by decade

Or maybe not. A few years ago, I would have found voices like Koonin’s and Pielke’s persuasive. Now I’m less sure. What intervened was a pandemic.

Just as I had once scoffed at the idea of climate doom, I had also, for almost identical reasons, dismissed predictions of another catastrophic global pandemic on a par with the 1918-20 influenza outbreak. After all, hadn’t we pushed through previous alarms involving Ebola, SARS, MERS and vCJD (mad cow disease) without immense loss of life? Hadn’t virology, epidemiology, public hygiene, drug development and medicine all come a long way since the end of World War I, rendering comparisons with past pandemics mostly moot?

That’s what I thought until the spring of 2020, when, along with everyone else, I experienced how swiftly and implacably nature can overwhelm even the richest and most technologically advanced societies. It was a lesson in the sort of intellectual humility I recommended for others and began to realize I could use more of myself.

It was also a lesson in thinking about risk, especially those in the category known as high-impact, low-probability events that seem to be hitting us with such regularity in this century: the attacks of Sept. 11, 2001; the tsunamis of 2004 and 2011, the mass upheavals in the Arab world that began with a Tunisian street vendor’s self-immolation.

Here were some questions that gnawed at me: What if the past does nothing to predict the future? What if climate risks do not evolve gradually and relatively predictably but instead suddenly soar uncontrollably? How much lead time is required to deal with something like sea-level rise? How do we weigh the risks of underreacting to climate change against the risks of overreacting to it?

I called Seth Klarman, one of the world’s most successful hedge-fund managers, to think through questions of risk. While he’s not an expert on climate change, he has spent decades thinking deeply about every manner of risk. He’s also one of the rare people with a capacity to change his mind — including, he readily acknowledges, about climate risk. “I’ve talked to so many experts and seen so much evidence,” he told me over Zoom, “I’m convinced the climate is changing, and addressing climate change has become a philanthropic priority of mine.”

“If you face something that is potentially existential,” he explained, “existential for nations, even for life as we know it, even if you thought the risk is, say, 5 percent, you’d want to hedge against it.”

How?

“One thing we try to do,” he said, “is we buy protection when it’s really inexpensive, even when we think we may well not need it.” The forces contributing to climate change, he noted, echoing Englander, “might be irreversible sooner than the damage from climate change has become fully apparent. You can’t say it’s far off and wait when, if you had acted sooner, you might have dealt with it better and at less cost. We have to act now.”

In other words, an ounce of prevention is worth a pound of cure. That’s particularly true if climate change is akin to cancer — manageable or curable in its earlier stages, disastrous in its later ones.

For Klarman, the simplest and most obvious climate hedge is a carbon tax. By “raising the price of oil, gas and coal to make alternative energy more economically attractive,” he said, “capitalists will be incentivized to act.”

Klarman recognizes that such a tax is easier said than done because, if it’s enacted by only a few nations, it becomes more of a form of virtue signaling than a serious climate change policy. Carbon taxes also tend to impose their burdens inequitably, favoring city dwellers over exurban and rural ones, knowledge businesses over manufacturers.

There’s a reason Barack Obama rejected a carbon tax, knowing it could be deeply unpopular among voters, and why France’s carbon tax sparked the “yellow vest” public revolt that has energized the far right.

As I’ve always believed, knowing there is grave risk to future generations — and expecting current ones to make immediate sacrifices for it — defies most of what we know about human nature. So I began to think more deeply about that challenge, and others.