Robinson Meyer for theatlantic.com, | October 20, 2021

The Key Insight That Defined 50 Years of Climate Science

A climate scientist has won the Nobel Prize in Physics for the first time. It’s a reminder that the field, which emerged from the mid-20th century’s biggest questions, hasn’t always been fraught.

Read at theatlantic.com

Look out the nearest window and imagine, if you can, an invisible column of air. It sits directly on the tufts of grass, penetrates clear through any clouds or birds above, and ends only at the black pitch of space. Now envision a puff of heat rising through this column, passing through all the layers of the atmosphere on its journey. What happens as it rises? Where does it go? The answer to that simple question is surprisingly, even ominously important for the climate. But for nearly a century, the world’s best scientists struggled to resolve it.

The problem starts with temperature: As the intrepid puff of heat rises, it will encounter cooler air at first, then warmer air, then cooler again, until eventually it reaches the stratosphere, which is frigid. These temperature changes are paired with changes in humidity: Because hotter air can hold more water—as anyone who has endured a July day in Atlanta can tell you—the atmosphere’s warmer layers will generally have more water vapor than the cooler ones. But—and here’s the rub—water vapor is the most powerful heat-trapping gas on Earth, so it also affects air temperature. If more water is in the atmosphere, it will warm up the cooler layers.

This is complicated further by the fact that water vapor is very fickle. It falls out of the atmosphere as rain or snow after a few days and only reenters because greenhouse gases—chiefly, carbon dioxide—keep the planet’s temperature high enough for it to evaporate and rise again.

So to describe that puff of heat moving through the atmosphere, “you have to kind of include all of the temperature effects, as well as all the greenhouse-gas effects,” says Paul N. Edwards, a lead author of this year’s Intergovernmental Panel on Climate Change report and the director of the Program on Science, Technology, and Society at Stanford. The first scientist to unknit those effects and solve the riddle was Syukuro Manabe. That work won Manabe, now a 90-year-old Princeton professor, the Nobel Prize in Physics earlier this month.

Manabe is one of the first climate scientists to win the physics Nobel. (When he received the call that he had won, he reportedly exclaimed, “But I’m just a climatologist!”) He shared this year’s prize with Klaus Hasselmann, a climate scientist at the Max Planck Institute for Meteorology in Germany, and Giorgio Parisi, a theoretical physicist at Sapienza University of Rome.

Manabe’s win is a reminder that climate science was not always the politically fraught undertaking it is today—and that it is, in itself, a major scientific achievement of the past half century. Climate science emerged from the invention of the digital computer, the military and economic need to understand weather and climate, and a series of pesky questions—such as the question of heat in the air column—that pen and paper alone could not resolve.

In the 1950s, a team of American scientists started trying to describe the climate not as a set of elegant Einsteinian equations, as had been tried by the researchers before them, but as a matrix of thousands of numbers that could affect one another. This brute-force approach was borrowed from work by John von Neumann, a physicist who had used it to investigate atomic explosions. Applied to climate, it was immediately successful, producing the first short-term weather forecasts and later the first general circulation models of the atmosphere.

Manabe, who is usually called Suki, was one of several Japanese scientists invited to America in 1958 to produce these models. “The original motivation of studying [the] greenhouse effect has very little to do with my concern over environmental problem[s],” Manabe said in a 1998 interview with Edwards. Instead, he researched out of curiosity: Carbon dioxide and water vapor were the most important factors in Earth’s climate other than the sun.

It was then that he began to study the movement of heat vertically through the atmosphere. “In a lot of ways, Manabe just kind of worried at that problem, again and again,” Edwards told me. In a series of crucial papers in the late 1960s, Manabe made several observations that set the stage for the next half century of climate science. He said, for instance, that doubling the amount of carbon dioxide in the atmosphere would raise Earth’s average temperature by 2.3 degrees Celsius—a reasonable lower bound for that number, scientists now believe.

Manabe also found that increasing the CO₂ in the atmosphere would increase the temperature of the troposphere, the layer of air closest to Earth’s surface, while lowering the temperature of the stratosphere, the next layer above it. That “fingerprint” of climate change was later found in the real world by the climate scientist Benjamin Santer.

Although Manabe was a talented mathematician, he did not know how to program the supercomputers that powered his work. Several of his seminal papers were co-authored with Richard Wetherald, a computer scientist who converted Manabe’s equations into code.

Manabe remained a major figure in the field for decades. In 1988, when James Hansen, then director of NASA’s Goddard Institute for Space Studies, warned a Senate committee that global warming “had begun,” Manabe was seated down the dais, according to Joseph Majkut, a climate scholar at the Center for Strategic and International Studies. Although Manabe’s language was not as dire as Hansen’s, he warned the Senate about the then-unusual drying-out of California. He retired from Princeton a decade later at age 68—then worked another 20 years in Japan, Edwards said. He now lives in Princeton.

Manabe is universally described as kind and almost ceaselessly curious. “When I was a graduate student, Suki was still around the building, and one of the things that was most engaging—apart from being around this very senior, important scientist—was the extent to which he still wanted to apply his curiosity and rigorous thought to the research we were doing as students,” Majkut, who holds a doctorate in atmospheric science, told me.

Manabe is also a champion of simplicity.

“One of the key insights is that he would remind us as students not to get too enamored of our computer models and focus on the scientific insights that they allowed us to probe,” Majkut said. “From him, I learned that you can often learn more from a simple model well interpreted than from something big and fancy.”