Although scientists have known since the 1970s that clouds can both ameliorate and contribute to the Earth’s warming, the role they will play in the planet’s heating remains one of the singular uncertainties in the field.
Out of the many clouds that help regulate the Earth’s climate, the Stratocumulus, those low-lying, grayish-white clouds that are often mistaken for rain clouds, are especially significant. They cover around 20 percent of the tropical ocean, cooling the planet by reflecting sunlight back toward the atmosphere.
Despite their importance, Stratocumulus clouds have been historically underrepresented in climate models, meaning their negative feedback on surface temperatures – or their cooling effect – hasn’t been accurately reflected in climate projections.
Tapio Schneider, a climate scientist at Caltech, decided to focus on Stratocumulus clouds in a small patch of subtropical oceans, running highly detailed calculations on supercomputers for several weeks.
In February, Schneider’s team published a paper saying Stratocumulus clouds in their model broke up into smaller Cumulus clouds and actually disappeared when carbon dioxide levels reached 1,200 parts per million (ppm), or levels that are three times higher than today.
“The moment you saw the calculations it was shocking, because until then, it was kind of a thought experiment,” Schneider says. “And then it started to feel a bit more real – that it actually could happen, which is scary.” Schneider is quick to point out, however, that there are still many uncertainties in the results and that it’s an extreme scenario that shouldn’t prompt immediate panic.
“The moment you saw the calculations it was shocking, because until then, it was kind of a thought experiment.”
Other climate researchers have criticized the paper, saying the findings are based on a narrow patch of clouds and cannot be extrapolated to the entire globe.
“It’s not enough to run a model of a little box and get some of the small scales correct; all of the intermediate factors have a strong influence on how the cloudiness evolves, and that’s what’s missing from that paper,” says Bjorn Stevens, a director at the Max Planck Institute for Meteorology in Hamburg.
To Schneider’s own surprise, his paper generated a slew of grim headlines, adding to the near-daily feed of news articles about climate calamity. “Climate change kills off clouds,” read one headline. Another got even more apocalyptic: “Climate change is eliminating clouds. Without them, Earth burns.”
The California researchers posit that the dispersal of the Stratocumulus would add some 8 degrees Celsius to the Earth’s temperature, in addition to the 4 degrees of warming caused by greenhouse gas emissions alone. The last time the Earth experienced such conditions was some 50 million years ago, when crocodiles swam in the Arctic.
A United Nations climate panel has estimated that human activities have contributed between 0.8 degrees and 1.2 degrees Celsius to the planet’s temperature since the pre-industrial era. That increase has already contributed to significant polar ice melt and led to a rise in wildfires, droughts and epic heat waves.
In May, the concentration of carbon dioxide in the atmosphere hit 415 ppm at the Mauna Loa observatory 11,000 feet above sea level in Hawaii, the highest measurement taken at the site since daily observations began in the late 1950s. Carbon dioxide levels are now higher than they have been for millions of years. If emissions continue at their current pace, the scenario modeled by Schneider’s team in which the Stratocumulus go extinct could be met in a century.