Stratocumulus clouds spread like swollen cotton balls in orderly rows above the ocean in subtropical regions. The low hovering clouds provide the shadow of the planet and help keep the Earth cool. But in a new study released this week, researchers say rising levels of carbon dioxide in the atmosphere could eliminate these clouds. The discovery means that in "normal" emission scenarios, the Earth could heat up to 14 degrees Celsius a century from now.
"We are disrupting a complex system that we do not yet fully understand and the system might respond in a surprising and non-linear way," said Tapio Schneider, a climatologist at the California Institute of Technology in Pasadena, who led the new research. The results of his team are "a warning shot" for the future, "he says.
Stratocumulus clouds act as umbrella for the planet. Low clouds reflect about 30 to 60% of the sunlight in the space. Although it is the most common type of cloud on Earth and covers nearly 20% of tropical oceans, global climate models have difficulty simulating them.
Part of the problem is that clouds drive climate processes at scales too small to be solved by our current computer models. Instead, current global climate models can estimate the impact of these cloud formations with the help of related variables such as temperature and humidity. Schneider's team, however, explains that this method underestimates the impact that stratocumulus and other low clouds could have on global temperatures.
In the new study, Schneider and his team modified the climate simulations. Rather than adjusting the simulation resolution on the basis of large – scale dynamics such as temperature or humidity, as do current climate models, the researchers solved the problem of dynamics at the same time. cloud scale. The analysis took several months and 2 million basic hours – number of hours running the simulation multiplied by the number of processor units – d & # 39; computer. But in the end, the complex computer survey revealed a critical point for carbon dioxide levels to break the clouds that cool the Earth.
When carbon dioxide levels in the atmosphere exceed about 1,200 parts per million (ppm), about three times today's level, stratocumulus clouds separate sharply. And if humanity continues to burn fossil fuels at the current rate, the Earth is expected to reach 1,200 ppm by the century. The researchers published their results on Monday in the journal Nature Geoscience. Schneider's team estimates that global surface temperatures will increase 14 degrees Fahrenheit without the shadow of clouds.
And, once they are gone, the stratocumulus can never take shape again. In the researchers' analysis, clouds only reformed when CO2 levels fell below current levels.
The results "point to a blind spot in climate modeling," said Schneider. "The stratocumulus clouds are important, the current models mimic them badly, and they seemed to have missed the opportunity to get strong returns."
"We need better models," he added. With his colleagues, he works on their construction.