Abstract: Stratocumulus clouds cover 20% of the low-latitude oceans and are especially prevalent in the subtropics. They cool the Earth by shading large portions of its surface from sunlight. However, as their dynamical scales are too small to be resolvable in global climate models, predictions of their response to greenhouse warming have remained uncertain. Here we report how stratocumulus decks respond to greenhouse warming in large-eddy simulations that explicitly resolve cloud dynamics in a representative subtropical region. In the simulations, stratocumulus decks become unstable and break up into scattered clouds when CO 2 levels rise above 1,200 ppm. In addition to the warming from rising CO 2 levels, this instability triggers a surface warming of about 8 K globally and 10 K in the subtropics. Once the stratocumulus decks have broken up, they only re-form once CO 2 concentrations drop substantially below the level at which the instability first occurred. Climate transitions that arise from this instability may have contributed importantly to hothouse climates and abrupt climate changes in the geological past. Such transitions to a much warmer climate may also occur in the future if CO 2 levels continue to rise.
Have I got this right? 8 K (8°C) is terrifying, but 1,200 ppm is almost 3x where we are now.
Correct. But the thing to remember is that we're going up by 2-3 PPM/year, and the arctic permafrost is almost certain to release its methane long before we get to 1200. Civilization is all but certain to collapse after that.
Full title is
“Possible Climate transitions from breakup of stratocumulus decks under greenhouse warming (2019)”. Condensed title because it was too long for the title field.