Possible climate transitions from breakup of stratocumulus decks under greenhouse warming

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 carbon dioxide levels rise above 1,200 ppm. In addition to the warming from rising carbon dioxide 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 carbon dioxide 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 carbon dioxide levels continue to rise.

The research was led by Tapio Schneider from California Institute of Technology, Pasadena, CA, USA and published in the journal Nature Bioscience 12, pages163–167 (2019).

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