Quadrupled CO2 Causes Changes in Cloud Responses

Extreme climate change has been found to alter cloud cover behavior throughout East Asia (EA).

Clouds provide a large feedback to the processes that cause global warming. Image Credit: Hua Zhang

According to recent research, a warmer climate with higher levels of CO₂ in the atmosphere and slow cloud responses to meteorological mechanisms result in a cooling effect above some regions of EA.

In certain areas of Asia, the opposite effect is noted. Climatologists trying to understand how CO₂ and clouds interact are interested in this novel dynamic.

Clouds play an important role in balancing the radiation budget, and they have a large feedback on global warming caused by the increase of greenhouse gases. The uncertainty of cloud feedback has the most impact out of all the climate feedbacks.

Hua Zhang, Professor, Climate Scientist, Chinese Academy of Meteorological Sciences

Prof. Zhang and her team from the Chinese Academy of Meteorological Sciences, the University of Chinese Academy of Sciences, and the Beijing Climate Center have published extensive cloud–climate feedback research in Advances in Atmospheric Sciences.

We can obtain the clouds’ responses to increased greenhouse gases from climate models and divide the feedback into fast responses with time scales of days to months and slow responses with time scales of years to decades.

Hua Zhang, Professor, Climate Scientist, Chinese Academy of Meteorological Sciences

In the research, the investigators segregated slow and fast cloud responses to an abrupt atmospheric CO₂ quadrupling over EA. They employed a conventional circulation model, BCC_AGCM2.0, created by the China Meteorological Administration to acquire quantitative data.

The research also considered a total cloud response, which included the following components: the low cloud cover (LCC), high cloud cover (HCC), and total cloud cover (TCC).

These variables revealed an increase north of 40 °N and a decrease south of 40 °N, excluding the Tibetan Plateau (TP).

The mean changes of the TCC, LCC, and HCC over EA in the overall cloud response are −0.74%, +0.38%, and −0.38%, respectively.

The quick cloud cover responses are often the opposite of the slow cloud cover responses. The slow reactions dominate the total responses, but the immediate response dictates the HCC change in the case of the TP.

The mean net cloud forcing (NCF) above EA under the quadrupled CO₂ warming scenario is −1.80 Watts per meter squared (W m⁻²), demonstrating a cooling effect and a slower cloud response.

According to scientists, this can at least partially counterbalance the warming effect brought on by the quadrupling of CO₂ concentrations.

The NCF over the TP, south China and northeast China, however, are −6.74 W m⁻², 6.11 W m⁻², and −7.49 W m−², respectively, which has the potential to increase global warming.

Studying cloud responses to quadrupled CO₂ over EA provides a better understanding of the changes and effects of clouds under extreme warming in the future, and our research especially reveals the role of the slow response of clouds.

Hua Zhang, Professor, Climate Scientist, Chinese Academy of Meteorological Sciences

Journal Reference

Zhou, X., et al. (2022) Decomposition of Fast and Slow Cloud Responses to Quadrupled CO₂ Forcing in BCC-AGCM2.0 over East Asia. Advances in Atmospheric Sciences. doi.org/10.1007/s00376-022-1441-7.