Response and Feedback of Cloud Diurnal Cycle to Rising Temperatures

TL;DR

This study investigates how shifts in the cloud diurnal cycle due to rising temperatures affect Earth's energy budget, highlighting the importance of accurately modeling these temporal changes for climate predictions.

Contribution

It provides a comprehensive analysis of cloud cycle phase shifts using satellite data and models, emphasizing their feedback effects on climate change.

Findings

CCP shifts earlier over oceans in warm periods

CCP shifts later over land in warm periods

Positive feedback on climate due to reduced solar reflection

Abstract

By reflecting solar radiation and reducing longwave emissions, clouds regulate the earth's radiation budget, impacting atmospheric circulation and cloud dynamics. Given the diurnal fluctuation of shortwave and longwave radiation, a shift in the cloud cycle phase (CCP) may lead to substantial feedbacks to the climate system. While most efforts have focused on the overall cloud feedback, the response of CCP to climate change has received much less attention. Here we analyze the variations of CCP using both long-term global satellite records and general circulation models (GCM) simulations to evaluate their impacts on the earth's energy budget. Satellite records show that in warm periods the CCP shifts earlier in the morning over the oceans and later in the afternoon over the land. Although less marked and with large inter-model spread, similar shifting patterns also occur in GCMs over the oceans with non-negligible CCP feedbacks. Over the land, where the GCM results are not conclusive, our findings are supported by atmospheric boundary layer models. A simplified radiative model further suggests that such shifts may in turn cause reduced reflection of solar radiation, thus inducing a positive feedback on climate. The crucial role of the cloud cycle calls for increased attention to the temporal evolution of the cloud diurnal cycle in climate models.