Hidden Warming Effects of Cloud Cycle Errors in Climate Models

TL;DR

This paper investigates errors in the diurnal cycle of clouds in climate models, revealing inconsistencies in amplitude and phase that impact radiation estimates and are linked to cloud parametrization issues.

Contribution

It quantifies cloud cycle discrepancies in models versus observations and highlights their potential effects on climate projections.

Findings

Mean cloud properties are reliable in models.

Diurnal cycle amplitude and phase show significant inconsistencies.

Overestimation of cloud liquid water path compensates for radiation errors.

Abstract

Clouds' efficiency at reflecting solar radiation and trapping the terrestrial one is strongly modulated by their diurnal cycle. Much attention has been paid to mean cloud properties due to their critical role in climate projections; however, less research has been devoted to their diurnal cycle. Here, we quantify the mean, amplitude, and phase of the cloud cycles in current climate models and compare them with satellite observations and reanalysis data. While the mean values appear to be reliable, the amplitude and phase of the diurnal cycles of clouds show marked inconsistencies, especially over land. We show that, to compensate for the increased net radiation input implied by such errors, an overestimation of the cloud liquid water path may be introduced during calibration of climate models to keep temperatures in line with observations. These discrepancies are likely to be related to cloud parametrization problems in relation to atmospheric convection.