Opposing trends of cloud coverage over land and ocean under global warming

Clouds play a key role in Earth's energy budget and watercycle. Their response to global warming contributes the largest uncertaintyto climate prediction. Here, by performing an empirical orthogonal functionanalysis on 42 years of reanalysis data of global cloud coverage, we extractan unambiguous trend and El-Nino-Southern-Oscillation-associated modes.The trend mode translates spatially to decreasing trends in cloud coverageover most continents and increasing trends over the tropical and subtropicaloceans. A reduction in near-surface relative humidity can explain thedecreasing trends in cloud coverage over land. Our results suggest potentialstress on the terrestrial water cycle and changes in the energy partitionbetween land and ocean, all associated with global warming.