|Title||Evidence for climate change in the satellite cloud record|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Norris JR, Allen RJ, Evan AT, Zelinka MD, O’Dell CW, Klein SA|
|Volume||advance online publication|
|Type of Article||Letter|
Clouds substantially affect Earth’s energy budget by reflecting solar radiation back to space and by restricting emission of thermal radiation to space. They are perhaps the largest uncertainty in our understanding of climate change, owing to disagreement among climate models and observational datasets over what cloud changes have occurred during recent decades and will occur in response to global warming. This is because observational systems originally designed for monitoring weather have lacked sufficient stability to detect cloud changes reliably over decades unless they have been corrected to remove artefacts. Here we show that several independent, empirically corrected satellite records exhibit large-scale patterns of cloud change between the 1980s and the 2000s that are similar to those produced by model simulations of climate with recent historical external radiative forcing. Observed and simulated cloud change patterns are consistent with poleward retreat of mid-latitude storm tracks, expansion of subtropical dry zones, and increasing height of the highest cloud tops at all latitudes. The primary drivers of these cloud changes appear to be increasing greenhouse gas concentrations and a recovery from volcanic radiative cooling. These results indicate that the cloud changes most consistently predicted by global climate models are currently occurring in nature.
We investigated whether the observed cloud changes are a manifestation of ENSO-like variability by calculating the correlation of the spatial pattern of cloud trends with the spatial pattern of the difference between observed La Niña composite cloud anomalies and El Niño composite cloud anomalies. The correlation between the observed La Niña–El Niño pattern and the observed trend pattern is only 0.13, and the spatial correlation between the observed La Niña–El Niño pattern and the ensemble mean ALL trend pattern is only 0.14. Considering that the spatial correlation between the observed trend pattern and the ensemble mean ALL trend pattern is 0.39, we think ENSO-like variability cannot be a major contributor to the global pattern of cloud change between the 1980s and the 2000s.