Open AccessExternal Influences on Modeled and Observed Cloud Trends
Author(s) -
Kate Marvel,
Mark D. Zelinka,
Stephen A. Klein,
C. Bonfils,
Peter Caldwell,
Charles Doutriaux,
Benjamin D. Santer,
Karl E. Taylor
Publication year - 2015
Publication title -
journal of climate
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.315
H-Index - 287
eISSN - 1520-0442
pISSN - 0894-8755
DOI - 10.1175/jcli-d-14-00734.1
Subject(s) - forcing (mathematics) , cloud computing , climatology , environmental science , coupled model intercomparison project , international satellite cloud climatology project , multivariate statistics , satellite , latitude , cloud cover , climate model , meteorology , computer science , atmospheric sciences , climate change , geology , geography , physics , geodesy , oceanography , machine learning , astronomy , operating system
Understanding the cloud response to external forcing is a major challenge for climate science. This crucial goal is complicated by intermodel differences in simulating present and future cloud cover and by observational uncertainty. This is the first formal detection and attribution study of cloud changes over the satellite era. Presented herein are CMIP5 model-derived fingerprints of externally forced changes to three cloud properties: the latitudes at which the zonally averaged total cloud fraction (CLT) is maximized or minimized, the zonal average CLT at these latitudes, and the height of high clouds at these latitudes. By considering simultaneous changes in all three properties, the authors define a coherent multivariate fingerprint of cloud response to external forcing and use models from phase 5 of CMIP (CMIP5) to calculate the average time to detect these changes. It is found that given perfect satellite cloud observations beginning in 1983, the models indicate that a detectable multivariate signal should have already emerged. A search is then made for signals of external forcing in two observational datasets: ISCCP and PATMOS-x. The datasets are both found to show a poleward migration of the zonal CLT pattern that is incompatible with forced CMIP5 models. Nevertheless, a detectable multivariate signal is predicted by models over the PATMOS-x time period and is indeed present in the dataset. Despite persistent observational uncertainties, these results present a strong case for continued efforts to improve these existing satellite observations, in addition to planning for new missions.