Trends in the CERES Dataset, 2000-13: The Effects of Sea Ice and Jet Shifts and Comparison to Climate Models

The Clouds and the Earth's Radiant Energy System (CERES) observations of global top-of-atmosphere radiative energy fluxes for the period March 2000-February 2013 are examined for robust trends and variability. The trend in Arctic ice is clearly evident in the time series of reflected shortwave radiation, which closely follows the record of ice extent. The data indicate that, for every 10(6) km(2) decrease in September sea ice extent, annual-mean absorbed solar radiation averaged over 75 degrees-90 degrees N increases by 2.5 W m(-2), or about 6 W m(-2) between 2000 and 2012. CMIP5 models generally show a much smaller change in sea ice extent over the 1970-2012 period, but the relationship of sea ice extent to reflected shortwave is in good agreement with recent observations. Another robust trend during this period is an increase in reflected shortwave radiation in the zonal belt from 45 degrees to 65 degrees S. This trend is mostly related to increases in sea ice concentrations in the Southern Ocean and less directly related to cloudiness trends associated with the annular variability of the Southern Hemisphere. Models from phase 5 of the Coupled Model Intercomparison Project (CMIP5) produce a scaling of cloud reflection to zonal wind increase that is similar to trend observations in regions separated from the direct effects of sea ice. Atmospheric Model Intercomparison Project (AMIP) model responses over the Southern Ocean are not consistent with each other or with the observed shortwave trends in regions removed from the direct effect of sea ice.