Observed Reductions of Surface Solar Radiation at Sites in the United States and Worldwide from 1961 to 1990 Beate Liepert Lamont-Doherty Earth Observatory of Columbia University and NASA Goddard Institute for Space Studies, New York presently at MPI for Meteorology, Hamburg

References: Liepert, B. G., Observed reductions of surface solar radiation in the United States and worldwide from 1961 to Geophys. Res. Lett., 29(10), Feichter, J. et al., Effects of Air Pollution on the Hydrological Cycle. Poster presentation IGAC

“ Absence of warming” in the United States, Hansen et al., 2001.

MFRSR Lamont Observatory, Palisades NY

Global Energy Balance Archive GEBA, Gilgen et al., Quality tested data base from World Radiation Data Center (WRDC) Broadband surface solar radiation measurements (0.3  m - 30  m) 252 records of monthly averages Monthly decadal means and differences for each record (1961 to 1970, 1971 to 1980, 1981 to 1990)

Global Energy Balance Archive: Decadal Mean Surface Solar Radiation for 1981 to 1990 W/m 2

Changes of Decadal Mean Surface Solar Radiation: minus W/m 2  F = -7W/m 2

United States  F = -19W/m Former Soviet Union  F = -2W/m 2

National Solar Radiation Data Base of the United States NSRDB, Maxwell et al Composites of ‘all’, ‘clear’, and ‘overcast’ sky conditions of each decade retrieved from additional cloud cover information of observer estimates. 33 records of broadband surface solar radiation in hour resolution from 1961 to (not complete!)

Overcast skies United States sites  F = - 18W/m 2 Clear skies United States sites Liepert/Tegen, JGR 2002  F = - 8W/m 2

Cloud Coverage % and Cloud Cover Frequencies of Various Cloud Conditions at United States Sites (Ac* broken cloudy coverage, Ac total cloud coverage)

From 1960s to 1980s observed global decline in surface solar radiation of 7 W/m 2 or 4% and 19 W/m 2 or 10% decline in the United States Clear sky less transparent and Clouds optically thicker in the United States Strongest reduction of surface solar radiation under “opaque” clouds Changes in cloud coverage: more overcast skies, less clear skies and unchanged total cloud coverage Summarizing Results of Observational Data Analysis: Surface cooling and tropospheric heating

Combined Effects of Greenhouse plus Aerosol Forcing, Feichter et al., 2002 IGAC Poster. Climate simulations with ECHAM4 GCM (atmosphere plus mixed layer ocean), fully coupled aerosol model HAM (Feichter, Lohmann, Roeckner), 176 years run, statistics over the last 50 years Verification see Kinne et al. IGAC 2002 poster presentation Two equilibrium experiments: “Present day” PD scenario: greenhouse gases and aerosol concentrations of ~1985 “Pre-industrial” PI - scenario: greenhouse gases and aerosol concentrations of ~1870 Assumption: differences PD - PI representative for climatic change

Reduction in net surface solar radiation in the United States and Europe.

“No change” in modeled cloud coverage in the United States and Central Europe.

Increase in liquid water content of warm clouds (increase in cloud optical thickness)

Less surface evaporation when solar radiation is reduced. Consequences for the hydrological cycle:

Increase in soil wetness Hypothesis: Soil wetness as climate memory Anthropogenic aerosols over land important for water storage (more important than cloud modification?) Increasing risk of flooding even without increasing precipitation

All sky effect:  F = - 19 W/m 2 Overcast cloud effect:  F o = - 18 W/m 2 Clear sky effect:  F cl = - 8 W/m 2 Observed 10-year Means of Surface Solar Radiation.

Partitioning of surface solar radiation All sky change of surface solar radiation at United States sites from 1960s to 1980s with fixed f cl, f o :  F = F(1980s) - F(1960s) = - 13 W/m 2

Partitioning of 10-year Means of Surface Solar Radiation of the United States Sites Calculated:F(1980s) - F(1960s) =  F = - 20 W/m 2 Observed:F obs (1980s) - F obs (1960s) =  F obs = - 19 W/m 2