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20th century changes in surface solar irradiance in simulations and observations
Author(s) -
Romanou A.,
Liepert B.,
Schmidt G. A.,
Rossow W. B.,
Ruedy R. A.,
Zhang Y.
Publication year - 2007
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2006gl028356
Subject(s) - longwave , solar irradiance , environmental science , climatology , atmospheric sciences , forcing (mathematics) , climate model , irradiance , cloud forcing , cloud cover , atmosphere (unit) , greenhouse gas , climate change , meteorology , radiative forcing , aerosol , radiation , cloud computing , geography , geology , physics , oceanography , quantum mechanics , computer science , operating system
The amount of solar irradiance reaching the surface is a key parameter in the hydrological and energy cycles of the Earth's climate. We analyze 20th Century simulations using nine state‐of‐the‐art climate models and show that all models estimate a global annual mean reduction in downward surface solar radiation of 1–4 W/m 2 at the same time that the globe warms by 0.4–0.7°C. In single forcing simulations using the GISS‐ER model, this “global dimming” signal is shown to be predominantly related to aerosol effects. In the global mean sense the surface adjusts to changes in downward solar flux instantaneously by reducing the upward fluxes of longwave, latent and sensible heat. Adding increased greenhouse gas forcing traps outgoing longwave radiation in the atmosphere and surface which results in net heating (although reduced) that is consistent with global warming over the 20th Century. Over the 1984–2000 period, individual model simulations show widely disparate results, mostly related to cloud changes associated with tropical Pacific variations, similar to the changes inferred from the satellite data analysis. This suggests that this time period is not sufficient to determine longer term trends.