In Search of a Mechanism for the Weak Solar Forcing of Climate CO2

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Many people believe that the changes in total solar irradiance that are observed at the top of the atmosphere over the 11-year solar cycle are simply too small to have a significant impact on earth’s climate. Nevertheless, numerous studies have identified an 11-year cycle in various types of proxy climate data throughout the world. Some researchers (Utrecht University of The Netherlands, Royal Netherlands Meteorological Institute and Max-Planck Institute for Chemistry of Mainz) thus conduct a model study in which they “use realistic variations in solar UV and total solar irradiance as external forcing to a fully interactive 3-D coupled chemistry-general circulation model ? to study the nature and extent of the tropospheric response.”

The authors say their “radiative forcing results show that the 11-year solar cycle effect on global mean temperature is negligible, but simulated responses of sea level pressure do suggest that regional effects are probably significant, e.g. by affecting the North Atlantic Oscillation.” Indeed, they conclude that “the solar effect is most probably real and its magnitude is sufficiently large to exceed the natural variability over 20 years.” They also note that “realistic changes of the solar UV radiation influence the stratosphere-troposphere system in a significant way,” producing circulation changes that “give rise to regional changes of weather and climate”.

This study, as well as the others it cites, clearly demonstrates that the 11-year solar cycle may indeed influence regional climate in a possibly profound way. Being regional, however, and switching back and fourth as rapidly as it does, the 11-year cycle’s impact on the long-term global temperature is not apparent.
(Science Magazine, 11 Jun 2003 Weekly Review, vol. 6, n.24)
Reference Tourpali, K., Schuurmans, C.J.E., van Dorland, R., Steil, B. and Bruhl, C.
2003. Stratospheric and tropospheric response to enhanced solar UV radiation: A model study. Geophysical Research Letters 30:
10.1029/2002GL016650.

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