New paper finds significant, persistent influence of solar activity on regional cloud cover & climate

A new paper published in Environmental Research Letters finds that changes in solar activity have a significant and persistent effect upon cloud cover in some key climate-defining regions. As noted by the authors, "A consensus regarding the impact of solar variability on cloud cover is far from being reached. Moreover, the impact of cloud cover on climate is among the least understood of all climate components." Using data from 1984-2009, the authors studied variations in both solar UV [which can vary by over 20% within solar cycles] and cosmic rays [the Svensmark hypothesis], finding, "For some key geographical regions the response of clouds to [solar UV] and [cosmic ray modulation of clouds] is persistent over the entire time interval indicating a real link." The authors urge that "any analysis of solar effects on cloud cover (and, consequently, on climate) should be done at the regional level."

The full paper is available here

M Voiculescu and I Usoskin 2012 Environ. Res. Lett. 7 044004 doi:10.1088/1748-9326/7/4/044004

Persistent solar signatures in cloud cover: spatial and temporal analysis

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M Voiculescu¹ and I Usoskin²

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AbstractReferences

Letter

A consensus regarding the impact of solar variability on cloud cover is far from being reached. Moreover, the impact of cloud cover on climate is among the least understood of all climate components. This motivated us to analyze the persistence of solar signals in cloud cover for the time interval 1984–2009, covering two full solar cycles. A spatial and temporal investigation of the response of low, middle and high cloud data to cosmic ray induced ionization (CRII) and UV irradiance (UVI) is performed in terms of coherence analysis of the two signals. For some key geographical regions the response of clouds to UVI and CRII is persistent over the entire time interval indicating a real link. In other regions, however, the relation is not consistent, being intermittent or out of phase, suggesting that some correlations are spurious. The constant in phase or anti-phase relationship between clouds and solar proxies over some regions, especially for low clouds with UVI and CRII, middle clouds with UVI and high clouds with CRII, definitely requires more study. Our results show that solar signatures in cloud cover persist in some key climate-defining regions for the entire time period and supports the idea that, if existing, solar effects are not visible at the global level and any analysis of solar effects on cloud cover (and, consequently, on climate) should be done at the regional level.