THE popular view on global warming is that the sun has had a negligible influence on climate – at least over the last few decades compared to carbon dioxide. But taking into account the entire range of possible total solar irradiance (TSI) satellite composite since 1980, Nicola Scafetta, just published in Journal of Atmospheric and Solar-Terrestrial Physics, concludes that the solar contribution to climate change could range from a slight cooling to a significant warming, as large as 65% of the total observed global warming.
Here’s a short extract suggesting the science is far from settled:
“DETERMING how solar activity has changed on decadal and secular scales is necessary to estimate the solar contribution to climate change. Unfortunately, how solar activity has changed in time is not known with certainty.
“Direct TSI observations started in 1978 with satellite measurements. For the period before 1978 only TSI proxy reconstructions have been proposed. These TSI proxy models significantly differ from each other, in particular about the amplitude of the secular trends.
“Unfortunately, TSI satellite composites since 1978 are not certain either. Two major composites have been proposed: the PMOD TSI composite which shows an almost constant trend from 1980 to 2000; and the ACRIM TSI composite which shows an increasing trend during the same period. GCMs and EBMs adopted by the IPCC (2007) assumed that TSI did not change significantly since 1950 and that, consequently, the sun could not be responsible for the significant warming observed since 1975.
“These estimates are based on TSI proxy models such as those prepared by Lean (2000) and Wang et al. (2005) which are apparently supported by PMOD. However, the above TSI proxy models would be erroneous if the ACRIM TSI composite more faithfully reproduces the TSI behavior during the last decades. The ACRIM-PMOD controversy is quite complex and, herein, a detailed discussion on this topic is not possible.
“A recent work by Scafetta and Willson (2009) reopened the issue by providing a careful analysis of the most recent TSI proxy model (Krivova et al., 2007) based on magnetic surface fluxes. This has been done by establishing that a significant degradation of ERBE TSI satellite likely occurred during the ACRIM-gap (1989–1992.5), as the ACRIM team has always claimed. Moreover, Scafetta and Willson invalidated the specific corrections to Nimbus7 that the PMOD TSI composite requires and confirm the opinion of the original Nimbus7 experimental team that no sudden increase of the Nimbus7 sensitivity occurred on September 29, 1989 (see Hoyt’s statement in Scafetta and Willson, 2009). Finally, Scafetta and Willson (2009) showed that the agreement between PMOD and the proxy reconstruction about the absence of a trend between the TSI minima in 1986 and 1996 is coincidental because a careful comparison between the proxy model and the unquestioned satellite data before and after the ACRIM-gap proves that the TSI proxy model by Krivova et al. (2007) is missing an upward trend…
Notes and Links
Empirical analysis of the solar contribution to global mean air surface temperature change. Journal of Atmospheric and Solar-Terrestrial Physics (2009), doi:10.1016/j.jastp.2009.07.007 By Nicola Scafetta, Department of Physics, Duke University, Durham, NC 27708, USA
The solar contribution to global mean air surface temperature change is analyzed by using an empirical bi-scale climate model characterized by both fast and slow characteristic time responses to solar forcing. Since 1980 the solar contribution to climate change is uncertain because of the severe uncertainty of the total solar irradiance satellite composites. The sun may have caused from a slight cooling, if PMOD TSI composite is used, to a significant warming (up to 65% of the total observed warming) if ACRIM, or other TSI composites are used. The model is calibrated only on the empirical 11-year solar cycle signature on the instrumental global surface temperature since 1980. The model reconstructs the major temperature patterns covering 400 years of solar induced temperature changes, as shown in recent paleoclimate global temperature records.
The photograph of the sun was taken from Lammermoor Beach, Central Queensland, last week by Jennifer Marohasy.