Sun's Direct Role In Global Warming May Be Underestimated

According to Scafetta, records of sunspot activity suggest that solar output has been rising slightly for about 100 years. However, only measurements of what is known as total solar irradiance gathered by satellites orbiting since 1978 are considered scientifically reliable, he said.

But observations over those years were flawed by the space shuttle Challenger disaster, which prevented the launching of a new solar output detecting satellite called ACRIM 2 to replace a previous one called ACRIM 1.

That resulted in a two-year data gap that scientists had to rely on other satellites to try to bridge. "But those data were not as precise as those from ACRIM 1 and ACRIM 2," Scafetta said in an interview.

Nevertheless, several research groups used the combined satellite data to conclude that that there was no increased heating from the Sun to contribute to the global surface warming observed between 1980 and 2002, the authors wrote in their paper.

But a 2003 study by a group headed by Columbia's Richard Willson, principal investigator of the ACRIM experiments, challenged the previous satellite interpretations of solar output. Willson and his colleagues concluded, rather that their analysis revealed a significant upward trend in average solar luminosity during the period.

http://www.sciencedaily.com/releases/2005/10/051001100950.htm