Nature 9/14 Issue - Human GHGs "Far Outweigh" Solar Variability - AFP

[hatrack]

Changes in the Sun's brightness over the past millennium have had only a small effect on Earth's climate, according to a review of existing results and new calculations performed by researchers in the United States, Switzerland, and Germany.

The review, led by Peter Foukal (Heliophysics, Inc.), appears in the September 14 issue of Nature. Among the coauthors is Tom Wigley of the National Center for Atmospheric Research. NCAR's primary sponsor is the National Science Foundation. "Our results imply that, over the past century, climate change due to human influences must far outweigh the effects of changes in the Sun's brightness," says Wigley.

Reconstructions of climate over the past millennium show a warming since the 17th century, which has accelerated dramatically over the past 100 years. Many recent studies have attributed the bulk of 20th-century global warming to an increase in greenhouse gas concentrations in the atmosphere.

Natural internal variability of Earth's climate system may also have played a role. However, the discussion is complicated by a third possibility: that the Sun's brightness could have increased. The new review in Nature examines the factors observed by astronomers that relate to solar brightness. It then analyzes how those factors have changed along with global temperature over the last 1,000 years.

EDIT

http://www.terradaily.com/reports/Changes_In_Solar_Brightness_Too_Weak_To_Explain_Global_Warming_999.html

[jpak]

1. Was just about to post this...abstract of Nature review paper

http://www.nature.com/nature/journal/v443/n7108/abs/nature05072.html

Variations in solar luminosity and their effect on the Earth's climate

P. Foukal1, C. Fröhlich, H. Spruit and T. M. L. Wigley

Abstract

Variations in the Sun's total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that detailed analysis of these small output variations has greatly advanced our understanding of solar luminosity change, and this new understanding indicates that brightening of the Sun is unlikely to have had a significant influence on global warming since the seventeenth century. Additional climate forcing by changes in the Sun's output of ultraviolet light, and of magnetized plasmas, cannot be ruled out. The suggested mechanisms are, however, too complex to evaluate meaningfully at present.

[hatrack]

2. Thanks - I was too busy checking the other news sites

:toast: