Evidence shaky for Sun's major role in past climate changes

Sep 30, 2004
The Sun

Computer models of Earth's climate have consistently linked long-term, high-magnitude variations in solar output to past climate changes. Now a closer look at earlier studies of the Sun casts doubt on evidence of such cycles of brightness, their intensity and their possible influence on Earth's climate. The findings, by a solar physicist and two climate scientists funded by the National Science Foundation, appear in the October 1 issue of the journal Science.

"The relationship between the Sun's variability and its influence on climate remain open questions," according to Cliff Jacobs, program director in NSF's division of atmospheric sciences, which funded the research. "This study adds another piece to the puzzle and will spur efforts to unravel this complex relationship."

Scientists have attributed observed climate changes to a combination of natural variations and human activities. Computer models of global climate reproduced an observed global warming during the first half of the 20th century when two solar influences were combined: a well-documented 11-year sunspot cycle and decades-long solar cycles now in dispute.

A more pronounced warming observed during the century's last decades is attributed to greenhouse gases accumulating in Earth's atmosphere and is not part of the study.

"Removing long-term solar cycles from the input to climate models takes away about a tenth of a degree [Celsius] of early 20th century warming," says Tom Wigley, a climate scientist at the National Center for Atmospheric Research (NCAR) in Boulder, Colo. "This suggests that other influences on past climate changes may play a greater role than the solar one."

Peter Foukal of Heliophysics Inc., Gerald North of Texas A&M University, and Wigley co-authored the paper.

The 11-year sunspot cycle is not questioned in the Science paper, but its effect alone is "probably too little for a practical influence on climate," the authors write. They also briefly consider possible influences of ultraviolet and cosmic ray fluxes in Earth's climate.

The scientists think that long-term brightness variations of the Sun may exist, but more convincing evidence is needed, they say. New technologies now available can provide better data for understanding Sun-climate relations, they conclude. NASA co- funded the research.

Source: National Center for Atmospheric Research

Explore further: Black hole chokes on a swallowed star

add to favorites email to friend print save as pdf

Related Stories

Peat fire emissions may shed light on climate change

Jan 16, 2015

Wildfires, which send hot flames and smoke high into the air, create black carbon emissions associated with climate change and risk to human health. Carbon emissions from wildfires in the contiguous U.S. ...

Recommended for you

Image: Striking lightning from space

4 minutes ago

Lightning illuminates the area it strikes on Earth but the flash can be seen from space, too. This image was taken from 400 km above Earth in 2012 by an astronaut on the International Space Station travelling ...

Are asteroids the future of planetary science?

4 minutes ago

I don't think I ever learned one of those little rhymes – My Very Educated Mother Just Served Us Nine Pizzas – to memorize the order of the planets, but if I had, it would've painted for me a minimalist ...

Asteroid flying past Earth today has mini-moon

40 minutes ago

Wonderful news! Asteroid 2004 BL86, which passed closest to Earth today at a distance of 750,000 miles (1.2 million km), has a companion moon. Scientists working with NASA's 230-foot-wide (70-meter) Deep ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.