The Influence of the Sun

This page gives links to articles that discuss the influence of the sun on changes to our climate.

Climate history and related archeology give solid support to the solar hypothesis. The 20th-century episode, or Modern Warming, was just the latest in a long string of similar events produced by a hyperactive sun, of which the last was the Medieval Warming. [posted by The Times on February 11, 2007]

Earth is heating up lately, but so are Mars, Pluto and other worlds in our solar system, leading some scientists to speculate that a change in the sun’s activity is the common thread linking all these baking events.
Others argue that such claims are misleading and create the false impression that rapid global warming, as Earth is experiencing, is a natural phenomenon. [posted by LiveScience on March 12, 2007]

Our finding of a direct correlation between variations in the brightness of the sun and earthly climate indicators (called “proxies”) is not unique. Hundreds of other studies, using proxies from tree rings in Russia’s Kola Peninsula to water levels of the Nile, show exactly the same thing: The sun appears to drive climate change.

Most leading climate experts don’t agree with Henrik Svensmark, the 49-year-old director of the Center for Sun-Climate Research at the Danish National Space Center in Copenhagen. In fact, he has taken a lot of blows for proposing that solar activity and cosmic rays are instrumental in determining the warming (and cooling) of Earth. His studies show that cosmic rays trigger cloud formation, suggesting that a high level of solar activity—which suppresses the flow of cosmic rays striking the atmosphere—could result in fewer clouds and a warmer planet. This, Svensmark contends, could account for most of the warming during the last century. Does this mean that carbon dioxide is less important than we’ve been led to believe? Yes, he says, but how much less is impossible to know because climate models are so limited.

To help nail down the effect of solar radiation, geophysicist Mike Lockwood of the University of Southampton, U.K., examined data available since 1955 on the monthly average output of the sun, including sunspots, magnetic activity, and cosmic-ray variations. Then he compared those data, month by month, with average global temperature records, as well as El Niño- and La Niña-induced weather cycles and the atmospheric effects of major volcanic eruptions. The result, Lockwood and colleagues report in two papers published online this week in the Proceedings of the Royal Society A, is that for the past half-century, the sun has exerted only a small influence on climate–about 3% compared with the warming influence of greenhouse gases and natural climate cycles (see illustration).

The sun has powered almost everything on Earth since life began, including its climate. The sun also delivers an annual and seasonal impact, changing the character of each hemisphere as Earth’s orientation shifts through the year. Since the Industrial Revolution, however, new forces have begun to exert significant influence on Earth’s climate.

Global warming is mainly caused by greenhouse gas emissions resulting from human activities; however, current climatic variations may be affected “around 15% or 20%” by solar activity, according to Manuel Vázquez, a researcher from the Canary Islands’ Astrophysics Institute (IAC) who spoke at the Sun and Climate Change conference, organised as part of the El Escorial summer courses by Madrid’s Complutense University.

The hypothesis they tested was that increased solar activity reduces cloudiness by changing cosmic rays. So, when clouds decrease, more sunlight is let in, causing the earth to warm. Some climate change skeptics have tried to use this hypothesis to suggest that greenhouse gases may not be the global warming culprits that most scientists agree they are.

Establishing a key link between the [11 year] solar cycle and global climate, research led by scientists at the National Science Foundation (NSF)-funded National Center for Atmospheric Research (NCAR) in Boulder, Colo., shows that maximum solar activity and its aftermath have impacts on Earth that resemble La Niña and El Niño events in the tropical Pacific Ocean.

The amount of energy the sun puts out varies over an 11-year cycle (this cycle also governs the appearance of sunspots on the sun’s surface as well as radiation storms that can knock out satellites), but that cycle changes the total amount of energy reaching Earth by only about 0.1 percent. A conundrum for meteorologists was explaining whether and how such a small variation could drive major changes in weather patterns on Earth. [posted by LiveScience on August 27, 2009]

Although Earth's surface overall continues to warm, the new analysis has revealed a correlation between periods of low activity of the Sun and of some cooling -- on a limited, regional scale in Central Europe, along the Rhine.