A Closer Look: The Solar Influence

Isn’t the Sun driving current climate change?

Last updated: February 9, 2009

No. Perhaps a better question would be, “Is the Sun contributing to current climate change?” In that case, the answer would be yes.

The Sun goes through a 22-year cycle consisting of two 11-year components. At the end of each of these 11-year cycles, the magnetic poles of the Sun switch, switching the hemispheric location for the magnetic north and south poles. So, it takes 22-years for the poles to return to their original positions. Through each 11-year component sunspots proceed from their maximum to their minimum, and it is this fluctuation in sunspot activity that can influence Earth. However, while it does fluctuate slightly through these cycles, the Sun’s overall irradiance (the Sun’s output) does not change significantly. If the Sun’s overall output did change and rise, scientists agree that such a rise would need to continue for decades to have a noticeable impact on Earth’s climate.

Satellite observation of the Sun’s output began in 1978, and, as you can see on the indicators page and in Figure 1 below, the output of the Sun has not increased over the 30 years of this direct observation.

Figure 1: Solar Irradiance, 1978-2004; Source: World Radiation Center

While solar output has decreased over the last 30 years, global surface and lower atmospheric temperatures have increased.

Figure 2: Global surface temperatures, 1979-2008; Sources: NASA GISS, HadCRUT, UAH, RSS

Also, planetary heating originating from the Sun would warm all levels of the atmosphere. Figure 3 notes the observed warming specifically of the lower troposphere near the Earth’s surface over the last 30 years.

Figure 3: Atmospheric Temperature Anomaly, Lower Troposphere, 1979-2008; Source: RSS

However, Figure 4 notes that the stratosphere in the upper reaches of the atmosphere has experienced a concurrent cooling during the same time period. While this cooling of the upper atmosphere is inconsistent with solar heating, it is consistent with warming derived from increases in greenhouse gas concentrations.

Figure 4: Atmospheric Temperature Anomaly, Lower Stratosphere, 1979-2008; Source: RSS

Additional Reading:

Sites

• Solar Physics (NASA MSFC)
• World Radiation Center: Solar Constant

Articles

• Changing Sun, Changing Climate? (American Institute of Physics, August 2007)
• No Sunshine for Global Warming Skeptics (Scientific American, September 13, 2006)
• Don’t Blame Sun for Global Warming, Study Says (National Geographic, September 13, 2006)
• The Trouble With Sunspots (RealClimate, September 13, 2006)
• Sun’s Direct Role in Global Warming May Be Underestimated (Duke University, September 30, 2005)
• How Unusual is Today’s Solar Activity? (Nature, July 28, 2005)
• The Lure of Solar Forcing (RealClimate, July 15, 2005)
• Solar Variability, Ozone, and Climate (NASA GISS, March 1999)

Studies

• Changes in Atmospheric Constituents and in Radiative Forcing (IPCC Fourth Assessment Report, 2007)
• Recent oppositely directed trends in solar climate forcings and the global mean surface air temperature (Proceedings of the Royal Society, May 25, 2007)
• Variations in solar luminosity and their effect on the Earth’s climate (Nature, September 14, 2006)
• Unusual activity of the Sun during recent decades compared to the previous 11,000 years (Nature, October 28, 2004)
• Solar Forcing of Regional Climate Change During the Maunder Minimum (Science, December 7, 2001)
• Solar Cycle Variability, Ozone, and Climate (Science, April 9, 1999)