Research Briefs

Turning down the heat

How would a grand solar minimum affect global warming?

sunrise over the Atlantic

A prolonged period of low solar output could slow global warming, but only temporarily. (Photo by Carlye Calvin. This image is freely available for media & nonprofit use.)

August 27, 2013 | Starting about five years ago, the Sun surprised observers with a sustained reduction in sunspots, accompanied by lower solar energy output. The change made some people wonder if the Sun was entering a multi-decade drop in solar energy, called a grand solar minimum. A long-term decrease in solar energy, though slight, would mean less heating of Earth, a potentially good thing for a planet facing climate change. So, climate modelers, including NCAR scientist Gerald "Jerry" Meehl, began to investigate how a grand solar minimum would affect global warming.

Meehl and his colleagues used a sophisticated computer modeling approach able to predict temperature and weather changes on land, in the upper levels of oceans, and in the atmosphere from ground level to the upper stratosphere. Their findings suggest that even if Earth experienced a 50-year grand solar minimum, the effects of global warming would be slowed, but not stopped, during the event and for a short time afterward.

“Even though we saw 20-30% less warming during the minimum, it rebounded pretty quickly,” Meehl said. “Within a couple of decades after the solar minimum ended, the temperatures caught up to where they would have been if there was no grand solar minimum.”

The scenario Meehl and his colleagues used was based on a real event called the Maunder Minimum, which was recorded by solar observers between 1650 and 1700. During that time, sunspots became very rare. The drop in solar energy is believed to have contributed to the “Little Ice Age” that persisted for several centuries.

The research team simulated Earth’s climate with reduction in solar energy (total solar irradiance) of 0.25% between 2020 and 2070. They compared those results with a control scenario that did not have such a reduction. To run the simulations, they used a version of the NCAR-based Community Earth System Model that incorporated the Whole Atmosphere Community Climate Model, enabling them to look in detail at the effect of relatively small changes in solar radiation.

The solar minimum simulation showed fairly uniform cooling worldwide compared to the control scenario, with a drop in surface temperatures by several tenths of a degree Celsius. These findings agreed with earlier results generated by other researchers who used more simple models.

The likelihood of another grand solar minimum actually occurring is unknown, Meehl said. Researchers believe there have been at least six multi-decade events, which they have identified using carbon dating in addition to records of sunspot observations. However, scientists don’t know why these periods occur, Meehl said. “We could go into another Maunder Minimum at any time—we can’t predict it or anticipate it,” he said.

Meehl, G. A., J. M. Arblaster, and D. R. Marsh (2013), Could a future “Grand Solar Minimum” like the Maunder Minimum stop global warming?, Geophysical Research Letters, 40, 1789–1793, doi:10.1002/grl.50361