What do we know about sunspot cycles and their effect on the climate? Not much, but the Times has some coverage:
Ever since Samuel Heinrich Schwabe, a German astronomer, first noted in 1843 that sunspots burgeon and wane over a roughly 11-year cycle, scientists have carefully watched the Sun’s activity. In the latest lull, the Sun should have reached its calmest, least pockmarked state last fall.
A panel of 12 scientists assembled by the National Oceanic and Atmospheric Administration now predicts that the May 2013 peak will average 90 sunspots during that month. That would make it the weakest solar maximum since 1928, which peaked at 78 sunspots. During an average solar maximum, the Sun is covered with an average of 120 sunspots.
Solar activity seems to tie into the climate change debate by mechanisms which are not clear:
The idea that solar cycles are related to climate is hard to fit with the actual change in energy output from the sun. From solar maximum to solar minimum, the Sun’s energy output drops a minuscule 0.1 percent.
But the overlap of the Maunder Minimum with the Little Ice Age, when Europe experienced unusually cold weather, suggests that the solar cycle could have more subtle influences on climate.
One possibility proposed a decade ago by Henrik Svensmark and other scientists at the Danish National Space Center in Copenhagen looks to high-energy interstellar particles known as cosmic rays. When cosmic rays slam into the atmosphere, they break apart air molecules into ions and electrons, which causes water and sulfuric acid in the air to stick together in tiny droplets. These droplets are seeds that can grow into clouds, and clouds reflect sunlight, potentially lowering temperatures.
The Sun, the Danish scientists say, influences how many cosmic rays impinge on the atmosphere and thus the number of clouds. When the Sun is frenetic, the solar wind of charged particles it spews out increases. That expands the cocoon of magnetic fields around the solar system, deflecting some of the cosmic rays.
But, according to the hypothesis, when the sunspots and solar winds die down, the magnetic cocoon contracts, more cosmic rays reach Earth, more clouds form, less sunlight reaches the ground, and temperatures cool.
“I think it’s an important effect,” Dr. Svensmark said, although he agrees that carbon dioxide is a greenhouse gas that has certainly contributed to recent warming.
Dr. Svensmark and his colleagues found a correlation between the rate of incoming cosmic rays and the coverage of low-level clouds between 1984 and 2002. They have also found that cosmic ray levels, reflected in concentrations of various isotopes, correlate well with climate extending back thousands of years.
But other scientists found no such pattern with higher clouds, and some other observations seem inconsistent with the hypothesis.
Terry Sloan, a cosmic ray expert at the University of Lancaster in England, said if the idea were true, one would expect the cloud-generation effect to be greatest in the polar regions where the Earth’s magnetic field tends to funnel cosmic rays.
“You’d expect clouds to be modulated in the same way,” Dr. Sloan said. “We can’t find any such behavior.”
Even without cosmic rays, however, a 0.1 percent change in the Sun’s energy output is enough to set off El Niño- and La Niña-like events that can influence weather around the world, according to new research led by the National Center for Atmospheric Research in Boulder, Colo.
Climate modeling showed that over the largely cloud-free areas of the Pacific Ocean, the extra heating over several years warms the water, increasing evaporation. That intensifies the tropical storms and trade winds in the eastern Pacific, and the result is cooler-than-normal waters, as in a La Niña event, the scientists reported this month in the Journal of Climate.
The Times closes with words from an expert:
“We still don’t quite understand this beast,” Dr. Hathaway said. “The theories we had for how the sunspot cycle works have major problems.”
MORE: TheTimes coverage coverage of quiet sunspots last fall included this on climate change:
Scientists are not sure why this minimum has been especially minimal, and the episode is even playing into the global warming debate. Some wonder if this could be the start of an extended period of solar indolence that would more than offset the warming effect of human-made carbon dioxide emissions. From the middle of the 17th century to the early 18th, a period known as the Maunder Minimum, sunspots were extremely rare, and the reduced activity coincided with lower temperatures in what is known as the Little Ice Age.