A new study in the journal Science by a team of international of researchers led by the National Center for Atmospheric Research have found that the sunspot cycle has a big effect on the earth's weather. The puzzle has been how fluctuations in the sun's energy of about 0.1 percent over the course of the 11-year sunspot cycle could affect the weather? The press release describing the new study explains:
The team first confirmed a theory that the slight increase in solar energy during the peak production of sunspots is absorbed by stratospheric ozone. The energy warms the air in the stratosphere over the tropics, where sunlight is most intense, while also stimulating the production of additional ozone there that absorbs even more solar energy. Since the stratosphere warms unevenly, with the most pronounced warming occurring at lower latitudes, stratospheric winds are altered and, through a chain of interconnected processes, end up strengthening tropical precipitation.
At the same time, the increased sunlight at solar maximum causes a slight warming of ocean surface waters across the subtropical Pacific, where Sun-blocking clouds are normally scarce. That small amount of extra heat leads to more evaporation, producing additional water vapor. In turn, the moisture is carried by trade winds to the normally rainy areas of the western tropical Pacific, fueling heavier rains and reinforcing the effects of the stratospheric mechanism.
The top-down influence of the stratosphere and the bottom-up influence of the ocean work together to intensify this loop and strengthen the trade winds. As more sunshine hits drier areas, these changes reinforce each other, leading to less clouds in the subtropics, allowing even more sunlight to reach the surface, and producing a positive feedback loop that further magnifies the climate response.
These stratospheric and ocean responses during solar maximum keep the equatorial eastern Pacific even cooler and drier than usual, producing conditions similar to a La Nina event. However, the cooling of about 1-2 degrees Fahrenheit is focused farther east than in a typical La Nina, is only about half as strong, and is associated with different wind patterns in the stratosphere.
Are these new findings relevant to scientific analyses of man-made global warming? The Christian Science Monitor reports:
For those wondering how the study bears on global warming, Gerald Meehl, lead author on the study, says that it doesn't – at least not directly….
Global warming is a long-term trend, Dr. Meehl says in a phone conversation. By contrast, this study attempts to explain the processes behind a periodic occurrence. But, he says, a model finally able to reproduce a complex phenomenon observed in the real world does suggest that our climate models – the same ones we use to predict what will happen to global climate as we ratchet up co2 concentrations – are improving. And that will, inevitably, have an affect on the climate discussion.
A recent paper in Eos considers the evidence that we could be in for an extended period with few sunspots:
Why is a lack of sunspot activity interesting? During the period from 1645 to 1715, the Sun entered a period of low activity now known as the Maunder Minimum, when through several 11- year periods the Sun displayed few if any sunspots. Models of the Sun's irradiance suggest that the solar energy input to the Earth decreased during that time and that this change in solar activity could explain the low temperatures recorded in Europe during the Little Ice Age.
Doesn't the Eos paper suggest that sunspot activity may not just affect weather but climate too?