David Fogarty at Reuters:
Small changes in the energy output of the sun can have a major impact on global weather patterns, such as the intensity of the Indian monsoon, that could be predicted years in advance, a team of scientists said.
The sun swings through an 11-year cycle measured in the number of sun spots on the surface that emit bursts of energy.
The difference in energy is only about 0.1 percent between a solar maximum and minimum and determining just how that small variation affects the world’s climate has been one of the great challenges facing meteorologists.
Using a century of weather observations and complex computer models, the international team of scientists led by the National Center for Atmospheric Research (NCAR) in the United States showed that even a small increase in the sun’s energy can intensify wind and rainfall patterns.
“Small changes in the sun’s output over the 11-year solar cycle have long been known to have impacts on the global climate system,” said Julie Arblaster, from the Centre for Australian Weather and Climate Research, a co-author of the study published in the latest issue of the journal Science.
“Here we reconcile for the first time the mechanisms by which these small variations get amplified, resulting in cooler sea surface temperatures in the tropical Pacific and enhancing off-equatorial rainfall.”
The changes occur like this: The slight increase in solar energy during the peak production of sunspots is absorbed by stratospheric ozone, warming the air in the stratosphere over the tropics, where sunlight is most intense. The additional energy also stimulates the production of additional ozone there that absorbs even more solar energy.
Since the stratosphere warms unevenly, with the most pronounced warming occurring nearer the equator, 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 — a peak of sunspot and solar storm activity we’re currently headed toward — 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, putting additional water vapor into the atmosphere. 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.
These two processes reinforce each other and intensify the effect.
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 (the opposite sister effect of the warm-water El Nino), is only about half as strong, and is associated with different wind patterns in the stratosphere.
The solar cycle does not have as great an effect on Earth’s climate as the El Nino cycle.
To tease out the elusive mechanisms that connect the Sun and Earth, the study team needed three computer models that provided overlapping views of the climate system.
One model, which analyzed the interactions between sea surface temperatures and lower atmosphere, produced a small cooling in the equatorial Pacific during solar maximum years. The second model, which simulated the stratospheric ozone response mechanism, produced some increases in tropical precipitation but on a much smaller scale than the observed patterns.
The third model contained ocean-atmosphere interactions as well as ozone. It showed, for the first time, that the two combined to produce a response in the tropical Pacific during peak solar years that was close to actual observations.
“With the help of increased computing power and improved models, as well as observational discoveries, we are uncovering more of how the mechanisms combine to connect solar variability to our weather and climate,” Meehl says.
Professor Reinhard Huettl, Chairman of the Scientific Executive Board of the GFZ (Helmholtz Association of German Research Centres) adds: “The study is important for comprehending the natural climatic variability, which – on different time scales – is significantly influenced by the sun. In order to better understand the anthropogenically induced climate change and to make more reliable future climate scenarios, it is very important to understand the underlying natural climatic variability. This investigation shows again that we still have substantial research needs to understand the climate system”. Together with the Alfred Wegener-Institute for Polar and Marine Research and the Senckenberg Research Institute and Natural History Museum the GFZ is, therefore, organising a conference “Climate in the System Earth” scheduled for 2./3. November 2009 in Berlin.
Ronald Bailey in Reason:
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?
In a related note, there’s a sun spot decline going on, apparently:
What was learned
First of all, they report that data they analyzed some four years ago (Penn and Livingston, 2006) showed that the magnetic field strengths of sunspots “were decreasing with time, independent of the sunspot cycle,” and that “a simple linear extrapolation of those data suggested that sunspots might completely vanish by 2015.” And now, with four more years of data in hand, they report that “the predicted cycle-independent dearth in sunspot numbers has proven accurate,” with sunspots still on track to totally disappear in four to five years.
What it means
The two researchers openly wonder whether their findings represent “an omen of long-term sunspot decline, analogous to the Maunder Minimum,” the period from 1645-1715 “when through several 11-year periods the sun displayed few if any sunspots,” the reason for their curiosity, of course, being that “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 (Lean et al., 1992).” Since the answer to their question should become apparent before too long (about the time of the next U.S. Presidential Election), it might be wise to wait to see what the answer actually is before enacting legislation to attempt to stop CO2-induced global warming that might well be needed to forestall another “Little Ice Age,” the cold of which (which was the most severe of the current interglacial) would likely prove much more deadly that the bit of extra heat we may — or may not! — otherwise experience.
FishOutofWater at Daily Kos brings the artwork:
Could these data be evidence that we are about to enter a period of prolonged solar inactivity like the Maunder Minimum in 1645 to 1715 when few if any sunspots were seen and the climate cooled into the “Little Ice Age”? Calculations have shown that the potential cooling effect would not reverse global warming. However, the effects of prolonged solar inactivity on climate change and weather patterns are hard to predict because we don’t understand the physics of the Maunder Minimum. The signals are mixed on the how inactive the upcoming solar cycle will be. Recent forecasts are predicting lower than normal activity but are not predicting a Maunder Minimum type event.
Ethiopian Review’s Mehret Tesfaye:
Overall, the Eos paper suggests that current data is consistent with a decline in the sun’s magnetic field activity, which could potentially end in a sunspot-free period. We care about this because sunspot numbers act as a proxy for the amount of radiation sent out by the sun, which can have a significant influence on the Earth’s climate. But the sun is one of a large number of factors that influence the climate, and the changes in solar radiance caused by sunspots appear likely to have a smaller impact on the climate than that caused by our ever-increasing levels of greenhouse gasses.
Still, even a relatively small effect may buy humanity valuable time in coming to grips with the CO2 we’re putting into the atmosphere (at least when it comes to temperatures—ocean acidification is a different problem entirely). According to the paper, we may know whether a new solar minimum is occurring as soon as 2015.
UPDATE: Stuart Clark at New Scientist