In light of news that the sun may be heading into a quiet period like the Maunder Minimum from 1645-1715, it is time to revisit a blog entry from last year.
Here’s a slightly revised version of what I wrote.
Something unusual has been going on in the Sun’s magnetic activity. For the last three centuries or so that we have been observing sunspots, we have seen a regular eleven-year cycle in their behavior. At solar minimum, sunspots are few and far between (sometimes totally absent). This has usually been followed by a sharp upsurge after about 16 months, but the last two cycles have been different.
According to the opening paragraph of an article posted at the Science Now website of the American Association for the Advancement of Science, “Scientists studying sunspots for the past 2 decades have concluded that the magnetic field that triggers their formation has been steadily declining. If the current trend continues, by 2016 the sun’s face may become spotless and remain that way for decades—a phenomenon that in the 17th century coincided with a prolonged period of cooling on Earth.”
Later, the article notes, “Sunspots disappeared almost entirely between 1645 and 1715 during a period called the Maunder Minimum, which coincided with decades of lower-than-normal temperatures in Europe nicknamed the Little Ice Age. But [William Livingston of the National Solar Observatory in Tucson, Arizona] cautions that the zero-sunspot prediction could be premature.”It may not happen,” he says. “Only the passage of time will tell whether the solar cycle will pick up.” Still, he adds, there’s no doubt that sunspots “are not very healthy right now.”
As expected, global warming skeptics are making a big deal about this report, arguing that this proves that solar effects are far more important to global climate change than human activity. If they are correct, does that mean we can continue to burn fossil fuels with abandon while atmospheric CO2 levels soar?
My answer is a resounding “No,” and here’s why:
(1) Correlation does not mean causality. The Maunder minimum may have been responsible for seven cool decades in the 17th-18th century, but there is no consensus on the physics of how changes in solar activity (and consequent changes in Earth’s ionosphere) could have resulted in global cooling. It may well have been coincidence. But even granting that it was causal does not change my position, as the subsequent points explain.
(2) We are not certain that we are on the verge of another Maunder minimum. Even if we are, it will likely only cool the Earth for a few decades while the effects of increased greenhouse gases in the atmosphere will continue beyond that.
(3) What does the increased level of greenhouse gases imply? Analysis of the large body of climate data has led to a strong consensus among climate experts that human activity which has increased atmospheric CO2, primarily the burning of fossil fuels, is responsible for most, if not all, of the global warming that has occurred in the last century. Even if sunspot activity temporarily mitigates the increase in global temperature, we still need to be concerned about the projected increases in the next few centuries.
There is a wide range of projected scenarios about what to expect, and I have been known to criticize those who overstate the case. But even mid-range scenarios project serious problems from sea-level rise, more extreme weather events (in number and intensity), the spread of tropical diseases, and disruption of agricultural patterns.
Deviations from those scenarios in a beneficial direction, as may result from changes in solar activity if the skeptics’ confidence in the causality of the Maunder minimum is correct, would be welcome. However, deviations in the opposite direction are also possible, and such deviations would be matters of great concern. Policymakers need to consider the most likely scenarios as well as the range of possible deviations in setting policy. They need to give some credence to worst case scenarios and be alert for signs that such scenarios are occurring.
In short, let’s all hope that the Sun is about to give us a reprieve from those worst case scenarios and use that reprieve, if it comes, to mitigate and eventually reverse our production of greenhouse gases. It would surely be nice to have another 70 years to solve the problem, but we would be wise to recognize that as an opportunity to change our actions, and not as an excuse to continue our risky actions.
Addendum to prevent this thread from become yet another place to rant, commenters please note: I don’t mind your disagreeing with me on the interpretation of the science if you know something about the subject, and I certainly don’t mind your disagreeing about the policies that are necessary to deal with climate change. But if this becomes a free-for-all with nonproductive rants, I will close this thread to commentary. I will also delete comments that I view as unproductive rants rather than substantive discussions.
Addendum 7 October 2010:
Nature News has an interesting article about the possibility that the decline in solar activity may be linked to the most recent warming. The article has key quotations from several scientists who view this result in the same way I do. It does not change the main conclusion that human activities are primarily responsible for changes in climate. For example:
The idea that scientists might not have quite understood the Sun’s effect on climate should not provide ammunition for climate-change sceptics, says Martin Dameris, an atmospheric scientist at the German Aerospace Center in Oberpfaffenhofen. “The findings could prove very significant when it comes to understanding, and quantifying, natural climate fluctuations,” he says. “But no matter how you look at it, the Sun’s influence on current climate change is at best a small natural add-on to man-made greenhouse warming.
Addendum, June 16, 2011:
As a scientist, I hope that we are indeed seeing a new Maunder Minimum, because then nature will be presenting us with a very interest research opportunity.
At this point, we only know that the previous Maunder Minimum was correlated with an episode of global cooling. Since we have a record of only one previous occurrence, we are unable to judge whether that correlation is due to coincidence or there is a causal effect. A second such episode should give us a better indication of the possibiliuty of causality.
If we get evidence of causality, then we need to explore what physical phenomena would tie changes in the ionosphere to changes in average global temperature. It may be time for climate scientists and atmospheric physicists to begin to explore that question and allow the changing solar behavior to provide test data for their models.