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It's the sun
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Thursday, 25 October, 2007

Are we heading into a new Little Ice Age?

Solar activity is not static - it shows long term trends of brightening or cooling as well as a distinct 11 year cycle. Currently, we're at the minimum of the solar cycle with no sunspots observed over the last few weeks. With the sun on the verge of entering a new cycle, there are speculations that we could be heading into a period of lower solar activity, leading to global cooling and possibly even a new Little Ice Age. Russian scientist Habibullo Abdussamatov predicts that around 2040, the sun will cool down to Maunder Minimum levels (Abdussamatov 2005). This was a period in the 17th Century with almost no sunspots for 70 years, coinciding with the Little Ice Age. Could a cooling sun overrule anthropogenic global warming?

Predicting the next solar cycle

Solar prediction is a problematic exercise as there are no proper physical models that allow predictions of even the next cycle. Therefore predictions tend to be based on statistical inference with little in the way of physics or modelling involved. For example, longer solar cycles tend to be followed by a weaker cycle.

The closest thing to a scientific consensus on solar prediction comes from the Solar Cycle Prediction Panel, consisting of members of NASA, NOAA, ISES and other US and International representatives. In March 2007, they released a consensus statement for the amplitude of the upcoming cycle 24. Their position:

"In light of the expected long interval until the onset of Cycle 24, the Prediction Panel has been unable to resolve a sufficient number of questions to reach a single, consensus prediction for the amplitude of the cycle. The deliberations of the panel supported two possible peak amplitudes for the smoothed International Sunspot Number (Ri): Ri = 140 ±20 and Ri = 90 ±10."

In other words, cycle 24 may be larger or smaller. The cycle is expected to begin in early 2008 and predictions are largely speculative until it begins. The one thing we do know is when Solar Cycle 24 begins, the warming sun will add to the global warming trend as it heads towards solar maximum, nearly doubling the projected temperature rise from greenhouse gases from 2008 to 2012 (Camp 2007).

Long term predictions of solar activity

Predicting solar cycles further into the future is even more speculative. A recent paper Grand minima and maxima of solar activity: New observational constraints (Usoskin 2007) found solar variations are defined by chaotic processes, casting significant doubts on long-term predictions using multi-periodic analyses. The sun is currently in a period of "grand maxima" where activity is higher than usual. Usoskin 2007 found the termination of a grand maximum is a random process. In other words, the timing of when the sun will start cooling from it's current 'grand maximum' state is random and hence prediction is problematic.

What if the sun did go through another Maunder Minimum?

However unlikely and difficult to predict, imagine for the sake of argument that the sun does go through another Maunder Minimum over the next century. What effect would this have on Earth's climate? The difference in solar radiative forcing between Maunder Minimum levels and current solar activity is estimated between 0.17 W/m2 (Wang 2005) to 0.23 W/m2 (Krivova 2007).

In contrast, the radiative forcing of CO2 since pre-industrial times is 1.66 W/m2 (IPCC AR4), far outstripping solar influence. And that's not including the extra CO2 to be added to the atmosphere in upcoming decades. In other words, the warming from CO2 dwarves any potential cooling even if the sun was to return to Maunder Minimum levels.

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Posted by John Cook at 20:10 PM

Comments

  1. Is it possible that cycle 24 won't get very big at all and we could be entering into a maunder minimum now?
    [ Response: Anything's possible but it's very unlikely that the next cycle will be a Maunder Minimum which was a rare occurance of no sunspots for a number of decades. The most likely predictions for the next cycle are slightly less than usual or slightly more than usual. However, the pertinent point is even if we did enter a maunder minimum, the forcing from CO2 emissions far outweighs the change in solar forcing. ]
  2. Thats a bummer, i was looking forward to a little ice age and thinking about how to prepare for one, todays society needs to be knocked down a peg or two.
  3. Consensus statements are meaningless in general, they are sort of popularity contest of who is more loud and famous, and who's got the biggest grants (not necessarily the best science). There's at least 2-3 solar models that have quite good track record at predicting coming solar cycles based on various patterns that hold quite well over time (i.e. statistically significant), some include physical mechanism and some are based on statistical relationships. We have much longer and better records for solar activity that for Earth's climate and they allow for much better verification. You can start with Sabatino Sofia's models, there are other less known as well.
    In conclusion: The graph you posted up there is quite misleading because it doesn't distinguish between quality of various models.
    [ Response: The point of mentioning "consensus" is that there is actually very little in the way of a single consensus position - that the solar prediction panel predicts either greater or smaller tells us little. But once again, the point is moot - the change in forcing even if in the extreme case of a Maunder Minimum is less than the forcing from CO2. ]
  4. Wondering Aloud at 05:05 AM on 15 November 2007
    ..."the change in forcing even if in the extreme case of a Maunder Minimum is less than the forcing from CO2. ]"

    Doesn't that depend on whether or not the size of the feedback effects, that are supposed to magnify the CO2 forcings, are correct?
    [ Response: It doesn't matter - feedback is dependent on temperature rise, not the nature of the forcing. The feedback from 1 degree of solar warming would be the same as the feedback from 1 degree of CO2 forcing. ]
  5. Wondering Aloud at 06:27 AM on 20 November 2007
    No, I was commenting on the size of the feedback effects predicted for CO2 caused warming. We are assuming that feedback will be positive and magnify the warming effect of the CO2. In the last 3 IPCC report the magnitude of these feedback effects was predicted to be 3-4 times what can be justified from observation, and the error bars have been huge. Without a large positive feedback effect there is really no way CO2 alone could cause enough warming to be any big deal.

    I don't know what assumptions the people trying to explain solar effects are using. However, the reason the predicted rise from CO2 is so large is because in the case of the CO2 they are assuming a large positive feedback that cannot yet be verified from observation. If, as the evidence suggests, the feedback effects are less than a third of what is predicted in the IPCC reports; than the amount of warming expected is much reduced.

    Since I like to end with a question, I can think of a way off the top of my head to cut CO2 emissions in North Amerrica by 50% in the next 10-15 years at zero net cost to the economy and with no new technology needed. If people in policy making positions are convinced of this impending disaster why are they wasting time with useless expensive junk like cap and trade and the Kyoto protocol?
    [ Response: Off the top of my head, I can think of several strong pieces of empirical evidence for positive feedback. Soden 2001 and Santer 2007 both use observations of atmospheric water vapour to confirm the positive feedback nature of water vapour (more on water vapour). And a climate sensitivity of around 3°C (which would require positive feedbacks to be that high) is empirically confirmed by Hansen 1993, Lorius 1990, Hoffert 1992, Gregory 2002 and Tung 2007 (more on climate sensitivity). But funny you should bring it up - I'm actually working on a new post describing other empirical observations of positive feedback (a followup to the model uncertainty post) - I'll post that within a week or two. ]
  6. "In contrast, the radiative forcing of CO2 since pre-industrial times is 1.66 W/m2 (IPCC AR4), far outstripping solar influence."

    The two simply cannot be compared. For one thing, as an INSULATIVE influence the effect of CO2 is itself totally dependent on the effect of the sun. A jumper, a windbreaker and three blankets will not warm a dead body.

    But secondly, the series of steps that one goes through to produce these various hypothetical FORCINGS are riddled with untenable assumptions. Truly these are flat earth calculations.

    The environment of leftist abuse within the profession has prevented superior paradigms from being formulated. While the skeptics stick with the leftists paradigms they will be constantly undercut, though there objections be valid.

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