Bob Henson, Weather Underground Blog
If you’re looking toward the sun to help explain this decade’s record global heat on Earth, look again. Solar activity has been below average for more than a decade, and the pattern appears set to continue, according to several top solar researchers. Solar Cycle 24, the one that will wrap up in the late 2010s, was the least active in more than a century. We now have outlooks for Cycle 25, the one that will prevail during the 2020s, and they’re calling for a cycle only about as strong as–and perhaps even less active than–Cycle 24.
While Henson tries to make the case that sunspots have little influence on the climate, citing Solar Cycle 24 low sunspot intensity, while planet experience rising global temperatures.
Newly precise measurements confirm that the total solar energy reaching Earth actually doesn’t change all that much from cycle to cycle. As a single cycle ramps up from minimum to maximum, the sun spits out as much as 10 times more energy in extreme ultraviolet wavelengths. However, the sun’s total energy output (irradiance) goes up by a mere 0.1% during a solar cycle, and this boosts global surface temperature by no more than 0.1°C per cycle, according to the Intergovernmental Panel on Climate Change.
Bolstering his argument with a chart from skepticalscience.com which seems to ignore the 20-year global warming pause in the satellite temperature measurements. I will leave that discussion for another time but it seems to me that the pause and a low solar cycle may have some connection. Moving on to more interest items in Bob Henson’s post, the future of Solar Cycle 25.
Outlook for the 2020s: Another modest cycle
The community of solar researchers has only recently come into consensus on the “polar predictor” method of using polar magnetic fields as the best predictor of solar cycles. A decade ago, various methods produced conflicting results on how strong Cycle 24 would end up. Forecasts based on polar fields at solar minimum did remarkably well; others had more trouble in capturing the cycle’s length and strength. “One of the things we learned is that the difference between the hemispheres is critical,” said McIntosh. The north half of the sun ran about two years ahead of the south during Cycle 24, and that overlap led to the double-peaked maximum (2011 and 2014) while lessening the cycle’s overall peak strength.
Researchers are now trying to push the limits of prediction further. They’re using statistical and dynamical models, plus some data-based intuition, to predict several years in advance how the subsurface magnetic fields will look when they emerge near the poles around 2020, and what, in turn, those fields may tell us about Cycle 25.
• David Hathaway (recently retired from NASA) and Lisa Upton (NCAR and Space Systems Research Corporation) expect a Cycle 25 about as strong as Cycle 24, or perhaps slightly weaker. They published their outlook in November in the Journal of Geophysical Research. Hathaway and Upton used an ensemble model to project the polar fields from now to the end of 2019, with the ensemble showing an uncertainty by that point of about 15%. Natural solar variations in the early 2020s could add to the uncertainty, they note.
• Leif Svalgaard (Stanford University) pioneered the idea of using solar polar fields as prediction tools with colleagues in the 1970s, and he successfully pegged the eventual weakness of Cycle 24 back in 2005. Svalgaard is calling for a weak Cycle 25, but perhaps just a bit stronger than Cycle 24, based on precursors that appear slightly more active this time around.
• NCAR’s McIntosh believes Cycle 25 could extend the recent string of progressively weaker cycles. “We anticipate that the growing degree of overlap between cycles means that Cycle 25 will be weaker than Cycle 24,” he told me.
• Also at NCAR, Mausumi Dikpati will release her outlook for Cycle 25 in a paper to be published later this year. Dikpati and colleagues predicted a stronger-than-average Cycle 24 (as did Hathaway and others). This didn’t materialize, but Dikpati did correctly forecast that Cycle 24 would begin later than usual. Dikpati is now doing a post-mortem on her Cycle 24 forecast, which was based on a pioneering model of the solar dynamo (the flow of plasma that produces magnetism within the sun). As with weather models, she expects that improved data assimilation–bringing the latest observations into the solar dynamo model–will help boost its accuracy.
With several decades of quiet solar activity, we will be experiencing a “Grand Minimum.” The open question is will this Grand Minimum produce a cooler plant, similar to the Dalton Minimum or the Maunder Minimum which is associate with the little ice age. Only time will tell. Your thoughts?
Bob Henson’s full post is HERE. It also includes an interesting discussion of the threat from solar eruptions to our electrical grid, even during a grand minimum.