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Science Alert: Experts Respond

UPDATED: Claims of a ‘mini ice-age’ ahead – Expert reaction

Posted in Science Alert: Experts Respond on July 14th, 2015.

An unpublished study examining solar cycles has created a flare-up of headlines claiming we are headed for a ‘mini-ice age’, but does the research stack up?

Widescreen-IceThe study presented at the UK National Astronomy Meeting this month outlined a new model of solar activity which was based on two separate internal cycles in the sun interacting.

According to a press release about the research: “Predictions from the model suggest that solar activity will fall by 60 per cent during the 2030s to conditions last seen during the ‘mini ice age’ that began in 1645.”

[Update: although not initially reported, the conference presentation was based on a peer-reviewed study published in The Astrophysical Journal]

Subsequently headlines around the globe have heralded the coming of a ‘mini ice age’. Examples include:

Stuff.co.nz: Now it looks like we’re in for an ice-age
New Zealand Herald: Sun cycle’s cold facts say mini ice age on way
TVNZ News: You think it’s cold now? ‘Mini ice age’ predicted for Earth in 2030

We asked experts to comment on whether this predicted drop in sunspot activity would have a significant impact on global temperatures.

The SMC collected the following expert commentary. Feel free to use these quotes in your reporting. If you would like to speak to a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).

NEW: Assoc Prof Gillian Turner, School of Chemical and Physical Sciences, Victoria University of Wellington, comments:

“Earth’s climate is in a constant state of change. The processes that control climate change are many and complex, they interact with one another, and depend on many variables that are difficult to quantify.

“The fundamental driver is the energy received from the sun – the solar irradiance. Any change of processes in the Sun may affect the rate at which it outputs energy, and this may initiate climate change on Earth via a whole range of interrelated processes.

“Climate change researchers are faced with two basic sets of questions: firstly how to measure solar activity and what it depends upon, and secondly what happens when the solar radiation reaches Earth – the effect of mounting greenhouse gases in the atmosphere is the most topical perhaps, but changes in many other parameters e.g. cloud cover, ocean circulation patterns, surface reflectivity due to ice cover, to name just a few, must all be factored into climate models.

“The current research, by Zharkova and others, concerns only the first of these. The authors combine a statistical study of solar activity – using a measure of the interaction of the solar wind, (which carries magnetic field out from the Sun), and Earth’s magnetic field as a proxy – with mathematical models of the dynamo that operates in the Sun and produces its magnetic field.

“The Sun’s magnetic field is a little different from Earth’s. The overall, more deep-seated field reverses in polarity approximately every 11 years (Earth’s field reverses randomly but on average at intervals of about 500,000 years). This seems to be related to the number of sunspots on the surface of the Sun, which themselves are a second source of magnetic field. The authors suggest that the deep-seated field itself has two components, and when combined with the sunspot field, a long term modulation in solar activity emerges. This, they say, produced a minimum in activity, the Maunder minimum, 300 years ago, when Europe went through the cold interval that has become known as the “Little Ice Age”. Zharkova and colleagues’ model predicts a similar minimum in solar activity for 15 years’ time.

“They readily acknowledge however that they have not looked at any of the second set of questions – what has changed in the Earth system since the Little Ice age. How will Earth react now to a similar decrease in the solar irradiation?

“Who knows? I’m not rushing out to stock up on firewood and winter woollies just yet!”

Dr Brett Mullan, Principal Scientist – Climate, NIWA, comments:

“This study claiming the Earth could go into a mini Ice Age in the 2030s was presented at a Royal Astronomical Society meeting in Wales, but has yet to be published. There are number of unclear claims made in the news reports, and as yet few mathematical details have been provided. The study appears to be based on just 3 sunspot cycles: in the climate literature this is considered too short a time period for reliable future extrapolations with a statistical model. So, in my opinion, it is premature to give too much attention to this prediction.

“In a Radio NZ interview Tuesday morning, Dr Zharkova [study author] indicated that solar irradiance may drop by 3 Watts per square meter during the 2030s. This is a very large change, ten times that of the difference between sunspot maximum and sunspot minimum. I will leave it to solar physicists to comment on the likelihood of a decrease of this magnitude, but would point out that the downward infrared radiation into the troposphere is increasing every year due to growing greenhouse gas concentration, and this would (at least) partially compensate a shortwave radiation decline, and would entirely negate a more modest decline than the one reported.”

Prof James Renwick, School of Geography, Environment and Earth Sciences, Victoria University of Wellington, comments:

“Recent statistical modelling from a group in the UK has shown a good fit to solar data covering the last three solar (sunspot) cycles, over the past 30 or so years. If that statistical model is used to predict into the future, it shows a large decrease in the size of the peak of the next two solar cycles, especially the one that starts in the late 2020s (cycle 26).

“Many [news] reports are talking about a ‘60% reduction in the sun’s output’ which of course would totally freeze the earth! What is really going on is a 60% reduction in the peak of the solar (sunspot) cycle, so we are talking about less than 0.1% decrease in total solar output (not 60%!)

“Extrapolation from a limited period of data is always risky and this result needs to be tested with other data sets and confirmed by other research groups before we can be confident that such a prediction is correct.

“If it was correct, it would mean that solar output reaching the earth would drop by 1-2 Watts per square metre — or by about 0.1% — for 2-3 decades. This would represent a milder version of what happened during the “little ice age” in the 1600s and 1700s. The big difference now is that there is a lot more greenhouse gas in the atmosphere than there was in the 1700s (about 40% more CO2 and more than twice the methane) which has added up to more than 2 Watts per square metre increase in the energy absorbed at the ground, compared to the 1700s.

“So, if the predicted decrease in solar output was to occur, it would roughly counter some of “global warming” that we have seen since the mid-20th century, for 20-30 years or so. But it would be a temporary respite at best and would not take away from the urgency of action on climate change and greenhouse gases, as that is what will shape our environment for centuries to come.”

“I’ve also been reminded that the little ice age in the 1600s-1800s was the result of more than a sunspot minimum. A series of major volcanic eruptions helped to cool the earth during that time. Plus there were other smaller factors that came together to give us what’s call the “little ice age”.  A reduction in solar output in the 2030s and 2040s would have an effect, but against the backdrop of continually rising greenhouse gas concentrations, it would be only a temporary drop from the warming trend.”

 Associate Prof Sean Oughton, Department of Mathematics, University of Waikato, comments:

“The prediction that there will be a significantly reduced level of solar activity for the next few decades is in line with extrapolated observations and some other models.  Whether the low level will be as low as, or last as long as, that of the most recent grand minimum (~1645-1710) is of course difficult to say.

“The historical data indicates that these sorts of multi-decade low-activity periods do occur.

“What is a bit disingenuous in the quote in the press release is end of the sentence: ‘conditions last seen during the mini ice age’.  If the prediction for solar activity holds up, then, yes, the conditions ON THE SUN will probably be similar to those during the Maunder minimum.  Of course that does not require that the conditions on the earth will be similar to those during the Maunder minimum.

“We also need to wait for the research to go through the peer-review process and get published. The National Astronomy Meeting is an important meeting, and presumably this solar activity work is all fine.  To judge it properly though, people will want to see the journal article, not just a talk at a conference.

“Two additional points:

1. The starting year of the Maunder minimum (~1645) was AFTER the start of what gets called the little ice age, so that suggests it didn’t cause the little ice age.

2. …As far as I know there is not a widely accepted model for how reduced solar cycle activity would cause global cooling on earth.  It’s being actively researched and there are plenty of ideas (eg, reduced UV output from the sun means less UV light entering earth’s atmosphere, leads to some cooling of it).  The usual warning that correlation does not imply cause also needs to be keep in mind.”

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