Solar predictions bring heat and light

Sun observed by the Soho satellite Image copyright NASA
Image caption The Sun appears to be calming but that does not necessarily mean cooling on Earth

Over the last few years, the politics of climate change have been amply forged in the fires of a changeable Sun.

And the story is here again, in the form of research unveiled this week at a meeting of the American Astronomical Society (AAS) Solar Physics Division in Las Cruces, New Mexico.

The solar science, described graphically in a Discover Magazine post - "an east/west river of gas" which "flows under the surface of the Sun" that can't be seen directly but which is inferred from "sound waves that travel from it to the surface" - is fascinating.

And what it suggests is that the Sun appears set to quieten further over the next solar cycle than it already has - with lower sunspot activity, and perhaps marginally lower energy output.

But as to the implications on Earth - well, for anyone who's followed this story for a while, they're very familiar, and the telling of them is laced with equally familiar political overtones.

The big question is this: if the predictions of an impending reduction in solar activity turn into reality, what would that mean for the global climate?

And that's why it becomes a political football - because if the answer is that it counteracts global warming, still more if it leads to global cooling, then moves away from fossil fuel use are at best unnecessary and at worst harmful.

The comparator here is the Maunder Minimum - a period of low solar activity running in the late 1600s and early 1700s - a "grand solar minimum" - which co-incided with a period of colder than usual temperatures - at least, in parts of Europe.

So you can probably name a few organisations likely to pounce on this latest work as evidence that another cool period is coming, and that society's logical response is to drill, baby, drill and burn, baby, burn like never before.

The Register doesn't disappoint, suggesting the solar cycle predictions will become "the science story of the century" and mean that the Earth is "heading into a mini Ice Age" - while the Daily Telegraph's James Delingpole treats it as fact - "It's official: a new Ice Age is on its way".

Image copyright SPL
Image caption The Earth may have been a "snowball" once but an imminent repeat seems unlikely

As it has been for years, the reality is rather different.

Firstly, the research itself has been presented at one rather small and rather select science meeting - not, as yet, formally published and peer reviewed.

Soundings taken by dot.earth's Andy Revkin suggest that not everyone in the solar physics community likes what they've seen - so publication could yet prove a hurdle.

Secondly, the predictions made about the next solar cycle would have to turn into reality - which might not happen, however sound the science.

Thirdly, even if all that happens, the Sun's activity would have to diminish enough to overwhelm the man-made contribution to the greenhouse effect.

Four years ago, in the midst of the Intergovernmental Panel on Climate Change's last major assessment of global climate and shortly after Henrik Svensmark's The Chilling Stars elaborated how the Earth's modern climate could be determined by solar effects on cosmic rays, I looked into this question for a feature article on this website - part of a series on scientific, social and political aspects of "climate scepticism".

The conclusions, in a nutshell, were these:

  • The Sun is the major determinant of the Earth's climate on long timescales
  • Cosmic rays have been a mediator of this effect
  • It is not the major issue on human timescales
  • Any effect from modern changes in solar activity is likely to be dwarfed by greenhouse gas emissions and associated issues such as sulphate aerosols.

That was four years ago; and since then, further research published in peer-reviewed journals has, if anything, weakened the solar case - whether involving cosmic rays or not.

Research on cloud formation in the real world suggests the cosmic ray amplification of cloud cover - the way the Svensmark idea works - isn't big enough.

A recent modelling exercise on the impact of any future grand minimum suggested it would cool the planet by a fraction of a degree Celsius.

Another recent paper concluded that while the major Ice Ages occurring every 100,000 are undoubtedly profound events, the so-called Little Ice Age that partially co-incided with the Maunder Minimum wasn't anything like that, bringing temperatures down globally by 0.3-0.4C.

Image copyright SPL
Image caption Changes in cosmic ray flux have altered climate in the past, but do not seem to be dominant now

Since the beginning of the industrial era, by comparison, temperatures have risen by about 0.7C.

Joanna Haigh, a solar physicist at Imperial College London, has spent a fair bit of research time investigating mechanisms that could potentially amplify solar changes into meaningful temperature variations on human timescales on Earth.

She summed up the importance of the latest research like this:

"In a future grand minimum, the Sun might perhaps again cool the planet by up to 1C.

"Greenhouse gases, on the other hand, are expected to raise global temperatures by 1.5-4.5C by 2100.

"So even if the predictions are correct, the effect of global warming will outstrip the Sun's ability to cool even in the coldest scenario.

"And in any case, the cooling effect is only ever temporary. When the Sun's activity returns to normal, the greenhouse gases won't have gone away."

She could have added that changes in solar output have no impact on ocean acidification, the other major impact of rising carbon dioxide concentrations.

Scientific research progresses; and occasionally something that appears to be solid gets overturned by a stunning new discovery.

It may be about to happen in particle physics - if neither the Tevatron nor Large Hadron Collider spots a Higgs boson soon, the standard model that scientists have worked with for years may have to be abandoned, or at least seriously reformed, and another built in its place.

And yes, the same thing could happen with man-made global warming.

But it hasn't yet.

All the studies I'm referring to above are out there in the public domain - which immediately raises a question over why some accounts claim big things for the new research but fail to take into account the context afforded by the larger body of published work.

The battle for public opinion on climate change is largely fought with memes; and solar changes leading to a cooling planet is one of them.

On this battleground, where the bigger picture can be conveniently forgotten, it has proven remarkably persistent.

Part of its appeal is that it has some scientific grounding; but it melts away in the light of the bigger research picture, and that's why it has little credence in mainstream scientific circles as a major factor in modern-day temperature fluctuations.