Opinion There's been criticism for the Intergovernmental Panel on Climate Change (IPCC) over its latest AR5 report from many quarters for many reasons. But today there's new research focusing on one particular aspect of that criticism.
The particular part of the IPCC's science in question is its accounting for the effects of changes in the Sun on the climate of planet Earth. Many climatologists have long sought to suggest that the effects of solar variability are minor, certainly when compared to those of human-driven CO2 emissions. Others, however, while admitting that the Sun changes only a very little over human timescales, think that it might be an important factor.
This matters because solar physicists think that the Sun is about to enter a "grand minimum", a prolonged period of low activity.
The current 11-year peak in solar action is the weakest seen for a long time, and it may presage a lengthy quiet period. Previously, historical records suggest that such periods have been accompanied by chilly conditions on Earth – perhaps to the point where a coming minimum might counteract or even render irrelevant humanity's carbon emissions. The "Little Ice Age" seen from the 15th to the 19th centuries is often mentioned in this context.
There are certainly plenty of scientists to say, along with the IPCC, that this isn't so. For instance climate physicist Joanna Haigh has this to say, in tinned quotes offered alongside the AR5 release by the UK's Science Media Centre:
"Even if the Sun were to enter a new ‘grand minimum’ state within the next century, [solar variation] would be very unlikely to provide more than a small, temporary, partial compensation for likely anthropogenic warming.”
And yet the Little Ice Age appears to have affected the climate powerfully. IPCC-leaning scientists, however, say that the Little Ice Age couldn't have been caused by solar variability - not even solar variability combined with sky-darkening volcanic eruptions - as the effects would have been too weak.
That school of science would often suggest that the Little Ice Age was actually caused by a sequence of unusually powerful North Atlantic Oscillation (NAO) atmospheric phenomena - or, in other words, that it was just a blip: rather like the current 15-year hiatus in global warming, so often pointed up by climate sceptics. Indeed, a hefty paper published in 2009 stated as much, that the Little Ice Age was caused by powerful NAO effects (and the Medieval Warm Period before it, another awkwardness for the IPCC camp as it is thought by many to have seen a warmer world than we have now, without any carbon emissions).
That paper, as is normal in science, stimulated other scientists to see if they could show it to be wrong. In this case, a group of top climate boffins at the University of Berne set to work with a supercomputer, databases and models - and apparently, yes, the idea that the NAO could have been responsible for the Medieval Warm and Little Ice Age periods was found to be wrong. A Berne university statement just issued tells us:
Another research team had postulated a persistent and very pronounced positive NAO during this warm period based on reconstructed precipitation data. Moreover, the researchers identified a clear transition to an oscillating, more negative NAO at the beginning of the Little Ice Age. Based on their results, they concluded that the NAO had a major influence on the Medieval Climate Anomaly and its transition to the Little Ice Age.
When the Bernese researchers failed to confirm these conclusions in their climate model simulations, they began to search for the plausible mechanism ...
The Swiss team now say that in fact the Little Ice Age most certainly could have been triggered by variations in the Sun. Rather as climate alarmists believe that the basic, relatively minor effect of carbon emissions will be enhanced by positive feedback mechanisms, the Berne group have shown that the comparatively minor effects of changes in the Sun are actually amplified seriously by feedbacks on Earth. We are told:
Bernese climate researchers Flavio Lehner, Andreas Born, Christoph Raible and Thomas Stocker reveal that the Little Ice Age was also able to take its course without the influence of the NAO, driven purely by the consequences of strong and frequent volcanic eruptions at the time, a reduced solar radiation, or both together.
For the scientists, the fact that all the slightly altered, realistic simulations and the synthetic ice simulation yielded consistent results is solid proof that the Little Ice Age was primarily governed by external triggers. Volcanic activity and less solar radiation initially caused an increase in sea-ice formation independently of atmospheric circulation..
So there we have it. In fact the coming solar minimum - and/or volcanic eruptions that may occur in coming centuries - though it might seem like a minor effect, could actually be quite capable of triggering another small Ice Age. It may well be that actually humanity will find itself battling cold rather than heat in the generations to come.
Professor Judith Curry, another eminent climate scientist who doesn't find herself part of the "consensus", cites other research today – including a report from the US National Research Council – which casts doubt on the cut-and-dried IPCC prognostication on solar factors. She writes:
What a relief that the IPCC consensus has decreed with high confidence that solar variations won’t influence the 21st century climate. For a minute there, after reading the NRC Report, Svensmark and Vahrenholt, I thought us scientists might have more work to do to figure out how the Earth’s climate system works.
The Berne researchers' new paper is published in the Journal of Climate. ®