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).