There has been a rather unnecessary blogosphere fuss about a TV report by BBC North East weatherman Paul Hudson, whose reports on the science of climate change have been the most informed of any reporter working for the BBC.
He produced a brief TV report suggesting that Northern Europe, and in particular his North East England region, might experience more severe winters in the future as a result of declining solar activity. In the report he interviewed Professor Mike Lockwood of Reading University who said the Sun was getting less active and that along with it came the increased probability of severe winters because of a tendency for more “blocking” low pressure regions that allow cold continental air to reach northern England. The effect found by Professor Lockwood is rather weak but said to be statistically significant. Fig 1 shows his correlation between Central England Temperature and a measure of solar activity. Click on image to enlarge.
The claim was also made by Prof Lockwood in the report that we have just witnessed the most rapid decline in solar activity in the past 10,000 years is based on the analysis of radioactive isotopes in ice cores. When solar activity is high the flux of Cosmic Rays incident on Earth is reduced due to the shielding effect of the strength and extent of the solar magnetic field. From the isotope measurements it is possible to derive a parameter called the solar modulation potential. Grand Solar Maxima like the one we have just come out of are defined as having a solar modulation of 600. Fig 2 is from Lockwood (2013) showing how this modulation potential varies for previous grand maxima going back 9,300 years. The reader can decide if the data for the most recent emergence from a Grand Solar Maxima – the long and low minimum between solar cycles 23 and 24 and the very weak cycle 24 – are an unusually rapid decline. Click on image to enlarge.
As is often the case in climate reporting those with a mind too came away from Hudson’s report believing they had seen different things. Despite Hudson saying the severe winters was a regional effect some took this prediction as global and with it the suggestion that the Sun’s declining activity may prevent greenhouse gas warming. To my mind there was nothing wrong with Hudson’s report, though Professor Lockwood claims he was misrepresented. I think the report was fair and after all it is Hudson’s report not Lockwood’s. I suppose the moral is if you don’t want to give a reporter the opportunity for supposed misrepresentation then don’t talk to reporters, who have to speak a different language.
New Maunder Minimum More Likely
The previous lengthy period of low solar activity was the so-called Maunder Minimum that occurred between about 1640 and 1710. This was coincident with a cold climatic spell called the Little Ice Age. This was once thought to be confined to North West Europe, then the Northern Hemisphere. However recent research is showing this cold spell to be a global phenomenon. It would be fair to say that no one knows why the Little Ice Age took place. Some believe that the relatively low solar irradiance inferred for the time from proxy data when combined with volcanic effects can account for it, but the argument is not convincing.
It is certainly true that the current decline in solar activity is accompanied by changes in solar activity parameters that have not been seen before since we have had equipment to measure them. Previously Professor Lockwood has said that the chance that we could be entering a new Maunder-like Minimum was rather low. However, in Hudson’s broadcast he increased substantially the probability that we are, although such estimates are rather subjective.
So what could happen in the future? It seems very likely that the Sun is entering a quiet phase that could last many decades and, if the past is anything to go by, it will have a cooling effect on the Earth’s climate (even if we don’t know exactly how.) The consensus is that this effect will pose only a small modification on the projected global temperature increase due to greenhouse gasses. See here, and here. But, there is a but.
It may be no coincidence that estimates of the turn-around in solar activity from grand maximum to decline might have occurred between 1985 – 95, and that global annual average surface temperatures have been flat since 1997. Previous work by Lockwood and Frolich (2007, 2008) that rules out any connection because they erroneously said that global surface temperatures were rising whilst solar activity was declining now seem rather wide of the mark. Also, one will have more confidence that the solar effect will be a minor component of a rising temperature when one has seen the temperature start to rise consistently once more.
This is an ongoing area of research. The weak effect seen by Lockwood in the data between low solar activity and severe cold winters in Europe has been questioned by van Oldenborgh et al (2013) who fail to find such a connection.
Looking further ahead a recent paper by Steinhilber and Beer (2013) look at the dataset obtained by merging isotope measurements in two ice cores, one from Antarctica and one from Greenland. They look at solar activity for the past 9300 years and extrapolate into the future. They expect low solar activity by 2100, moderate activity by 2250, followed by high activity between 2350 – 2400, then a decline. None of us will be around to see if this turns out to be the case.