Who has noticed that the period 2014-2015 keeps on turning up in the debate on greenhouse science? For that is when greenhouse proponents say the long-delayed global warming apocalypse will start happening. In addition, that general date has turned up in forecasts made by an arch sceptic, and two researchers in the US have forecast that sunspot activity will cease entirely by 2014.
As the two sides do not agree on anything else at all this is odd - odd enough to be worth exploring.
One group to point at the 2015 date is led by Noel Keenlyside of the Leibnitz Institute of Marine Science in the German city of Kiel. As reported in the journal Nature (letters, May 1) Keenlyside and colleagues added the affect of climate cycles to the Intergovernmental Panel on Climate Change models to forecast that global temperatures will remain stable or perhaps even dip down for the next few years, before heading up. The paper does not give a date for the expected kick up in temperatures but in a subsequent interview with the Daily Telegraph in the UK Keenlyside stated that the earth will start to warm again in 2015.
Keenlyside was forecasting from his research into the powerful Atlantic meridional overturning circulation (AMO) climate cycle which, he says, has a global effect and will weaken to its long term mean. He also emphasises that his work in no way contradicts that of the IPCC - he is merely adding climate cycles on top of the panel’s predictions - but his work seem to have horrified the hardliners. There have been internet reports that prominent scientists have tried to challenge the Keenlyside team to bets on temperature trends. However, other climate cycles seem to be following the AMO lead. In April, NASA announced that the Pacific Decadal Oscillation has shifted from its warm mode to its cool mode - a switch that will not be discussed here but may also result in significant cooling.
More recently, another group observing the sun has also come up with the date 2014 but for quite different reasons. As has been noted a few times in the media, the sun has gone quiet - too quiet - with the next solar cycle so far not putting in an appearance. Scientists have known for a very long time that the earth has a distinct 11-year cycle. At its height, indicated by lots of sunspots, the sun is very active giving off lots of flares and solar storms which affect satellites. At the bottom of the cycle there are few or no spots, and a marked lack of activity.
The last cycle was officially declared over by NASA in March 2006 with one group at the space agency putting out a release confidently forecasting that the next cycle would be 20 to 50 per cent stronger than the old.
The sun responded to this piece of scientific hubris by going quiet. A few spots from the new cycle have been sighted, as well as a few spots from the old - scientists can tell which spots the cycle belongs to by their magnetic polarity - but very little has happened.
At the time of writing the sun is still spot free. NASA solar physicist David Hathaway points out, quite rightly, that the sun’s behaviour is within major statistical limits - just. The average solar cycle lasts 131 months plus or minus 14 months and the current cycle - the quiet period counts as part of the old cycle - has lasted nearly 143 months. The solar cycle went quiet for years at the beginning of last century before restarting, Hathaway notes, so nothing out of the ordinary has happened - at least, not yet.
Another group at the US National Solar Observatory in Tucson, Arizona, William Livingston and Matthew Penn, believe that there may be a deeper process at work. Sunspots are highly magnetic regions that are somewhat cooler than the rest of the sun’s surface (they appear dark compared to the rest of the sun, but if seen separately would appear very bright) and the two researchers have been tracking both the temperature and magnetic strength of the spots. They found that the spots have been warming up and becoming less magnetic. An average of the trend is a straight line going down which hits the bottom of the graph at 2014. They have concluded that, although sun spots may appear briefly from time to time in the next few years, they will disappear by 2014.
This conclusion is in a paper submitted to the journal Science three years ago but rejected in peer review. With the sun now so quiet the paper has been resurrected from a filing cabinet in the observatory and circulated informally. Dr Livingston told me (by phone from his office in Tucson) that the paper had been rejected on the grounds that it was a purely statistical argument so it would be better to wait and see what happened, and he considered that a fair point. They are now waiting “for the right moment” to resubmit.
But what happens after 2014? Dr Livingston says that as they are using a purely statistical argument, without any theory to back it, they do not know. All they know is that the trend reaches zero in 2014. Conventional theory on the sun’s inner workings never forecast anything like this - in fact, forecast the exact opposite - but has been revised to say that the sun will restart some time next year.
With the sun being quiet for a surprisingly long time, plenty of commentators are pointing to the possibility of a Maunder Minimum - a period from 1645 to 1715 with very few sunspots which is associated with a series of bitter winters known as the Little Ice Age. Although it is widely acknowledged that there must be some link between the sun’s activity and climate, the nature of the link and its effectiveness is hotly debated. The IPCC models, the ruling orthodoxy, gives star billing to the effect of industrial gases in the atmosphere and places solar variations in the also ran category. However, as we shall see those models have proved largely useless for forecasting - in the short term, at least - and there are no rival climate theories. The sceptics largely decline to forecast, pointing out, with some justification as it turns out, that there is as yet no means of forecasting what the sun will do.
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