Some people may have noticed that amid all the footage of snow-laden roads and stranded airline passengers that has filled our 24-hour news services over the last few days, very little has been said about the causes of the extraordinary weather Britain, and most of North West Europe, has been experiencing since the end of November. During some weather forecasts, some graphics showing a meandering jet stream have occasionally been presented, and the effects of this described; but little mention has been made of the cause, or causes, of this unusual phenomenon, an omission which is all the more surprising in that a number of contributory factors are clearly identifiable.
The most important of these is the fact that we are now emerging from one of the most extended periods of minimal solar activity in over a century.
Solar cycles normally last 22 years: 11 years from minimum activity to maximum; and then 11 years back again to the minimal phase. As can be seen from Figure 1, however, the most recent minimal phase lasted nearly two years, from the end of Cycle 23 in early 2008, to start of Cycle 24 in late 2009.
The significance of this is that solar cycles have long been correlated with weather patterns. Solar flares, seen from earth as sun spots, produce an enormous amount of high-energy radiation, known as the solar wind. This is deflected around our planet by the earth’s magnetic field, but can be seen above the poles in the form of aurora. Among its other numerous effects, however, it also increase the amount of ozone in the upper atmosphere. This causes it to heat up, which in turn affects the strength and direction of winds all the way from the stratosphere to the earth’s surface. In effect, the greater the solar activity, the more energised our atmosphere becomes. Unfortunately, the opposite is also true. Periods of minimal solar activity effectively allow the upper atmosphere to cool, weakening the currents of air it otherwise thermally drives. In this instance, the critical effect has been upon the jet stream, which instead of rushing across the Atlantic, from west to east, in an almost straight line at the latitude of the English channel, is now meandering north towards the Arctic with all the lassitude of an exhausted polar explorer, before curving south again toward the Mediterranean, dragging the Artic air with it to lay siege to most of North Western Europe.
The two questions to which this immediately gives rise, of course, are: ‘How long is this going to last? and ‘Is this just a one-off event?’ Unfortunately, the answer to the first is impossible to predict. But it could be some time. Not a happy thought if one is struggling with energy bills. The answer to the second, however, could be even more worrying. For as one can see from Figure 1, Solar Cycle 24 has not got off to an exactly flying start. To my untrained eye it doesn’t even look like it’s going to achieve the projected values for 2010/2011 indicated on the graph. Indeed, the protracted nature of this period of inactivity, and the sluggishness of the recovery so far, has even led the journal of the American Geophysical Union, Eos, to publish a paper suggesting that the sun might be returning to a state similar to that of the Maunder Minimum, which caused the ‘Little Ice Age’ in Europe during the 17th century.
Of course, it is too early to be sure of this or even entertain it as a possibility. However, another cycle, of a completely different kind, would suggest that, in Britain at least, we may be in for some considerably colder winters for some years to come. This is because in 2009 the AMO (Atlantic Multidecadal Oscillation), as shown in Figure 2, went into the negative part of its cycle for the first time since 1994.
The AMO is a cyclical pattern of sea surface temperatures (SST’s) in the North Atlantic, with warm and cool phases each lasting between 20 and 40 years. The variation in temperature, at just ±0.5°F above or below the mean, is not dramatic; but in such a large body of water, the effect is significant, with air temperatures following the SST’s fairly closely. There are some anomalies, as in 1964 for instance, when the air temperature was significantly lower that the SST, but for the most part they are fairly consistent. It should also be noted that the AMO is perfectly natural, is quite independent of global warming, for instance, and that the same pattern has been consistently recorded since the mid 19th century.
The fact that the AMO dropped into the negative part of its range in 2009 does not, of course, mean for certain that we have entered another cool phase. Again it is too early to tell. Fifteen years is actually quite a short period for a full warm phase. As can be seen from Figure 3, on the other hand, longer phases are sometimes interspersed by shorter ones. Indeed, the 20th century norm of roughly 60 year cycles (20-30 years hot, 20-30 years cold), is somewhat different from the 19th century norm, suggesting that there could be cycles within cycles. In any event, the dip into the negative part of the range in 2009 would indicate that the trend is now most definitely downward. One way or another, therefore, it seems likely that, for the next two or three decades, winters in Northern Europe are going to be more like those we experienced in the sixties and seventies than those of nineties and noughties.
The bigger question, however, is how all this fits into the prevailing theory of global warming. If we are in for a weak solar cycle and the Atlantic is cooling, does this mean that the earth, generally, might be entering a cooling phase? Unfortunately, no. If we take the Atlantic, for instance, it is just part of global ocean system, with currents moving from ocean to ocean in a cycle that last around 1600 years. While some parts of the system are cooling down, therefore, other parts may be warming up. Moreover, the AMO graphs above have already been detrended. That is to say that the effects of global warming have already been taken out. If one were to look at a graph of the actual SST’s, one would see that the whole oscillation has been gradually rising, by around 0.22°C, in fact, over the last 150 years.
This is not to say that, in the North Atlantic, many of the effects of global warming won’t be reversed over the next two or three decades as the AMO goes through its cold phase. At its lowest point, for instance, the Arctic ice is likely to return to more or less what it was like during the eighties and nineties. When it returns to its warm phase, however, the melt is likely to be even more severe and extensive than it has been during the last ten years. This is because the AMO both exaggerates and disguises global warming. During the warm phase, it exaggerates it. Thus, over the last ten years we have been constantly shown pictures of ice melting and polar bears losing their habitat. This, we have then been told, is a consequence of global warming. But this is not true. It has rather been the consequence of the AMO being at or close to its high point. Ten or fifteen years from now, however, the ice will have returned, and people will then say that global warming was just a load of nonsense. Again, it won’t be true. Global warming will simply be being disguised by the cold phase of the AMO. But it may be hard to convince people of this.
In fact, this may cause both climatologists and politicians some quite considerable problems. If so, however, they’ve only got themselves to blame. For at no point during the last fifteen years did they actually tell us that most of the Artic ice melt was due to the AMO. They may have thought that this would confuse people or send a conflicting message; but treating people as mushrooms is only ever a short-term strategy. Eventually they find out, usually in ways that cause more problems than would have been caused by telling them the truth in the first place. And in this case, the effect is likely to be even more exaggerated, in that the policy of disclosing as little actual scientific information as possible and relying largely on emotive images and polemics to get the message across has rendered the entire climate change debate essentially irrational. Instead of being given unequivocal, empirical evidence and a clearly argued case, people who question global warming, and in particular its man-made origin, are simply branded climate-change deniers and are bracketed, both morally and intellectually, with holocaust deniers. The backlash, when it comes, therefore, is likely to be all the more violent.
The problem for both climatologists and politicians, however, is that there doesn’t seem to be any way out of this potential mess. For the simple fact is, of course, that unequivocal, empirical evidence for man-made global warming doesn’t actually exist. The accumulation of greenhouse gases in the atmosphere is simply the best theory anyone has so far come up with to explain that part of global warming for which it is otherwise impossible to account. For global warming is a fact. Over the last century, the Earth's average temperature has increased by approximately 0.6°C, only 25%, or 0.15°C of which, can be attributed to other identifiable causes, predominantly the sun. That, therefore, leaves us with 0.45°C unaccounted for. And given the way greenhouse gases in the upper atmosphere reflect radiation back down to the earth’s surfaces instead of allowing it to escape into space, this is an explanation that certainly fits. But its not proof. It is a piece of inductive reasoning. And as Sir Karl Popper taught us, conclusions drawn from inductive reasoning can never be verified, only falsified. At this point, in other sciences, therefore, experiments would be set up to test the hypothesis. But climate science doesn’t really lend itself to experimentation. It has to rely on simulation, using mathematical models, which in all realms of science have often proved to be somewhat unreliable. One only has to miss out or underestimate the influence of one variable and one’s forecast can end up very wide of the mark. It would be interesting to know, for instance, whether our current climate change model anticipated the current solar minimum and whatever long term effects it may yet have. Indeed, it would be interesting to know whether solar activity is even factored into the equation. The one thing of which I’m sure, however, is that no climate scientist is ever going to tell us.
Given the nature of the science, of course, this defensiveness is quite understandable. People want black and white answers where there is only the balance of probability. And it is this that places climatologists in such a dilemma. For if they explain to people the real nature of the science, a lot of people, particularly the more aggressive type of TV journalist, will then say that it is therefore just a theory, that there’s no proof. As a result, people will then be far less likely to act on it. Tell them that anthropogenic global warming is a fact, on the other hand, and we might just save the planet. The only problem is that, strictly speaking, it’s a lie. It also leads to further lies: lies of omission – things one cannot say; explanations one cannot give – so that when the country is covered in snow, and we are experiencing the worst winter in decades, climatologists are nowhere to be found, and the BBC is left showing endless hours of abandoned cars and people waiting in queues for Eurostar. Perhaps, therefore, its time to stop treating people like mushrooms, to tell the truth and open up a proper debate. At least we might get some proper journalism from our 24 hour news services. Or is that just wishful thinking?
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