Is it so nuts to talk of ice age?
A woman walks through the snow as she makes her way through central London in heavy snow.
'The sun is god!" cried painter JMW Turner as he died, and plenty of other people have thought there was much in his analysis. The Aztecs agreed, as did the pharaohs. We are an arrogant lot these days, and tend to underestimate the importance of our governor and creator.
We forget that we were once just a clod of cooled-down solar dust; we forget that without the sun there would have been no photosynthesis, no hydrocarbons - and that it was the great celestial orb that effectively called life into being on Earth. That we are able to heat homes, turn on computers or drive to work is thanks to the unlocking of energy from the sun.
As a species we human beings have become so blind with conceit and self-love that we genuinely believe that the fate of the planet is in our hands - when the reality is that everything, or almost everything, depends on the behaviour and caprice of the gigantic thermonuclear fireball around which we revolve.
Members of The Household Cavalry Mounted Regiment ride along Horse Guards Parade during a snow flurry.
I say all this because I am staring through the window at the flowerpot and the bashed-up barbecue, and starting to think this series of winters is not a coincidence. The snow on the flowerpot, since I have been staring, has got about an inch thicker. The barbecue is all but invisible. This is now the fifth year in a row that we have had an unusual amount of snow; I mean snow of a kind that I don't remember from childhood: snow that comes one day, sticks around for a couple of days, followed by more.
I remember snow that used to settle for just long enough for a single decent snowball fight before turning to slush; I don't remember winters like this. I was cycling through Trafalgar Square and saw icicles on the traffic lights; and I am sure plenty of readers will say I am just unobservant but I don't think I have seen that before. I am all for theories about climate change, and would not for a moment dispute the wisdom or good intentions of the vast majority of scientists.
But I observe that something appears to be up with our winter weather, and to call it "warming" is to strain the language. I see on the BBC website there are scientists who say "global warming" is indeed the cause of the cold and snowy winters we seem to be having. A team of Americans and Chinese experts has postulated that the melting of the Arctic ice means that the whole North Atlantic is being chilled as the floes start to break off - like a martini refrigerated by ice cubes.
I do not have the expertise to comment on the martini theory; I merely observe that there are at least some other reputable scientists who say that it is complete tosh, or at least that there is no evidence to support it. I wish I knew more about what is going on, and why. It is time to consult once again the learned astrophysicist, Piers Corbyn, who has a very good record of forecasting the weather. He has been bang-on about these cold winters and he thinks we should be paying more attention to the sun. According to Piers, global temperature depends not on concentrations of CO2 but on the mood of our celestial orb. Sometime too bright the eye of heaven shines, said Shakespeare, and often is his gold complexion dimmed. That is more or less right. There are times in astronomical history when the sun has been churning out more stuff - protons and electrons and what have you - than at other times. When the sun has plenty of sunspots, he bathes the Earth in abundant rays.
When the solar acne diminishes, it seems that the Earth gets colder. No one contests that when the planet palpably cooled from 1645 to 1715 - the Maunder Minimum, which saw the freezing of the Thames - there was a diminution of solar activity. The same point is made about the so-called Dalton Minimum, from 1790 to 1830. And it is the view of Piers Corbyn that we are now seeing exactly the same phenomenon today.
Lower solar activity means - broadly speaking - that there is less agitation of the warm currents of air from the tropical to the temperate zones, so that a place like Britain can expect to be colder and damper in summer, and colder and snowier in winter. "There is every indication that we are at the beginning of a mini ice age," he says. "The general decline in solar activity is lower than NASA's lowest prediction of five years ago. That could be very bad news for our climate. We are in for a prolonged cold period. Indeed, we could have 30 years of general cooling."
I am not for a second saying that I am convinced Piers is right; and to all those scientists and environmentalists who will go wild with indignation at this article, I say, relax. I certainly support reducing CO2 by retrofitting homes and offices - not least since that reduces fuel bills. I want cleaner vehicles.
I am speaking only as a layman who observes that there is plenty of snow in our winters these days, and who wonders whether it might be time for government to start taking seriously the possibility - however remote - that Corbyn is right. Of course it still seems a bit nuts to talk of the encroachment of a mini ice age. But it doesn't seem as nuts as it did five years ago. I look at the snowy waste outside, and I have an open mind.
>> Boris Johnson is mayor of London.