The last day of February marks the end of the meteorological winter, but the weather doesn’t seem to have noticed yet. As we sit shivering into March you could be forgiven for thinking that winter is never going to end.
Weather is as much about perception as statistics and the general feeling across the country is that our winters are getting colder. Which seems to contradict the idea that by putting greenhouse gases into the atmosphere in ever-increasing amounts the planet should be warming up. Actually, both could well be true.
We’ve had a couple of decades of being told that the climate is changing and that we are in a period of global warming, and while it’s correct that the planet is warming up, how can we, on this small island of ours, be experiencing colder, snowier winters?
This winter is set to be one of the coldest in the past 50 years. Certainly the past few winters, with the exception of 2011–2012, have been cold and often snowy. And who can forget December 2010, which was the coldest December in over 100 years? The bad news for those who hate the cold is that it looks like we could still get some severe winters in the years to come.
The atmosphere, and the weather connected to it, is very complex and there are several explanations for our recent cold, snowy winters, but one particular reason, which I agree with, is interesting the research scientists more than any other. It is not El Niño or its counterpart La Niña, both of which have an effect on the global temperature of the Earth. Nor is it solar activity, though this, too, plays an important role. The reason is Arctic sea ice.
The jet stream, which sits some five miles above the Atlantic, is a very strong band of winds and is the mechanism that generally drives the rain-bearing weather fronts to us from the Atlantic, keeping us mild and wet through the winter. But with the warming of the planet, more of the Arctic sea ice melts during the summer, which in turn warms the atmosphere above it and weakens the jet stream. This allows the high pressure over Scandinavia during the winter to become more dominant, bringing winds from cold Continental Europe to us in the UK and blocking the milder wetter Atlantic weather.
So when are we going to get out of this cold winter weather and into the milder, brighter conditions of spring? Well, meteorologically speaking, spring starts on 1 March and continues until the end of May, but that is just for the sake of convenience, splitting the year into four equal parts. Astronomically speaking, spring begins on 20 March as the sun crosses the equator and heads north.
In Sweden, spring starts when the average daytime temperature exceeds 0° Celsius for seven consecutive days, meaning that it varies from place to place. Even in this country the old Celtic tradition says spring is based on daylight and the strength of the noon-day sun, generally beginning in early February and ending towards the end of May.
Some gardeners where I come from in Devon will tell you it’s spring when the first daffodils bloom in south-west England and it then moves north roughly at walking pace to reach northern Scotland some eight weeks later. Or it’s when the magnolia, cherries and quince start to blossom.
So what can we expect in the next few weeks? I think this cold continental weather will last a little longer and we will have to wait until the middle of March to see much of a change – and this is when I always believe spring has sprung because it’s my wife’s birthday on 17 March and she’s once again older than me!
Bill Giles was senior weatherman at the BBC Weather Centre.