Weather: Why our winters are unavoidably delayed
We all know that it's cold in winter because the tilt in the earth's axis of rotation points us away from the sun at this time of year. We can see the sun lower in the sky, and the dark mornings and early sunsets confirm that we are receiving less solar warmth. So far, so good; but if the shortest day of the year - which must be when we receive the least solar energy - falls a few days before Christmas, why does the weather continue to get colder for the next couple of months?
The way the sun provides warmth is not as simple as it seems. Since the air is a poor conductor of heat, most of the warmth we feel round us is radiation from the Earth itself. The sun heats up the Earth, which then warms up the air by radiation. This explains why the higher you go, the colder it gets. The top of a mountain may be nearer to the sun, but that counts for nothing compared with the fact that it is farther away from the nice warm ground.
What makes the real difference, however, is the difference between the land and the sea. Water is far more efficient than land at storing heat. Indeed, it may be said that the oceans are a reservoir not only of water, but also of the world's heat. Not only are the waters more efficient at storing heat, but it takes more heat energy to warm them up in the first place. This results in the oceans providing a sort of temporal thermal lagging around the continents. Water temperatures will rise and fall more slowly than those of nearby land.
Both the land and the sea warm up during the periods of maximum sunshine, then gradually cool down, radiating their warmth into the air. When the sun is less generous with its energy, the world cools down, and needs some time to warm up again before we begin to feel the benefit. We are living on a massive storage heater, simultaneously operating on two different tariffs: the quick-release land storage and the slow-release ocean storage.
Over land that is far from the sea, there is about a one-month time-lag between the shortest day and the coldest day (or the longest day and the hottest day). Over the oceans it is about two months. In Britain, where our weather is dominated by the seas around us, the hottest day of the year generally falls in the middle of August (it was 10 August last year) - two months after the summer solstice.
One aspect of all this, however, remains perplexing: if there is such a time-lag between our receiving solar energy and experiencing its effects, why is long-range weather-forecasting still such an inaccurate science? One might naively think that with all the solar energy stored up a month or two in advance, we ought to be able to predict what will happen when it is released. Yet it does not seem to work like that. The diffusion of heat between various sea depths, and the vagaries of heat transfer by ocean currents, seem to make predictions impossibly difficult.
As with so many aspects of the weather, the key to successful long-term forecasting is a better understanding of the oceans.
Life & Style blogs
Other popular areas include Didsbury, Clifton in Bristol, central Cambridge and West Bridgford
Doctors are allowed to have personal beliefs, just as long as these beliefs do not interfere with th...
BBC journalist Justin Webb talks about his experiences of the advances in preventing heart attacks a...
The 10 Best Scotch Whiskies
Meet David Karp, the 26-year-old high school dropout worth $275m after selling Tumblr to Yahoo
Game on: Xbox 720 and PS4 go head to head with Microsoft set to launch console today
'The ultimate all-in-one home entertainment system': Microsoft finally unveils its Xbox ONE console
Virtually Stephen Fry: Star launches (possibly) the world's most self-regarding app
- 2 Gay couple beaten in park urge MPs to moderate language on gay marriage
- 3 After woman sells virginity for $780,000, here are the results of our prostitution survey
BMF is the UK’s biggest and best loved outdoor fitness classes
Win anything from gadgets to five-star holidays on our competitions and offers page.
Excellent Salary Package - £60K to £120K: Austen Lloyd: We have an exciting op...
£200 - £250 per day: Progressive Recruitment: Java Developer - Urgent Requirem...
£70000 - £95000 per annum + Bonus, flexible working hours, remote work: Progre...
£50000 - £56000 per annum + Benefits package, flexible working hours: Progress...