Here in the UK, the cold weather is finally upon us. Cold air over continental Europe will, this week, hold back the giant anti-cyclones out in the Atlantic and result in cold and frosty mornings – at least that’s the forecast. When one lives in Britain, one gets used to the weather being a subject of constant review.

Meanwhile, discussions continue in Copenhagen about the future of our planet, our contributions to global warming and what we plan to do about rising sea-levels, increasingly violent storms, spreading deserts and all the other effects brought on by man’s thirst for energy. At least we seem to have agreed that something must urgently be done and that we will all have to play our part.

With the weather very much in the news, it seemed to me to be an appropriate moment to look back at how our weather used to be, in particular during the Little Ice Age, a period lasting about 300 years from approximately 1550 – 1850. This affected the whole world and was caused by a number of coincident factors. There was a period of reduced solar activity – effectively the sun cooled a little. Then there were a number of large and violent volcanic eruptions, causing tiny particles of ash to be thrown into the upper atmosphere and an increase in emissions of sulphur, both of which caused more of the suns light to be reflected back into space rather than fall on the Earth. The Black Death, a plague which caused significant reductions in human population and consequent re-forestation of some areas of Europe, resulted in a decreased amount of carbon dioxide in the atmosphere. Even then, man played a part in climate change.

It may seem odd to talk about a period of global cooling when we’re all discussing global warming, but I believe it may be of interest to consider the effect that even small changes in global temperatures can bring about — and it was a small change. During the Little Ice Age, global temperatures fell by less than one degree Celsius. This is a far smaller change than is predicted for global warming where most models predict a global rise of more than two degrees Celcius by 2100, even if we take action. If we continue as we are, it will probably be more like five degrees.

So what happens when the Earth cools by less than one degree?

The Frozen Thames, 1677. Original painting in the collection of the Museum of London. Artist not known.

In 1536, King Henry VIII travelled from Westminster to Greenwich by sleigh along the river Thames. Approximately thirty years later, Queen Elizabeth I donned a pair of skates and “shot at marks”, a form of archery-on-ice on the river. King Charles is known to have eaten from an ox roasted whole on the river at Whitehall. It seems that the frozen Thames provided the equivalent of a photo-opportunity for the monarchy.

In the winter of 1683 to 1684, the Great Frost was recorded. During this period the river Thames froze over solid for two months. London Bridge, which was the lowest point at which the river could be crossed by bridge, was a toll crossing and you had to pay to cross. In the Great Frost, Londoners, ever watchful for a bargain, began crossing the ice rather than paying to cross the bridge. The river soon became a thoroughfare.

An eyewitness recorded: “On the 20th of December 1683, a very violent frost began, which lasted to 6th February, in so great extremity that the pools were frozen 18 inches thick at least, and the Thames was so frozen that a great street from the Temple to Southwalk was built with shops and all manner of things sold.”

Frost Fairs continued through the Little Ice Age, though the effects of the cold were not all beneficial. The diarist John Evelyn recorded: “The fowls, fish and birds, and all our exotic plants and greens [were] universally perishing. Many parks of deer were destroyed, and all sorts of fuel so dear that there were great contributions to keep the poor alive…London, by reason for the excessive coldness of the air hindering the ascent of the smoke, was so filled with the fuliginous steam of the sea-coal…that one could hardly breath.”

The last frost fair was held on February 1st, 1814 and lasted four days. This was at the end of the Little Ice Age, the weather was growing milder and improvements to the flow of the Thames (including the removal of the medieval London Bridge) made the river less likely to freeze. Even then, the river was so frozen that an elephant was led across the ice below Blackfriars Bridge.

Today, in commemoration of the Frost Fairs, there are five slabs of slate with an insciption by the artist Richard Kindersley on the pedestrian underpass of  Southwalk Bridge which are carved with scenes from the frost fair and with the following inscription:

Behold the Liquid Thames frozen o’re,
That lately Ships of mighty Burthen bore
The Watermen for want of Rowing Boats
Make use of Booths to get their Pence & Groats
Here you may see beef roasted on the spit
And for your money you may taste a bit
There you may print your name, tho cannot write
Cause num’d with cold: tis done with great delight
And lay it by that ages yet to come
May see what things upon the ice were done

These are just local fragments of what happened when the Earth cooled by less than one degree. There were typhoons, famine, bread-riots and disease. Finland’s population fell by a third and the Norse colonies in Greenland vanished due to starvation. In 1607 there was ice on Lake Superior in June, and in northern Europe in winter, it was possible to sledge from Poland to Sweden, across the Baltic Sea, stopping overnight at temporary inns built upon the ice.

All of this from a change of less than one degree.

From a Copenhagen perspective, within two or three generations our world will be transformed by a change of at least three times the magnitude of the Little Ice Age but in the opposite direction. The world will get much warmer, that is now inevitable.

Just how bad the change will become is up to all of us, but whatever happens, we are going to be witnesses to changes far more significant than those recorded here.