WEATHER LORE

CLIMATE CHANGE

How do we know that the world’s climate is changing? Records in developed countries such as ours stretch back over 150 years; but other parts of the world, the open oceans, most of the Southern Hemisphere in general and Antarctica in particular, have little information on which we can base our assumptions.

Of course there are historical sources other than the official records. Weather diaries and records have been kept by amateur meteorologists, and books, paintings and engravings can also give a flavour of past climates, such as those depicting fun, fairs and frivolity on the river Thames.

Even the cave paintings of France show a time of icy chill and animals of the tundra.

Staying in France, the ‘Mer de Glace’ a glacier in the Alps near Chamonix has been charted for hundreds of years. It has exhibited a general retreat of

around 1500 metres in the past 200-250 years, evidence for

global warming, perhaps?

But going back further, before modern human beings were around, what can we base our claims for past climatic change on?

Some of the evidence is to be found inside the world’s ice caps. As layer upon layer of snow builds up, slowing turning to glacier ice, microscopic air bubbles can be trapped within the ice.

These air bubbles, when sampled in ice cores going back to conditions that existed up to 10,000 years ago, give us information about atmospheric air density and gaseous content. Even tiny volcanic dust particles have been found informing us about past volcanic eruptions.

Then there’s dendrochronology, the study of annual growth rings of trees; the word itself combines two Greek words, ‘dendron’ for trees and ‘chronos’ for time.

The size of the growth rings can give important information about climate since temperature, the length of the growing season and frosts are key elements controlling the growth of trees.

Perhaps the best and most widely used method for reconstructing climatic conditions over the past 15,000 years is pollen analysis. Ever since the snowy wasteland of Britain was colonised by herbs, plants and trees after the last ice age, pollen has been scattered to the four winds.

Microscopic pollen grains are very resistant to decay and are usually well preserved in peaty sediments. The numbers and types of plants that were present as shown by the pollen grains and the plant communities that existed are firm evidence of past climates. And, luckily, there’s lots of pollen, well, there should be since one flower can produce up to 1 million grains!