Heatwaves, flooding, hurricanes and expanding deserts - scientists believe they are all indications that the Earth is undergoing climate change. Most scientists agree the earth is now getting hotter, and at a faster rate than any observed before. And it's human activity which is being blamed. The Big Question: What is happening to the earth's temperature?

Suraje Dessai, is a graduate student at the Tyndall Centre, a leading climate change research institution. He tells The Big Question that the 20th Century saw an average increase in temperature around the world of between 0.2 to 0.6 Celsius. In its last report in 2001, the Intergovernmental Panel on Climate Change (IPCC) predicted that from 1990 to 2100 average surface temperatures are projected to rise by between 1.4 to 5.8 Celsius.

Emma meets Professor Phil Jones at the Tyndall Centre, who tells her it is not the first time the earth's temperature has changed. Our climate has always varied, but in the past those changes are thought to have been due to natural causes. Professor Jones charts variations in temperature over thousands of years by documenting differences in tree rings and ice cores.

So the earth is getting hotter. Why? All the evidence suggests that most of the warming observed over the past 50 years is down to human activity. In the 2001 IPPC report , the finger is pointed clearly at mankind.

The way we live is making the earth hotter -- emissions of carbon dioxide and other 'greenhouse gases' in the atmosphere have risen steeply since the industrial revolution. The burning of fossil fuels, deforestation and other human activities, spurred on by economic and population growth, have boosted these gases. Without any of those greenhouse gases at all, the earth would be substantially colder than it is now. But with levels of these gases rising, the result is global warming - they form a blanket that prevents heat from the earth escaping into space.

One of the results of climate change is a rising sea level. The IPCC predicts that between 1990 and 2100, sea levels will rise by between 0.1 to 0.9 metres. Some areas of the world are already suffering flooding and erosion.

Emma travels to the East Anglian coastline in the UK, where some people have lost their homes as the cliffs they were built on crumbled into the waves. Pat Gowen, the head of the North Sea Action Group, used to own a bungalow by the sea. In 1988, it fell into the sea. Among other factors, he blames global warming.

Whole ecosystems are under threat from climate change - including Fynbos in South Africa, known as the Cape Floral Kingdom. Dr Guy Midgley from the National Botanical Institute tells The Big Question that even species in protected areas are under threat from climate change.

This edition of The Big Question was first broadcast on 24th July 2004

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