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Tuesday, 25 August, 1998, 11:49 GMT 12:49 UK
Life in the greenhouse


Under normal conditions, shown in the top diagram, the Sun's heat warms the Earth, with some heat being radiated back into space. The so-called 'greenhouse effect', shown in the bottom diagram, happens when more heat is trapped in the atmosphere by greenhouse gases like carbon dioxide, methane and CFCs.


Every time severe weather strikes, global warming seems to be blamed but what is global warming and should we be worried?

Records show that the average temperature of the planet is climbing quite rapidly, and, although it is not absolutely certain, most scientists now believe that human influence is responsible for the change.

The average air temperature has gone up by between 0.3C and 0.6C since the late 19th century which may not seem a great deal until this statistic is compared to figures for the last ice age. There has only been a five degree change in average temperature since the coldest part of the ice age some 20,000 years ago.

Although the global weather system is extremely complex and not wholly understood, experts say that such a rapid change in temperature is bound to have severe implications for future weather and climate patterns.

Climate researchers are predicting that the Earth's average temperature will continue to increase by between 1.5C and 4.5C in the next 100 years.

If this prediction is correct, the rate of change over the last two to three centuries will have been greater than any other time in the last 10,000 years.

Most scientists believe this recent global warming has been generated by human influence on a naturally-occurring phenomenon called the greenhouse effect.

The Sun's energy heats the surface of the Earth, although some of that heat is radiated back into space and the planet cools. Some gases in the atmosphere, called the greenhouse gases, prevent this radiation and so trap the heat.

Since the Industrial Revolution, humans have been pumping out huge quantities of greenhouse gases, most notably carbon dioxide.

Before 1850 human activity had little influence on the amount of carbon dioxide in the atmosphere but by 1930 we were generating one billion tonnes of carbon. In 1995 that figure was up to six billion tonnes. We have also produced large volumes of other greenhouse gases such as methane and chlorofluorocarbons, or CFCs.

Again since the Industrial Revolution, concentrations of carbon dioxide in the atmosphere have increased by about 30%, methane has increased by 145% and nitrous oxide by 15%. Burning fossil fuels is responsible for most of the increase in carbon dioxide while the upsurge in concentrations of methane is due to gas produced by livestock and rice paddies.

A report prepared by the Intergovernmental Panel on Climate Change in 1995 said that general warming is expected to lead to an increase in the number of extremely hot days and decrease in the number of extremely cold days. It also says warmer temperatures will lead to more severe droughts and floods in some places, and because rapid climate changes are unpredictable may lead to some "surprises".

Perhaps one of the most significant implications of global warming is a rise in sea level due to the thermal expansion of the water and ice melt.

Dr Geoff Jenkins
Dr Geoff Jenkins warns of the implications of a rise in sea level
Dr Geoff Jenkins, the head of the climate prediction programme at the Hadley Centre in the UK, says research suggests that ocean levels could rise by around 70cm in the next 100 years, though he adds that it could even be double or half that figure. The global sea level has already risen by between 10 and 25 cms over the last 100 years.

Low lying countries like Bangladesh, the Maldives and some areas around the Mediterranean and the Florida coast will suffer, especially as a result of larger and more frequent storm surges.

"A cyclone hitting Bangladesh can kill thousands of people - that's exactly the sort of thing that will happen if you get sea level rises," said Dr Jenkins. He explained that with higher sea levels a typical cyclone would kill more people and the frequency of other storms was likely to increase.

"In certain locations even in the UK small sea level rises would make storm surges much bigger," he said.

The Hadley Centre research paints an alarming scenario for some parts of the world with all sorts of implications for crop production, range and incidence of diseases, and weather patterns. But Dr Jenkins said there are so many uncertainties that exact predictions are difficult to make at the present time.

Future trends may also depend on any action humans take to modify their activities.

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