In this audio section, BBC World Service environment specialist Richard Black explains the so-called greenhouse effect, global warming, the implications for the human race and the significance of the Kyoto summit.

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That is because the CO2 greenhouse effect is weak and marginal compared to natural causes of global temperature changes.

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Since both of these chemicals are more potent greenhouse gases than carbon dioxide, this effect, too, should help combat global warming.

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Dr Harries's conclusion is that the greenhouse effect has changed over the past few years in exactly the way that those who believe in global warming would have predicted.

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