Temperatures start to rise. Large parts of the planet become drier and deserts spread. Others receive more rain and floods come. The oceans warm up and expand, washing over islands and coastlines. Fierce storms occur where they never did before. Crops fail and vulnerable communities abandon their homes to migrate elsewhere. As the climate changes faster than ever before in human history, a crowded and troubled world struggles to cope.

Will this grim climate change scenario become reality? While the climate has always varied naturally, scientists now believe that industrial and agricultural emissions of carbon dioxide and other gases may cause a permanent, one-way change in climate. Atmospheric concentrations of these gases, which help to create a natural "greenhouse effect" that keeps the planet warm enough for human life, have risen dramatically over the past 100 years. This could lead to higher temperatures and new climate patterns in the coming decades and centuries.

Many questions remain, and researchers are working hard to answer them. But while scientific certainty is still some years away, the world's Governments have decided that the risks are simply too big to ignore.