If human society continues with rapid economic growth and high levels of burning fossil fuels - oil, gas and coal - then the world's temperature could rise by 6.4ºC by 2100. This would make agriculture, even life, almost impossible over much of the Earth and it could occur in the lifetime of the grandchildren and great-grandchildren of today's generation of parents.

This report from the Intergovernmental Panel on Climate Change, based on a three-year study, is humanity's loudest wake-up call yet - and it specifically makes a link between human behaviour and global warming.

The devastating predictions of the scientists bring the 20-year wrangle over whether global warming is happening or not to an end. And they confidently destroy the doubts that have been used as an excuse for not doing anything - particularly by the George Bush administration.

They are saying explicitly that if the human race cannot or will not reduce greenhouse gas emissions the results will be disease, drought and famine. The figure of six degrees is a global average - it means higher rises in high latitudes, with more severe droughts, increased storms and the melting of ice and glaciers.

But the problem is not one of information. We know what we have to do. The issue - and one that threatens the very future of mankind - is that not enough is being done.

As individuals we can make a difference by recycling, ensuring we don't drive gas guzzlers and protecting our own small patch of the globe.

But what is really needed is radical action and the public appetite for this is growing in Ireland and beyond.

The Americans are the world's biggest carbon polluters but developing nations, led by China, will soon take over. It is more essential than ever now to create a regime to succeed the Kyoto protocol, which ends in 2012. The world's political leaders have our lives in their hands.