Lord May of Oxford, the president of the Royal Society, will say that the devastation caused by Hurricane Katrina is an example of the sort of extreme weather event that climate change can trigger.

The impacts of climate change are many and serious, he contends. They include rising sea levels, changes in the availability of drinking water, and an increase in the risk of extreme weather such as floods, droughts and hurricanes.

Lord May, a former chief scientist for the Government, will say the seriousness of weather extremes, exemplified by Katrina's impact on New Orleans, "invite comparison with weapons of mass destruction".

In his final address to the Royal Society as its president, and to coincide with the Montreal meeting on climate change, Lord May will tomorrow criticise President George Bush for failing to follow through on the climate change commitments made by his father when he was president.

The current President Bush failed even to mention climate change, global warming or greenhouse gases in a 2,700-word speech on energy that he made immediately after the Gleneagles G8 communiqué, Lord May will say.

"In short, we have here a classic example of the problem or paradox of co-operation ... the science tells us clearly we need to act now to reduce inputs of greenhouse gases but unless all countries act in equitable proportions, the virtuous will be economically disadvantaged while all suffer the consequences of the sinners' inaction. In this sense, the climate-change disaster which looms this century is an appallingly large-scale experiment in the social sciences."

"If this experiment is to end in success for humankind, then it is essential that progress be made at the Montreal meeting." Carbon dioxide, the principal greenhouse gas generated by man-made emissions, has risen from 280 parts per million (ppm) before the Industrial Revolution to 380 ppm today. It is projected to increase to 500 ppm by the middle of the century.

"It is worth noting that the last time our planet experienced greenhouse gas levels as high as 500 ppm was some 20 to 40 million years ago, when sea levels were around 100m higher than today.'' Average global temperatures were projected to rise by between 1.4C and 5.8C by 2100 because of global warming, yet many, including some economists, found it difficult to grasp the significance of the figures given that daily temperatures could fluctuate by as much as 10C.

"There is a huge difference between daily fluctuations, and global averages sustained year on year; the difference in average global temperatures between today and the last ice age is only about 5C."

Lord May will say that the Montreal meeting should initiate a study of target levels for greenhouse gas emissions as a basis for discussing an action plan. Countries must sever the link between economic growth and increasing emissions of greenhouse gases.

"Appropriately constructed economic instruments, such as a carbon tax, could help motivate a reappraisal of this perverse message. Initiating such a study of target levels in Montreal should not diminish the pressure for all countries to start cutting emissions now.''