The latest predictions from scientists are for a 2.5 degree centigrade increase in average temperatures by the end of the next century and that sea levels will rise by around one foot as the warmer oceans expand. The cause: a build up of gases which trap solar heat in the atmosphere. Most of them come from the burning of fossil fuels and forests.
Those climate changes may not sound drastic, but they would be the most rapid since the last Ice Age ended about 10,000 years ago. The temperature increase will be spread unevenly around the planet with the poles, for instance, warming up much more than the global average.
Along with the warming will come changes in rainfall and snowfall, wind patterns and ocean currents. Some places will get wetter, others may shift into being true deserts.
Of course wildlife has been challenged by more drastic, but entirely natural swings in climate many times before. But the world is a much less congenial place for nature these days. In large parts of every continent, natural and semi-natural habitats such as forests are fragmented. Separating them are huge stretches of farmland and urban development. Any species rooted to one place could be in trouble.
Coastal freshwater wetlands which provide breeding and feeding grounds for many bird species will be invaded by seawater. Mudflats lining estuaries will also shrink. In the past when sea levels rose the coastline could change with it. But that is far less likely to happen in future, for large parts of it are developed and defended by sea walls, which a has a knock- on effect on migrating birds.
A recent WWF report says that half a dozen bird species which breed in tundra-like habitats in Britain may stop nesting here if the climate warms substantially. Tree species that have adapted to the long, cold winters of high latitudes may die in warmer conditions.
Some species are likely to expand their populations in a world where one species, us, is altering the entire climate system. A few insect and bird species from further south in Europe, such as Cetti's warbler, have begun breeding in Britain in recent decades.
If we could instantly cut our emissions of ''greenhouse gases'' such as carbon dioxide and methane by two thirds then the man-made climate change would slow down and stop within a couple of decades.
The rate of increase is about 2 per cent a year. Meanwhile developed nations, which have pledged to freeze their rising annual emissions at the 1990 level by the year 2000, are mostly failing to keep their promise.
So while you may hear plenty of talk about tackling global warming, a lot of it is hot air. Which is why conservation organisations like WWF campaign hard for governments, industry and the public at large to take the issue seriously.