The latest scientific evidence already suggests that the impact of climate change on the UK could be sharper and faster than was previously thought. Already 1.8m residential properties in England and Wales are currently at risk from flooding, as are 1.4m hectares of agricultural land. And if we don't build climate change into our flood defense plans, we can expect a 65% increase in river flooding and a four-fold increase in coastal flooding in the second half of this century.
But what is not realized is that the process of climate change may turn out to be much more unpredictable and unstable, with potentially catastrophic consequences in the long run. Many people imagine that temperatures will rise slowly but evenly, so that Britain will gradually take on the same warm temperatures as the Côte d'Azur - Manchester on the Riviera. It may well turn out to be disastrously different.
That is why I am so disappointed that this week the US refused to reconsider coming back into the climate talks for 10 years. The need for action is urgent. The acknowledgment that there is a problem is welcome but the response is not adequate. There are two strong reasons for doubting the comforting US picture that there's plenty of time to deal with the problem. One is that climate change may be not steady but abrupt; the other is that the pressures we inflict on the climate may trigger wholly unexpected developments from feedback effects.
For the past 400,000 years, for which data exist from drillings in the Antarctic ice sheets, the Earth's ecosystem as measured by atmospheric carbon levels has been relatively stable throughout the ice age cycles. However, the present emission of carbon is already too high for the planet's self-regulation to cope, so it is frightening to think what might be the effects if global carbon emissions increased multifold during the next century or two.
Abrupt climate change occurs suddenly when the climate system is forced to cross some threshold into a new regime, creating widespread havoc and destruction. Ecosystems could break down suddenly, decimating wildlife and allowing diseases such as cholera, malaria, dengue and yellow fever to spread out of control. Grasslands could dry out and turn into dustbowls, whilst forests are extinguished in huge fires.
But is such an apocalyptic scenario likely to happen? The US National Academy of Sciences recently noted that abrupt changes in climate, the effects of which may be very long lasting, have occurred several times in the past 100,000 years. Given that the burning of fossil fuels is expected to double the carbon dioxide pumped into the atmosphere this century (unless the world takes decisive action to stop it), scientists predict drastic effects.
The UN intergovernmental panel on climate change, underpinned by thousands of scientists worldwide, has forecast that global average temperatures will rise by between 1.4 to 5.8 degrees centigrade by 2100. That may not sound much. But it is worth remembering that the last ice age, when much of the northern hemisphere was buried under an ice-pack thousands of feet thick, was triggered by a fall in temperature of only some five degrees centigrade.
The UN study predicts that a temperature rise of up to 5.8 degrees could melt the glaciers and the Greenland ice sheet, cause a seawater rise which could submerge island nations and low-lying countries, generate massive forest dieback, and accelerate species extinctions. But even this has now been challenged as too limited as it used static models which excluded the feedback between climate and biosphere.
The Hadley Center of the UK Met Office has now tried to correct this with a three-dimensional carbon-climate model. This shows that as feedbacks kick in, perhaps as little as 20 years from now, the Amazon forest begins to die back as it warms and dries out.
Even this more alarming model still does not contain the full range of possible feedbacks. It omits, for example, the release of methane from melting permafrost as well as oceanic deposits of methane hydrates. It omits, too, the climatic effects of human-induced land use changes, in particular deforestation and massive displacement of people through agribusiness.
But the findings are stark enough to warn us clearly about the consequences if we do not fundamentally alter our social and economic behavior. We do not have much time and we do not have any serious option. If we do not act quickly to minimize these runaway feedback effects, we run the risk of making this planet, our home, uninhabitable.
Michael Meacher is environment minister and MP for Oldham West and Royton.
© Guardian Newspapers Limited 2002