Ecologist readers cannot have failed to notice that the UN’s Intergovernmental Panel on Climate Change (the IPCC) recently published its long-awaited Summary Report for Policymakers (the ‘SPM’) on the physical science basis of climate change. The publication of this document (and of the three volumes that are soon to follow) marks a watershed in our understanding of our impacts on the world’s climate and, along with the Stern Review, constitutes the most important alarm-call to date about the dangers of climate change.

An important point to bear in mind about any IPCC report (this is the fourth they have produced – the last was in 2001) is that it is the result of a hard-won consensus amongst many hundreds of climate scientists from many countries around the world. Every word has been fought over with careful deliberation, a process that effectively weeds out extreme views at either end of the spectrum. What remains is thus a guardedly conservative assessment about the likely effects of climate change by the end of this century.

So what then are the IPCC’s conclusions? To my mind, perhaps the most important phrases in the SPM are these: “Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global average sea level”, and there is now a “…very high confidence that the globally averaged net effect of human activities since 1750 is one of warming”. The term “very high confidence” is a precisely formulated scientific statement – it means that there is a 9 in 10 chance of being correct. If I was a betting man, I know where I would put my money.

So it is now virtually beyond doubt that we have warmed our world, but how great is the effect and what are the likely consequences? Depending on the development model that we pursue from now – that is, on how much additional CO2 and other greenhouse gasses we pump into the air – the IPCC predicts that global average temperatures will rise between 1.1C and 6.4C by 2100.

These are large numbers – just reflect on the fact that 5C is the temperature difference between now and the last ice age. And the possible effects of these temperature increases are also large - the SMP predicts that global warming and the thermal expansion of the oceans will continue for many centuries. Even if by 2100 we manage to stabilize emissions at moderate levels, we could experience an utterly catastrophic 0.3 - 0.8m rise in sea level by 2300.

Under all the emissions scenarios considered, by 2100 snow cover around the world shrinks significantly, as does sea ice in the Arctic and the Antarctic. There is widespread thawing of the world’s permafrost, and extreme heat waves and heavy rain become far more frequent. Tropical cyclones become more destructive, and storm tracks move poleward, changing wind rainfall and temperature patterns all over the world. It is very likely that there will be more rain at high latitudes, and less in the subtropics, leading to severe water shortages in southern Africa and the Mediterranean.

There is good news too – the now famous oceanic thermohaline circulation that brings warmth from tropical seas to Britain is very likely to slow down, but is very unlikely to abruptly flip into its contracted mode during this century. Furthermore, The IPCC thinks that the Antarctic ice sheet will remain too cold for widespread melting, a conclusion that has puzzled scientists working in the Antarctic, who have documented the gradual loss of ice in the polar continent.

Despite this disagreement, the latest IPCC report is a great advance in our understanding of our impacts on climate. A major breakthrough is that some of the feedbacks between land plants, soils and marine phytoplankton on the one hand and air and ocean on the other have been taken into account - at last the massive influence of life on climate has been recognized. But the results are deeply disturbing – as the world heats up, ecosystems in land and ocean tend to release their carbon to the air– further warming the world in a vicious cycle of positive feedback.

So what can we do about an accelerating crisis that seems likely to wipe out many species and ecosystems, and which threatens billions of people around the world? Many fixes have been suggested – solar energy deflectors in space, artificially seeded clouds, the capture and storage of CO2 underground, but ultimately there is only one ‘fix’ that has any hope of working – a concerted turning away from our hugely destructive consumer-driven lifestyles. Rather than growing the global economy, we must ‘grow’ materially simpler but existentially richer life-styles embedded in our local communities. Continue with our current, more selfish path, and our civilization will not remain long on this planet.
(By Stephan Harding, The Ecologist, 08/02/2007)
http://www.theecologist.org/archive_detail.asp?content_id=741