The author of 'A Modest Proposal to Save the Planet' proposes only 450 ppm as 'the maximum concentration in the atmosphere that can be con­sidered safe'." There is no 'safe' level, and 450ppm is likely to be very dangerous indeed, leading to global warming well in excess of 2°C, which in turn will enhance the probability of catastrophic 'discontinuities'. Never­theless, even achieving that modest target will require a revolution in the way in which the world - North and South alike - does business.

There is (as with all the other parameters) a wide range of uncer­tainty about the reduction in carbon emissions that would be needed to stabilize the concentration of carbon dioxide al 450ppm. The IPCC's Third Assessment Report suggested that, in the worst case scenario, world emissions of carbon would have to come down from about eight gigatonnes to about three by 2050. In view ol the advances in understanding that have occurred since then, we can be pretty sure that the worst case scenario is actually worse than this Since 450ppm is very probably too high to keep warming down to 2"C, and 2°C looks as if it will be far worse than it seemed when the standard was adopted, reducing carbon emissions to two gigatonnes cutting them to a quarter - makes more sense as an objective. Even then, we must bear in mind that this constitutes a massive violation ol the 'precautionary principle' - but we must also bear in mind that the principle may be literally inapplicable here because it is possible that the average temperature would rise to a dangerous level even if emissions of carbon fell to zero tomorrow and stayed there for a long time.

Divided between 6.3 billion people, 2 billion tonnes of carbon in 2050 is around 0.3 tonnes per head. Of course, the population will be bigger then, but I have argued that current numbers should be taken as the basis for national allocations. (The equity of that proposal, however, depends on the rich countries implementing all the policies that I proposed to keep the increase down.) To put this figure into perspective, China is already well over the limit, while the rest of Asia (minus Japan) is not far off. Africa is the only continent well below. At the other end of the scale, the United States has to get its emissions down to about 5 per cent of the current level, Australia and Canada to about 6 per cent and the other industrialized countries to about 12 per cent on the average.

Reductions would, of course, be phased in over a period, but would still have to come down fast to hit the target.The rich countries would have time to adapt, and could also cushion the blow, especially al the beginning, by buying unused quotas from other countries. This option would fade away as quotas dropped and countries in surplus, such as India, increased their production. The answer has to lie first in more energy-efficient production and building. This painless (though not cheap) move would by default probably enable the profligates to reach the emission level of the other rich countries. Fossil fuels would have to give way rapidly to renewable sources of energy, generating electricity from the sun with photovoltaic cells and the wind with im bines. Research and investment in capturing the unlimited power of the waves and the tides would have to become a priority. In the end, however, we cannot get round the fact that all of this put togethet would not be anywhere near enough without a change in the way ol life in rich countries. Cars will no longer be possible except for short trips and electrically powered trains will have to be the primary means of long-distance travel. (Laying the tracks over existing motor­ways would help to achieve both ends simultaneously.) Air travel is especially pernicious because it pumps carbon dioxide straight into the upper atmosphere, but it also just produces too much carbon to be consistent with a low-emissions regime. The end of flying would mean that the pace of life would have to slow down, making it less stressful.

What would this do for justice? First, and most obviously, treating the atmosphere as a global commons to be divided up equally would itself constitute a just distribution of a scarce resource. Second, there would be brisk bidding for surplus emissions quotas by the rich coun­tries, which would make for redistribution towards poor countries. Third, over and above this, the rich countries would have to pay for the poor countries to industrialize using renewable energy, because there is no alternative.

Brian Barry 2005 Why Social Justic Matters Polity Press