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1980s by climate scientist James Hansen and others, climate change has risen up the political agenda inexorably over the last two decades. Its visibility was given a massive boost by the influential Stern Review published in 2006. A former World Bank economist, Nicholas Stern was asked to lead a review of the economics of climate change for the UK Treasury. The review concluded that a small early hit on GDP (perhaps as low as 1 per cent of GDP) would allow us to avoid a much bigger hit (perhaps as high as 20 per cent of GDP) later on.20 It’s telling that it took an economist commissioned by a government treasury to alert the world to things climate scientists – most notably the Intergovernmental Panel on Climate Change (IPCC) – had been saying for years. This is partly a testament to the power of economists in the policy world. But the impact of the Stern report Prosperity Lost 11 3475 EARTH Prosp Without Growth 23/9/09 4:10PM Page 11 was also due to the seductive nature of its message. Climate change can be fixed, it said, and we’ll barely notice the difference. Economic growth can go on more or less as usual. We’ll have occasion to look at that message a bit more closely in what follows. The history of climate policy certainly suggests some caution in believing things will be that easy. The Kyoto Protocol committed the advanced economies to greenhouse gas emission reductions equivalent to about 5 per cent over 1990 levels by 2010. But things haven’t worked out that well. Globally, emissions have risen by 40 per cent since 1990. In the meantime, the science itself has moved on. The Stern Review took as its target the task of stabilizing carbon emissions in the atmosphere at 550 parts per million (ppm).21 Most scientists – and Stern himself – now accept that that target won’t prevent dangerous anthropogenic climate change. The IPCC’s Fourth Assessment Report argues thata 450 ppmtarget will be needed if climate change isto be restricted to an averageglobal temperature increase of 2°C.22Achieving thattarget could mean reducingglobal emissionsby up to 85 per centover 1990 levels by 2050.23 Two articles published in the journal Nature in April 2009 challenge even that conclusion. The authors argue that what matters is the total greenhouse gas budget we allow ourselves over the period to 2050. Global atmospheric concentrations arealready at 435 ppm.And if we want a 75 per cent chance of staying below 2°C, the global economy can only afford to emita total of 1 thousand billion tonnes ofcarbon dioxide (CO2) betweenthe year 2000 andthe year 2050.Crucially, they show that by 2008 we had already used up a third of this budget. Staying within the budget is going to be more demanding even than existing 450 ppm stabilization scenarios suggest.24 The message from all this is aprofoundly uncomfortable one. Dangerous climate change is a matter of decades away. And we’re Prosperity without Growth 12 3475 EARTH Prosp Without Growth 23/9/09 4:10 PM Page 12 using up the climate ‘slack’ too quickly. It may take decades to transform our energy systems. And we have barely started on that task. As the science improves it becomes clearer that a warming world may pose the gravest threat to survival we face. Though it came late to the party, the climate may just turn out to be the mother of all limits. Beyond the limits This brief sketch of