ON SEPTEMBER 23rd 120-odd presidents and prime ministers gathered in New York for a UN meeting on climate change. It is the first time the subject has brought so many leaders together since the ill-fated Copenhagen summit of 2009. Now, as then, they will assert that reining in global warming is a political priority. Some may commit their governments to policies aimed at reducing greenhouse-gas emissions. What few will say is how many tonnes of carbon dioxide these will save—because they almost never do. According to scientists, cutting carbon-dioxide emissions is an essential part of reducing catastrophic risks from climate change. Yet governments are persistently averse to providing estimates of how much carbon a policy saves. That may be because, in countries where climate change is controversial, it makes more sense to talk about the other benefits a scheme offers rather than its effect on carbon. Or it may be that, in countries which are enthusiastic about renewable energy, pointing out that it may not save that much carbon is seen as unhelpful. Or perhaps governments think climate change is so serious that all measures must be taken, regardless of cost (though their overall lacklustre record suggests this is not the case). Whatever the reason, the end result is that while the world’s governments have hundreds of policies for tackling climate change, some of them very expensive—China, America and the European Union spend $140 billion a year on subsidising renewable energy—it is hard to say which policies are having the greatest effect. So The Economist has made a stab at a global comparison of carbon-mitigation efforts. Chart 1 is the result. It ranks 20 policies and courses of action according to how much they have done to reduce the atmosphere’s stock of greenhouse gases. We have used figures from governments, the EU and UN agencies. As far as we know, this exercise has not been carried out before. The Economist.
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