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来源:http://www.economist.com/news/special-report/21678951-not-much-has-come-efforts-prevent-climate-change-so-far-mankind-will-have-get
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作者:Econmist
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发布时间: 2015-11-30
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1716 次浏览
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The promises they will bring to Paris, known as “intended nationally determined contributions”, are diverse and hard to compare. Still, some are plainly more ambitious than others. America pledges that by 2025 it will cut its greenhouse-gas emissions by 26-28% below 2005 levels. South Korea says that by 2030 its emissions will be 37% below where they would be if the recent upward trend in emissions were projected forward. But even if it manages this, South Korea will be emitting 81% more greenhouse gases in 2030 than it did in 1990.
On one matter the conference delegates have already agreed: global temperatures must not be allowed to rise by more than 2°C (3.6°F) above pre-industrial levels. Politicians and green groups have argued for years that anything more would be wildly dangerous. Almost every book and report about climate change treats this limit as inviolable.
A question of degree
Barring a global catastrophe or the spectacular failure of almost every climate model yet devised, though, emissions of greenhouse gases will warm the world by more than 2°C. “It’s nice for people to talk about two degrees,” says Bill Gates, a philanthropist and investor. “But we don’t even have the commitments that are going to keep us below four degrees of warming.”
Changes in the atmospheric level of carbon dioxide, the biggest contributor to global warming, persist for centuries. So it is useful to imagine that mankind has a fixed carbon budget to burn through. Pierre Friedlingstein, a climatologist at Exeter University, calculates that if temperature rises are to be kept below 2°C, the world can probably emit about 3,200 gigatonnes of carbon dioxide in total. The tally so far is 2,000 gigatonnes. If annual emissions remain at present levels, the budget will be exhausted in just 30 years’ time.
Global greenhouse-gas emissions might indeed hold steady for a while. Total man-made emissions in 2014 were about the same as in 2013, according to the International Energy Agency. This year’s figure could even be slightly lower than last year’s. As this special report will show, the pause has little to do with the forests of wind turbines and solar panels that have popped up in Western countries, and much to do with developments in China. Still, given the steep rise in greenhouse-gas emissions in recent years (see chart), it is welcome.