Good News at Last?

The climate may not be as sensitive to carbon dioxide as previously believed…

CLIMATE science is famously complicated[注：complicated：=complex]， but one useful number to keep in mind is “climate sensitivity”. This measures the amount of warming that can eventually be expected to follow a doubling in the atmospheric concentration of carbon dioxide[注：a doubling in the atmospheric concentration of carbon dioxide：大氣中二氧化碳濃度翻倍。]. The Intergovernmental Panel on Climate Change， in its most recent summary of the science behind its predictions， published in 2007， estimated that， in present conditions， a doubling of CO2 would cause warming of about 3℃， with uncertainty of about a degree and a half in either direction. But it also says there is a small probability that the true number is much higher. Some recent studies have suggested that it could be as high as 10℃.

If that were true， disaster beckons[注：disaster beckons：（如果二氧化碳濃度每增加一倍溫度就升高10℃）那災難就向我們招手了。]. But a paper published in this week’s Science， by Andreas Schmittner of Oregon State University， suggests it is not. In Dr Schmittner’s analysis， the climate is less sensitive to carbon dioxide than was feared.

Existing studies of climate sensitivity mostly rely on data gathered from weather stations， which go back to roughly 1850. Dr Schmittner takes a different approach. His data come from the peak[注：peak：山峰，頂點。] of the most recent ice age， between 19，000 and 23，000 years ago. His group is not the first to use such data（ice cores， fossils， marine sediments and the like）to probe[注：probe：探索，探究，調(diào)查。] the climate’s sensitivity to carbon dioxide. But their paper is the most thorough. Previous attempts had considered only small regions of the globe. He has compiled[注：compiled：收集。] enough information to make a credible stab[注：stab：嘗試。] at recreating the climate of the entire planet.

The result offers that rarest of things in climate science — a bit of good news. The group’s most likely figure for climate sensitivity is 2.3℃， which is more than half a degree lower than the consensus figure， with a 66% probability that it lies between 1.7° and 2.6℃. More importantly， these results suggest an upper limit for climate sensitivity of around 3.2℃.

Before you take the SUV out for a celebratory spin[注：spin：If you go for a spin or take a car for a spin， you make a short journey in a car just to enjoy yourself.]， though， it is worth bearing in mind that this is only one study， and， like all such， it has its flaws[注：flaw：缺點，缺陷。]. The computer model used is of only middling sophistication[注：middling sophistication：前一句提到了“it has flaws”，再由這一句中的“only”一詞、“Schmittner博士承認”，下一句中的“That may be one reason for…”可猜測詞義，能理解它代表提到的“flaw”就可以不必再追究了。]， Dr Schmittner admits. That may be one reason for the narrow range of his team’s results. And although the study’s geographical coverage is the most comprehensive so far for work of this type， there are still blank areas — notably in Australia， Central Asia， South America and the northern Pacific Ocean. Moreover， some sceptics complain about the way ancient data of this type were used to construct a different but related piece of climate science: the so-called hockey-stick model， which suggests that temperatures have risen suddenly since the beginning of the industrial revolution. It will be interesting to see if such sceptics are willing to be equally sceptical about ancient data when they support their point of view. 

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鏈接：公地悲劇 (tragedy of the commons)：當資源或財產(chǎn)有許多擁有者，他們每一個人都有權使用資源，但沒有人有權阻止他人使用，由此導致資源的過度使用，即為“公地悲劇”。如草場過度放牧、海洋過度捕撈等。