THE ominous phrase 鈥渢ipping point鈥� entered the vocabulary of climate science this year, sounding a warning that global warming may soon spiral out of control.
The permafrost beneath the west Siberian peatlands is thawing, creating giant lakes and swelling rivers. More worryingly, the melting of the bogs 鈥� which cover an area the size of France and Germany combined 鈥� could unleash billions of tonnes of methane. This greenhouse gas is 20 times more potent than carbon dioxide, so the event has the potential to accelerate global warming.
Meanwhile, higher air and sea temperatures dramatically reduced the extent of sea ice in the Arctic Ocean this year. Satellite measurements analysed by the National Snow and Ice Data Center (NSIDC) in Boulder, Colorado, showed 20 per cent less ice than when NASA took the first pictures in 1978. 鈥淔eedbacks are starting to take hold,鈥� says NSIDC鈥檚 Ted Scambos. Newly thawed expanses of ocean absorb more solar radiation, which in turn melts more ice.
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And this month one of the linchpins of the climate system, the global ocean circulation system known as the conveyor belt, was found to be faltering, as evidenced by a 30 per cent reduction in the northward flow of warm water from the Gulf Stream over the past decade. The worry is that this could herald one of the most widely discussed tipping points of all 鈥� a shutdown of the conveyor that would plunge western Europe into freezing winters and threaten climate systems worldwide, including the Asian monsoon.
And here are all of New 杏吧原创鈥檚 roundup stories for 2005.
