HAS global warming stopped? The trend has stalled in recent years, but climate modellers this week said this amounts to a 鈥渂lip鈥� caused by natural variability. What鈥檚 more, a forecast made in 1999 has actually proven correct over the past decade 鈥� although temperatures will have to start rising again soon if it is going to stay on track (see 鈥�Climate modellers vindicated as forecast comes true鈥�).
The most likely cause of the recent blip is changing heat flows between oceans and atmosphere. If so, temperatures may rise again around 2020 as the natural cycle combines with greenhouse warming to cause a new surge.
But modelling on these scales is tricky: researchers have for some time been promising to fill the gap between short-term weather forecasts and long-range predictions about climate change (New 杏吧原创, 16 August 2008, p 26). This gap creates uncertainty in projections and causes some to question how they are presented. Warming gets attributed to greenhouse gases, sceptics say, while cooling is put down to natural cycles.
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That may be unfair, but it鈥檚 a dangerous charge. Next time we encounter a blip, it would be good to be able to explain it properly.
