What has caused the rapid loss of Arctic sea ice over the past few decades? A modelling study says that greenhouse gas emissions have undoubtedly warmed the region, but natural variation in the climate has also played a part.
Jennifer Kay of the National Center for Atmospheric Research in Boulder, Colorado, says that natural variation may allow Arctic summer sea ice to expand again, but only for about a decade.
She used a state-of-the-art climate model to tease human and non-human factors apart, and found that natural variability accounted for about half the lost ice. But in the long term, natural variations cancel each other out, while greenhouse gas emissions steadily turn the thermostat up, resulting in more lost ice.
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鈥淣atural variations cancel each other out, while greenhouse gas emissions turn the thermostat up鈥�
To Kay鈥檚 surprise, the model showed that natural effects can temporarily reverse the effect of greenhouse warming on summer ice (Geophysical Research Letters, ). 鈥淔or periods of 10 years or less, it was equally likely that sea ice would increase or decrease.鈥� But such cool spells would be minor detours on the road to a warmer world.