WHEN the global warming catastrophe movie The Day After Tomorrow was released in 2004, climate scientists found themselves in the unenviable position of having to put the facts in the way of a good story. The premise of the film is that climate change causes the Gulf Stream to shut down abruptly, plunging the northern hemisphere into a sudden and catastrophic ice age. Although loosely based on science, the deep-freeze scenario is wildly implausible and scientists queued up to pour cold water on it. “It is safe to say that global warming will not lead to the onset of a new ice age,” two distinguished climate scientists wrote in the journal Science.
In a curious instance of life imitating art, scientific anxiety about the Gulf Stream also had cold water poured on it around the same time. The idea that the North Atlantic current – a northern extension of the Gulf Stream – could shut down was first proposed in 1961. By the late 1990s, the scientific consensus was that it had stopped in the past and could do so again, possibly with disastrous consequences – albeit not overnight.
Gulf Stream anxiety reached its apogee in 2005 when scientists at the University of Southampton, UK, discovered that the North Atlantic current had weakened by a third. But follow-up measurements by the same team showed no clear trend. In 2006, the science was clear enough for New Scientist to declare: “No new ice age for western Europe.”
“Recent reports of a winter heatwave in the Arctic suggest that all is not well in the far north”
This is science at its best: hypothesis testing through the careful accumulation of data, and a willingness to change one’s mind when the evidence demands it. In fact, the change of consensus over the Gulf Stream is a good counterargument to climate deniers’ claim that climate science is policed by a rigid and alarmist orthodoxy.
But science is never settled and the fate of the North Atlantic current is back on the agenda. New findings from the Irminger Sea south of Greenland suggest that fresh water from melting ice is impeding the normal ocean currents, reigniting fears that the system is heading towards an irreversible tipping point (see “Polar melt may shut down the Atlantic current that warms Europe”).
There is nowhere near enough data to suggest another U-turn is on the cards. But it tells us that the situation in the North Atlantic still requires careful monitoring. It also reminds us that climate change is a developing and worsening situation. The Gulf Stream may have been stable in 2006, but since then we have spent more than a decade recklessly pouring greenhouse gases into the atmosphere.
Recent reports of a winter heatwave in the Arctic, with daily mean temperatures 20°C warmer than average, suggest that all is not well in the far north. The related polar freeze that struck Europe and North America brings home the fact that we live in an interconnected world and that what happens in the Arctic doesn’t stay there. That weather could yet prove to be an anomaly, but could also be the new normal. The Day After Tomorrow remains a wild exaggeration, but life in the northern hemisphere may soon become a lot less comfortable than it was.
This article appeared in print under the headline “Trouble at the top”
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