Sea changes could warn of “Day After Tomorrow” scenario
09 May 2008
In the movie The Day After Tomorrow, the world froze pretty quickly when a major ocean current, dubbed the “ocean conveyor belt”, turned off.
While that was a work of fiction, slowdowns of the conveyor are possible and researchers have now found a way of giving us a few years’ advance notice.
Although even 10 years’ warning would be too late to do anything about preventing such an event, it could help people plan ahead to adapt, they say.
The ocean conveyor plays a major role in spreading heat around the globe – keeping Europe warmer than it otherwise would be, for example.
To look for possible early warning signs of such a slowdown in the current, Ed Hawkins and Rowan Sutton of the University of Reading, UK, used a climate model developed by the Met Office’s Hadley Centre.
The study “is the first to demonstrate that such rapid changes are potentially predictable,” Hawkins says. “It is a first step in designing a possible ‘early warning system’.”
The climate model – based on pre-industrial CO2 data – ran for 1100 virtual years. Over this period, a few natural fluctuations were big enough to make the ocean conveyor suddenly slow or speed up by about 15% within a decade.
A few locations in the north Atlantic ocean were harbingers of this change, the researchers found, showing warning signs as many as 10 years before the ocean conveyor did.
“Ten years’ warning would not be enough to do anything about the change itself, but could aid adaptation planning on regional scales,” Hawkins says.
The key indicators were a drop in the sea-surface temperature and salinity of water in the Nordic seas, and a drop in flow through the Denmark Strait.
However, since the study looked at natural variations, the signals for any slowdown of the conveyor might show up in different places if global warming data are included.
“The markers for a slowdown due to global warming might be very different,” Hawkins says.
According to the latest IPCC report, continued global warming is “very likely” to slow the current this century.
The results are interesting, says Ronald Stouffer of the Geophysical Fluid Dynamics Laboratory in Princeton, New Jersey, US. “Carefully monitoring these high latitude seas is a good idea.”
Journal reference: Geophysical Research Letters, in press (DOI:10.1029/2008GL034059)