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In the 2004 blockbuster
The Day After Tomorrow, abrupt climate change plunges the world into chaos. According to new research published Monday, the idea that underpins the film's plot—that rapid Arctic ice melt could cause dramatic changes to the global climate system—just got one step closer to reality.
Of particular concern are the profound changes happening in the Greenland ice sheet: It appears that the
massive amount of freshwater from melting Greenland glaciers has now begun to slow the ocean's circulating currents.
Monday's study, published in the journal
Nature Climate Change, is as frightening as it is significant. Among its authors are some of the biggest names in climate science: Jason Box, a glaciologist at the Geological Survey of Denmark and Greenland, whose ongoing
"Dark Snow" project is measuring the rapid melting of ice in Greenland; and Michael Mann, a meteorologist at Penn State University, whose famous 1999
"hockey stick" graph showed the sharp influence of human greenhouse gas emissions in context of 1,000 years of temperature data from ice cores and tree rings. Mann's graph was so powerful it
became a lightning rod of climate denial.
Fresh water is less dense than saltwater. So when glacial melt from Greenland enters the ocean, it resists the natural sinking motion at the northern edge of the Gulf Stream and slows down the Atlantic's deep current—creating a ripple effect across the entire planet.
The study uses a library of ice cores, tree rings, coral, and sediments to generate a new reconstruction of the historical strength of the Atlantic's circulation based on temperature changes. The team found
recent changes in ocean circulation are "unprecedented" since at least the year 900 A.D., about as far back as these proxy data can reliably go. According to the paper, the probability of a similar circulation slowdown caused by natural variability alone (with
no influence from human-caused climate change) was less than 0.5 percent.
Comment: At least one of the reasons for the slow down in the gulf stream is man made, and is leading to an ice age:
The effects of the slow down are also discussed here: Britain faces big freeze as Gulf Stream loses strength