The Gulf Stream is an ocean current that modulates climate in the Northern Hemisphere by transporting warm waters from the Gulf of Mexico into the North Atlantic and Arctic oceans1, 2. A changing Gulf Stream has the potential to thaw and convert hundreds of gigatonnes of frozen methane hydrate trapped below the sea floor into methane gas, increasing the risk of slope failure and methane release3, 4, 5, 6, 7, 8, 9. How the Gulf Stream changes with time and what effect these changes have on methane hydrate stability is unclear. Here, using seismic data combined with thermal models, we show that recent changes in intermediate-depth ocean temperature associated with the Gulf Stream are rapidly destabilizing methane hydrate along a broad swathe of the North American margin. The area of active hydrate destabilization covers at least 10,000 square kilometres of the United States eastern margin, and occurs in a region prone to kilometre-scale slope failures. Previous hypothetical studies3, 5 postulated that an increase of five degrees Celsius in intermediate-depth ocean temperatures could release enough methane to explain extreme global warming events like the Palaeocene–Eocene thermal maximum (PETM) and trigger widespread ocean acidification7. Our analysis suggests that changes in Gulf Stream flow or temperature within the past 5,000 years or so are warming the western North Atlantic margin by up to eight degrees Celsius and are now triggering the destabilization of 2.5 gigatonnes of methane hydrate (about 0.2 per cent of that required to cause the PETM). This destabilization extends along hundreds of kilometres of the margin and may continue for centuries. It is unlikely that the western North Atlantic margin is the only area experiencing changing ocean currents10, 11, 12; our estimate of 2.5 gigatonnes of destabilizing methane hydrate may therefore represent only a fraction of the methane hydrate currently destabilizing globally. The transport from ocean to atmosphere of any methane released—and thus its impact on climate—remains uncertain.
The above text is the abstract for a paper published last October in the journal Nature, snappily titled Recent changes to the Gulf Stream causing widespread gas hydrate destabilization. If the abstract didn’t make it clear to you, I’ll let John Michael Greer, the Archdruid of The Archdruid Report, splain it for you:
The end of the last ice age saw sharp increases in methane concentrations in the atmosphere, the rapid melting of continental glaciers, and a steep rise in global temperature that peaked around 6,000 years ago at levels considerably higher than they are today. A controversial theory, the “clathrate gun” hypothesis, argues that the warming was triggered by massive methane releases from the oceans. Whether or not that was the major factor, ice cores from Greenland document rising levels of methane in the air around the same time as the stunningly sudden global warming – an increase of more than 15°F in global average temperatures in less than a decade – that triggered the final collapse of the great ice sheets.xThe first point to grasp from this is that methane releases aren’t the end of the world. Our ancestors got through the last rounds of it without any sign of massive dieoff, and it’s been argued that the nearly worldwide legends of a great flood may embody a dim folk memory of the vast postglacial floods that took place as the ice melted and the seas rose. For that matter, during most of Earth’s history, the planet has been much hotter than it is now; only a few tens of millions of years ago – yes, that’s practically an eyeblink in deep time – crocodiles sunned themselves on the subtropical shores of Canada’s north coast, at a time when Canada was nearly as close to the North Pole as it is today.xOn the other hand, that doesn’t mean that a methane spike in the Arctic can simply be ignored. Since the dim folk memories that might be embodied in flood legends are the only records we’ve got for the human experience of abrupt global warming, we simply don’t know how fast the temperature shift might affect, for example, the already unstable Greenland ice sheet, which contains enough water to raise sea level worldwide by around 30 feet. Some theoretical models argue that Greenland’s ice will melt slowly, while others argue that water pooling beneath the ice could cause huge sections of it to slide off into the sea in short order, filling the North Atlantic first with icebergs, then with meltwater. Which model is correct? Only Gaia knows, and she ain’t telling.xEqually, we don’t know whether the melting of the Greenland ice sheet will make nearby continental shelves unstable, as it did the last time around, and reproduce the same set of conditions that caused gargantuan tsunamis at the end of the last ice age. There’s abundant evidence for these; one of them, according to recent research, flooded the North Sea and carved the English Channel in a single day around 8000 years ago; we don’t know how soon those might become a factor around the Atlantic basin, or even if they will. It’s unsettling to realize that we may have no way of finding out until the first one hits.xAll that’s certain at this point is that something potentially very troubling is happening in Arctic waters, and the possibility that it might have destructive consequences on a local, regional, or continental scale can’t be ruled out. Panic is the least useful response I can think of, so I’ll say this very quietly: if the news from Arctic waters in the months and years to come suggests that things are moving in the wrong direction, and those of my readers who live close to the shores of the northern Atlantic basin happen to have the opportunity to move inland or to higher ground, it might not be unreasonable to do so.