Climate activists have pinned a two-degree-Celsius increase in global average temperature as the maximum our globe can withstand without suffering catastrophic environmental change, but new studies of Siberian caves suggest that that target may be far too optimistic. According to a study published Thursday in Science Express, a rise in temperature of 1.5°C may well be enough to trigger widespread melting of the earth's permafrost, which holds twice the greenhouse gases already contained in the Earth's atmosphere. And we're already almost halfway there.
The study, led by researchers from Oxford, examined stalactites and stalagmites from limestone caves in Siberia. These cave formations grow when there's abundant liquid groundwater to deposit calcium carbonate as it drips and evaporates: in colder periods when the available groundwater is locked away in permafrost, the cave formations dry up and stop growing. By taking core samples of the formations, the researchers were able to chart when the formations grew and when they didn't, thus creating a calendar of sorts of when the land above was frozen.
The team found that formations in a cave north of the current southern boundary of permafrost, near Lake Baikal, grew during a period when global temperatures were just 1.5°C above the modern, pre-industrial baseline, which suggests that temperatures only slightly warmer than those we experience today could trigger the melting of massive areas of permafrost, in Siberia and likely elsewhere.
That's a big problem. Permafrost, which covers about a quarter of the land in the Northern Hemisphere, is an important reservoir for gigatons of both carbon dioxide and methane, and melting permafrost releases those greenhouse gases to the atmosphere -- further accelerating global warming.
That melting might take some time, perhaps decades, before it releases enough CO2 and methane to have a noticeable effect on the climate. But the changes might well be irrevocable long before we notice the change. And 1.5°C seems to be, as lead researcher Anton Vaks told The Guardian, "something of a tipping point."
That's 1.5°C higher than the pre-industrial average temperature, by the way. We've already covered almost half of that increase: we're currently around .6-.7°C warmer than that pre-industrial average.
In its coverage of the study, Reuters adds some startling context:
The United Nations Environment Programme (UNEP) estimates that permafrost contains about 1,700 billion metric tons of heat-trapping carbon, or twice the amount in the atmosphere.
The more fossil fuel we burn, the sooner that permafrost starts to melt.