 First, what are clathrates anyway? Methane clathrates, or hydrates, are ice-like substances that trap methane gas in a cage of water molecules. They form where there is a combination of high pressures and low temperatures. We find clathrates at, or just below the seabed, usually in ocean depths of greater than 500 meters. When they are dredged up from the deep, they fizz out methane and you can set them alight. The picture on the left shows white streaks of clathrate and a lump of dredged-up mud that's about a foot across. The photo on the right shows methane gas burning as it is released out of the hydrate cage. Clathrates are also found in the Arctic in places where there are thick sections of permafrost. In these conditions, clathrates can form at depths as shallow as 200 meters below the surface, either on land or under a shallow ocean shelf. These diagrams show the conditions where clathrates are stable. Typical conditions for permafrost clathrates are shown on the left and for deep sea clathrates on the right. Clathrates become unstable as soon as the temperature goes up or the pressure goes down. So why should we care about Arctic clathrates? We care. Firstly, because there's more carbon-storiding clathrates than there is in the entire atmosphere. The great majority of them are found beneath the deep sea bed, with about 1% in areas of continuous permafrost, according to the latest estimates. Secondly, it would take the release of only a fraction of 1% of the world's hydrates to double the concentration of methane currently in the atmosphere. That would make for a big addition to man-made global warming. Finally, the clathrates found in the Arctic are the most vulnerable to climate change because this area is one of the most rapidly warming areas on Earth. The good news is that clathrates are quite well protected from man-made global warming. It will take a lot of time for the recent man-made global warming to reach them. Probably thousands of years or more for the majority of clathrates that occur in deep oceans or that are buried under hundreds of meters of frozen rock. More good news, for the atmosphere at least, is that when deep sea clathrates become destabilized, most of the methane gets consumed in the sediments in the sea bed. Some methane may make it into the water still. But even then, the methane in the bubbles is absorbed before it gets to the surface. The released methane will locally deplete the oxygen in the seawater and also worsen ocean acidification. Some of it will eventually be released to the atmosphere as carbon dioxide. There are clathrates located on continental margins at the upper limits of their stability range that are emitting methane into the seawater today. However, this is a process that's been going on for many thousands of years. And because the water is so deep there, the methane doesn't reach the atmosphere. Nevertheless, many people, a few scientists, and many lay people are concerned that methane hydrates might be destabilized on a large scale by recent global warming and that they pose a serious and imminent threat to the Earth's climate. For example, a recent article in the journal Nature estimated the economic impact of the warming that would be provoked by a sudden release of 50 billion tons of methane from the shallow seas of the East Siberian Arctic Shelf. The paper was criticized by many scientists for failing to make it clear that it was looking at the consequences of a very unlikely occurrence. Studies in this remote part of Siberia are in their infancy because it's difficult and expensive to operate in the harsh conditions there. Nevertheless, recent research has shown that there is methane bubbling up from the frozen seabed in that area. The Siberian shelf is quite shallow, averaging around 50 meters, and some of the methane released makes it to the atmosphere, especially when storms stir up the water. One thing we don't know yet is if the methane emissions in this area have increased recently as a result of global warming or if they are just part of a slow release that's been going on for many thousands of years. We also don't know if the methane is coming from normal biological processes at the seabed or from destabilizing clathrates. Some of the gas, maybe sort from organic matter, buried much deeper in the sediment column, gas that has found its way up through holes in the permafrost. Our knowledge of when clathrates naturally form makes it look unlikely that there should be any present near the seabed on this shallow shelf. There have been no actual samples or geophysical indications of clathrates there yet. Another argument against large-scale, present-day clathrate destabilization is that in geologically recent periods, in the early Holocene, 8,000 years ago, and at the time before the last Ice Age, 120,000 years ago, when temperatures were a little warmer than today, there's no record of a massive and sustained methane release from destabilized hydrates, nor is there evidence of any sudden global climate catastrophe at those times. It's a myth, therefore, that catastrophic clathrate destabilization is already upon us. Although the theoretical potential exists for this to become a problem after a long period of human cause, global warming, we're not there yet. It would be jumping to conclusions to suggest that we are at risk of an imminent climate catastrophe from large quantities of clathrates suddenly becoming unstable. But if we continue to fail to limit emitting carbon dioxide from fossil fuels, we will certainly bring forward the day when clathrates really do become a problem. However, there's plenty to worry about in the Arctic, even so. As this picture shows, there are plenty of potential sources of greenhouse gases in the Arctic, apart from clathrates. Some of these sources of carbon dioxide and methane are already active today, and many of them will grow in importance over the next several decades as the region quickly warms and their permafrost thaws and glaciers and ice sheets retreat. These human-accelerated natural emissions may add a fraction of a degree to the average global temperature by the end of the century. Of all the stores of Arctic carbon, in the short term, clathrates are probably the best insulator from man-made warming because they are only present far below the surface. Nevertheless, clathrate destabilization remains a concern for the climate over the centuries and millennia to come. Luckily, it's not happening just yet, and in the estimation of the IPCC, it's very unlikely to be a big problem during the rest of this century.