Methane matters

The release of vast amounts of greenhouse gas methane from the melting permafrost of the Arctic is a huge concern. Methane, said to be abundant below the frozen lakes in the Arctic, is 20 times more potent than carbon dioxide as a greenhouse gas, says C Sivaram

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Concern about global warming and its consequences like melting of polar caps has focused hitherto mainly on carbon dioxide emissions due to burning of fossil fuels — which provide most of the world power — as being the main culprit. A release of a trillion tonnes of carbon dioxide could be catastrophic. The melting of Arctic ice is now conspicuous and if the west Antarctic ice sheet holding more than two million cubic kilometres of ice melts, sea levels could rise by several metres, inundating all coastal areas.

Ozone holes, which are associated with the Antarctic, have also appeared over the Arctic. These holes let in harmful ultraviolet radiation as is well known. A question often asked is why the ozone holes appear only over the frozen Arctic and Antarctic at the end of each winter. The reason, as pointed out by Paul Crutzen who shared the 1995 Chemistry Nobel Prize for pioneering research on how Chlorine burnt a hole in the Antarctic ozone layer, is that Chlorine compounds — used in the CFC refrigerants, aerosols etc. — need ice particles to destroy ozone in large quantities and this is why ozone holes appear over the Arctic and Antarctic! He pointed out that if we had used bromine — a close halogen relative of chlorine — instead, we would have had something far worse as bromine does not need ice particles to destroy ozone!

If bromine had been used instead of chlorine, the entire upper atmosphere would have lost its ozone 50 years ago (in the mid 1970’s)! Thanks to our choice of chlorine we have luckily escaped such a fate.

Recently, other consequences of melting Arctic ice have been highlighted. One is the effect on the North Atlantic circulation of which the Gulf Stream is an important result, partly due to ice formation in the far north. The freezing replaces the dense saline water which sinks to the ocean floor by warm water from the tropics. This is crucial to moderate global climate. Warming would cause rapid decline of this deep water formation. Data show that the warming ocean currents have declined by 20 per cent over 50 years. This in turn has caused Siberian temperatures to rise by half a degree every decade. We had the unusual phenomenon of warm summers in Moscow and other European cities.

However, a more serious consequence is the release of vast amounts of greenhouse gas methane from the melting permafrost. It is estimated that more than a trillion tonnes of methane lies below the frozen lakes in the Arctic. Sometime back, a US Geological Survey estimated that the methane locked in the ice — in the form of hydrates and clathrates — could contain more carbon than the entire world’s coal, oil and gas put together. The important point is that the manner in which the methane absorbs the warm infrared radiation from the terrestrial surface is more than 20 times effective in heat trapping, and thus warming than carbon dioxide! Currently, it is estimated that there are five billion tonnes of methane in the Earth’s atmosphere! A million square kilometre tract of Siberian permafrost contains 50 billion tonnes of potential methane. Indeed, several companies have evinced enthusiasm in large-scale methane energy technologies.

Recent analysis of the economic cost of Arctic melting, however, suggest that the East Siberian Arctic shelf could release a gigantic gaseous belch at any time that could advance global warming by 30 years, creating an economic setback of a year’s global GDP. There are also positive aspects like creation of ice-free shipping lanes, improved fishing routes and access to ocean bed minerals.

That more than a trillion tonnes of methane lie under the shelf (at depths perhaps as shallow as 30 metres) trapped inside hydrate lattices has led to concern about a possible sudden eruption. Some studies have found methane plumes a kilometre wide bubbling to the surface. Through areas of melting enhanced by geological faults, a release of 50 billion tonnes is predicted to be possible within a decade by Arctic ocean experts. As stated earlier, methane, being 20 times more potent than carbon dioxide as a greenhouse gas, could trigger climatic catastrophes. A tenfold increase in the atmosphere methane content could raise temperatures by one-and-a-half degree Celsius. This could advance the date at which temperatures would globally rise by two degrees above pre-industrial levels by 30 years. And all this methane release has nothing to do with current human activity! Vast methane upsurges from the melting Arctic permafrost can occur any time.

There are two other interesting points to be noted in this context: One is that India with its bovine population of half billion was once marked out as contributing to the methane emission. A cow is supposed to belch about three hundred litres of methane a day, so the total bovine methane works out to hardly 50 million tonnes per year.
It would take hundred years to double the existing atmospheric methane from this source. This is nothing compared to the predicted Arctic’s belches! If these icy methane reservoirs melt over the next century, the gas released could recreate climate conditions that existed during a 3,000-year warm spell that began 15,000 years ago.

After that, melting slowed for the next 10,000 years and all the lakes refroze, stopping the release. But global warming now seems to have accelerated the Arctic methane release. It would still be very important to reduce the fossil fuel emissions, as carbon dioxide release causes further global warming which in turn would release more methane in the increased melting of Arctic regions, enhancing the warming further. Global warming is not just about carbon dioxide. It has many more complexities involved.