How and why does a scientist like me study the gas methane? The 'why' part of the question is often easier to answer than the 'how' part so I'll answer that first.
Methane, like carbon dioxide, is an important greenhouse gas but it differs from the more widely reported CO2 in a couple of important ways.
Firstly, methane is more powerful at trapping the suns rays. As a greenhouse gas it is actually more than 20 times as powerful as CO2.
Vince collecting samples
The second important difference relates to its lifetime in the atmosphere: methane lasts around 10 years in the atmosphere where as CO2 can stay in the atmosphere more than 10 times as long.
The relatively short lifetime of methane means that atmospheric concentrations of the gas, and therefore its contribution to the greenhouse effect, is sensitive to short-term changes in sources and sinks of the gas. These sources include natural wetlands, rice paddies, land fill and cow burps.
The other key reason for studying methane is that over the past century, the concentration of the gas has been increasing - although in the past decade the pace of this change has been decreasing and, until a very recent rise was reported, had almost halted.
The reasons behind this pattern of growth are important to understand so that we can improve predictions of climate into the future.
Collecting methane samples in Flitwick
I am interested in the controls on the emission of methane from the largest individual source: wetlands. Natural and artificial wetland ecosystems such at peat bogs and rice paddies produce methane as a consequence of anaerobic decomposition in saturated soils.
My work chiefly deals with chemical controls over the production of methane in these ecosystems and pathways the gas takes in making the transition from the soil to the atmosphere. Much of my work has examined the effect of sulphur pollution in acid rain on the emission of methane from wetlands and rice paddies.
This is important because methane emitting wetland areas receive sulphur pollution via long-range transport of pollution. They also get sulphur from a natural form of pollution – volcanic eruptions.
The sulphate component of acid rain pollution is thought to stimulate one set of microbes that then out-compete methane-producing microbes for food. The result is a reduction in methane emission, and this seems to be sufficient to offset the growth in wetland methane emissions that would be expected to result from global warming.
We've also investigated the effects of a large Icelandic volcanic eruption that deposited sulphate over a wide area of the northern hemisphere in 1783 and 1784 and found that changes in atmospheric methane concentration at the time, as recorded in ice-cores, are consistent with our understanding of how sulphur pollution affects the wetland methane source.
My other interest is in novel pathways for anaerobically produced methane to leave saturated soils and get into the atmosphere. Until recently, methane was thought to leave soils through diffusion, bubbling or through the hollow vessels of wetland adapted herbaceous plants like sedges and rushes.
In recent studies we've found that wetland trees contain some of the same adaptations as sedges that enable them to survive in sodden soils and this enables mature trees to emit methane from their trunks – an important finding given that many of Earth's wetlands are forested.
Together with a team of PhD students, we shall be going to the Kalimantan peat swamp forests of Borneo in early 2009 to investigate whether tropical wetland trees in Borneo are also functioning in the same way.
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Stephen Self explains why the 1783 Icelandic eruptions affected the whole of Europe.
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