* Astronomy

Volcanoes may have a stronger cooling effect on the Earth than previously thought, an Open University team says.
In Geophysical Research Letters, the UK scientists say large eruptions can kick off a contest between different types of bacteria in peat bogs and wetlands.
Scientists know dust and gas (aerosols) from eruptions block out UV light, cooling Earth for two or three years.
New data show bacteria producing the greenhouse gas methane are suppressed by other microbes, further cooling Earth.



"This showed that the potential impact could be extended up to decadal scales and it's all done by little bugs" -Vincent Gauci, Open University

Micro organisms that live within wetlands produce methane, a gas responsible for an estimated 22% of the present human-enhanced greenhouse effect.
Climate affects the microbes' rate of methane production, which increases with warm temperatures and high rainfall.
Bacteria that reduce sulphur compete with these microbes, keeping methane production in check. Previous research by Vincent Gauci of The Open University and colleagues has shown that artificially dosing wetlands with small amounts of sulphur lowers methane emissions, but little was known about whether areas that "naturally" experience sulphur pollution coincide with wetlands.
The time needed for the methane-producing bacteria to recover to pre-eruption levels is between five and 10 years.

The latest study shows that the impact of acid-rain fallout on methane-producing bacteria can outlive the short-term cooling effect of sulphuric acid in the atmosphere.
Sulphur dioxide in volcanic plumes turns to sulphuric acid in contact with water and falls to Earth as acid rain.

"Our findings show that volcanic eruptions have another, more indirect, effect. Volcanoes have been known to influence climate in the past, but this showed that the potential impact could be extended up to decadal scales and it's all done by little bugs" - Dr Vincent Gauci, co-author, earth sciences department at the Open University, Milton Keynes.

To assess how worldwide sulphur deposition might affect wetland methane production, Gauci's team constructed separate models of global wetland methane emissions and global sulphur deposition from 1960 to 2080.
The researchers then combined the two models to examine where sulphur deposition and wetlands overlapped.
Based on results from this combined model, the scientists estimate that sulphur pollution may currently reduce climate-induced growth of methane emissions as much as 8%, a proportion that could grow to 15% by 2030.
Because these estimated reductions are about as large as methane proportions absorbed by known sinks, the authors suggest that documented increases in atmospheric methane concentrations since the late 19th century are likely due to factors other than global warming of wetlands.

Over much of geological time, natural wetlands have been the major contributor of global methane. Today, natural and man-made wetlands (rice paddies) contribute about 50% of the total methane source.
The team intended to simulate the sulphurous fallout from the Laki Craters volcanic eruption in Iceland during the summer of 1783.

They dosed 20, 2x2m plots of peatland in Scotland's Moidach More with sodium sulphate on a weekly or monthly basis between July 1997 and December 1998.
Some of the plots served as controls, while others were subjected to varying levels of sulphate deposition.
The researchers measured the methane using static gas exchange chambers on each plot. The results show that methane production from the plots had fallen by between 30-40% in the by 1998, the last year of treatment.
"When we went back in 2000, we were surprised to find methane production was still suppressed"
The researchers think that the abundant emissions after a volcanic eruption allow sulphate-reducing bacteria in the wetlands to out-compete the methane-producing microbes (methanogens).
The methanogens become excluded from exploiting a significant proportion of their energy source, resulting in lower methane production.

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