A new study has revealed why the levels of methane, an important heat trapping greenhouse gas, which had risen steadily in the atmosphere since the last 200 years, had started to stabilize since the 1990's. However, scientists who took part in the study have warned that this leveling off may not last, and the atmospheric methane levels will probably rise in the coming years, leading to global warming.
International scientists who conducted the study found that one cause of the decline seen in the levels of atmospheric methane was linked to a decrease in levels of methane from natural sources. The muddy wetland areas decompose organic matter leading to emission of methane and this forms one of the biggest natural sources of the gas. But, during the 1990's, the wetland areas had a drying out on account of tropical droughts, which caused a reduction in levels of methane.
Interestingly, the scientists found that the methane emissions caused due to human activity and industry and other man-made sources had begun to rise since 1999, particularly in Asia. Some sources of methane release due to human activity are when fossil fuel is burnt, or cattle ranching or it is sometimes released accidentally while drilling for sources of natural gas.
The booming of the Asian economy and in particular China, resulted in increased emissions due to increase in use of fossil fuel, which has led to a rise in atmospheric levels of the greenhouse gas since 1999. On the other hand, decline in natural sources due to wetland areas drying, balanced the rise due to man-made sources. Nevertheless, scientists have warned that this trend of the gas to stabilize is only a temporary phase and the atmospheric levels of methane will increase again.
Although the levels of carbon dioxide are up to 200 times more than the levels of methane, the heat retaining capacity of methane is 20 times more than that of carbon dioxide.
Study author, Dr Paul Steele of Commonwealth Scientific and Industrial Research Organisation (CSIRO) in Australia, said: "Had it not been for this reduction in methane emissions from wetlands, atmospheric levels of methane would most likely have continued rising. This suggests that if the drying trend is reversed and emissions from wetlands return to normal, atmospheric methane levels may increase again, worsening the problem of climate change."
"What this work demonstrates is that there have been two opposing processes at work that together have resulted in stable methane emissions and no increase in atmospheric concentration over the past eight years," said Dr Paul Fraser, senior scientist at CSIRO. "On the one hand, wetlands have been drying up globally and thus emitting less methane. On the other, economic growth in the northern hemisphere, especially in China, has generated increasing amounts of methane from the mining and use of fossil fuels. Though it is difficult to predict what will happen to wetlands in the future, it is more than likely that overall methane levels in the atmosphere will increase in the future, due to increasing demands for energy," he added.
The study details have been published today in the journal Nature.
