Global methane levels on the rise again
After eight years of near-zero growth in atmospheric methane concentrations, levels have again started to rise. This is bad news for future global warming, says CSIRO’s Dr Paul Fraser, who co-authored a paper to be published in Geophysical Research Letters, a journal of the American Geophysical Union.
Over recent years, the growth of important greenhouse gases, namely methane and the CFCs, had slowed. This tended to offset the increasing growth rate of carbon dioxide that results mainly from large increases in the consumption of fossil fuels, particularly in the developing world. But now that methane levels have resumed their growth, global warming may accelerate.
Methane is the second most important greenhouse gas in the atmosphere after carbon dioxide, accounting for nearly 20 per cent of global warming since the industrial revolution. Methane is emitted to the atmosphere from natural wetlands, rice fields, cattle, forest and grassland fires, coal mines, natural gas leakage and use, and other sources.
Over the past decade these methane sources have been close to balancing the absorption of methane through atmospheric oxidation and into dry soil, Dr Fraser says. This fragile balance has resulted in little growth of methane in the atmosphere. Apparently some sources have been increasing, such as from fossil fuel use, cattle, and rice, while others have been decreasing, particularly natural tropical wetlands. However, over the past year, the total sources have overwhelmed the total sinks, and methane has again started to rise.
Dr Fraser says that recent analyses of global data by CSIRO and collaborators at the Massachusetts Institute of Technology, Scripps Institution of Oceanography and the University of Bristol suggest that the methane increase is, at least in part, due to methane releases in the high latitudes of the Northern Hemisphere.
One surprising feature of this recent growth is that it occurred almost simultaneously at all measurement locations across the globe. However, the majority of methane emissions are in the Northern Hemisphere, and it takes more than one year for gases to be mixed from the Northern Hemisphere to the Southern Hemisphere. Hence, theoretical analysis of the measurements shows that if an increase in emissions is solely responsible, these emissions must have risen by a similar amount in both hemispheres at the same time.
A rise in Northern Hemispheric emissions may be due to the very warm conditions that were observed over Siberia throughout 2007, potentially leading to increased bacterial emissions from wetland areas. However, a potential cause for an increase in Southern Hemispheric emissions is less clear.
An alternative explanation for the rise may lie, at least in part, with a drop in the concentrations of the methane-destroying OH. Theoretical studies show that if this has happened, the required global methane emissions rise would have been smaller, and more strongly biased to the Northern Hemisphere. At present, however, it is uncertain whether such a drop in hydroxyl free radical concentrations did occur because of the inherent uncertainty in the current method for estimating global OH levels:
energy :: sustainability :: biomass :: bioenergy :: land use :: wetlands :: emissions :: methane :: climate change :: atmosphere ::
To help pin down the cause of the methane increase, Ronald Prinn - TEPCO Professor of Atmospheric Chemistry, in MIT's Department of Earth, Atmospheric and Planetary Science - said, "the next step will be to study this using a very high-resolution atmospheric circulation model and additional measurements from other networks." But doing that could take another year, he said, and because the detection of increased methane has important consequences for global warming the team wanted to get these initial results out as quickly as possible.
"The key thing is to better determine the relative roles of increased methane emission versus an idecrease in the rate of removal," Prinn said. "Apparently we have a mix of the two, but we want to know how much of each" is responsible for the overall increase.
It is too early to tell whether this increase represents a return to sustained methane growth, or the beginning of a relatively short-lived anomaly, according to Rigby and Prinn. Given that, pound for pound, methane is 25 times more powerful as a greenhouse gas than carbon dioxide, the situation will require careful monitoring in the near future.
The Intergovernmental Panel on Climate Change (IPCC) has identified the need to understand causes of the variations of methane growth rates as a priority area of research. The reality is that scientists have only a very basic understanding of these methane variations, Dr Fraser says.
In order to predict the future contribution of methane to climate change, continuing high-quality observations, in particular in tropical and boreal locations, are required as input to, and verification of, sophisticated climate models.
References:
M. Rigby, R. Prinn, P. Fraser, P. Simmonds, R. Langenfelds, J. Huang, D. Cunnold, P. Steele, P. Krummel, R.Weiss, S. O’Doherty, P. Salameh, H. Wang, C. Harth, J. Mühle, L. Porter. "Renewed growth of atmospheric methane", Journal of Geophysical Research. 28 pages 2008
Over recent years, the growth of important greenhouse gases, namely methane and the CFCs, had slowed. This tended to offset the increasing growth rate of carbon dioxide that results mainly from large increases in the consumption of fossil fuels, particularly in the developing world. But now that methane levels have resumed their growth, global warming may accelerate.
Methane is the second most important greenhouse gas in the atmosphere after carbon dioxide, accounting for nearly 20 per cent of global warming since the industrial revolution. Methane is emitted to the atmosphere from natural wetlands, rice fields, cattle, forest and grassland fires, coal mines, natural gas leakage and use, and other sources.
Over the past decade these methane sources have been close to balancing the absorption of methane through atmospheric oxidation and into dry soil, Dr Fraser says. This fragile balance has resulted in little growth of methane in the atmosphere. Apparently some sources have been increasing, such as from fossil fuel use, cattle, and rice, while others have been decreasing, particularly natural tropical wetlands. However, over the past year, the total sources have overwhelmed the total sinks, and methane has again started to rise.
Dr Fraser says that recent analyses of global data by CSIRO and collaborators at the Massachusetts Institute of Technology, Scripps Institution of Oceanography and the University of Bristol suggest that the methane increase is, at least in part, due to methane releases in the high latitudes of the Northern Hemisphere.
One surprising feature of this recent growth is that it occurred almost simultaneously at all measurement locations across the globe. However, the majority of methane emissions are in the Northern Hemisphere, and it takes more than one year for gases to be mixed from the Northern Hemisphere to the Southern Hemisphere. Hence, theoretical analysis of the measurements shows that if an increase in emissions is solely responsible, these emissions must have risen by a similar amount in both hemispheres at the same time.
A rise in Northern Hemispheric emissions may be due to the very warm conditions that were observed over Siberia throughout 2007, potentially leading to increased bacterial emissions from wetland areas. However, a potential cause for an increase in Southern Hemispheric emissions is less clear.
An alternative explanation for the rise may lie, at least in part, with a drop in the concentrations of the methane-destroying OH. Theoretical studies show that if this has happened, the required global methane emissions rise would have been smaller, and more strongly biased to the Northern Hemisphere. At present, however, it is uncertain whether such a drop in hydroxyl free radical concentrations did occur because of the inherent uncertainty in the current method for estimating global OH levels:
energy :: sustainability :: biomass :: bioenergy :: land use :: wetlands :: emissions :: methane :: climate change :: atmosphere ::
To help pin down the cause of the methane increase, Ronald Prinn - TEPCO Professor of Atmospheric Chemistry, in MIT's Department of Earth, Atmospheric and Planetary Science - said, "the next step will be to study this using a very high-resolution atmospheric circulation model and additional measurements from other networks." But doing that could take another year, he said, and because the detection of increased methane has important consequences for global warming the team wanted to get these initial results out as quickly as possible.
"The key thing is to better determine the relative roles of increased methane emission versus an idecrease in the rate of removal," Prinn said. "Apparently we have a mix of the two, but we want to know how much of each" is responsible for the overall increase.
It is too early to tell whether this increase represents a return to sustained methane growth, or the beginning of a relatively short-lived anomaly, according to Rigby and Prinn. Given that, pound for pound, methane is 25 times more powerful as a greenhouse gas than carbon dioxide, the situation will require careful monitoring in the near future.
The Intergovernmental Panel on Climate Change (IPCC) has identified the need to understand causes of the variations of methane growth rates as a priority area of research. The reality is that scientists have only a very basic understanding of these methane variations, Dr Fraser says.
In order to predict the future contribution of methane to climate change, continuing high-quality observations, in particular in tropical and boreal locations, are required as input to, and verification of, sophisticated climate models.
References:
M. Rigby, R. Prinn, P. Fraser, P. Simmonds, R. Langenfelds, J. Huang, D. Cunnold, P. Steele, P. Krummel, R.Weiss, S. O’Doherty, P. Salameh, H. Wang, C. Harth, J. Mühle, L. Porter. "Renewed growth of atmospheric methane", Journal of Geophysical Research. 28 pages 2008
4 Comments:
Yep, here we go again. 1,000 Years of this and you will have an effect equal to a 6% rise in CO2 levels. (approx. 27 ppm of CO2)
Don't you guys Ever read the fine print?
Rufus, it seems like you systematically try to downplay the danger of rising greenhouse gas levels.
Are you denying the reality of climate change, or the fact that current global warming is a human made process?
Of course I am. It's total nonsense. But, that has nothing to do with the amount of methane, or NF3 in the air. The facts are what they are; and, the fact is it would be a non-story even if the AGW schtup were ALL TRUE.
And, most importantly, you do the cause of bioenergy/poverty no service when you allow yourselves to be drug off into this thicket of silliness.
This limousine-liberal lunacy will have spent it's force in a couple of years, but the world's need for sustainable energy systems will be even greater.
The need for a "Credible" spokesman will be great, and you don't want to find yourselves "Damaged Goods."
Just look at the reality of it, guys. The PDO has turned negative, and another La Nina is on it's way. We'll probably have the coolest back-to-back years since the seventies. Three or four more years of a negative Pacific Decadal Oscillation (they run in 30 yr. cycles, you know) and you won't be able to sell this idiocy to Al Gore, his own silly self.
Try to figure out how to get more biodiesel in the world. That's what's needed, Now.
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