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What is methane's contribution to global warming?

What the science says...

While methane is a more potent greenhouse gas than CO2, there is over 200 times more CO2 in the atmosphere. Hence the amount of warming methane contributes is 28% of the warming CO2 contributes.

Climate Myth...

It's methane
 

"A United Nations report has identified the world's rapidly growing herds of cattle as the greatest threat to the climate, forests and wildlife. ...

 

...Livestock are responsible for 18 per cent of the greenhouse gases that cause global warming, more than cars, planes and all other forms of transport put together.

 

Burning fuel to produce fertiliser to grow feed, to produce meat and to transport it - and clearing vegetation for grazing - produces 9 per cent of all emissions of carbon dioxide, the most common greenhouse gas. And their wind and manure emit more than one third of emissions of another, methane, which warms the world 20 times faster than carbon dioxide." (Geoffrey Lean)

 

While methane is a more potent greenhouse gas than CO2, there is over 200 times more CO2 in the atmosphere. Eg - CO2 levels are 380 ppm (parts per million) while methane levels are 1.75ppm. Hence the amount of warming methane contributes is calculated at 28% of the warming CO2 contributes. Here is a graph of the various forcings that influence climate (methane is CH4, right above CO2).

This is not to say methane can be ignored - reducing methane levels is definitely a goal to pursue. The good news is since the early 1990's, the trend in increasing methane has slowed down and even leveled off in the last few years (Dlugokencky 2003).

Atmospheric Methane Concentration

Last updated on 9 July 2010 by John Cook.

Printable Version  |  Offline PDF Version  |  Link to this page

Comments

Comments 1 to 19:

  1. Re: "This is not to say methane can be ignored - reducing methane levels is definitely a goal to pursue. The good news is since the early 1990's, the trend in increasing methane has slowed down and even leveled off in the last few years (Dlugokencky 2003)."
    Gee, what a coincidence!
  2. It would be better if the graph went back somewhat more than 20yrs. Preindustrial concentrations are estimated around 700ppb, just 40% of modern concentrations. Much of the rise has to do with population increase and dietary habits. Population increases in the east have demanded increased rice production and the consequent increase in methane emission. Western diets are highly biased to meat consumption resulting in huge growth in ruminant numbers since 1960, another large methane source.
    Also, I am not too sure if the overall effect of methane is included in models? Methane breaks down into water and CO2 and I would expect the total GG effect of methane to include the secondary effect of these.
    I recently read that global methane emissions is on the rise...will have to find that paper again........
  3. Note:
    Methane intially reacts with ozone in a 'chain' reaction that ultimately produces CO2 and water vapour.

    You could summarise the reactions into:

    (3)CH4 + (4)O3 = (3)CO2 + (6)H2O

    Oxidation of methane is the main source of water vapor in the upper stratosphere
  4. The question is not about what's in the atmosphere, but about what humans are responsible for emitting. Maybe there is a lot more CO2 in the atmosphere than methane, but what percentage of each those gases are human activities responsible for?

    Historically(averaging over the past 400,000 years) CO2 is around 240ppmv, and now it is around 385ppmv(60% higher). Methane is historically(over past 1,000 years) around 700ppb and now at 1700ppb(140% higher). The % for CO2 is smaller if we start from the warm period average of around 280ppmv.

    While the sheer volume of human released carbon dioxide and its warming affects probably are far greater than that of human released methane, humanity seems to have changed the concentration of atmospheric methane much more than that of carbon dioxide.

    The fact is that changes in agriculture and diet are the easiest way for an individual to lesson his or her environmental impact. Local, organic, and vegetarian diets are a simple highly effective remediation strategy.

    Disclosure: I am a vegetarian and so strongly biased on this particular issue, but this point cannot be ignored.

    sources:
    http://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth's_atmosphere
    http://ecen.com/eee55/eee55e/growth_of%20methane_concentration_in_atmosphere.htm
  5. "Hence the amount of warming methane contributes is calculated at 28% of the warming CO2 contributes"

    Does the first graph relate to the relative historic influence of each greenhouse gas emission to the radiative forcing we experience today? If so do we really need to know the relative effect of each greenhouse gas we emit today projected forward onto a certain timeframe to establish their real importance?

    Either way the graph needs to be clarified and referenced
  6. Methane concetrations have stalled int the atmosphere since approximately 1998. Have scientists figured out why? And is melting permafrost contributing enough methane to significantly raise its concentration in the atmosphere yet?
  7. Karmanski @6,

    That graph needs to be updated:



    [source: http://www.esrl.noaa.gov/gmd/aggi/]
  8. Does anyone have a reference that supports the Methane is 21 times CO2 thesis?

    I have seen this figure referenced all over the internet, but I haven't seen how it is calculated.
    Response:

    [DB] Recent topical discussion on Methane over at Tamino's.

    Chris Colose, Eli Rabett (and also here) and Steve Bloom all weigh in with good points.

  9. AndyS
    the claim that CH4 is "more powerfull" than CO2 is a bit ambiguos. It's not clear to what it refers. I suggest a good discussion on this topic at Chris Colose site.
  10. I wonder if someone could clarify a point for me? When sceptics say "you'll have to stop breathing then, because you're exhaling CO2" I point out that animal respiration is just part of the natural carbon cycle, (circulating 400Gt of CO2 a year), and that any carbon we breathe out was first captured from the atmosphere through photosynthesis to enter the food chain.

    Cow burps are treated differently however, and are seen as part of the problem. Is that because the carbon from the plants going through the cow is being converted (in part) to the more greenhouse active CH4, rather than merely being returned as CO2? (I realise cattle have a broader greenhouse footprint because of transportation and energy used in grain cultivation and so on, but I'm just curious about the methane here.) Many Thanks.
  11. Crispy, my understanding is that the accounting for methane is based on effect that methane has before it is oxidised to CO2 compared fate of plant carbon if it hadnt been eaten by ruminant. You might like to look up the GWP (global warming potential) for more detail.
  12. 1. Authors of super-freakonomics have said that eating kangaroo meat as opposed to a ham-burger is good for climate as methane is a greater threat! Is that scientifically correct?

    2. Same book mentions that methane is 25 times more potent than CO2 as greenhouse gas. If CO2 level is 200 times CH4 how does it contribute 28% warming than CO2? (I am assuming law of proportions to hold. Correct if wrong)

    3. Will emitting sulpher in atmosphere help cooling the planet? After what altitude exactly does sulpher cease being trouble (acid rain etc..)

    Thanks!
  13. Hi, abhi541.

    1. I have no idea, but someone here might.
    2. See this thread and the comment stream that follows it.
    3. See this thread.

    Post further questions on the relevant threads.
  14. abhi541
    1) i didn't know about kangaroo meat. A quick search led me here. Apparently there's some merit in eating this meat.

    2) Methane is some 25 times more potent on a molecule by molecule basis, though the effect, i.e. the forcing, is not proportional to concentration.

    3) sulphate aerosols have a cooling effect. In a geo-engeneering framework, you want them in the stratosphere.

    Sorry for the short and schematic answer. Follow DSLs suggestion, maybe someone else will give you more details, assuming you want more :)
  15. 1/ I have heard this too. Kangaroos (and rabbits) are not ruminants so methane/kg-human-product is less than sheep/cattle. Kangaroos requires less processing than rabbit but are challenging to farm to say the least.
  16. Is there any research into estimating what percent each of the greenhouse gases is due to anthropomorphic activity? If the intent is to stabilize the concentrations of greenhouse gases it would be nice to know how much of an effect our actions have on each molecule. IE is there a study that shows us what policy will give us the most bang for our buck?
  17. 16 - Heircide

    Have a look at the wedges
  18. It seems to me that we have an opportunity to make serious reductions in methane emissions by using bio-digesters for most of our organic waste. Nearly all living things release methane as they decay. When our farm waste rots in the fields or our sewage decays in a treatment plant, most of the methane generated is released to do its damage. If we offer carbon credits at the rate of 21 pounds of CO2 to 1 pound of methane removed from our emissions, we would make methane production for fuel a profitable enterprise. Of course methane is basically natural gas, which is plentiful right now in the USA. There are, however, considerable benefits to making methane from our organic waste. A very significant one is the compost and fertilizer produced in the process. This adds fertility to our soils to help bring them back to life after years of pesticides and artificial fertilizers. The natural fertilizer byproducts of microbe digestion contain all of the micro-nutrients removed by the plants that were composted. The added organic material also allows our soils to support normal soil enhancing worms and insects like the common earthworm. As an important benefit, these organic elements will also help our soils retain moisture in the hot dry weather we seem to be creating by our bad habits.

    What do you think about giving power plant carbon credits for capturing methane? They could burn the methane also to assist in power production or sell it for transportation fuel.

    Should we encourage natural gas conversion for our cars and trucks? It could really have a low carbon footprint if the methane comes from micro-digester production by the power companies. At the present time around 50% of our natural gas is used to make artificial fertilizer. I understand that we can convert most cars to run on natural gas for under $1000. (That could employ a couple of hundred thousand people.) If the government wants to invest in infrastructure that will pay dividends into the long term future, why not build a natural gas distribution system? (Another couple hundred thousand jobs.) Our need for imported petrolium products would decline sharply and keep considerable fund here in the USA to finance needed investments.

    It is possible to affect methane levels if we look at data from China. They claim to have a 9% reduction in methane emissions in the last 5 years. The rice production has also gone up considerably from the use of the byproduct fertilizer from the process.
  19. Methane levels started to increase again, about 6 or 7 years ago, so this explanation needs updating.

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