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Comments 1 to 25 out of 52:

1. Quietman at 15:48 PM on 24 March, 2008
   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. Mizimi at 20:20 PM on 27 August, 2008
   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. Mizimi at 05:10 AM on 29 August, 2008
   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. Joe at 07:30 AM on 4 March, 2010
   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. perseus at 04:31 AM on 27 August, 2010
   "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. Karamanski at 12:20 PM on 10 October, 2010
   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. Albatross at 12:25 PM on 10 October, 2010
   Karmanski @6, That graph needs to be updated: [source: http://www.esrl.noaa.gov/gmd/aggi/]
8. AndyS at 08:41 AM on 5 June, 2011
   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. Riccardo at 09:01 AM on 5 June, 2011
   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. Crispy at 12:51 PM on 21 June, 2011
    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. scaddenp at 13:31 PM on 21 June, 2011
    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. abhi541 at 03:45 AM on 10 October, 2011
    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. DSL at 03:58 AM on 10 October, 2011
    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. Riccardo at 04:17 AM on 10 October, 2011
    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. scaddenp at 06:51 AM on 10 October, 2011
    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. heircide at 06:37 AM on 15 February, 2012
    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. les at 06:52 AM on 15 February, 2012
    16 - Heircide Have a look at the wedges
18. IRTDave at 11:56 AM on 5 August, 2012
    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. TonyW at 17:35 PM on 10 August, 2013

    Methane levels started to increase again, about 6 or 7 years ago, so this explanation needs updating.

20. deathtokoalas at 18:46 PM on 4 August, 2015

    the more important point is that agriculture itself (minus land-use issues, transportation, pesticides, etc) should be carbon neutral, in the long run. the methane only takes a few years to decay back into c02, and then it gets recycled. if you ignore the transportation, and you take the pesticides out, and you offset the land-use with new planting, there isn't a net increase - it's just a redistribution from the soil to the trees, which can then be pulled back to the soil.
    
    this argument is still floating around. that's the key point in combatting it: the only net source of carbon into the atmosphere is from underground, that is fossil fuels. organic farming with proper offsets for clearing is (excluding transportation issues) actually carbon neutral in the long run.

21. bozzza at 13:08 PM on 5 August, 2015

    So, you are saying why Carbon-Soil Initiatives will never be an accepted method to combat climate change?!!?

22. malkazoid at 21:57 PM on 5 March, 2016

    Deathtokoalas - that's a lot of factors you're asking us to ignore, and they are factors that are not being dealt with so I'm not sure why we should ignore them.  What matters it the current impact of agriculture, not what it could be if we wished away various aspects of it, wouldn't you say?

    Your argument is misleading.  Increased rumination due to our apetite for animal flesh puts methane and the resulting CO2 and water vapor into the atmosphere.  This is the bottom line - as long as these animals release gas, this will remain true.  Where would the constituents of methane be if they were not being farted out?  They would be in trees that would be, on net, absorbing CO2 instead of releasing it.  When the trees die, their carbon returns beneath ground (unless we burn the wood).

    So the effect of clearing massive swathes of forest (which is not being offset by replanting), plus pushing carbon from plant growth into methane and up into the atmosphere, is not neutral at all... or am I missing something?

23. Dipper at 20:06 PM on 7 July, 2016

    I've done some calculations and got to the following point and would like someone please to tell me where I've gone wrong.

    My question is "what are the relative contributions of greenhouse gases to the excess heating we experience this year?"

    Firstly, for excess we need to take the difference from pre-industrial levels, so CO2 is (2011 levels) 391 - 278 = 113 ppm and for methane is 1.803 - 0.7 = 1.103 ppm.

    Second is the rel warmoing potential which for CO2 is 1 and for methane over a 100 year period is 28. But that 28 is because methane progressively breaks down in to CO2 so for the last 50 years or so most of the methane has disappeared. To calculate the warming potential of methane right now I took the 100 year number, the 20 year number of 84, took logs and extrapolated back to 0 to get a native number of 110.

    so

    contribution from CO2 = 113 x 1 = 113

    contribution from CH4 = 1.103 x 110 = 121

    Hence the extra warming generated this year comes slightly more from methane than from CO2.

    I've tried to work out what is wrong with this but have failed. Can anyone help?

     

    thanks

24. HK at 22:53 PM on 7 July, 2016

    @23 Dipper:
    Your math seems to be correct!

    I think the problem is that the warming potential for CO₂ vs. methane compares units of mass while your calculation compares units of volume.
    CO₂ is 2.75 times heavier per molecule (or ppm) than methane, so the numbers for methane have to be divided by that if you are comparing the climate impact from each on a ppm basis.

    Doing that, you get these results for methane vs. CO₂:
    100 years: 28 / 2.75= 10.2
    20 years: 84 / 2.75 = 30.5
    Instantly: 110 / 2.75 = 40

    And from pre-industrial to 2011:
    CO2: 113
    Methane: 121 / 2.75 = 44

    This figure shows the annual growth of forcings from the well-mixed greenhouse gases after 1950. Since the late 1990s the contribution from non-CO₂ has only been about 20-25 %, but that fraction was up to 50 % until the early 1990s. Note that the methane forcing nearly stabilized in the early 2000s, but has started to increase again.

    

25. Tom Curtis at 23:43 PM on 7 July, 2016

    Dipper @23, the Global Warming Potential is defined by the IPCC as follows:

    "Global Warming Potential (GWP) An index, based on radiative
    properties of greenhouse gases, measuring the radiative forcing following
    a pulse emission of a unit mass of a given greenhouse gas in the presentday
    atmosphere integrated over a chosen time horizon, relative to that of
    carbon dioxide. The GWP represents the combined effect of the differing
    times these gases remain in the atmosphere and their relative effectiveness
    in causing radiative forcing. The Kyoto Protocol is based on GWPs
    from pulse emissions over a 100-year time frame."

    You will notice that, first, the GWP is a function of mass, not volume (as pointed out by HK @24); and, second, that it is a function of emitted mass, not atmospheric concentration.  

    If you want to calculate the relative effect from atmospheric concentrations, you just use the formula for radiative forcing.

    Thus, for CO2, the formula is 5.35 x ln(C/C_o), which for the values you give is 1.82 W/m^2.

    For Methane, the formula is ΔF = 0.036(M^½ - M_o^½) - [f(M,N_o) - f(M_o,N_o)]

    where f(M,N) = 0.47ln[1 + 2.01x10^-5 (MN)^0.75 + 5.31x10^-15M(MN)^1.52] and M stands for a Methane concentration, and N stands for a Nitrogen Oxide concentration.

    Ignoring the Nitrous Oxide adjustment, and using your figures, this yields Methane forcing of 0.02 W/m^2, or 1/91st of the forcing due to CO2.  There is a further, small adjustment due to the relative effectiveness of different forcings but it does not bridge the gulf in the relative impacts between the two.  The result is that, per unit concentration, methane is approximately 12% more effective at warming than CO2 at near current cocentrations, but the significantly larger increase in CO2 concentration means that CO2 is the primary warmer.

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