• Steve Case

    “[Methane]traps at least 25 times more heat in the atmosphere than carbon dioxide over the long term”

    What exactly does that mean, or more to the point, armed with that knowledge and given methane’s concentration and annual increase, how much will it run up global temperatures by the end of the century?

    Good journalists like Lisa Gardiner should make the effort to find out and report that to their readers.

    Steve Case – Milwaukee, WI

    • ajbarba

      From Lisa Gardiner: Thanks for your question Steve! Its a complicated answer: The global warming potential (GWP) (https://www.epa.gov/ghgemissions/understanding-global-warming-potentials) of different gases is used to describe their impact on climate. Because it takes into account the lifespan of molecules in the atmosphere, the GWP changes depending on the timeframe you look over.

      Because methane stays in the atmosphere about 10 years, methane emitted today has a larger impact on climate change now than it does in future decades. However, when methane breaks down it creates carbon dioxide, so it keeps having an impact on climate.

      How much does methane cause climate to change? Methane is responsible for about 28% of recent warming. Carbon dioxide, while less efficient at trapping heat, is responsible for most of the warming because there is 200 times more of it in the atmosphere than methane. (Other greenhouse gases, like nitrous oxide, cause a smaller amount of warming.)

      To project out 100 years into the future, it’s helpful to know how much methane we are releasing into the atmosphere over time. Unlike global carbon dioxide levels, which have been closely monitored for yearly 60 years, there hasn’t been as much monitoring of global methane.

      The Global Carbon Project (http://www.globalcarbonproject.org/) is getting a handle on global methane emissions. Their 2016 study found the amount of methane in the atmosphere increased over the past decade and that humans are responsible for 60% of that methane. About 20% of the methane coming from humans is from oil and gas. Farms and rice paddies emit the majority of methane in the past decade.

      There are also complicating factors that scientists are trying to better understand – such as how future warming will affect the rate at which methane is released from thawing Arctic permafrost and whether warming puts frozen methane on the ocean floor at risk of thaw.

      Figuring out how much methane is released today through studies that gather data on the current emissions from various sources, and studying methane sinks (where it leaves the atmosphere) helps scientists improve projections of future climate.

      • ajbarba
        • Steve Case

          There should be a number a median value plus or minus so many degrees. So far I haven’t seen it.

          • ajbarba

            From Lisa: The uncertainty is too high to say with confidence exactly how much methane will impact climate in 2100. Models runs typically take the whole earth system into account instead of individual components. I can’t find studies that break methane out separately. Since methane forms carbon dioxide when it breaks down in the atmosphere, these greenhouse gases are tied together.

            Overall, here’s the projections for 2100:
            The IPCC projections (from the 2014 AR5 report) are based on different scenarios for how people will act in the future. In the scenario in which greenhouse gases drop after 2020, climate is projected warm 0.3-1.7C by the end of the century. In the scenario in which we don’t reduce greenhouse gases emissions, climate is projected to warm 2.6-4.8C by the end of the century.

          • ajbarba
          • ajbarba

            Thanks Steve, we appreciate the back and forth and the need for clarity on this issue. Let’s keep researching and talking about it! Alisa

          • Steve Case

            In the simplest of terms, first find out how much methane is going to be added to the atmosphere and then figure out how much a similar amount of CO2 will run up global temperature and multiply that result by 25.

            I’m off to camp in the north woods for a few days – my best to all (-:

          • Steve Case

            “The uncertainty is too high to say with confidence exactly how much methane will impact climate in 2100. Models runs typically take the whole earth system into account instead of individual components.”

            Or how little methane will impact climate.

            “I can’t find studies that break methane out separately.”

            But scientists tell us that methane is anywhere from 25 to 86 times more potent or powerful than CO2.

            The reason for the range of those coefficients is twofold it’s a standard that is based on the concentration of methane which constantly increases. Seems kind of silly to use a standard that changes all the time, but that’s what it is.

            Also sometimes it’s a volume to volume comparison and sometimes it’s mass as in pound for pound methane is 86 times more potent. That means the formula weights of 16 and 44 for CH4 and CO2 need to be considered which results in the much higher numbers.

            CO2 is in the air at 400 parts per Million and methane is around 1800 parts per Billion and increases about 6 or 7 parts per billion annually. So by 2100 it will increase nearly 600 ppb or about 0.6 ppm. All that is needed is to figure out how much an addition of 0.6 ppm CO2 will run up global temperatures and multiply by 25 or 86 as the case may be.

            So CO2 increases from 400 ppm to 400.6 ppm. Given that CO2’s absolute climate sensitivity is 1.2°C per doubling* and the range from 400 to 400.6 is small the effect would be linear so 400.6÷400=1.0015 and that multiplied times 1.2°C is 1.2018°C and the difference of 0.0018°C times the coefficient of 25 is 0.045°C. So CH4 will run the temperature up about 0.05°C by 2100.

            There are a lot of insignificant place holders in that arithmetic which means the whole notion of 25 or 86 times more potent is meaningless.

            *In the idealised situation that the climate response to a doubling of atmospheric CO2 consisted of a uniform temperature change only, with no feedbacks operating … the global warming from GCMs would be around 1.2°C (Hansen et al., 1984; Bony et al., 2006)
            http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch8s8-6-2-3.html

      • Steve Case

        Thanks for the reply, I appreciate it.

        I was hoping for an actual number like 0.05°C or 0.5°C or 1.5°C etc. and then ± something.

        People need to know what the actual story is. Lisa’s 100+ word answer really doesn’t say.

        From time to time I send emails to reporters and scientists and this is most I’ve ever gotten
        back.

      • Steve Case

        There should be a ball park answer in degrees C such as 0.01°, 0.05°, 0.1°, 0.5°,1.0°, 1.5°, or maybe even 2.0°C. Telling people methane is 25 times or sometimes you see 86 times more potent than CO2. sounds scary but doesn’t convey any actual temperature information which is what people need to form an opinion about the topic.

      • AnOilMan

        I already had a long argument with him about this. His purpose is to spread FUD about Methane concerns. After I figured out this little meme, he went off the rails;
        https://disqus.com/home/discussion/desmogblog/five_ways_alberta_can_raise_the_bar_on_methane_regulations/#comment-3451631146

    • AnOilMan

      As I previously stated. You don’t actually want the answer to your question. You are JAQing (Just Asking Questions) off which is a common technique used to cast aspersions on real work without actually saying it. A lot of people who hang out at Watts Up With That behave that way.

      You already answered your own question. First we know that 2-4% of the methane in the atmosphere dissipates every year. So, by 2100, the bulk of the methane in the atmosphere will emitted between here and then.

      Looking at AR5 we can see that by 2100 the world will be 2.2C to 3.7C hotter… and we know that CH4 is 16% of that so .35C to .6C. According to you the bulk of that heat is methane emitted between now and then.
      https://en.wikipedia.org/wiki/Representative_Concentration_Pathways

      Here’s IPCC AR5 summary for you. Methane is currently 16% of global warming (using older lower numbers for GWP);
      http://ar5-syr.ipcc.ch/topic_summary.php
      http://ar5-syr.ipcc.ch/ipcc/sites/default/files/AR5_SYR_Figure_SPM.2.png

      The reason all this is a concern is of course because we are currently on RCP 8.5, and there is a big push for Natural Gas. Ingraphea Howarth 2011 showed that fracked natural has is seriously leaky, on par with coal, and since then, we’ve seen that the leaks are in fact worse.
      http://mde.md.gov/programs/Land/mining/marcellus/Documents/GHG_article_Howarth_EtAl_2011.pdf
      http://www.worldclimatereport.com/wp-images/howarth_fig1.JPG