The methane feedback effect. When I reviewed the Kleinen study two days ago I made note (in the fourth paragraph) of a stunning implication of the research this group had done—the possible existence of a methane feedback effect that would make it comparable in a number of ways to the water vapor feedback effect that is commonly accepted as a fact. Methane feedback effects are often witnessed in particular situations, but are rarely mentioned, if ever, as an everyday possibility that can be realized on a large scale across the entire globe. If such a thing exists it could have serious implications for climate forecasting. We have no idea of what its strength would be, because there has never been an attempt to measure it, but even a low level of strength would have some kind of a rising impact on future temperatures. At the very least, a common tendency to regard methane as only a minor player, compared to CO2, in making climate changes, would need to be reviewed and probably revised.
What got my attention in the Kleinen study was the amazing similarity in the total mechanism that would enable each of these two separate feedback effects to operate. First of all, both of the gases can be said to originate as airborne particles because of their high sensitivity to the level of warming of the planetary surface. For water vapor nothing else matters. It only forms by means of evaporation from liquid water on the surface, a substance which abounds in most parts of the globe. When any of the water is warmed its rate of evaporation increases. Otherwise it just continues at the same rate. When water freezes over evaporation all but stops. In methane’s case we must first remember that a not-large majority of what is now in the air originates in a variety of ways that are not at all comparable to water vapor. We can only set them aside and focus on the remaining minority, all of which is of origins attributed to natural sources. As we learn from the study, with much support from other references, this origination occurs “with wetland emissions being by far the largest component.” Like plain water, but to a lesser extent, wetlands are found in great multiplicity, always on the surface. They get warmer or cooler in the same way that plain water does. When they get warmer they emit more methane, cooler, less, etc. There is little more than a bare minimum of contrast with the evaporation process.
Water vapor and methane are both greenhouse gases, by measurement two of the strongest three GHGs. As soon as they have been emitted to the atmosphere they start sending photons of energy back down to the surface, making the surface warmer as they do so. Their molecules naturally spread out in the atmosphere, methane more so than water vapor, so plenty of waters and wetlands will be feeling the warming effects of this energy. And when these surfaces have felt the effects they both respond in a regular way, by more evaporation and more emission. But that’s only part of the story. Each such response results in a modicum of still more warming on the surface, causing yet more evaporation and emission, creating a positive feedback loop that multiplies the effect, until sharply declining units of response cause it to fade away.
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The best takeaway from this study need not be dramatized in any way in order to realize its importance relative to the likelihood of significant declines that current models are predicting for future levels of methane concentrations. The authors express a great deal of confidence in coming to this contrary conclusion: “CH4 emissions will remain larger than in the historical period for a long time, likely for as long as CO2 and temperatures remain above present levels.” They expect this to hold true even under the most favorable scenarios for CO2 emission reduction rates, which would not by themselves enable a reduction in the established level of its atmospheric concentration, now around 417 ppm and rising.
Carl