The Fuss about Methane

The Fuss about Methane

Part 1: Science and bizarre facts

Methane is getting a whole lot of attention in climate debates. There was even a “Methane Day” last Tuesday on the climate conference in Glasgow. Several latest regulations controlling methane emissions have been adopted recently, including two latest rules for the US oil and gas sector announced last week. There’s a latest informal international agreement to limit methane emissions, and a still-unresolved effort to place a charge on methane emissions into the forthcoming reconciliation bill. And more methane initiatives are surely on the best way.

There are several good reasons for this. Methane is important to regulate, since stabilizing climate requires reducing all anthropogenic greenhouse-gas emissions to net-zero. Methane is a fairly large contributor to heating, second only to CO₂. Furthermore, for reasons I’ll explain below, cutting methane brings especially strong advantages over the subsequent few many years. There are even indications that near-term cuts is perhaps easier to realize for methane than for CO₂, for a mixture of technical, economic, and political reasons. None of this implies methane controls can replace CO₂ controls; but it surely does make methane an especially attractive candidate for immediate and steep cuts.

This post is an introduction to methane in climate change: where it comes from, the way it’s different from CO₂, how those differences matter, and what that each one means for controls. I won’t go into details on the present state of methane controls and proposals for brand new ones. That’s for a subsequent post.

Background: More science than you would like

Methane, chemically CH₄, is the smallest and simplest hydrocarbon. “Hydrocarbon” means just what it seems like: molecules containing only hydrogen and carbon. Other familiar hydrocarbons include the propane (C₃H₈) within the tanks at your off-grid survivalist cabin, the butane (C₄H₁₀) in your cigarette lighter and camp stove, and the non-specific mixture of hexanes through octanes (similar molecules containing six to eight carbon atoms) in your automotive’s tank, which you call “gasoline.” The lightest hydrocarbons, like methane, are gases at room temperature, in order that they’re either delivered through pipes or compressed into tanks. As you progress from smaller to larger hydrocarbon molecules, you first get light, volatile liquids (Aah, the small of gasoline), then increasingly heavy and sludgy liquids (diesel fuel, kerosene, heating fuel oil, marine bunker fuel), then soft spreadable solids (Ever wonder why Vaseline known as “petroleum jelly”?), then more solid solids like paraffin.

We most frequently encounter methane as the biggest component of natural gas: methane makes up 75 – 95% of the gas coming to your stove and furnace.

“Natural gas” was a marketing term for this then-new, safer gas pumped through urban distribution pipes starting within the Nineteen Forties. It replaced an earlier, more dangerous, product called “town gas” or “coal gas,” which consisted mainly of hydrogen and carbon monoxide and was produced by heating coal in

the absence of air. In comparison with town gas, natural gas has the nice advantage that it’s not toxic: that’s why nobody kills themselves by sticking their head inside an (unlit) oven in literature or film set more recently than the Fifties. Natural gas also has the next energy content, so your kettle boils faster – but these advantages come at the fee of a greater explosion risk. Fires and explosions from leaky pipes were fairly common as the brand new gas was rolled out through distribution systems within the Nineteen Forties and Fifties, until the utilities got higher at controlling leaks – although as we’ll see below, this improvement was enough to limit local explosion risk but not enough to regulate methane’s contribution to climate change. An enormous early challenge to effective leak control was that methane and the opposite constituents of natural gas are all odorless, so you may’t smell leaks. To unravel this problem, utilities got here up with the clever innovation of putting just a little little bit of stinky stuff into the gas, so people reliably report leaks. This stinky stuff is a mix of reduced sulfur compounds, which all have strong smells, even though it doesn’t include the best-known of those stinky reduced-sulfur compounds, Hydrogen sulfide or rotten-egg gas (H₂S), due to its high toxicity. The odorant is normally a combination of dimethyl sulfide, tetrahydrothiophene, and various mercaptans. Different utilities use different mixes, aiming to make the smell really strong, but not quite like the rest: a touch of skunk, but not an excessive amount of; just a little little bit of kerosene; a smidgen of rotten eggs; etc. Once I first learned about this, I wondered (and still wonder) about who does that job: specifically, are they perfumiers who didn’t make it in the massive leagues? “Marcel, je regrette to tell you that your nez, he is simply too crude for Chanel, so it’s off to Gaz de France for you!”

Just about all the methane on Earth is formed in two ways. First, by chemical conversion of organic material at hot temperature and pressure deep underground: that’s how many of the methane in natural gas is formed. Second, by microbial respiration in anoxic environments. The clever microbes that do that, mostly Archaea (i.e., not plants, animals, fungi, or bacteria), get their energy by breaking down organic molecules via a distinct chemical pathway than we air-breathers use to get our energy, which doesn’t require oxygen and ends in methane as a substitute of carbon dioxide and water. This anaerobic respiration has to happen where there isn’t any oxygen, so it mainly happens in two places on Earth. First, underwater – in sediments on the underside of swamps, lakes, and the ocean. And second, in the center of animals – termites, cows and other ruminants, and us. We’re not a giant source – even with legume-heavy diets, the cows emit far more than we do – but I mention it to honor the amusement (rude to make sure, but only barely dangerous) practiced since time immemorial by adolescents brought up as badly as me.

OK, on to methane within the environment: The headline here – whether you’re talking about atmospheric concentrations, climate impacts, or emissions – is that there’s quite a bit less methane than CO₂, but it surely’s a stronger climate heater and it’s increasing faster.

Atmospheric concentrations

CO₂ is at about 410 parts per million by volume (ppm) within the air, about 50% higher than before the beginning of large-scale fossil-fuel use. Methane is at about 1,890 parts per billion by volume (ppb) or 1.89 ppm, but that level is about 2.6 times the pre-industrial concentration. Methane’s concentration increases have been more variable over time than those of CO₂, and these variations usually are not fully understood. For instance, methane stayed roughly flat for a few decade from the late Nineties, but has increased rapidly since then – by nearly 16 ppb in 2020 over 2019.

Climate impact

That small concentration of methane within the atmosphere makes an outsized contribution to global heating. Human-source atmospheric methane now adds barely lower than 1 watt per square meter (W/m²) of radiative forcing, versus 1.7 W/m² from elevated CO₂. Or when it comes to temperature effect, anthropogenic methane accounts for about 0.5°C of the worldwide heating already realized, CO₂ for about 0.75°C. (Note: you may find these figures confusing, since total heating is barely about 1.2°C. The problem is that total human radiative forcing includes several parts that heat and a few that cool, so counting separate heating contributions like this leaving out the cooling parts gives an excessive amount of heating.)

Emissions

Here too, CO₂ is way greater, but methane is growing faster and punches above its weight. Anthropogenic emissions of CO₂ are about 36 billion tons per yr (GtCO₂/yr), while methane emissions are several hundred million tons per yr (MtCH₄/yr). Essentially the most recent comprehensive estimate is that worldwide methane emissions from all sources are about 570 Mt/yr (range ~ 550-600), of which about 60% (360 Mt) come from human sources, the opposite 40% from natural sources. Of that human-source share, about 35% comes from fossil-fuel production, processing and use (oil and gas 23%, coal mining 12%); 40% comes from agriculture (livestock 32%, flooded rice fields 8%), and 20% comes from waste, mostly landfills (because they’re packed so tight that air can’t get in) and wastewater. The natural emissions are mostly from wetlands (about 85%), the remaining from termites, wild ruminants, and a number of miscellaneous sources.

There may be a good amount of uncertainty in these emissions budgets. These numbers are “top-down” estimates – inferred from observing how atmospheric concentrations vary over time and placement. In contrast, “bottom-up” estimates observe the operating levels of activities that emit methane, measure emissions from a sample of those – this natural-gas field, this feedlot, this dairy operation – then assume the emissions-to-activity ratios measured at those sources apply to the entire sector. Bottom-up emissions estimates are presently about 30% higher than top-down estimates, however the latter are considered more reliable. There are significant uncertainties in anthropogenic sources, but the biggest uncertainties are for natural emissions, especially wetlands.

Uncertainties and Confusions 1: Watch out what (and the way) you measure

There are a number of persistent sources of uncertainty and confusion about methane, that you simply run across repeatedly in policy debates and news accounts. Essentially the most basic of those – a source of potential confusion, not an uncertainty – concerns measure emissions, concentrations, and their effects, with a view to provide the premise to match different greenhouse gases.

There are two issues: do you measure and compare by volume or by mass, and in case you measure by mass do you count the mass of the entire molecule or simply the carbon a part of it? This latter issue is definitely a much bigger source of confusion for CO₂ than for Methane. Within the early days of the climate issue, when discussions were mainly scientific, normal practice was to measure CO₂

by the mass of only the carbon atom within the molecule, not the entire thing. More recently, as climate change moved into broader public and policy debate, it became standard to measure CO₂ by the mass of the entire molecule. Since one carbon atom has a mass of 12 Atomic Mass Units (AMU), while one oxygen atom has mass of about 16 AMU, the overall mass of a CO₂ molecule (one carbon plus two oxygen atoms) is 44 AMU. Measuring by mass of CO₂ is now so standard that even IPCC reports have mostly switched to doing it that way. But that ratio, 44/12 or 3.67, still crops up repeatedly in conversations about CO₂ emissions, reduction costs, and policies. So in case you see a reported emissions figure that seems much too small, or an emissions price or cost of reduction that seems much too big, it’s probably expressed in tons carbon reasonably than tons CO₂. Careful writers at all times write units explicitly as tCO₂, or (if comparing multiple gases) tCO₂e, where the “e” is for equivalent. But not all writers are at all times careful. The identical issue applies to methane, but its effect is numerically smaller. In a methane molecule that mass of the carbon is again 12, while the entire molecule is about 16 because each hydrogen atom is 1 AMU. As with the trendy convention for CO₂, most reporting of methane counts the mass of the entire molecule and careful writers make that explicit by writing tCH₄. But when some figure seems mysteriously off by a few quarter, the very first thing to ascertain is whether or not someone is reporting just the mass of the carbon.

Each measuring by mass and measuring by volume are used usually, so you will have to watch out. Generally speaking, emissions – each methane and CO₂ – are reported by mass, but atmospheric abundance is reported by volume, in what is often called a “mixing ratio.” Measuring by volume is such as counting molecules, since in gases at the identical conditions (meaning the identical temperature and pressure), volume is proportional to the variety of molecules present. For those who remember your highschool chemistry, this known as Avogadro’s Principle: in words branded on my brain by rote repetition, “equal volumes of any two gases at the identical temperature and pressure contain equal numbers of molecules.” Which means that one molecule of methane within the atmosphere occupies the identical volume as one molecule of CO₂, but has less mass by the factor 16/44. So to match the relative heating contributions of methane and CO₂, you will have to be clear whether you’re comparing molecule to molecule or ton to ton. The heating contribution of 1 methane molecule is about 25 times higher than that of 1 CO₂ molecule. But since the mass of that methane molecule is barely just a little greater than one-third that of the CO₂ molecule, comparing mass to mass means you’re counting the effect of nearly thrice as many methane molecules as CO₂ molecules. So on a mass-to-mass basis, methane has a heating contribution about 70 times higher than CO₂. Methane also has indirect effects on heating, on account of chemical interactions by which methane changes the degrees of other greenhouse gases. Including these indirect effects increases methane’s heating effect to 45 times that of CO₂ comparing molecule to molecule, or 125 times that of CO₂ comparing mass to mass.

Uncertainties and Confusions 2: Isn’t scientific progress exciting?

Scientific knowledge of atmospheric methane has made substantial advances over the past decade and continues to accomplish that, but these advances sometimes generate confusion because numerical estimates of physical quantities or other results of various vintages often get circulated without explaining and even noting the differences.

Crucial recent change was a latest measurement of methane’s infrared absorption in 2016. Previous estimates had only included methane’s absorption within the thermal infrared region, that spectral region of wavelengths around 8 to 14 microns where most of each the natural greenhouse effect and current human-driven heating occur. But methane also has a few absorption bands within the shortwave infrared region, closer to visible light (around 1.65 and a couple of.3 microns, when visible light is from about 0.4 to 0.7 microns). Including these bands increased methane’s calculated total heating contribution by about 25 percent.

As well as, several recent studies have substantially revised prior estimates of methane’s emissions budget – meaning how much comes form what sources, and where it goes. The one biggest effect of those changes has been to extend estimates of emissions from the oil and gas sector – a change that has occurred in parallel with a giant increase in actual emissions on account of rapid, fracking-enabled growth of production, especially in the US . One 2018 study combined on-site and aircraft measurements to estimate US oil and gas sector emissions about 60 percent higher than within the official emissions inventory. This higher figure implied a leakage rate of two.3% of total US gas production, versus the official estimate of 1.4%. One other study published this yr measured methane within the air throughout the Boston metropolitan area, aiming to enhance estimates of emissions from natural-gas distribution and end-use (which is the most important source in a giant city that doesn’t have oil or gas wells, refineries, agriculture, or landfills nearby). This study found emissions roughly triple the estimates derived from activity-based inventories, suggesting that leakage rates from the entire system are even higher than present in the 2018 study, from 3.3 to 4.7% of total production.

Lots of these advances in understanding methane emissions are coming from more quite a few and advanced satellite instruments which are providing increasingly fine-grained coverage in space and time, together with improved models and analytic methods to integrate observations from multiple platforms and sources. Along with generally increasing estimated emissions, these advances in observational precision are also increasingly showing that only a few sources and events, often related to accidents or equipment malfunctions, contribute a much larger than expected share of total emissions. This means that fine-grained, continuous emissions monitoring and a rapid response capability are far more necessary for emissions control than was previously recognized.

Uncertainties and Confusions 3: Wait, how much worse is methane than CO₂?

Perhaps the most important source of confusion in understanding methane’s role in global heating doesn’t much come from scientific uncertainty, but from the intrinsic ambiguity involved in attempting to represent in a single number the relative heating effects of two gases with widely different atmospheric lifetimes after they’re emitted.

How far more does methane contribute to global climate change than CO₂? You hear a surprisingly big selection of answers. It’s 7 times stronger. No, it’s 25 times stronger. No, it’s 80 times stronger. No, it’s 125 times stronger. These numbers are all different examples of “global warming potentials” (GWP) – a regulatory metric that defines convert emissions of various gases into a standard scale, type of just like the exchange rate between two currencies. Any regulatory system that covers multiple gases under a single control mechanism has to specify such an exchange rate, to find out how much credit you get for reducing a ton of 1 gas, relative to a different.

Since GWP’s are all measured relative to CO₂, the GWP of CO₂ is at all times one, by definition. For other gases, the GWP will depend on two different properties of the gas: how strongly it absorbs infrared radiation; and the way long it stays within the atmosphere after it’s emitted. Only just a little of the big selection in GWP figures comes from changing scientific knowledge over time. Most of it comes from differences in atmospheric lifetime, and crucially, different judgments of take account of those atmospheric lifetime. To chop to the chase: methane heats far more strongly than CO₂ while it’s present within the atmosphere, but it surely doesn’t stay long. CO₂ has a weaker heating effect but stays around for much longer. Relative to CO₂, methane lives fast, dies young.

How much a unit of gas contributes to heating while it’s there’s measured by its instantaneous radiative forcing, or infrared absorbance: how much energy it absorbs and re-emits per unit mass relative to CO₂. This is decided by the gas’s absorption spectrum, and it might probably be measured at a single moment in time. Once I said above that a unit mass of methane heats 70 times more strongly than CO₂, or 125 times more strongly including indirect effects, those were comparisons of instantaneous infrared absorbance or instantaneous radiative forcing per unit mass.

However it’s not particularly useful to measure total contributions to heating at a single quick of time, because we care about how hot it should get and getting hotter takes time. Each gas’s total contribution to heating thus also will depend on how long it stays within the atmosphere to maintain heating once it’s emitted: its atmospheric lifetime.

Atmospheric lifetimes don’t operate like an on/off switch. If something has an atmospheric lifetime of 10 years, that doesn’t mean all of it stays for ten years then immediately disappears. Reasonably, atmospheric species are all removed by processes that operate repeatedly, but at widely different speeds. Atmospheric removal processes typically remove a relentless fraction of whatever amount is present in every time interval: ten percent the primary yr, ten percent of what’s left the second yr, and so forth. If a species is removed by processes that work this manner, its remaining amount decreases exponentially over time, just like the decay of a radioactive material. The speed at which any radioactive material decays is described by its “half-life”: the time it takes for any starting amount of the fabric to diminish by half. It’s characteristics of exponential change, whether growth or decay, that changing by a given factor, on this case reducing by half, takes the identical length of time, irrespective of how much you begin with. Atmospheric lifetimes may be expressed as half-lives, but for computational simplicity they are frequently expressed because the time required to diminish, not by an element of two but by an element of “e” (an irrational variety of about 2.72, the bottom of the natural logarithms).

This discussion of atmospheric lifetimes is barely strictly correct for substances which have only one exponential removal process. Many atmospheric gases are removed by multiple process, operating at different speeds. On this case, atmospheric lifetimes mix the results of those different loss processes. Methane is removed by a number of different processes, but one among them – oxidation by the hydroxyl or OH radical – is crucial, so methane’s atmospheric lifetime is near its atmospheric lifetime relative to simply this loss process. There may be, nevertheless, one additional wrinkle that affects methane’s atmospheric lifetime. Those hydroxyl radicals are really necessary, but are also really rare – on order one part in 10¹⁸ of air. This concentration is so tiny that researchers often count OH abundance not as volume ratios, but when it comes to the variety of molecules present per cubic centimeter of air, with those numbers as little as lots of or hundreds of molecules per cm³. In consequence, methane concentrations as little as parts per billion can deplete the OH, so the more methane is present within the air, the longer its atmospheric lifetime: It’s type of like methane survives longer by overwhelming its predators (in ecology) or flooding the defensive zone (in sports). Researchers handle this wrinkle by individually counting the common lifetime of all methane molecules present within the air (about 8 years), versus the lifetime of a further little bit of methane added to the current amount (about 12.5 years). Because emissions are actually increasing the quantity of methane present, it’s the latter of those lifetimes, 12.5 years, that’s relevant for calculating the incremental heating from methane emissions.

Unfortunately, the one atmospheric trace gas to which an easy exponential representation of atmospheric lifetime matches the worst is CO₂. It’s removed by several processes that operate at vastly different speeds, from weeks to hundreds of thousands of years. For practical purposes, people just consider its lifetime as hundreds of years or longer. That complexity doesn’t affect GWP calculations, nevertheless, since CO₂ is the baseline relative to which the heating effect of other gases is calculated.

OK, we’re able to calculate GWP. Suppose that at some given starting time, you emit one ton of CO₂ and one ton of methane. How much does each of those contribute to global heating? As noted above, right after they’re emitted that ton of methane is heating 125 times more strongly than the ton of CO₂. That factor of 125 measures how much harder the methane is pushing the climate to heat up, the instantaneous forcing. But you most likely care about atmospheric heating not this week, but over some longer period. As time passes, each gram of methane remaining within the atmosphere keeps pushing just as hard, but fewer grams remain to do this pushing: to stretch the sports metaphors further, each member of the team is just as strong, but there are fewer people left on the team. With an atmospheric lifetime of 12.5 years, only just a little greater than a 3rd of the unique ton emitted stays within the atmosphere after that point, just a little greater than one-eighth after 25 years, and so forth.

The whole heating effect of that ton of methane after any time is then the product of that instantaneous forcing per unit, multiplied by the quantity of the original ton that continues to be, added up (or in calculus terms, integrated) from the starting time up until the time you’re taking a look at. The whole heating effect of the initial ton of CO₂ is calculated the identical way: the heating push per unit mass, multiplied by the mass remaining from the initial one ton emitted, added up (integrated) from the starting time to the time at which you’re measuring. The ratio of those two calculated total heating effects (Ta-da!) is the worldwide warming potential of methane.  (Trigger warning: Don’t have a look at the figure if integral signs scare you.)

There are two things to notice about this calculation: First, keep in mind that the GWP of CO₂ is about identically equal to 1. That doesn’t mean the heating contribution of CO₂ is fixed – it does decrease over time, albeit very slowly – it just signifies that the heating effect of CO₂ is used because the unit of measurement, relative to which all of the others are calculated.

Second, and crucially, once you compare two gases with different atmospheric lifetimes, that ratio goes to alter quite a bit depending on the time horizon you utilize to do the calculation. You possibly can calculate the one-week GWP of methane in case you wanted. Since essentially not one of the initial ton is removed that fast – a 12.5-year atmospheric life is brief, but it surely’s not that short – this is able to be nearly similar to the ratio of instantaneous radiative forcings, 125. Over longer periods, the ratio between the cumulative heating effect of methane and CO₂ decreases, since the added-up effects over time include increasingly time when little or no of the initial ton of methane stays, while the fraction of the unique CO₂ remaining is way closer to constant. So once you do the comparison over 20 years, methane’s heating contribution decreases to about 85 times that of CO_. After 100 years, it’s right down to 30 times that of CO₂, and the further ahead you look, the smaller the ratio gets. What would the GWP of methane be over one million years? Your first guess is perhaps that it’s zero, and that may be entirely reasonable. Over periods that long, the ratio of the 2 summed (integrated) heating effects goes to be completely dominated by hundreds of years over which the unique methane emission is basically gone, while the unique CO₂ is generally still there and still heating.

There are a pair more wrinkles, nevertheless, that make this intuitively attractive answer not quite right. The unique methane emission is perhaps gone, but what happened to it? If the methane went away by the dominant loss process, OH oxidation, then each methane molecule got become a CO₂ molecule: a much weaker heater than methane, but still a heater. That might suggest that over very long periods, methane’s GWP should converge to 1 reasonably than zero. But as the latest IPCC assessment report identified, there continues to be yet one more wrinkle: the really really total heating contribution of methane will depend on how the methane got made. If it was formed by anaerobic decomposition of organic matter (those cows and rice fields), then the carbon atom within the methane molecule was faraway from the atmosphere recently by photosynthesis, so counting the entire system life-cycle you don’t need count the CO₂ molecule that continues to be in any case the methane is oxidized: that carbon atom was taken from atmospheric CO₂ by photosynthesis inside the past few years, and now it’s back there. But when the methane got here from oil, gas, or coal production, then its carbon atom had been stored away from the atmosphere for hundreds of thousands of years, so that you do must account for putting it back. In consequence, the brand new IPCC assessment for the primary time reports two separate values for methane’s GWP over every time period: a rather lower one for biological-source methane, and a rather higher one for fossil-source methane.

Isn’t this an Environmental Law blog? Putting all of it together.

This all leads to some of small print for greenhouse-gas control.

First, it’s impossible to reply the query “how much worse is methane,” without specifying the time period over which you’re making the comparison. This needs to be the time period over which you care about climate effects. If what you care about is limiting global heating within the yr 2100, then immediate control of a short-lived gas like methane shouldn’t be an efficient place to focus your efforts, since current emissions will essentially all be passed by then in any case. But in case you are most concerned about reducing global heating over the subsequent few many years, short-lived gases like methane are much higher priorities for control. That ton you narrow today would have had very strong heating effect over the subsequent 10-20 years, which will be avoided by cutting the emission now. The GWP quantifies this shift in relative priorities depending on the time-horizon of concern. It shouldn’t be a scientifically determined quantity: it’s a regulatory parameter that will depend on each scientific knowledge, and normative judgments about what time horizon we most care about.

Second, scientific knowledge keeps moving, so understanding of environmental impacts changes over time. That’s an excellent thing for effective environmental policy, since it signifies that laws and policies will be based on increasingly accurate understanding of the thing being controlled. But when snapshots of today’s knowledge get written into laws or policies that can stay constant over time – as when GWP estimates from one source today get written right into a control that can stay on the books – there’s a tension between keeping regulations aligned with the very best current scientific understanding, and keeping regulations stable to limit regulatory uncertainty for long-term investments.

This tension may be very much alive in using GWPs to control. Various regulatory decisions – in several countries, and over time – have taken GWP estimates from some recent study or assessment report, then continued to make use of them without updating as scientific knowledge changes. Essentially the most outstanding issue has been a change over time wherein duration of GWPs are prioritized. In early days, the main target was on long-term climate control so most actions that used GWPs used a 100-year time horizon. Even the Paris Rulebook specifies 100-year GWPs, even though it also authorizes using other metrics (i.e., shorter time-horizon GWPs). And after all, because the Paris Agreement doesn’t specify any binding control levels, the alternative of metric doesn’t yet directly affect regulations. But over time, as views of climate change have shifted toward regarding it as an urgent crisis, near-term effects have develop into more necessary, so many assessments and regulations have shifted toward using 20-year GWPs, with the specific intention of prioritizing control of shorter-lived gases to cut back near-term heating.

Conclusions:

In conclusion, there are many good reasons for the present priority give attention to controlling methane. It’s a giant source of worldwide heating, second only to CO₂ and contributing a few quarter of the present radiative forcing from long-lived greenhouse-gases. It’s increasing rapidly, and latest scientific results are each showing its effect is larger than previously thought – because emissions from human activities, especially from oil and gas operations, appear to have been substantially under-estimated – and likewise suggesting where and most effectively goal controls, with increasing recognition of the massive contributions from a number of super-emitting sources and events.

This cuts each ways. On the one hand, continued expansion of natural-gas production at anything near present leakage levels could be seriously harmful, probably putting climate goals just like the Paris 1.5°C goal definitively out of reach. Conversely, the near-term advantages of controlling methane will be very large. One recent study suggested that additional feasible methane cuts could eliminate 20 to 45 percent of the gap between present commitments and the Paris goal, reducing heating in 2045 by nearly 0.3°C.

Finally, serious control of methane emissions appears to be technically tractable – because emissions are concentrated in a number of sorts of activities that admit of technological controls. Furthermore, lots of these controls can be low cost. A recent study from the International Energy Agency estimates that three-quarters of present emissions from the oil and gas sector will be reduced with presently available technology, and that 40 percent of those cuts would carry zero or negative net cost. It’s ironic that that attractiveness of control arises because natural gas is a invaluable fuel that the most important emitters are already within the business of selling, but hey, I’ll take it. That also implies, after all, that the fraction of cuts that will be costless or profitable will depend on the value of gas. The IEA also estimated that the massive drop in gas prices that occurred during 2020 temporarily brought that no-net-cost fraction down from 40 percent to 10 percent.

That is all much-needed, relatively excellent news, but don’t be misled. All this well-deserved attention to the second-biggest source of worldwide heating doesn’t mean that the imperative for strong motion is reduced for the most important source, CO₂. Methane is one slice of the reduction pie, but the entire pie must be eaten. It’s lucky that methane controls are immediately available and comparatively easy, but that is only a down-payment on the required total reduction

Climate Change, climate science, Greenhouse gas emissions