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The 30% solution

24 Nov 2021 | News Roundup

It seems that natural gas is in for a quick trial and slow hanging despite Michael Mann’s reassurances that they’re imagining the whole thing and it serves them right. Long ago a colleague observed that if you throw a number into a media vacuum it starts to appear everywhere, regardless of whether it has a sound statistical basis or even a flimsy one. Journalists love numbers because they sound authoritative, and generally do not understand them at all. Including a new one that just appeared and looks set for a spectacular run. First “methane is responsible for about 30 percent of global warming to date” according to New Scientist on Nov. 2. Then “Methane is responsible for around 30 percent of the global rise in temperatures to date” according to Canada’s Minister of Natural Resources on Nov. 18. A month ago it was nowhere. Look for it to be everywhere in a month as the cool kids don’t follow trends, they make them, in herds. And don’t look for journalists to ask “How do you know” or anything party-spoiling of that sort.

We should probably be grateful for the “around” and “about” in those two formulations since normally you get a decimal place not an admission of uncertainty. On the other hand that “to date” is a real sockdolager. To date from when? Does it mean since 1950? Since 1650? Since 1250? Since 49 BC? If it really is a calculation the answer should not be hard to find.

An inquiry to the Natural Resources ministry went unanswered as of press time. But other interesting questions present themselves to the inquiring mind. For instance, is methane responsible for 30% of all warming or just of the human proportion? And how do they tell which is which? Also, is the problem all methane or just the human-generated portion? Is methane from natural sources perhaps responsible for 30% of the natural warming and methane from human-sources responsible for 30% of the anthropogenic warming? Or is it some other proportion? Surely natural methane does not do no warming at all while the human kind travels like a burning flame.

Curiously, the Globe & Mail just poured scorn on “the fuel currently responsible for about 30 per cent of the world’s carbon emissions”. But they meant coal. And one way to make such a calculation would presumably be simple: by weight of carbon molecule. But unfortunately emissions and warming aren’t the same thing… are they? Are all carbon outputs created equal?

People are remarkably casual in talking about “carbon emissions”. Or “carbon pollution”, but one complaint at a time. The point here is that in fact the measure in question is “CO2 equivalent”. Which means? Again you would not want to surprise most climate reporters with that question. Is a gram of carbon dioxide (CO2) as bad as a gram of methane (CH4) even though the molecular weight of the former (44.01 g/mol) is nearly three times that of the latter (16.04 g/mol) because two oxygen atoms vastly outweigh four puny hydrogens? Or is enough carbon dioxide to contain one gram of actual carbon as bad as enough methane to contain one gram of actual carbon? And what about baddies like sulfur hexafluoride (SF6) that contain no carbon at all?

Glad you asked. See, according to the British “Department for the Environment, Food & Rural Affairs” (yes, it’s one ministry), “Carbon dioxide (CO2) equivalent is a measure of how much a gas contributes to global warming, relative to carbon dioxide. You calculate the carbon dioxide equivalent of a quantity of F gas by multiplying the mass of the gas (in tonnes), by the gas’ global warming potential (GWP).” Oh, just that? It’s GWP? Yes. See for instance “the global warming potential of HFC 404A is 3,922. Therefore the tonnes CO2 equivalent of 10kg of HFC 404a is calculated as follows: Mass (in tonnes) of F gas multiplied by GWP of F gas = (10/1,000) * 3,922 = 39.2 tonnes CO2 equivalent.”

Sorry you asked? Maybe you should be, because all this hocus pocus depends on them knowing the GWP of the HFC to… say… four digits. Man, that’s precision. Or pseudo-precision. Especially as GWP hinges not just on how long a molecule hangs around before something happens to it like reabsorption or a chemical reaction (and if the latter what it turns into and so forth) but on the mind-bogglingly complex business of absorbing and emitting radiation at various points on the spectrum. And on a bunch of assumptions you put into your computer model and then come back with no visible error bars.

Bear in mind that it’s all basic high-school physics. Because otherwise you might be puzzled that the U.S. Environmental Protection Agency says “Methane (CH4) is estimated to have a GWP of 28–36 over 100 years” before inviting you to “Learn why EPA’s U.S. Inventory of Greenhouse Gas Emissions and Sinks uses a different value” while Wikipedia gives it as 56, 72, 84/86 and 96 over… um… the same 20-year period and 21, 25, 28/34, 32, 39 and 40 over a century.

In Canada we farmed it out to the IPCC and got 21 over a century in the 2nd Assessment report and 25 in the 4th. But at Climate Change Connection they did something else and got “Releasing 1 kg of CH4 into the atmosphere is about equivalent to releasing 84 kg of CO2” except it’s not because “Methane’s 100-year GWP is about 28x CO2 – but it only persists in the atmosphere for a little more than a decade. The 100-year GWP is used to derive CO2e.” So it’s a game anyone can play, with no obvious boring rules.

Fear not. Canada’s Minister of Natural Resources knows all this stuff because he too used to be our Minister of the Environment before the Greenpeace scofflaw with the train tour got the job. Also he is a former Rhodes Scholar with a degree from Oxford University in… um… “international relations, politics, and economics”. So 30% it is, with 97% of scientists agreeing that 99.9% of them agree that we’re all going to die.

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