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Comment by Merrill | Hacker News Reader

>Methane, by contrast, is mostly removed from the atmosphere by chemical reaction, persisting for about 12 years. Thus although methane is a potent greenhouse gas, its effect is relatively short-lived.

https://www.theguardian.com/environment/2012/jan/16/greenhou...

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And then it breaks down to CO2. That is a basic and well understood part of climate science, that’s how the calculations are made which show an 80 fold higher impact for Methane per unit mass than for CO2 over a 20 year period, and 20 fold higher impact over a 100 year period.

As the climate scientist says in the article, this doesn’t disprove mainstream climate science, and the calculations are correct but banal, and just presented in a way to give a misleading impression of a smaller impact. The author is quite open about preparing the paper specifically to give ammunition to efforts to roll back Oil and Gas regulations.

"per unit mass" is the operative term since there is far far less methane being emitted.

Methane was only relevant because it was such a strong greenhouse gas. As CO2, it becomes just a drop in the bucket.

It becomes in combination 80 fold higher over 20 years and 20 fold higher over 100 years, per unit mass.

Incidentally the reaction from Methane to CO2 produces 2.5 times more mass of CO2 than the Methane it starts with, which is one reason why the impact remains quite high. And of course everyone knows Methane emissions are relatively low, otherwise given their potency their effect on GHG warming would be a lot more than the 15% of thereabouts which it is at the moment.

This is all like attacking an IPCC claim that the sea level is going to rise by 1m over 100 years by saying it won’t rise by 5m, but by on average 1cm a year for 100 years. We know that already.

What exactly are you trying to say with this? The tone of your comment sounds as if you're trying to disagree with your parent comment or somehow put it in perspective, when in fact you're just stating a related fact that is totally compatible with it.

Methane is 16.04 g/mol and CO2 is 44.01 g/mol. PPM of CO2 is 415 and PPM of Methane is something like 1.8 PPM.

Increase in CO2 is something like 15PPM/decade. Increase in Methane is 0.1PPM/decade (or less).

So in absolute terms, the relative effect of Methane compared to CO2, using the 80x figure is (1.8 * 16 * 80) / (415*44.01) = 12.6%.

And in growth terms, the relative effect of Methane is 19%.

However, since methane is limited by total land under cultivation, and it has actual hit a stable PPM in the last decade (unlike CO2 which grows exponentially), CO2 is by far the larger component in any climate models projecting into the future.

In conclusion, Former White House adviser can actually math while your 80x figure needed to be put into context. I do not know where you get your information from, but I expect that it is from someone trying to make a tendentious environmental case against cows more than it's about someone trying to present unbiased facts.

since methane is limited by total land under cultivation

This isn't true. There have been numerous stories of methane stores (e.g. Siberia) that have begun leaking in recent years.

Don't get your news from the places peddling that stuff. Here is what CH4 has been doing since 1985 (notice ppb, not ppm):

https://imgur.com/gaKEU3g

Historical data can't refute an argument about future melting permafrost...

An argument without any data can't refute an argument with historical data, either.

You don't disagree with me on the science. Methane has a limited half life, this is well understood and built into the models. You are repeating the science as if it were different, and then drawing different conclusions from it.

I don't see what the absolute numbers have to do with whether or not oil or gas installations should be able to vent a particular quantity of methane.

Or why it matters that another unrelated source of Methane is limited. If cattle produced a similar but different molecule that would reduce the Methane absolute numbers dramatically, but in reality would have no impact on the question at hand. This is all like saying that driving a car in North Dakota matters less than in California, because North Dakota has lower total absolute emissions. It is sophistry.

To summarize your comment, you're calculating that methane contributes around 12% to atmospheric heat trapping (when only considering methane and CO2), and conclude that it is therefore irrelevant.

I don't think your own calculation supports that conclusion.

CO2 is growing exponentially. CH4 is not. If CO2 were stuck at the current level forever, nobody would care about global warming. It's future expected doublings that are driving the danger scenarios.

Let me make it extremely simple: there are future expected doublings of CO2 ppm, but there are none for CH4. The share of warming for CH4 compared to CO2 is low and will only get lower.

The NOAA Global Greenhouse Gas Reference Network [1, 2] is a great resource for this. Their data on methane goes back to 1984, so I compared methane and CO2 concentrations in the 1984-2019 time frame. In this time frame, the atmospheric CO2 concentration grew by 19.7% (from 344 to 412 ppm), the concentration of methane grew by 14.7% (from 1630 to 1870 ppb).

So, you're right that CO2 is growing a bit faster, but the difference really is rather small.

In addition to this, there are highly nonlinear effects that may occur in the future that others have alluded to, such as the clathrate gun hypothesis [3]. Even in the absence of such dramatic effects, you would expect methane levels to further increase with increasing meat consumption in countries that are getting wealthier (e.g. in India, China).

Edit: I should also point out that the claim that only future doublings in CO2 concentration matter is totally wrong. Even in the IPCC report's worst case scenario, CO2 concentrations will grow to ca. 1000 ppm by 2100, just over a single further doubling [4]. In the best case scenario, they stabilize a bit under 500 ppm, which is just another 20% increase from today. In that best case scenario (B1), global temperatures are still expected to rise by slightly more than 1.5°C by 2100 [5]!

[1] https://www.esrl.noaa.gov/gmd/ccgg/trends_ch4/

[2] https://www.esrl.noaa.gov/gmd/ccgg/trends/

[3] https://en.wikipedia.org/wiki/Clathrate_gun_hypothesis

[4] https://en.wikipedia.org/wiki/File:Projected_changes_over_th...

[5] https://www.ipcc.ch/site/assets/uploads/2018/02/ar4-wg1-chap... (Fig. 10.4)

  CO2 is growing exponentially.

No, it isn't. 68 parts per million in 35 years isn't remotely "exponential" growth. It's roughly half a percentage point a year.

Meaningful, yes. Exponential, not hardly.

Saying it is a few percent per year is proof that it is an exponential growth, per its definition.

That why we look at the "global warming potential" [1]. But even with a time horizon of 100 years, methane is still 30 times potent than CO2. How can it be irrelevant?

[1] https://en.wikipedia.org/wiki/Global_warming_potential

The numerator integral must decline rapidly as a function of TH unless the radiative efficiency is a strong function of time, which seems unlikely. Most of the actual warming effect of a methane release would occur in the first three decades, after which there would be a long tail of slight warming. Methane is not irrelevant, but "global warming potential" seems to obscure the actual time varying nature of the relative impacts. Methane is actually a much stronger greenhouse gas than carbon dioxide in the short run and less strong in the long run that global warming potential would indicate.

30 times more potent for a similar mass. But we emit far far more CO2 than methane. To know if it's important you'd need to know by how much.

Well, methane is one the reasons why livestock and paddy fields emit so much greenhouse gases. These two examples are not insignificant.

Significance is almost beside the point. Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels. This "methane is worse" proposition was used to argue that livestock production is as bad as burning fossil fuels, but of course that completely falls apart if the main problem with methane is the carbon dioxide into which it degrades. That carbon dioxide may have been methane for the last 12 years, but immediately before that it was grass and immediately before that it was the same existing carbon dioxide that it is again now. There isn't something magical about a cow's gut that somehow multiplies carbon levels.

This has always been my thought as well, and I have never gotten a good explanation as to why it's wrong. If anyone has one I would love to hear it.

It was explained to me as: "even if an activity is carbon neutral, if it increases the net free atmospheric carbon it can have a negative effect."

The areas we devote to cattle raising are increasing (often at the cost of carbon fixing native flora). So the amount of free methane and carbon are on the rise just by nature of human expansion.

I'm not sure that is the whole story, but I always found that explanation helpful for questions like, "Why can't we switch to using charcoal based local power if its carbon neutral?"

You are right saying that the carbon cycle is a closed cycle, there is no net change over time in carbon dioxide concentrations (as you are not using fossile fuels or burying grass). But during the 12 years lifespan of methane you will have considerably more radiative forcing.

> Any methane "emitted" by livestock is already present in the carbon cycle: cows eat grass which is made of atmospheric carbon. It isn't sensible to compare that to carbon from fossil fuels.

Considering that:

a. most cows in today’s world don’t eat grass, or rather, they eat a lot more soy, corn and other foods grown for them

b. the feed for the cows is grown using conventional methods to keep costs under control, which also implies using fertilizers that are produced from fossil fuels (also add the fossil fuels used in the transport of feed as well as the animals)

I don’t understand how your entire argument holds true. Seems like there are gaps in your model of the world.

With a traditional grazing system he's right. You don't need any fertilizers, cows will just eat grass. Of course you can't feed billions of people with it nor you will be able to eat meat every day.

But even if you are carbon neutral over time, the methane released will still have a negative effect as it trap more energy than CO2.

https://www.nzagrc.org.nz/faq-1,listing,464,how-do-livestock...

Most European cattle are grass fed, it's nothing to do with the amount of people you can feed with it. US and Canadian cattle are grain fed because the US grows huge amounts of subsidised grain and it's cheap. It really is that simple.

Some studies claim you get a sixth of the methane from grass fed cows.

Even USA herds mostly feed on grass or hay. Animals only go to the feedlots for a few months before slaughter. They do add a lot of mass in that period. Anyway, beef consumers can certainly vote on this topic. If you prefer the taste or morality of grass-fed beef, it's available for purchase.

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