[Latty]

This was my thought, methane is much worse than carbon when not burned, but just released. Any claims of carbon neutrality that rely on assuming perfect storage and transport without leakage are fantasy.

If anything, when you are calling it "easily transportable" at the same time, as they do, you are actively misleading. You can't have both: it's either easily transportable and you are accepting a bunch of methane released (and thus terrible for climate change), or it's carbon neutral and you are baking in the cost of making sure it doesn't leak in transport/storage (and thus not easily transportable). They are having their cake and eating it too by claiming both.

[__MatrixMan__]

I'd be interested in a quantitative analysis here. Methane is much worse, but sunlight has broken most of it down after a decade or so. CO2 is comparatively forever.

Presumably there's a point where the lines cross and leaking green methane is still a win. I guess it just comes down to where those lines cross and whether we deem that an acceptable goal.

[CrazyStat]

Sunlight breaks methane down into CO2, so I don’t think there’s much of a win there.

[__MatrixMan__]

But that methane "started" as CO2 in the atmosphere, so after the breakdown happens you're carbon neutral. Carbon capture and storage are still relevant topics, but "stop making the problem worse" is a good start.

If we all switched to still-leaky synthetic methane today, things would continue getting worse only until the atmospheric breakdown rate equalled the leak rate. That's still a decade of things getting worse, but it's possible that the alternatives are even more problematic.

I'm not saying it's the right or wrong path, I haven't done that analysis, I'm just saying that approaches to it could use a bit more pragmatism.

[scq]

Of course there is. CO2 and methane are not equally bad, methane is about 100x worse initially. After about 60-70 years the lines cross and the impact of a tonne of methane released is less than a tonne of CO2 released at the same date.

[CrazyStat]

> After about 60-70 years the lines cross

Methane's global warming potential is estimated to be ten times CO2 after 500 years [1].

> and the impact of a tonne of methane released is less than a tonne of CO2 released at the same date.

A ton of methane released into the atmosphere breaks down into 2.75 tons of CO2 [2]. There is no possible way that this statement can be true.

[1] https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6..., Table 7.15 (page 1017)

[2] Simple stoichiometry: CH4 (weighing ~16 g/mol) breaks down into CO2 (weighing ~44 g/mol) at a 1:1 ratio. 44/16 is 2.75.

[scq]

Seems I misinterpreted. The lines that cross are radiative forcing, not GWP.

Source: https://web.archive.org/web/20150116044523/https://www.see.e...

[__MatrixMan__]

Wow that table is over my head, I spent a fair bit of time trying to unwind the acronyms but I gave up.

Can you help me understand how a gas with a lifetime of 11.8 years is having a different impact on the climate at 500 years than it did at say... 11.8 years? That's 488.2 years of being in the same state as where it started prior to the carbon capture that made the CH4.

[CrazyStat]

1. 11.8 years is a halflife, not a "all the methane is gone after 11.8 years" lifetime.

2. Methane doesn't just warm the atmosphere up a little bit and then disappear with no side effects. In addition to carbon dioxide, methane decomposition creates ozone and water vapor, which are both greenhouse gases. The additional heating effects of these decomposition byproducts are also included in the global warming potential calculations.

3. We care about cumulative effects over time. GWP is "how much additional heat will the atmosphere absorb because of this gas over X amount of time", scaled relative to carbon dioxide (so CO2 always has a GWP of 1). Methane's GWP-20 is about 80, which means that if I release one ton of methane today, over the next 20 years it will absorb about as much heat as if I had released 80 tons of CO2 instead. The longer the time frame the less bad methane looks, because it mostly decomposes, but even over a 500 year time frame releasing 1 ton of methane absorbs as much additional heat as if you had released 10 tons of CO2 instead. GTP is similar to GWP except it's about how much global average temperatures will rise instead of how much heat is absorbed.

4. If you can create methane out of atmospheric CO2 for free, you can subtract 2.75 from each of the GWP numbers for methane (since you remove 2.75 tons of CO2 to create one ton of methane). This is essentially what the table is showing on the CH4-non fossil line (notice each of the GWPs on this line is 2.8 less than on the CH4-fossil line).

-----

Imagine I had a magical gas called timelockium. It is not a greenhouse gas (no radiative forcing), but after exactly 10 years it decomposes to an equal mass of CO2 with no other byproducts.

The GWP-10 for this gas would be zero: over the first ten years, releasing a ton of timelockium is equivalent (in terms of heat absorbed by the atmosphere) to releasing zero tons of CO2.

The GWP-20 for this gas would be 0.5: over the first twenty years, releasing a ton of timelockium is equivalent to releasing 0.5 tons of CO2. This is because it does nothing for the first ten years, and then for the next ten years it is just CO2 [1].

For longer time frames, the GWP of timelockium would approach 1. Over 500 years, emitting a ton of timelockium would be nearly equivalent (0.98) to emitting a ton of CO2.

---

Now I have another magical gas, decayium. It is equivalent to CO2 for 10 years and then magically disappears. Again it has no other side effects or byproducts.

The GWP-10 of decayium would be 1--over the first 10 years it's identical to CO2. Over the next ten years it contributes nothing to warming, so the GWP-20 would be 0.5. For longer time frames the GWP of decayium would approach 0. the GWP-500 would be 0.02.

---

Superdecayium is like decayium except much worse. It's equivalent to 100x as much CO2 for the first ten years and then magically disappears with no side effects or byproducts. The GWP-10 is 100. The GWP-20 is 50. The GWP-500 is 2.

This last scenario is more analogous to methane, except methane chemistry is much more complicated, with gradual decay and byproducts that are also greenhouse gases. Like superdecayium, methane's GWP decreases over longer time intervals, but even over 500 years it is still worse than an equivalent mass of CO2. ---

[1] For the sake of simplicity I'm ignoring CO2 dynamics here, assuming it's just static in the atmosphere.

[solid_fuel]

But that CO2 is then theoretically recaptured to make more fuel, right? At least if the carbon in the methane is sourced from the atmosphere in the first place.

[trueismywork]

You are conflating carbon neutral with global warming neutral.