Comment by photochemsyn | Hacker News Reader

Comment by photochemsyn | Hacker News Reader

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This is a bit overblown. The methane being emitted is sourced originally from atmospheric CO2 via photosynthesis, and while there is some anaerobic production of methane in rice paddies, the methane gets converted back to CO2 in the atmosphere with a half-life of 10-20 years IIRC.

This is fundamentally different from natural gas emissions, in which carbon atoms are being transferred from stable geological reservoirs into the atmosphere, where they increase the CO2 levels after the methane is oxidized.

There are also other risks to switching to this cultivation method:

> "Researchers note potential risks. Because PR23 enables farmers to till less, fungi and other pathogens can build up in the fields. Insects can persist in the stubble after harvest, because it’s not plowed under, then transmit viruses when they feed on the regenerating sprouts in the spring. And without tilling, weeds can flourish; the researchers found that fields with PR23 needed one to two more herbicide treatments than regular rice. They also note that it’s more work to resow the perennial rice when its yield falters, because its larger and deeper roots need to be killed."

https://www.science.org/content/article/perennial-rice-saves...

Atmospheric methane has a half-life of about 10 years and is well over 10x as greenhouse effecting as CO2. Converting atmospheric CO2 to atmospheric methane is less bad than releasing sequestered methane into the atmosphere but still terrible.

> Converting atmospheric CO2 to atmospheric methane is less bad than releasing sequestered methane into the atmosphere but still terrible.

Sure, if this conversion led to more and more methane in the atmosphere, it would be terrible. In this case, however, the overall amount of methane in the atmosphere due to rice will stay the same, since it's a cycle.

It's all about cycle length. CO2 from shallow ground cycles into the air, then it quickly cycles back into the ground. The forest burns, the forest regrows. CO2 leaves, CO2 returns.

Fossil fuels are also a cycle. We bring up the fossil fuels from deep ground and a million years later that CO2 returns to deep ground. That's a long cycle, that's a problem.

Isn't it the case that a lot of fossil fuels were biomass accumulated in a time before microorganisms had evolved to be capable of digesting woody plants and so are largely non-repeatable because the circumstances which can lead to coal are now narrower?

> and while there is some anaerobic production of methane in rice paddies, the methane gets converted back to CO2 in the atmosphere with a half-life of 10-20 years IIRC.

Methane is a far, far worse greenhouse gas than CO2, even accounting for the fact that it eventually decays back to CO2.

Methane is something like 25 times as effective at absorbing outgoing infrared radiation in the Earth's atmosphere relative to carbon dioxide, but there is > 200 times as much CO2 in the atmosphere as methane (1.9 ppm vs 420 ppm).

https://www.noaa.gov/news-release/increase-in-atmospheric-me...

So the net effect of all the methane is about 50 ppm. About 30% comes from fossil fuels. This leaves a big burp relative to preindustrial levels (comparable to 20 ppm CO2), likely from the expansion of human agriculture, more cows, maybe forest removal.

We're locked into it now due to permafrost melt and increased rainfall in to the tropical belt, swapping out one strain of rice for another will have marginal effects at best.

> "NOAA scientists are concerned that the increase in biological methane may be the first signal of a feedback loop caused in part by more rain over tropical wetlands that would largely be beyond humans’ ability to control."

The tipping point has come and gone, we're heading for the Pliocene. Plan accordingly.

And melting permafrost.

And liquifying undersea methane hydrate ice.

> Methane is something like 25 times as effective at absorbing outgoing infrared radiation in the Earth's atmosphere relative to carbon dioxide, but there is > 200 times as much CO2 in the atmosphere as methane (1.9 ppm vs 420 ppm).

No, this is incorrect. The number you cite (25x) is a 100-year global warming potential (GWP) figure. That is, if I release 1 ton of methane into the atmosphere today, over the next hundred years it will contribute to global warming about as much as if I'd released 25 tons of CO2.

But this is not an appropriate way to analyze the composition of the atmosphere at a point in time. We're not releasing 1.9 tons of methane and 420 tons of CO2 and looking at how that will effect global warming over the next 100 years. Instead we're looking at the CO2 that has built up over the past few hundred years, and the methane that has built up over the past few decades, and looking at how that affects global warming now. We want to integrate over past contributions and look at the resulting warming at a point in time rather than look at emissions at a point of time and integrate over future warming.

The effect of methane when you look at it this way is much higher. The IPCC estimates[1] that methane radiative forcing (i.e contribution to global warming at a point in time, based on current atmospheric concentration) is about 0.48 W/m^2, vs. 1.82 W/m^2 for CO2. That is, the ratio of (warming due to methane) to (warming due to CO2) is about 1:3.8, not 1:8.4 (50 ppm:420 ppm from your calculation). More than twice as bad as the calculation based on GWP!

The good news is that since methane has a short half life, if we can cut methane emissions that portion of the total radiative forcing will respond quickly (1-2 decades). Cutting CO2 emissions takes much longer to show effects.

[1] https://www.ipcc.ch/site/assets/uploads/2018/02/WG1AR5_Chapt...

Look, the only plausible route to stabilizing the atmospheric chemical composition is to stop pumping carbon out of geological reservoirs into the atmosphere.

That's really all there is to it, you have to eliminate fossil fuels from the system if you believe climate change is a real issue.

Of course, at this point, even that won't stop the climate from steadily warming for the rest of your life, i.e. for the next 100 years at least. The trigger has been pulled.

I advise against buying property on the coasts, in flood plains, etc.

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