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Comment by soperj | Hacker News Reader

Not to mention some of it's hydropower is dirtier than coal in terms of methane & co2 produced.

https://www.newscientist.com/article/dn7046-hydroelectric-po...

Isn't this just cycling carbon in ecosystem? Same as planting tree on 100 year scale is pointless... I would imagine that hydro is ~neutral on 100 year scale, while coal is not, since we introduce carbon into ecosystem. What am I missing?

Produces methane, not CO2 because the plants decompose in an oxygen free environment. Because of the cycling of water throughout the year, during the dry seasons plants grow along the shoreline (which varies considerably because of the use of hydro), and then are covered up during the rainy season. This can be hundreds of kms every year.

Methane isn't great, but unlike CO2 is has a pretty short lifetime in the atmosphere (just 12 years). So the impact of the methane release from hydro is basically static rather than an ever increasing problem.

This is not true! Methane is not only 84x more warming than CO2, it is at a record high at <1900ppb and rising, the current level is higher than the RCP 4.5 warming scenario by the IPCC (which is in the middle level of a warming scenario), and there is evidence that the atmospheric lifespan might be increasing

This is what my quick google turned up [1].

> A molecule of methane traps more heat than a molecule of CO2, but methane has a relatively short lifespan of 7 to 12 years in the atmosphere, while CO2 can persist for hundreds of years or more.

Doesn't mean it's correct though so I'd be happy to see different thinking on this.

That being said, IIRC, isn't one of the models for the increasing methane the melting permafrost [2]? So the levels are somewhat expected to be increasing pretty rapidly as a result of global warming in general.

[1] https://climate.nasa.gov/vital-signs/methane/

[2] https://earth.org/data_visualization/what-is-permafrost/

https://climate.mit.edu/ask-mit/why-do-we-compare-methane-ca... "Over 20 years, the methane would trap about 80 times as much heat as the CO2. Over 100 years, that original ton of methane would trap about 28 times as much heat as the ton of CO2."

So converting a bunch of atmospheric CO2 to methane evey year is not good.

Well, shoot, that's awful.

It's continuously releasing methane, and methane degrades into.... CO2.

> So the impact of the methane release from hydro is basically static rather than an ever increasing problem.

You can also say the same thing about the coal plant.

It is not dirtier. In the first week of operation it is dirtier, but then at some point it crosses a threshold and becomes permanently less dirty. As that article you link to attests.

Uh, no. Nowhere in that article do they mention coal. Not do they do not do a comparison of hydro plant and fossil fuel plant emissions per megawatt-hour generated.

If scientists can't agree on the impact of methane, they probably can't say whether it is worse than coal or not.

https://en.wikipedia.org/wiki/Balbina_Dam

"As a result of the methane released from its vast reservoir, proportional to its output, the Balbina Dam emits ten times more greenhouse gases than a coal plant."

This is going to depend very heavily on where the dam is placed. Balbina is particularly bad because it sunk a ton of organic material with a bunch of acreage taken up.

Almost a worst case for a dam really.

Yes he is using as an example what is probably the most inefficient dam in the world.

I don't know that the dams in Canada are any better in terms of sunk organic material Williston reservoir in BC and the Manicouagan Reservoir are nearly as big and they didn't clear either of them. The Smallwood Reservoir is 3 times the size of Balbina's.

That’s extremely misleading to the point of being false. The dam is creating zero carbon and Methane breaks down to CO2 which is then counted as part of its global warming impact on some timescale.

When you remove the dam the total global warming impact from all the methane produced over a ~100 year lifespan quickly goes to 0. That doesn’t happen from a coal power plant.

~100 years still too late. In 2050 we already risk catastrophic impacts if we keep business as usual.

It began operating in February 1989 making it 35 years old and thus it’s currently adding in effect 1/8th the net methane as year one and that keeps dropping every year. As only ~13% of the methane it released 35 years ago is still around.

We can reduce atmospheric methane by a trivial amount if we removed it early, but it would currently be replaced by fossil fuels a net loss for the environment.

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