I really have no idea how they're calculating that other than a lot of hand-wavy math. It will vary greatly depending where you are. If I'm in Vancouver and I access CDN or hosting resources from a massive datacenter located in WA or OR, it's highly likely that 98% of the energy for my home, and all of the telecom/ISP sites in between, and the datacenter itself are all hydroelectric powered.

That power could be used elsewhere in your power grid. It probably makes sense to look at CO2/kWh averaged over the whole grid.

Despite our government repeating it over and over, it turns out that Hydro is actually worse than all fossil fuels in terms of GHGs (over double coal) depending on what you flood. If it's forest, it's the worst. For the W.A.C Bennett dam in BC, 350,000 acres of former forest land was flooded.

That would be a strong argument against new hydropower projects, but now that those dams are built, it seems like we have sunk costs (pun not intended) that would make it a bad choice to decommission, if we'd have to wait 100yr for the forests to begin to recover? That seems to jibe with critical studies I see [1].

1: http://blogs.edf.org/energyexchange/2019/11/15/long-consider...

That's not true. Decomposition of trees happens over a long period of time in a anaerobic environment. That's what causes the large methane emissions.

I see, that makes sense - though then it'd be a comparison of energy and emissions already put into the making of the dam, the power it outputs (which could otherwise be from fossil fuels) and the atmospheric impact of those methane emissions. My instinct would be the impact of pouring all that concrete etc. would be very large, so decommissioning would still be very costly, but it does strengthen the argument against new dam projects.

Honestly, compared to the ongoing methane releases from some of the worst offending dams, the concrete emissions are negligible.

> it turns out that Hydro is actually worse than all fossil fuels in terms of GHGs

That's a bad comparison. You can't simply compare them without any context.

Hydro has a one-time high carbon cost, while fossil fuels have a small ongoing cost. You can't simply state that one is better than the other, you need at minimum to restrict the comparison into a time-frame.

(By the way, nobody does a large hydro project without first cleaning out the previous vegetation nowadays. Historical data isn't good either.)

It's not a one time cost is what I'm saying. The trees in the forest that is flooded decompose slowly, and release methane the entire time. Specifically to BC, the entire ecosystem also got screwed, the fish in tributaries, up and down from the dams have mercury poisoning.

It is a constant amount emitted, for generating power during the entire lifetime of the plant. While fossil fuel plants emit an amount that is proportional to the power they generate.

How is that helpful though? They're basing it on the dams actual theoretical use. If they don't use it, the emissions will still occur, but we get nothing from it.

It's absurd to claim that every hydroelectric dam is causing emissions from rotting trees. The land flooded by the Grand Coulee dam was not forested. The area it flooded looks pretty much like the area you can see around it today in google earth, desert scrub land.

The area flooded by the Hoover dam was not forested.

The area flooded by the Glen Canyon dam was not forested.

I could go on...

I didn't make that claim. If your read what I wrote it specifically says "depending on what you flood."

You're also wrong about the Grand Coulee dam. Didn't bother checking the others.

"In late 1938, the Works Progress Administration began clearing what would be 54,000 acres (220 km2) of trees and other plants."

OK, but it's not being re-flooded constantly, it's already done and can't reasonably be undone.

So, long-term, it's a fantastic renewable resource with practically zero emissions.

See sibling comment. Practically zero emissions is false. It results in over double the GHG emissions per year than a coal fired plant producing the same amount of energy.

That is crazily misleading.

For the initial construction, yes. Ongoing? No.

At a point in time, the amortized emissions become zero.

It's not misleading. The vegetation that is flooded decomposes anaerobically and releases methane. So there's an ongoing release over the years that it decomposes. They've measured these emissions at different dams over time, and the worst (where forest is flooded) results in nearly 2.5 times the GHG emissions as the worst coal plants.

For instance the Balbina hydroelectric reservoir in Brazil was responsible for 39000 tons of methane each year (https://www.researchgate.net/publication/252089237_CO2_emiss...)

That was a 2011 paper on a dam that was finished in 1989.

That is still misleading, grossly.

More happens in the water than just releases of methane - there's plant and animal life producing oxygen and consuming decomposing materials.

Plus 1989 is a brand new dam. The Hoover Dam was completed in 1936[1], and is expected to have a service life of at least 10,000 Years.[2]

10,000 years at a minimum. It will have paid dividends in renewable energies so many times over by then, that it's not even worth discussing.

Do you think the solar panels installed on your roof will last 10,000 years? Will they even last 10 years without needing replacement or repairs?

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

[2] https://delzottoproducts.com/2017/03/15/long-will-take-concr....

How is it misleading? Explain please.

What I see is a 250MW dam built in 1989, that produces in 2011 the equivalent GHGs of a 1000MW coal plant.

And at a point will not produce equivalent GHG's, which your coal plant will continue to do so.

The coal plant won't even be able to operate in 10,000 years, this dam will continue to do so.

Do you even read your own links? There's no way the dam will be operating in 10,000 years time.