How long would one of those have to generate electricity to make up for its own construction? 10,000 tons of concrete and steel probably cause quite a lot of CO2 pollution to make.
The steel used was by and large the biggest energy cost.
> At a dam in Brazil, where the flooded basin is wide and the biomass volume is high the methane produced results in a pollution potential 3.5 times more than an oil-fired power plant would be. A theoretical study has indicated that globally hydroelectric reservoirs may emit 104 million metric tonnes of methane gas annually [2].
There is no green gas free energy only different cost, even nuclear. But maybe we can reduce emissions and some day catch them back.
[1] https://en.wikipedia.org/wiki/Life-cycle_greenhouse_gas_emis...
[2] https://en.wikipedia.org/wiki/Environmental_impact_of_reserv...
https://en.wikipedia.org/wiki/James_Bay_Project#Mercury_poll...
Except the carbon in that methane comes the atmosphere so the the long term global warming impact of existing dams is approximately zero.
Now increasing methane production can have an impact, but it just doesn’t stack linearly like CO2 does.
Add that to the fact that methane is 84 times better at trapping heat within the atmosphere than C02. Most methane production from Hydro isn't even counted because it's considered green.
All the methane for the last N years is decaying as you move forward. Say at day 1 you released X methane that’s being directly added to the global total. Now move forward to day X0,000, in some ways your adding X methane but because a little methane is decaying from every prior day the net result is not an increase of X, but an increase of X * 1/2^(some number that keeps increasing).
So, sure the hover dam is adding net methane. But after 84 years it’s less than 1/2 ^(84 /9.1) or 0.17% as much as directly measured. Further, the GWP of methane is calculated under the assumption it released from the ground where most sources like cows are releasing Carbon and Hydrogen that used to be in the atmosphere in the first place before photosynthesis etc eventually turned it into methane.
Also, unlike CO2 it’s really easy to reduce considerations simply by lowering emissions.
PS: I have seen several estimates around 7 years, I used 9.1 because the exact number isn’t that important.
> Warm climate reservoirs generate methane, a greenhouse gas when the reservoirs are stratified, in which the bottom layers are anoxic (i.e. they lack oxygen), leading to degradation of biomass through anaerobic processes.
In warm climate it is methane generator, biomass constantly added with river flow.
The issue is you don’t get an accurate number for the amount of methane in the atmosphere from a dam by multiplying average annual methane release by the number of years it’s in operation. Thus the the rate of doesn’t correlate to future global warming making such statements absolutely meaningless.
PS: Also, all of this is assuming the study adjusted for what happens when the dam is not there and nearly the same process occurs when the river dumps into an ocean somewhere.
Methane does not return upstream only, river flows into ocean, open system.
My argument supported by published article and nice picture, look at sediments [1].
Your argument "calculated yearly is not yearly", maybe you should bring some citations, maybe it is you who do not understand what is described.
[1] https://en.wikipedia.org/wiki/Ocean_storage_of_carbon_dioxid...
https://phys.org/news/2019-10-global-ocean-methane-emissions...
Dams are collecting the exact same sediments that would end up in estuaries and as that article points out some of that is then turned into Methane.
Natural methane is just part of the carbon cycle. It’s generally ignored in oversimplified explanations like you just linked.
> In deep waters, methane is likely to be oxidized as it travels its long route from the seafloor to the atmosphere.
Coastal waters emissions does not imply all biomass. Open system — what escapes to deep waters stays there. Quote above implies dam water is warmer.
Most sediment collected by dams ends up there because it weighs more than water and so filters out as soon as the water stops flowing. As rivers reach the ocean that process generally produces vast and very shallow silt deposits. https://en.wikipedia.org/wiki/Estuary You can even read about what happens in dam removal when that same sediment flows down stream and ends up very near the surface. There are some very striking images of this processes when muddy flood water reaches the ocean.
PS: Also by deep water their talking miles deep. Dead fish end up falling miles in most of the ocean.
Turbine gets water not from the surface. There was a project to extract enough methane to increase energy production.
What is this based on? The dams producing the most methane have actually flooded forests without removing the trees.
As to peak methane production, yea that seems reasonable. Though a great many dams didn’t cover forests, so the extremes aren’t representative of the average.
But until we can set a market price for CO2 emissions, current emitters will continue to treat it as a zero-cost externality.
I thought it was up there with smelting.
E.g. If you bought coal/gas for the cost of the project how much co2 and energy would you produce.
Most estimates are about 3 to 6 months to recover energy used to produce a wind turbine.
Still there and working today!
https://www.energyvoice.com/opinion/92008/forties-at-40-the-...
The steel cables holding up the suspension bridge Golden Gate Bridge in San Francisco (87 years old), clouded in fog and arguably one of the harsher saltwater environments (near-constant 20mph winds 8 months out of the year) is still using it's original steel cables, and there are no plans to replace them.