New Sci Fi Setting Seeds

[PTTG]

Problem with any geoengineering proposal that reduces insolation: food crops are going to take it in the shorts.

[Astromancer]

The sea thermal power plants, which pull up cold oxygen and nutrient rich water to the surface, and thus generate vast amounts of biomass, suck down atmospheric carbon. As safe a geoengineering project as I can think of.

[AlexanderHowl]

That would actually be counterproductive. Unlike carbon sequestration in soil, which locks carbon in the form of organic material in the soil, the oceanic biomass releases methane and carbon dioxide when it dies and starts to decompose, storing much less carbon than even one tenth the equivalent area of land. It is much better to allocate the resources to land carbon sequestration or even atmospheric extraction since you will get more bang for your buck. It took us a couple centuries to get to this point, it really is not possible to reverse the damage in less than fifty years.

[TGLS]

But only after sinking into the cold waters and remaining there (or below) for hundreds of years. Besides that, increased production of dimethyl sulfide could increase cloud coverage and further slow warming.

[AlexanderHowl]

What cold waters? Remember, the entire point of the geoengineering was bring up the cold water to the surface, so the organic material will decay on the surface. In addition, creating billions of metric tons of dimethyl sulfide every year is not an acceptable.

[malloyd]

Originally Posted by AlexanderHowl

What cold waters? Remember, the entire point of the geoengineering was bring up the cold water to the surface.

What keeps it floating while it decays? You bring deep cold water up *above* deep cold water, so anything that dies near there and sinks....

[AlexanderHowl]

Anyhow, there are energy limitations to pumping that much water. The oceans contain 1.335 billion cubic kilometers of water, or 1.335 quintillion (US) metric tons of water. If you want to circulate enough water to allow for increase growth on the surface of the oceans, you would need to pump 1% of the water every year, averaging a flow rate of around 1.5 trillion metric tons per hour, which would be pumped from an average depth of 1 km.

The pump power calculation for a perfect pump is Ph(kW) = q * ρ * g * h / (3.6*10^6). 'q' is flow rate in metric tons per hour (~1.5 trillion), 'ρ' is the density of the fluid in kg per meter cubed (~1000), 'g' is gravity in meters per second squared (9.81), and 'h' is the differential head in meters (1000). The required power ends up being ~4.1 PW of continuous energy. A more realistic pump with a 60% efficiency would require ~6.8 PW of continuous energy.

With an estimated average wholesale electricity price of $48/MW-h (a workable average based off average wholesale electricity prices on the USA in 2017), that would mean that the scheme would require ~$2.9 quadrillion worth of electricity per year. While renewable energy prices are going down for consumers, that is largely due to generous subsidies given by their governments (either before purchasing through grants or tax breaks or after purchasing through buyback prices or tax credits), which would dry up long before renewable energy was capable of producing 68 TW, much less 6.8 PW. While it might not be as elegant, vaporizing mountains is probably a more feasible solution to buying time.

[Daigoro]

Originally Posted by AlexanderHowl

The required power ends up being ~4.1 PW of continuous energy. A more realistic pump with a 60% efficiency would require ~6.8 PW of continuous energy.

From the link that Astromancer helpfully provided:
The resource potential for OTEC is considered to be much larger than for other ocean energy forms [World Energy Council, 2000]. Up to 88,000 TWh/yr of power could be generated from OTEC without affecting the ocean’s thermal structure.


ETA:
Oops, those aren't equivalent units. Convert that "h/yr" bit and you get 10TW, but that's "free" energy in regards to your calculation. It's pumping water to generate electricity, not using electricity to pump the water.

And in any case, 1% of all the ocean's water seems like a spurious calculation. First figure out how much sequestration could be processed by the OTECs described, and see if it makes a dent in the carbon load.

[Astromancer]

Originally Posted by Daigoro

From the link that Astromancer helpfully provided:
The resource potential for OTEC is considered to be much larger than for other ocean energy forms [World Energy Council, 2000]. Up to 88,000 TWh/yr of power could be generated from OTEC without affecting the ocean’s thermal structure.


ETA:
Oops, those aren't equivalent units. Convert that "h/yr" bit and you get 10TW, but that's "free" energy in regards to your calculation. It's pumping water to generate electricity, not using electricity to pump the water.

And in any case, 1% of all the ocean's water seems like a spurious calculation. First figure out how much sequestration could be processed by the OTECs described, and see if it makes a dent in the carbon load.

My assumption was that the nutrient and oxygen rich cold water when brought to the surface, would, once sunlight hit it, be a great place for algae to grow. Fish would eat the zooplankton and other organisms that would thrive with the algae. Then the fish, in W.C.Fields memorable words would "Function." This would send carbon to the bottom. Dying plankton and other organisms sinking into the abyssal depths would sequester carbon.

[Daigoro]

Originally Posted by Astromancer

My assumption was that the nutrient and oxygen rich cold water when brought to the surface, would, once sunlight hit it, be a great place for algae to grow. Fish would eat the zooplankton and other organisms that would thrive with the algae. Then the fish, in W.C.Fields memorable words would "Function." This would send carbon to the bottom. Dying plankton and other organisms sinking into the abyssal depths would sequester carbon.

Richard Branson says it could work, which is good enough for me:
We can make estimates of fertility enhancement and sequestration, but a guess is that an OTEC plant designed to optimize nutrification might produce 10,000 metric tonnes of carbon dioxide sequestration per year per MW. The recent challenge by billionaire Sir Richard Branson is to sequester one billion tonnes of carbon dioxide per year in order to halt global warming, so an aggressive OTEC program, hundreds of several hundred MW plants might meet this. (Source!!)

Although it does mention a risk of releasing more CO2 already held in deep water sinks.

But really, there's a point where too much homework is expected to justify a setting. If you want a pre-apoc cy-fi setting where coastal cities use oceanic heat pumps for power while saving the environment to play in, go for it. I don't see how going "but actually..." and then banging away on Excel for half an hour helps make a more interesting or gameable setting.

Besides which, it doesn't actually have to be successful for people to try to do it. Society does all sorts of things that turn out to be bad ideas later. There's nothing wrong in having a setting where they haven't realised things won't work out yet- that's the definition of a pre-environmental apoc setting, innit?