The following text is also available as a pdf with diagrams here.

As the world overheats, etc. we know we need to reduce net CO2 emissions fast. However, many coal fired power stations are still planned or under construction around the world, and the fossil fuel companies are still bullish about their sales for decades to come. Renewables have reached parity in some parts of the world, but the recent debunking of Jacobson and Delucci’s 100% renewables claim suggests the fossil fuel companies are probably right (until cheap, waste burning nuclear power starts to be rolled out around 2026 at the earliest). However, we also know that drawing down CO2 from the air is too expensive – $600/tonne.

But CO2 is 140 times more concentrated in seawater and can be degassed by warming it up, then drawing it through a vacuum chamber where the water is agitated with baffles and ultrasound. Commercial degassers already exist for mud slurries and aquaculture. See my conceptual diagram below for seawater degassing.

Commercial degasser documentation states that it takes about 2 mins for most of the dissolved bicarbonate in water to convert to CO2 so it can bubble out (CO2 in seawater is about 93% bicarbonate). The vapour pressure of dissolved CO2 increases with temperature but I’m suggesting water heating should not be a problem if coastal power stations could be adapted to provide some of their waste heat for that purpose.

We also know from the CarbFix project, that CO2 can be permanently sequestered into basalt rock where it forms carbonates, becoming part of the rock in around 2 years. This is done by pumping highly carbonated water underground into the rock. Fortunately, basalt rock is very common around the world, especially under the oceans.

I’m also not a geologist, but with today’s fracking technologies able to drill vertically and horizontally for kilometres, it would seem that suitably located coastal facilities may be able to sequester significant quantities of CO2 that way.

I’ve done a ‘back of an envelope’ calculation to work out the cost of decarbonising the oceans back to preindustrial levels over 50 years, based on the power required to pump sufficient water. Rounding it up, it comes to $10 trillion or $500 billion/yr. The power requirement comes out at 200GW – about 1/60th total global power consumption of 12TW.

But who would pay for such a scheme? I’m hoping it’s not beyond the wit of financial experts to come up with a way to raise required the funds, in order to avoid the following looming problems:

  1. The prospect of a financial crash from the so-called carbon bubble. Corporations are currently valuing their fossil fuel reserves along the lines of ‘business as usual’, as if climate change poses no risk. If effective carbon pricing were to appear, many of these assets will lose significant value overnight. A ‘Task Force on Climate Related Disclosures’ has been set up by Michael R Bloomberg, to try to prepare for this somewhat inevitable crash: https://www.fsb-tcfd.org/
  2. $Tens of billions are already being lost by insurance companies in climate related events, which are set to increase exponentially with average temperature rise.

If largescale ocean degassing actually worked at sufficient scale it ought to keep such a financial crash at bay, and over time, reduce the losses attributable to climate change.

If a way could be found to decarbonise the atmosphere or at least find a way to reduce net global emissions affordably, I wonder if financial experts might try to lobby for carbon taxation revenue, perhaps to fund degassing directly. If border adjustments were to be applied as part of a carbon taxation regime, the tax would spread around the world – theoretically at least. (Finance ministers would rather raise such a tax domestically, than watch their exporters pay the border adjustment to foreign governments.) If done as a carbon tax it would add the order of $10 to a barrel of oil.

 

Energy Calculation

If we take a rough approximation and say the atmosphere is about the same volume as all the oceans, and take CO2 concentration in seawater to be 140 times that of the atmosphere (as indicated by the US Navy). Given atmospheric CO2 has been increased by 1/3rd, and assuming most of the CO2 could be degassed from seawater in a single pass, the amount of ocean to be degassed would be 1/(140 x 3) or 0.24% of all the oceans.

The volume of the oceans is (from Google) about 1.4 x 109 km3

So the amount to be degassed would be 1.4 x 109  x 0.0024  = 3.36 x 106 km3

Over 50 years that’s 3.36 x 106 / (50 x 365 x 24) = about 7.67 km3/hr.  Unsurprisingly, that’s still a very big operation.

But the global fossil fuel infrastructure is also a very big operation, probably a bigger one.

This document on optimising the efficiency of pumping stations, contains a graph that suggests 1500 litres/hr can be pumped with a power of 80kW: http://evidence.environment-agency.gov.uk/FCERM/Libraries/FCERM_Project_Documents/Pump_report.sflb.ashx

This graph pasted below (from p51) suggests a sort of rough figure for the power needed to pump water.

Converting 1500 l/s to m3/hr:                      1500 x 60 x 60 / 1000   = 5.4 x 103 m3/hr

 

Converting the ocean volume to be processed to m3/hr:  7.67 km3/hr =  7.67 x 109 m3/hr

 

So the power needed to pump 7.67 km3/hr would be:

80 kW x 7.67 x 109 / 5.4 x 103   =  114 GW

 

That doesn’t seem too bad.  More power would be needed to force the water past the degassing baffles, but the order of magnitude would surely be the same. Perhaps 200GW would be a more realistic figure. Of course, this power requirement would be spread over a number of degassing plants spread around the world to degas several ocean locations concurrently.

 

Annual Cost Calculation

 

To supply 200GW over a year, assume an electricity price of $50/MWh:

= 200 x 50 x 103 x 24 x 365 = 87.6 x 109 = $87.6 Billion per year

N.B. I’ve so far taken no account of the cost of building and operating degassing platforms, so let’s round up $87.6 billion to $200 billion/yr.

That only caters for removing CO2 at about the rate it’s being added by current emissions. To additionally remove historical emissions would require double the effort, so let’s call it $400 billion / year.

 

Marginal cost per additional barrel of oil extracted

Current CO2 emissions amount to around 40Gt CO2/yr (= 40 x 109 tonnes/yr)

If $200 billion pays for capture of 40Gt. The cost/tonne = 200/40 = $5/tCO2

CarbFix costs around $4/tCO2 so let’s round up the cost/tCO2 to $10/ tCO2

One barrel of oil when burnt releases around 0.43 tCO2. So the marginal cost per new barrel extracted (cost to society) is 0.43 x 10 = $4.3/barrel.

This is very small compared to the massive swings in the oil price seen in recent years.

 

 

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