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What's More Productive: CO2 Sequestration or Ocean Heat Sequestration?

Fossil fuel purveyors flaunt their dominance of the energy sector, self-servingly claim unequaled performance of their products in media they control by virtue of their advertising dollars and to the extent they acknowledge problems, offer carbon capture and sequestration (CCS) as a prophylaxis. Their preferred method of sequestering CO2 is not surprisingly; to inject the gas into depleted oil fields, to re-pressurize the formation, to enhance the recovery of the otherwise stranded oil.

Aside from enhanced oil recovery, which is a dubious accomplishment in a world where between 60 and 80 percent of the world’s fossil fuel reserves have to remain in the ground to meet the global warming target – 2°C – that virtually every country on Earth has agreed to, CCS has not been proven anywhere to be a commercial success.

In a world where energy efficiency is valued, CCS would consume as much as 25 percent of the output of a coal fired power plant fitted to capture and sequester its flue gases.

Studies indicate CCS can cause earthquakes that in turn lead to leakage.

History notes that massive CO2 leaks are lethal. So not surprisingly a paper by Stanford researchers in the  Proceedings of the National Academy of Sciences of the United States of America points out, “CCS is a risky, and likely unsuccessful, strategy for significantly reducing greenhouse gas emissions.”

Then there is the question of whether or not we are beyond the point where reducing greenhouse gas emissions alone solves the climate problem. Richard T. Wetherald, et al., in a paper Committed warming and its implications for climate change, suggests that is the case by stating, “much of the warming due to current greenhouse gas levels is yet to be realized.”

The oceans of the world are the principal repository of global warming heat and they have massive thermal inertia. Wetherald points out that even if radiative forcing (due to greenhouse gases) is held fixed at today’s levels, the global surface air temperature will rise an additional 1.0K before equilibrating with the oceans, which is a larger increase than the .6 K warming that has been observed since 1900.

Or is that necessarily so?

What if the bulk the equilibration that takes place occurs between the upper ocean, which as the following diagram indicates is the repository of the bulk of the heat attributed to the radiative imbalance, and the much larger volume of the deeper ocean.

 

The following NOAA diagram indicates that may already be occurring. From about 1998, the ocean to an average depth of 2000 meters has been warming faster than the ocean to a depth of 700 meters.

 

Gerald A. Meehl et al. in a paper Model-based evidence of deep-ocean heat uptake during surface-temperature hiatus periods point to the fact that during roughly the same period, 2000–2009, observed globally averaged surface-temperatures showed little positive or even a slightly negative trend (a hiatus period).

The study, “World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010, by  S. Levitus et al. estimated that the mean warming of the 0–2000 m layer  of the World Ocean between 1955 and 2010 was .09oC and that if all of that heat was instantly transferred to the lower 10 km of the global atmosphere it would result in a volume mean warming of this atmospheric layer by approximately 36oC.

The average depth of the world’s oceans is 3,682 metres thus there is nearly as much ocean volume again into which the heat absorbed by the upper 2,000 can further dissipate as the second law of thermodynamics dictates it will.

Levitus et al. acknowledge that the instantaneous transfer from the ocean to the atmosphere will not happen but point to their computation as a perspective on the amount of heating that the earth system has undergone since 1955.

I suggest it also highlights the fact the oceans have a great capacity to absorb heat to limited effect. The principle impact of this .09 oC  rise is thermal expansion, leading to sea level rise but here too a movement of surface heat to the depths mitigates the problem. The thermal coefficient of expansion of ocean water at 4 oC  and a pressure of 1000 meters, where surface ocean heat would be moved in an ocean thermal energy conversion operation, is half that of the tropical ocean’s surface.

On the surface that heat is the driver for tropical storms and excess evaporation that causes deluge in some areas and drought in others.

As has been point out on these pages numerous times, OTEC replicates the events that have lead to the climate change hiatus and in the process offers the potential to produce at least the amount of energy we are currently deriving from fossil fuels, while concurrently addressing the tropical storm and sea level problems.

Win, win, win and win!

The answer to the question posed by this piece is self-evident.

Content Discussion

Greg Rau's picture
Greg Rau on November 13, 2013

If OTEC were to tap into (and reduce) thermal gradients to produce “carbon-neutral” energy, it would also reduce the strong vertical gradient in CO2 content in the ocean, releasing CO2 to the atmosphere. What then is the net effect of OTEC to atmospheric CO2 and climate?  Then there are the marine biological consequences of vertically stirring the ocean, increasing surface ocean CO2 (acidity) and nutrients(?)

Greg Rau's picture
Greg Rau on November 13, 2013

Also, I agree that CCS as currently promulgated is unlikely to save our bacon.  That is why we need to consider alternative CO2 point source and air capture and sequestration methods, and not ignore 70% of the Earth’s surface in doing so:

http://pubs.acs.org/doi/pdf/10.1021/es102671x

http://pubs.acs.org/doi/pdf/10.1021/es800366q

http://www.pnas.org/content/early/2013/05/30/1222358110.full.pdf

May I also suggest that coupling OTEC to the latter electrochemical methods of producing C-negative H2 could be a way of tapping into offshore ocean energy in a way that truly benefits the atmosphere, the ocean, and our energy predicament – win, win, win.

 

 

 

Max Kennedy's picture
Max Kennedy on November 13, 2013

An overall warmer ocean absorbs more CO2, which becomes carbonic acid, which increases ocean acidification and environmental degradation.  Also at what temperature do the methane clathrates found in the deep cold ocean regassify.  As with everything it is necessary to ask the question what are the limits.  OTEC can contribute to our solution but only if it is not taken too far.

Max Kennedy's picture
Max Kennedy on November 13, 2013

Lets not make the mistakes of the past and do the science fast.  OTEC has some potential, just how much without becoming damaging itself remains to be seen.

Greg Rau's picture
Greg Rau on November 16, 2013

Max,

Am with you on ocean chemistry impacts. Certainly a rapid transitioning to non-fossil energy is required, but failng that here are some other ideas:

http://www.nature.com/nclimate/journal/v2/n10/full/nclimate1555.html

Then there are hybrid approaches. Consider merging your nuclear with my C-negative H2 production method that converts air CO2 to beneficial ocean allkainity. Non-fossil transportation fuel generated/chem feed stock generated – win, atmospheric CO2 burden reduced – win, alkalinity added to ocean to offset effects of oean acidification – win (!?):

http://pubs.acs.org/doi/pdf/10.1021/es800366q

http://www.pnas.org/content/early/2013/05/30/1222358110.full.pdf

More research needed, but what are we waiting for, more Haiyans and dissolving coral reefs?