The integrated thermodynamic geoengineering/negative emissions OTEC model

Abstract

This paper advances the view posited in The Atlantic article Climate Change Can’t Be Left to the Scientists that scientists can only study climate change; they can’t solve it. Engineers, technologists, and energy-system designers will solve it and the cost of their solution should be borne by redirected fossil fuel subsidies that are tantamount to an undercharge for the social cost of fossil fuel production. Environmental remediation costs are as real as energy supply costs yet are being inadequately funded while fossil fuels are being liberally subsidized. The solution advanced in this paper is an amalgam of energy production through the conversion of the heat of global warming to productive energy, (thermodynamic geoengineering (TG)), solar radiation management (SRM) through load balancing trapped solar energy and carbon-dioxide removal (CDR) thru negative-CO2-emissions ocean thermal energy conversion (NEOTEC). It addresses the sustainable development goals of the United Nations as well as the concerns of the most economically disadvantaged and advances the view that some climate modeling has set back the climate/energy cause, most is theoretical and that the historical record is a better yardstick upon which policy should be formulated.

Integrated assessment models

Integrated assessment models (IAM) try to link society and the economy with the biosphere and the atmosphere.  They integrate academic disciplines including economics and science to model energy systems and land-use changes to estimate possible future scenarios and provide policy answers.

The IPCC Special Report Global Warming of 1.5 ºC shows to achieve a 1.5^oC warming target, anthropogenic CO₂ emissions need to decline by 45% by 2030 (relative to 2010) and by 2050 will need to reach “net-zero” or by 2075 to meet a 2℃ target. Emissions greater than these will require the removal of CO₂ already in the atmosphere.

The three decades since the Intergovernmental Panel on Climate Change was founded have been focused intensely on emissions control, with no parallel plan to test, scale or implement alternative energy sources or carbon removal technologies or notice their economic, social, legal and ethical dimensions.

Over this period emissions have continued to grow and in 2018 the annual rate reached a record 37.1 billion tonnes.

Since emissions control isn’t working, geoengineering or climate engineering has been offered as a hedge against climate catastrophe.

It is a fallback plan if temperature rise can’t be capped at a manageable level and the IPCC has given its engineering research its tentative approval.

Currently, only two approaches are being considered, CDR and SRM.

CDR tackles the root cause of global warming by removing greenhouse gases from the atmosphere, while SRM ignores emissions and instead offsets the impact of greenhouse gas by reflecting sunlight away from the earth. Both are mainly based on theoretical models and have been criticized for being untested, risky and offer false hope at a time when policy-makers are under the gun.

The IPCC differentiates between the two because it sees CDR as a climate mitigation measure, which it has incorporated into nearly all its safe pathways, while SRM, which is not a fix for emissions, has the potential to reduce a temperature overshoot.

Solar radiation management

The IPCC names extreme temperatures, rate of sea-level rise and intensity of tropical cyclones as impacts that could be lessened by SRM, but its endorsement is highly qualified because of implementation challenges with governance, public perception, development impacts, and potential “termination shocks”.

"While theoretical developments show SRM is technically feasible, global field experiments have not been conducted and most of the knowledge about SRM is based on imperfect model simulations and some natural analogues," according to the IPCC.

"There are also considerable challenges to the implementation of SRM associated with disagreements over the governance, ethics, public perception, and distributional development impacts."

The IPCC also warns of the risk of "termination shock" if the practices are suddenly stopped, causing rapid temperature rise.

It explores four SRM strategies including, stratospheric aerosol injection, marine cloud brightening, Cirrus cloud thinning and ground-based albedo modification. Each with their distinctive feasibilities and safety concerns.

The paper Geoengineering as a design problem describes how previous climate simulations prescribed a particular strategy and evaluated its modeled effects, whereas the authors turn this approach around by first choosing climate objectives and then designing a strategy to meet those objectives.

Climate objectives, however, should be self-evident to even the minimally well informed.

What is needed is energy production that fulfills mankind’s needs while returning the atmosphere and oceans to their preindustrial condition.  

The authors of this paper note that the climate result of SRM research depends not only on the amount of geoengineering but also the spatial pattern that are both, at least in part, design choices. The objectives of geoengineering, therefore, may involve balancing multiple criteria, such as maintaining Arctic temperature without disrupting tropical precipitation. For example, one of the results from geoengineering that is repeatedly discussed is that offsetting the global mean radiative forcing from a CO₂ increase by reducing solar irradiance results in an overcooling of the tropics and an undercooling of the poles because CO₂ concentrations are mostly evenly distributed in climate models.

CO2 forcing, therefore, has a much weaker latitude dependence than forcing from solar irradiance.

Thermodynamic geoengineering

Instead of overcooling the tropics at the expense of overwarming the poles with SRM, TG cools the tropical surface and the poles by transferring heat to deep-water. A strategy that has been overlooked by the IPCC and the climate modelers.

As shown in Figure 1, solar irradiance is a highly latitude dependent form of climate forcing. At the equator, approximately 80 watts per meter squared net forcing occurs (320 watts shortwave radiation - 240 watts longwave radiation). At latitudes higher than 40 degrees, the energy surplus reverts to a deficit but for the approximately 384 terawatts of trapped energy represented by global warming.

Figure 2 shows how this trapped energy accumulating near the equator can be converted to productive work in a heat engine. The conversion rate can be as high as 7.6% so, the heat of warming can produce about 29 terawatts of energy a year or about twice as much as the 14.5 terawatts currently derived from fossil fuels. The purple arrows show how heat is move by TG from the surface at a rate of about 75 meters a sec and diffuses back to the surface from a depth of 1000 meters at a rate of 4 meters a year (1 centimeter a day) for the initial 225 years and 1 meter a day the last 100 meters of the mixed layer.   

Figure 3 combines the previous two figures to demonstrate that the conversion of warming heat to work cools the surface without offsetting warming of the higher latitudes or producing sea-level rise due to icecap melting or increasing the intensity of tropical cyclones.

Figure 3

The heat moved back to the surface in Figure 2 is then available to produce additional work in the heat engine and this recycling can be repeated until all the heat of global warming has been converted.

Heat move to a depth of 1000 meters produces less sea level rise due to the differential between the thermal coefficient of expansion at the two depths per Figure 4 below.

Figure 4

The Stefan-Boltzmann Law E = σT⁴ where E represents the rate of radiation (energy flux) times the Stefan-Boltzmann constant (5.67 x 10^-8W/m²K⁴) times the temperature in Kelvin to the fourth power dictates the power radiated by a black body in terms of its temperature.

By reducing the ocean surface waters by 1^oC, you reduce the outgoing longwave radiation shown in Figure 1 by about 5.8 W/m2 at an ocean average surface temperature of 295K (22°C) the ocean radiates 430 W/m2 x ( 1 - 4deltaT / T )). Which would be offset by reduced surface evaporation, an increased albedo resulting from increased polar ice production and the fact that energy produced by the heat engine would be consumed at the surface where the waste heat of production would be dissipated.

The paper, World ocean heat content and thermosteric sea level change (0–2000 m), 1955–2010 showed that between the years 1955-2010 the oceans to a depth of 2000 meters experienced a volume mean warming of 0.09°C that if instantly transferred to the lower 10 kilometers of the global atmosphere would result in a volume mean warming of this layer by approximately 36^oC.

Such a release can’t occur. At least until the atmospheric greenhouse concentration is returned to 280 parts per million.

With TG the ocean heat content to a depth of 1000 meters would be increased by about four times as much as accumulated between 1955-2010 but this heat would be released back to the atmosphere over the course of 2960 years ((100/7.6) * 225 year cycles) so, the surface would be warmed only .05°C annually, which would be dissipated immediately back to space in a world of 280 parts per million CO₂.    

It has been proposed TG might impact the thermohaline circulation, which is critical to global climate patterns, but that isn’t likely. The diffusion rate of heat moved into the depth back to the surface with this process is the same as the cycle rate of the global conveyor belt.  

The latter is driven by density gradients measured in Sverdrup (Sv) equal to 1,000,000 cubic meters per second. The Gulf Stream increases to a maximum of 150 Sv south of Newfoundland at 55°W longitude and the Antarctic Circumpolar Current is the largest ocean current at approximately 125 Sv.

Figure 5 on the left is schematic of the Thermohaline Circulation and to the right is the intertropical convergence zone (ITCZ) where TG would be implemented and where the ocean is only minimally impacted by this circulation.

Figure 5

The top 75 meters of the oceans have warmed an average of .01 degrees Celsius per year since 1971, whereas between 500 to 2000 meters they have warmed by about .002 degrees a year so, cooling the surface flow at the expense of the deep flow with TG should be a wash.

Wikipedia shows a hypothetical current like the Gulf Stream 150 km wide, 500 m (0.5 km) deep, and moving at 2 m/s transporting 150 Sv of water. The Atlantic, however, is about 4,830 km wide between the United States and northern Africa and 2 m/s is 31,536,000 times faster than the rate of heat diffusion from at depth of 1000 meters with TG. Luis Vega in his Ocean Thermal Energy Conversion Primer estimates that 4 m3/s of warm seawater and 2 m3/s of cold seawater, with a nominal temperature difference of 20 °C is required per MW of power with an OTEC system. With TG these heat exchangers are only 13 meters deep, rather than 500 meters with the Gulf Stream, and the flow of water through the heat exchangers is perpendicular to the Gulf Stream so the impact on the thermohaline circulation should be negligible. The surface water remains in place with such a system as does the deep water, but for diffusion so, there would be less need for water to service the heat exchangers. It is only the latent heat of the boiled and condensed working fluid that moves between the heat exchangers as opposed to the movement of heat as the sensible heat of water from 1000 meters to the near the surface as with conventional OTEC.

The paper Atmospheric consequences of disruption of the ocean thermocline points out, technologies utilizing vertical ocean pipes have been proposed as a means to avoid global warming, either by providing a source of clean energy, increasing ocean carbon uptake, or storing thermal energy in the deep ocean.

It goes off the rails however when it claims increased vertical transport of water can drastically alter the ocean thermocline.

The authors performed a set of simulations involving “idealized” disruption of the ocean thermocline by greatly increasing the vertical mixing in the upper ocean to evaluate the “likely” thermal and hydrological response of the atmosphere.

Modeling a disruption of the ocean thermocline by simulating an increased background vertical diffusivity in the top 1000m of the water column 60cm2/s, whereas, conventional OTEC would disrupt the vertical diffusivity by only 1 meter/day and TG would disrupt it only 1 centimeter/day is neither an “idealized” simulation nor are results of the modeling even remotely “likely”. They render meaningless the conclusion of the paper that increased vertical transport in the upper ocean decreases upward short and longwave radiation at the top of-the-atmosphere due primarily to the loss of clouds and sea-ice over the ocean causing an effective radiative forcing of ≈15.5–15.9 Wm/2.

As witness, the 5.8 W/m2 of negative forcing produced for a 1^oC cooling of the surface noted above.

Nonetheless, the UN Joint Group of Experts on the Scientific Aspects of Marine Environmental Protection (GESAMP) report High Level Review of a Wide Range of Proposed Marine Geoengineering Techniques cite this paper and made its  findings part of its holistic approach to assessing marine geoengineering, whereas shaking up the top 1000 meters of the water column as if it was a can of soda pop and then degassing the CO₂ to the atmosphere as was modeled is not only ill-advised, CDR will likely be needed to reduce warming.

Carbon dioxide removal

There are different CDR techniques that are less latitude dependent than forcing from SRM, including bioenergy with carbon capture and storage (BECCS), which the IPCC has already incorporated in its models, direct air carbon dioxide capture storage (DACCS) soil carbon sequestration (SCS), afforestation and ocean fertilization, and Negative emissions OTEC (NEOTEC).

BECCS work and is feasible but the IPCC has doubts it can be scaled in time to make a difference and there is disagreement about the availability of land for biomass plantations.

For example, per Table 1, to return current atmospheric concentrations of CO₂ to the preindustrial level over 1 trillion tons of emissions would have to be sequestered.  

Table 1

The Empress Splendor tree is the fastest growing hardwood tree in the world. It reaches maturity within 10 years and can sequester 103 tons of CO₂ per acre. Per Table 2 planting Empress Splendor trees exclusively, which is problem in its own right, it would take the land mass of 4 Canadas to bring atmospheric emissions level down to preindustrial levels.

Table 2

The paper, Putting Costs of Direct Air Capture in Context says the lowest-priced DACC technology provider thinks it can reach a cost of $50 a ton, which would make the cost of all emissions sequestration over $52 trillion, nevertheless, the IPCC considers some CDR a given in its modeling for safe pathways forward.

As to safety, it says chemical capture and storage of CO₂ deep underground is seen as generally secure for thousands of years and natural carbon sinks like soil and trees reverse earlier, so they need to be used with care.

In this regard fires, both wild and manmade, are rapidly turning important natural carbon reservoirs from sinks into major emitters.

Negative emissions OTEC

NEOTEC is a triple threat energy, SRM and CDR strategy addressed in the paper Negative-CO2-emissions ocean thermal energy conversion. It is the only one that encompasses all three capabilities. This paper also notes, “Given the global abundance of the base minerals and salt electrolyte required, the scale of the process might only be limited by the cost and availability of non-fossil-derived electricity.”

NEOTEC is twice as mineral and CDR efficient as the mineral carbonation discussed in the recently published paper Evolution of carbon capture and storage by mineral carbonation, discounted by the UN on the basis of the extreme modeling of the paper Atmospheric consequences of disruption of the ocean thermocline and is completely ignored in the National Academies of Science Engineering and Medicine’s 20 year CDR agenda.

The triptych of the worlds major oceans shown in Figure 5 (from Google Earth screen captures) reveals the dominant hue of our planet.

Figure 6

More than 90% of the Earth's surface carbon exists in the form of dissolved mineral bicarbonates in the oceans and adding more would help counter ocean acidity and yet mineral “carbonation” has to date monopolized the CDR agenda.

Figure 7 shows a schematic of NEOTEC on the left and a blow-up of the electrolyzer from the paper Direct electrolytic dissolution of silicate minerals for air CO2 mitigation and carbon-negative H2 production on the right.

Figure 7

IAMs model land-use changes but it is in the oceans where 93 percent of global warming is going and from whence 93 percent of the world’s stored solar energy can be converted to useful work.

The editorial The race to remove CO2 needs more contestants notes, allocation of R&D resources within and across approaches needs to be continually evaluated and adjusted based on objective and transparent comparisons of R&D results, including their economic, social and ethical dimensions.

Fossil fuel subsidies have been estimated at as much as $5 trillion a year, whereas revenues from the fossil fuel sector were estimated at only $3 trillion for 2017. Any replacement for the fossil fuel sector, therefore, that avoids the need for subsidies is effectively energy too cheap to meter.

Table 3 shows the economic dimension of TG and the assumption on which these assumptions were made.

Table 3

Of note, all TG plants with capacities greater than 100 megawatts are cheaper on an annualized basis than the 2017 fossil fuel revenues and produce twice as much energy.   Plants of 400 megawatts or more are also cheaper than the best case for the lowest cost DACCS scheme while others are as much as 20 times higher. Notwithstanding the fact, these schemes have energy sourcing concerns and carbon footprints of their own, while TG is first and foremost a method of producing energy.

Table 4 calculates the number of years it would take for NEOTEC to sequester all of the total CO₂ tonnage shown in Table 1.

Table 4

From then on TG would be produced with a configuration as shown in Figure 8.

Figure 8

Absent the requirement of supplying minerals at depth, a deep water electrolyzer can take advantage of the ambient pressure of deep-water with graphene sieves to produce freshwater for use in the electrolyzers thus avoiding the production of chlorine at the anode. Hydrogen produced at depth also arrives at the surface 70% of the way towards the pressure necessary for most transportation applications. The downside is the installation and maintenance issues with deep-water installations that can be worked on over the course of 73 years.

Installation and maintenance issues associated with TG infrastructure would be avoided by operating the systems within the ITCZ where tropical cyclones and hurricanes do not form per Figure 9.

Figure 9

Conclusion

Climate models are future projection whereas the historical record demonstrates current greenhouse gas concentrations have produced seas higher 35 meters higher and Arctic temperatures 8 degrees Celsius higher. Fortunately, we have the savvy to design our way out of such a climate catastrophe, but we need to quit listening to the schills hammering away at the message fossil fuels will be the lowest cost solution for years to come.

The IPCC warns of the risk of "termination shock" if we suddenly stop geoengineering activities but why we would want to stop producing twice the energy we are using now while producing none of the environmental consequences?