Solar geo-engineering, Negative Emission tech, Carbon Capture and Storage

What’s this about:

  • Solar geoengineering technologies, assessment of advantages and uncertainty
  • Negative Carbon Technologies (NET), Carbon Storage and Capture (CCS)
  • To know more about what NETs and CCSs there are, see this other post of mine.
  • used abbreviations:
    EOR= enhanced oil recovery system, which extracts 40% more than normal oil recovery systems
    CCS= Carbon Capture and Storage
    CCUS= Carbon Capture Utilisation and Storage),
    NET= Negative Emission Technology
    DAC= A type of NET, Direct Air Capture
    BECCS= A type of CCS, Bioenergy with Carbon Capture and Storage
    CDR= Carbon Dioxide Removal

The following are not personal opinions, just overviews of these two articles:

  • Haszeldine et al. (2018) Negative emissions technologies and carbon capture and storage to achieve the Paris Agreement commitments, Phil. Trans. Roy. Soc. A, 376:20160447
  • MacMartin et al.. (2018) Solar geoengineering as part of an overall strategy for meeting the 1.5°C Paris target, Phil. Trans. Roy. Soc. A, 376:20160454


Solar geo-engineering: reduce solar radiation by reflecting sunlight

stratospheric sulphates – currently achievable – advantage: this is what
happens when volcanoes erupt and reduce sunlight irradiation, which means we have empirical basis of how this works.

Stratospheric aerosols – achievable but success depends on type of aerosol – disadvantage: they are not naturally occurring in the stratosphere and so it’s uncertain if they will bind with other molecules in the stratosphere or basically “rain back on us”

Marine cloud brightening (MCB) – very uncertain as we don’t know if the effect we expect will actually occur – advantage: would be a way to manipulate albedo short term, which means e.g. create more clouds one specific point In the sea – disadvantage: it can only be done in the sea, which means 10% of world surface

Cirrus thinning – very uncertain as not well studied – advantage: works on long-wave radiation – disadvantage: works only where cirrus is already present

Space-based albedo modification – we know how it works but we don’t know how to do it – advantage: best kind of manipulation of solar irradiation – disadvantage: expensive!

Maximum cooling potential of these technologies is unclear, but certainly have to be deployed together with mitigation strategies.
Using solar geoengineering will reduce radiative forcing everywhere in the same way, and not cool the places which are hotter due to high GHG (e.g. we could be overcooling the tropics and undercooling the arctic)

Climate warming has two effects on precipitation:

  1. warmer climate holds more moisture, which enhances hydrological cycle
  2. warming of troposphere due to GHG leads to increased stability reduce precipitation
  3. transpiration reduced with increasing CO2, such that precipitation decreases

Cooling of the planet via solar geoengineering will further reduce precipitation, more than if we only mitigated climate change à if we use solar geoengineering to get to pre-industrial levels, we will overcompensate precipitation

Uncertainty sources:

  1. Uncertainty in processes that result in negative processes of radiative forcing
  2. Uncertainty in how climate is responding to forcing
  3. Deployment of solar engineering technology can reduce uncertainty of climate models in the RCPR

Response of other climate variables to mitigation and solar geoengineering techniques:

-ocean acidification will not be affected by geoengineering as surface ocean carbonate chemistry is not that sensitive to changes in air temperature (but rather sensitive to atmospheric CO2 concentrations),

-stratospheric ozone less would increase, GM precipitation restored to pre-industrial levels

-reduced precipitation levels and cooler temperatures (+ enhanced CO2 levels) show positive trend in crop yield

Carbon Capture & Storage

Basic idea: Reuse and recapture of CO2 deployed in past and being released in the atmosphere. CCS is considered a strategy comprising three steps:

  1. separation of carbon dioxide from fossil fuel, industrial processes and feedstock
  2. compression and transport of CO2 via a pipeline to storage destination
  3. injection of CO2 in pores of a natural borehole to store it in perpetuity

Open questions: where do we store it? Who pays for it?
Reservoirs of fossil fuels alone are enough to meet 1 trillion GtC to get 2degrees of warming. Emissions need to decrease 3% yearly by 2050 to meet Paris Agreement.
Emissions by 2035 will increase to overall growing wealth and population


  1. CSS has no political drivers, such that (in the case of 2050), deployment would be 100 time short for mitigating warming below 2degrees.
  2. CSS is not restricted only to electricity, but also gas, oil, supply heat to domestic households, combustion of biomass for feedstock etc. CCS was pitched in the wrong way: final product of decarbonised electricity put in a market where subsidized renewable electricity can be produced at prices comparable to or cheaper than conventional high carbon power.
  3. On a cost basis, CCs is cheaper than cost of decarbonisation by a factor of 2.5 if CCS are not deployed. Retrofitting coal-fuelled power plants has not worked because new green tech has become cheaper as it has been heavily subsidised and have shown super quick price reduction.
    –> incentivise policy
    –> certificate of CO2 storage for fossil carbon industry

How to tackle adequate subvention of mitigation technologies:
Non-immediate effect of climate change is a reason for lacking subventions for NET and CSS. Alternative way proposed for funding these technologies are:

  1. national identification of carbon storage facilities, country-wide and relative
  2. strategic storage evaluation of country-budget to consider decision of acquiring CSS or NET technology from global market from 2020
  3. current commitment to reduce overall emissions by 3% are not sufficient. And Bureaucratic hurdle to gain carbon storage permits does not incentivise CSS.
    1. g. world’s largest carbon pricing mechanism, the EU Emissions Trading Scheme (EU-ETS) has not functionally supported CCS development as a mitigation technology. The EU-ETS allows continued CO2 emissions, through an increasing price of permits for each tonne of CO2; thus lack-of-emissions saves money, but storage is not encourage.
      Counterexample: Norwegian taxation of offshore hydrocarbon production emissions of GHG
    2. Carbon storage certificate awarded to fossil carbon extractors



To achieve net-zero CO2 emissions we require CCS to reduce greenhouse gas emission rates, and NET to capture previously emitted greenhouse gases.


  1. NET are few, small and need 10 years to be deployed
  2. CCS exists at low costs, but has no political drivers to enforce deployment.
  3. If CCS were to be deployed onto biomass, requires conversion of crops to biomass land.
  4. BECCS (bioenergy with carbon capture and storage) does not exist on industrial scale.
  5. DAC (direct air capture) no long duration storage destination
  6. Article analyses all CCS projects to 2050 and shows they are 100 times too slow.
  7. Surface mineralisation: Injection of CO2 into the subsurface in rock utilising reacting mineralogy to get a mineral form of CO2.

Development of CCS tech:

Commercial method to incentivise CCS and Co2 storage: CO2 EOR (enhanced oil recovery system, which extracts 40% more than normal oil recovery systems).
EOR could be used to capture anthropogenic emissions à should be incentivised via tax allowanced (see Petra Nova Boundary Dam in Texas) or low carbon price

  • advantage of EOR is that it increases carbon dioxide being stored securely (it uses porewater reservoirs instead of physical retention with seal mudrocks in an aquifer store)
  • ensure eor projects not to emit more co2 by making sure that co2 injection continue after oil is extracted, so more carbon than the one produce can be stored
  • All in all: Co2 EOR can be a low cost co2 capture and separation technique that’s fast to achieve storage of millions of tonnes per year
  • Sell-price of CO2 should be such that it will recover costs of capture: benefits would be reduction of net emissions, making money and long duration storage of co2
  • Note that to sell co2 into energy sources one has to change the compound Co2 to another compound, which requires energy. Also note that CO2 storage by enhancing horticulture in greenhouses will be short term as the tomatoes grown in the greenhouse store the CO2 which is then emitted when eaten basically.

CCUS example: The solvent makers are happy because they sell their product, the coal plant operators are happy because some of their CO2 is captured. The captured CO2 is converted (using extra energy) to a chemical which is locally in short supply and is currently imported. A new local supply is welcomed by the government (reducing imports) and by the user (less cost). The chemical is used—as a flux in glass making to produce cheaper glass, but within that flux process the chemical becomes a reagent and CO2 is emitted as a gas to atmosphere. All actors along the chain are making money, and some claim to be reducing emissions—especially through more efficient capture at a power plant. But the overall effect is to increase emissions to atmosphere due to higher energy requirements.

CCS tech in the past:
exists since 1970, government supported projects to help commercialise capture were mainly focused on electricity.

CCS in future:
either new funding or new build CCS projects will cease globally, i.e. no new progress by 2020 –> introduce subsidies or require CCS certificates from fossil carbon industry.
To achieve a large number of CCS installations, we must assume that tech is wanted (ie lower cost or achieving objectives), but neither of these are the case.

Where to apply CCS:

  • Separation of CO2 from hydrocarbons (since 1920) operates in the production of natural CH4 and hydrogen in refineries.
  • To sell hydrocarbons, CO2 and SO2 have to be separated from hydrocarbons. SO2 is re-injected for disposal as it is an hazardous gas and CO2 is vented to the atmosphere because there is no penalty for doing so (while there is for SO2)
    Solution: tax Co2 emission from associated gases

NETs: parameters to incentivise practical enactment of technology:

NET and CDR recapture carbon already used and recycle into productive use.

  1. global impact (how much carbon py (per year) can on NET accept
  2. security of storage, how reliable storage for next 1000 years for earth to re-equilibrate
  3. maintenance, effort and attention and money to input so that carbon storage performance remains secure
  4. tech feasibility, can nets be built now such that in 10-20 years they will be high impacts operations
  5. energy efficiency, can these processes and they work efficiently extracting co2 from air will use more energy than extracting co2 from flue gas i.e. novel methods are needed to consume minimal additional energy
  6. cost, can we foresee a complete pathway that is cheaper than or compete with geological CCS?

There are 10 different methods of carbon storage suitable for long duration NET. 3 of 10 relate to Co2 injection via CCS. 7 of 9 NET potentially available, there are 3 viable to 2035. Limitations to these 3: manufacturing ability, permissions gaining, financial profitability

CCS for BECCs and DAC: CCS tech needed according to AR5 to keep below 2 warming.

BECCS: capture of CO2 from corn based methanol, streams from brewing and sitilling, combustion of wood, power plant can convert rom coal to combustion of biomass like Drax (UK), bu is without CCS.
Problems: Provenance authentication of sustainable biomass and carbon balance sustainability is hard to verify. If CCS is enacted as biomass (BECCS), then we will need huge land covers dedicated to crops for biomass.

DAC: no consensus on how to separate CO2 from air, still it its initial status of research.
Engineering process may need 10 times the energy of a regular concentrated flue gas capturing. Brandani, House et al. à unsure on how to do engineer process.

Subsurface mineralization: injection of Co2 into the subsurface in rock types to crease mineal co2. à could use borehole technology and access large depots in a quick way without needing much planning. Don’t know how to do it for hundresa millions tonnes of co2 py. Inject Co2 dissolved in brine into sediments and lavas in southwest Iceland (carbFix). Very low cost, transport and public permission will be problematic. Ocean floor basalt, is a storage resource but more difficult to exploit.

Enhanced weathering: deposit relevant minerals on Earth’s surface to promote extraction of Co2 from atmosphere (weathering!) à carbonate minerals or soluble carbon These are then transported through water courses inland and to the ocean. Low cost, but capacity of the ocean to accommodate soluble cations and bicarbonate is unclear from regulatory position.

Ocean alkalinity and direct injection co2 dissolution:
Ocean acidity measures 30% more than pre-industrial levels as co2 is half being dissolved in the upper surface of the ocean
As the residence time of carbon in ocean is 200000 years, it is a long enough storage facility for climate recovery. Directly injecting co2 into deep ocean, means co2 dissolves and increases co2 content and water acidity.
Injection can be deployed rapidly but if the alkalinity to inject and dissolve liquid co2 exists, it is unclear who will pay for it, how co2 will be collected and stored up until that point. Moreover, it goes against conventions of dumping in sea (was tested and found opposition. United nations convention of Law of the Sea (1982) restricts emerging marine activities. 1972 London convention and 1996 London protocol are considered protecting against marine geoengineering).

Note: Ocean acidification will continue even if CDR is undertaken to reduce warming, so there is not point against CDR in ocean. Oceans have the capacity to store co2 excess anthropogenic emissions are doing so and will continue doing so, even without tech.

Caveat: We need to understand how the ocean carbon cycle will change if we impact the alkalinity with dumping co2 in it.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s