On May 30th-31st, 2011, about 35 leading scientists from around the world met for the International Workshop on Modeling and Policy of CO2 Removal from the Atmosphere at the International Center for Climate Governance, Island of San Giorgio Maggiore, Venice – Italy. We talked about technologies allowing to remove CO2 from the atmosphere. Planting trees and not cutting them down, for example. Or mixing some (torrefied) wood pellets with the coal in a power station which has a system to capture the CO2 from the exhaust fumes and bury it underground. This is called Biomass Energy with Carbon Capture and Storage, BECCS in short. Here are the memes I take away home from the conference along with more subjective reflexions. As usual, the discerning reader will recognize that the sentences starting with I think that... or To me... are personal opinions. Here I remind that in this blog everything is written only under my own responsibility, and I do not try to represent exhaustively the debates.

  1. CO2 removal from the atmosphere is not an insurance against abrupt climate change. If something nasty and nonlinear starts to happen with the icesheets, the permafrost or [insert your preferred touchy part of the climate system here], it would be more effective to directly reduce radiative forcing than the concentration of greenhouse gases. Spreading reflecting particles in the atmosphere, for example, to mimic the cooling effect of a large volcanic eruption like the Pinatubo. This could produce results in a few years, while it would take decades to build and operate air capture systems and bring down the concentration to safer levels.
  2. Still, air capture matter because if that worse-case scenario happens, we will also want to bring down concentrations to safer levels. Geoengineering might bring a quick emergency relief, but the root cause of the problem will need fixing too. My subjective probability of this happening is higher than I would like: big social changes are oftentimes made in a reactive rather than proactive mode, I am still not convinced that the Uncle Sam would not like to see Uncle Chu's feet in the water, and the Canadians, the Saudians and the Australians have enough hydrocarbons underground to make sure it happens. Sorry.
  3. Direct Air Capture (DAC) of CO2 with chemicals is more entrepreneurship than science today. There are at least four startups in the market of providing CO2 from the air for industrial and agricultural applications. David Keith's Carbon Engineering, does absorbtion with NaOH, then high temperature regeneration. Klaus Lackner's Kilimanjaro energy builds artificial tree consisting of a ion-exchange material, with a moisture swing adsorption cycle. Aldo Steinfeld's Climeworks is using Amine-immobilized silica sorbents. Graciela Chichilnisky and Peten Eisenberger's GlobalThermostat has Hyperbranched aminosilica (HAS) solid sorbents developped by Chris Jones at Georgia Tech. A report from the American Physical Society on DAC says this is very very expensive. The jury is still out on Virgin's Earth Challenge 25 millions, they are not taking applications anymore. In my view, as long as it is private money and they clearly represent the risks to the investors, it's exciting to see people trying to push the technical feasibility frontier ! I would link here to the Feature article on climate entrepreneurs in the latest Nature Climate Change, if it were Open Access.
  4. Fossil fuel exporting countries may be interested in air capture to decarbonize their products. In a not-too-distant future, some clients may prefer their barrels of oil bundled with an equivalent amount of CO2 abatement certificates.
  5. Massive Direct Air Capture has no place on the agenda at the 2050 planning horizon. It is rational to use it only after the carbon dioxide produced at all large point sources have been captured and stored. This does not exclude niche markets. We should not overestimate the degree of ambient rationality either.
  6. Net negative emissions is troublesome because it may give procrastinationists a reason to delay action. In my model for example, for a CO2 concentration peak at around 600 ppmv the optimal abatement level in 2040 goes from 7.3% if air capture is not possible, to 7.0% if air capture is possible. However, p17s please take good note that a 0.3% change in abatement level is a small number. Especially compared to the uncertainty on the climate policy target: for a concentration peak at around 500 ppmv, the optimal abatement level is 15.5% even with air capture.
  7. Net negative emissions are necessary to achieve the most strict climate policy targets. More precisely, most integrated assessment models in EMF 22 did not find solutions for the 450 ppmv constraint if they did not have an explicit representation of BECCS.
  8. Radiation management may be a game-changer. This is because a small coalition could technically do it alone, and may have strong incentives for doing it. UNFCCC COPs will ever be interesting Who did we say owns the property rights on monsson's patterns already ?
  9. Climate change scientists should not be carried away by politicians' euphoria. Last year the delegates recognized in Copenhagen "the scientific view that the increase in global temperature should be below 2°C". The Copenhagen Accord's last line even mentions 1.5°C. Thus the social demand this year is to look at low trajectories, 450 ppmv or below. Yet ten years ago many modelers did not take lower than 450 ppmv targets as practically relevant, as the costs to reach them were presumed to be excessively high (we accepted overshooting trajectories since). While there is a co-construction of knowledge, scientists should not take political statements naïvely at face value. Models should explore the whole feasibility space. Simulations of low trajectories are needed, but +3°C and +4°C scenarios are still worthwhile.
  10. Fertilizing the ocean is potentially catastrophic. The idea is, for example, to add iron to the waters of South Pacific to increase the biomass productivity. More biomass means more CO2 in the ocean, so less in the atmosphere. The big problem is, more biomass also means more consumption of other nutrients. This depletes the nutrients stocks locally, then globally because the south pacific is an important source of nutrients for all other oceans. In fifty years, there are no nutrients available everywhere else and you can say goodbye to the biomass productivity on this Planet's oceans.
  11. The externalities of bioenergy are not all known and accounted for. Greenhouse gases concentration is not the only target of sustainability, and CO2 is not the only greenhouse gas. Cutting down lots of forests would have a cooling effect by increasing the albedo. This is not a reason to do it !
  12. Torrefied Pellets are technically superior to regular wood pellets as a biomass energy carrier. I am bullish on this technology, see this presentation for an introduction to TOPs. The global market in TOPs will probably expand impressively by a few orders of magnitudes in the next decade. But will it have the legs to carry on momentum and bite significantly into the coal market ?
  13. The technical potential for biomass energy is as large as the current fossil energy use.
  14. Diets are the key driver in land use scenarios, therefore in biomass energy scenarios.
  15. Algae biomass are not only for fuel but also food. To me this also seem to be an investor's frontier.