Oceanic CO 2 removal options: Potential impacts and side effects Andreas Oschlies IFM-GEOMAR, Kiel

The Problem (?) Global Warming (GISTEMP, Hansen et al., 2009)

Possible/likely risks Individual attribution to global warming difficult

The cause: Anthropogenic CO 2 Atmospheric CO 2 concentration rises (only about half as fast as emissions!) Charles Keeling ( )

Risk assessment  IPCC Scenarios (IPCC, AR4, 2007)

IPCC Scenarios & Reality (Manning et al., 2010)

Projected global warming (Meinshausen et al., 2009)

Challenge: halving global emissions by 2050 reduce global emission by factor 2 population growth by factor 2 energy consumption at current EU-niveau: factor 5 required reduction in individual emissions: 2 x 2 x 5 = 20 Reaching this by transition to carbon-neutral power sources requires installation of ~1GW/day (until 2050). (perhaps not impossible, but VERY challenging: in 2009 Germany installed ~5GW/yr, close to required 10GW/yr)

Options Anthropogenic impact on the climate system Mitigation Reducing emissions requires collaboration

Options Anthropogenic impact on the climate system Common welfare Mitigation Reducing emissions Adaptation requires collaborationperception of costs

Options Anthropogenic impact on the climate system Climate systemCommon welfare Mitigation Reducing emissions Climate Engineering Adaptation requires collaborationperception of costsunilateral option?

Climate Engineering (Keith, 2001)

“Solar Radiation Management” Atmospheric CO 2 lifetime is long (Archer et al., 2009)  No short-term SRM solution without CO 2 -sequestration CO 2 -Rest von 1000 GtC

“Solar Radiation Management” (Archer et al., 2009) CO 2 -Rest von 5000 GtC Atmospheric CO 2 lifetime is long  No short-term SRM solution without CO 2 -sequestration

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Afforestation Culturally often viewed “positively” Limited potential (space) Restricted to growth phase Afforesting Australia ~10% of current emissions for ~100yr Impacts ecosystems Competes with food production

Afforestation Forests generally darker than crop land Particularly at high/mid latitudes in winter Net warming or cooling?

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

“artificial trees” expensive (300 $ /ton CO 2 ?), Energy intensive (net CO 2 -sink?) Still requires storage of CO 2 (courtesy David Keith) (courtesy Klaus Lackner)

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Lack of fertilization? Present-day sea-surface nitrate concentrations mmol/m 3 Mean profile (Conkright et al., 1994) lack of macronutrients (e.g., NO 3, PO 4, Si(OH) 4 ) lack of micronutrients (e.g., Fe)

Ocean fertilisation  Macronutrients (NH 4, NO 3, PO 4 ) need 140kg NH 4 to fix 1t C (+70kg PO 4 ) Input from land, e.g. Ocean Nourishment TM Artificial upwelling, e.g. AtmOcean  Micronutrients (Fe) need g Fe to fix 1t C (Planktos, Climos)

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Artificial upwelling Sea surface Z(mix) CO 2, O 2 organic matterinorganic nutrients nutrients,  CO 2 z pumping by surface wave-driven valves

Simulated artificial upwelling potential  pCO 2 (in ppm) for pipes up to 1000m deep. Mean: -18ppm (might get more negative/better with time!)

Simulated artificial upwelling potential  pCO 2 (in ppm) for pipes up to 1000m deep. Mean: -18ppm (might get more negative/better with time!) Potential: about 80 GtC over 100 years (~10% of current emissions) BUT: Small oceanic contribtion! (Oschlies et al., 2010)

Side effect 1: Where is the missing C? In the soils! C oc C ter C soil  SAT kgC/m 2

Side effect 2: “irreversibility” (Oschlies et al., 2010) Whenever ocean upwelling is stopped, mean temperatures soon exceed those of a world without Climate Engineering. Earth’s radiation balance:  Planet with colder surface waters stores more energy

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Ocean Iron Fertilization Present-day sea-surface nitrate concentrations mmol/m 3 Mean profile (Conkright et al., 1994) lack of micronutrients

Iron Fertilization at Sea “Give me a tanker load of iron and I will give you the next ice age” (John Martin, early 1990s)

“Give me a tanker load of iron and I will give you the next ice age” Iron Fertilization at Sea SERIES, 2002 SOIREE, kg Fe removed ~ 400 t C

Natural Southern Ocean Fe fertilization: Crozet Islands (Pollard et al., 2009)

Simulated Southern Ocean Fe fertilization fertilized area global Potential: 60 GtC over 100 years Global uptake < local CO 2 flux  non-local backflux (Oschlies et al., 2010)

Possible side effect: Suboxia OIF-induced decrease in simulated suboxic volume!

Possible side effect: Acidification Reduced acidification in remote surface waters!  pH

More (serious?) side effects: N 2 O, ecology Jin & Gruber (2003): offsetting effect of enhanced N 2 O emissions: ca 5-20% Ecological effects poorly understood Ecological effects intended Will have winners and losers

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Dissolution of carbonate and silicate rocks Alkalinity enhancement = neutralizes carbonic acid Reduces pCO 2 of surface water  enhances air-sea CO 2 flux Major mining operation! Limited by ocean circulation to <1GtC/yr sequestration (to avoid oversaturation; Köhler et al., 2010) Contamination by trace metals likely.

CO 2 alkalinity enhancement afforestation storage reservoirs direct injection Fe fertilization artificial upwelling artif. trees CO 2 CO 2 -Sequestration (Oschlies, 2010)

Direct CO 2 injection into the ocean Currently not allowed (London “Anti-dumping” convention & protocol)

Direct CO 2 injection into the ocean According to 3D ocean circulation models, deep injection has life times of hundreds of years. (Orr et al., 2001)

Conclusions  Sequestration potential of all methods limited to about 1GtC/yr over 100 years, each. Artificial upwelling: messes up Earth’s radiation balance Fe fertilization: messes up ecosystem, but has natural analogs Alkalinity enhancement: major mining operation, impurities  Direct injection has large potential but is currently considered as dumping.  Validation? Not locally possible (if at all)