Post 2035: Fossil Emissions and the Paris Agreement Stephen Pacala Carbon Mitigation Initiative (CMI) Princeton University April 14, 2016 CMI Annual Meeting London 2016

The Paris Agreement’s 2050 objective Article 4, Section 1: Sources to balance sinks after 2050. Result: Constant atmospheric CO2.

A new scenario exactly matching Paris RCP 2.6: Fossil emissions drop from today’s level of 33 GtCO2/yr in 2020 to 12 GtCO2/yr in 2050, at which time the source is balanced by net sinks in the oceans and on land. RCP 2.6 concentration peaks roughly at mid-century, which is consistent with the Paris Agreement at least until 2050.

Fate of Anthropogenic CO2 Emissions (2004-2014 average) “Carbon-neutral” and carbon sinks Over half of emitted CO2 is kept from the atmosphere by natural sinks in forests and the ocean. Climate change may weaken these sinks, but work by the CMI reduces concern about their near-term loss. 9.5±1.8 GtCO2/yr 26% 33.0±1.8 GtCO2/yr 91% + 3.4±1.8 GtCO2/yr 9% 10.9±2.9 GtCO2/yr 30% 16.0±0.4 GtCO2/yr 44% Atmosphere Fossil Emissions Land Biosphere Land Use Emissions Oceans Fate of Anthropogenic CO2 Emissions (2004-2014 average) Source: CDIAC; NOAA-ESRL; Houghton et al 2012; Giglio et al 2013; Le Quéré et al 2014; Global Carbon Budget 2014

Fate of Anthropogenic CO2 Emissions (2004-2014 average) “Carbon-neutral” and carbon sinks Sinks have grown for 50 years. Atmosphere Fossil Emissions Land Biosphere Land Use Emissions Oceans Fate of Anthropogenic CO2 Emissions (2004-2014 average) Source: CDIAC; NOAA-ESRL; Houghton et al 2012; Giglio et al 2013; Le Quéré et al 2014; Global Carbon Budget 2014

Cumulative contributions to carbon in the atmosphere The cumulative contributions since 1870 Figure concept from Shrink That Footprint. Source: CDIAC; NOAA-ESRL; Houghton et al 2012; Giglio et al 2013; Joos et al 2013; Khatiwala et al 2013; Le Quéré et al 2015; Global Carbon Budget 2015.

Paris negative-carbon wedges

Paris negative-carbon wedges CCS Negative-carbon wedges

Negative emissions options Grow trees (afforestation/reforestation) Build soil carbon, e.g., by planting perennial species and/or burying “biochar”. BECCS – biofuel or biopower with CCS DAC-CCS – direct air capture of CO2 with CCS Accelerate CO2 mineralization to CaCO3 or MgCO3 Fertilize oceans to accelerate deep-sea C storage

Negative wedges by building up biocarbon stocks = Tons of carbon (tC) in vegetation = Tons of carbon (tC) in soil Note: 1 ton of carbon equals 44/12 or 3.67 tons of CO2. 100 tC 200 tC 5 tC 9 tC 2 tC 75 tC 150 tC 125 tC Primary Forest Grassland Pasture Cropland Carbon stored in a hectare of habitat

Negative wedges via BECCS Bioenergy with CCS (BECCS) is the favorite CO2 removal strategy in IPCC AR5, Working Group III. Bioenergy in a “two-degrees” scenario in 2100 is comparable to total energy in 2000; half is BECCS. Huge land demands: 600 million hectares of new cropland just for bioenergy, adding to 1500 million hectares for all cropland now. Sources: van Vuuren, et al., “The representative concentration pathways: an overview,” Climatic Change, 109: 5-31, 2011. van Vuuren, et al., “RCP2.6: exploring the possibility to keep global mean temperature increase below 2°C,” Climatic Change, 109: 95-116, 2011.

The scale of sinks wedges at mid-century A sink wedge: Remove 0.6 GtCyr (2.2 GtCO2/yr) in 2050 CCS from 500 GW coal or 1000 GW gas BECCS: Cellulosic ethanol to CCS power, with 100% carbon captured, on 100 Mha (roughly half of US cropland today). Temperate afforestation on 200 Mha or tropical afforestation on 100 Mha. DAC (direct air capture): Structures 10 m high capturing 75% of the CO2 in 4 m/s air, with 4000 km total length. Restore lost soil carbon on 20% of global cropland or half the lost carbon on 40% of the cropland Manage pastures for soil carbon storage (i.e. breed for grasses with lignified roots, reduce overgrazing) BECCS cellulosic ethanol: 1 liter/m^2 rule of thumb. Also 6tC/ha-yr tropical [check] perennials. C in ethanol is 4/7 of total mass. Afforestation: 4t/ha-yr in tropical, 2t/ha-yr in temperate – as trees grow. Soil carbon: See LM3 and Global Carbon Project: 69 GtC lost through agriculture, can be restored. Pasture can probably be restored too. Add gas for coal. Do these freshly.