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

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

3. 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.

4. 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 % +
3.4±1.8 GtCO2/yr %
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 ( average)
Source: CDIAC; NOAA-ESRL; Houghton et al 2012; Giglio et al 2013; Le Quéré et al 2014; Global Carbon Budget 2014

5. 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 ( average)
Source: CDIAC; NOAA-ESRL; Houghton et al 2012; Giglio et al 2013; Le Quéré et al 2014; Global Carbon Budget 2014

6. 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.

7. Paris negative-carbon wedges

8. Paris negative-carbon wedges
CCS
Negative-carbon wedges

9. 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

10. 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

11. 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, van Vuuren, et al., “RCP2.6: exploring the possibility to keep global mean temperature increase below 2°C,” Climatic Change, 109: , 2011.

12. 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.