1. Saturday, 14 February 2015: 8:30 AM-11:30 AM
Physical Science of the Global Carbon Cycle as It Relates to Carbon Dioxide Removal
Ken Caldeira  Carnegie Institution for Science, Stanford, CA USA

2. Carbon Dioxide Removal and the Natural Carbon Cycle
Many carbon dioxide removal and storage proposals involve increasing rates of processes that already occur in the natural carbon cycle.
Removing CO2 from the atmosphere causes outgassing of CO2 from the land biosphere and ocean.
For storage times of many thousands of years or more, there must be a physical or chemical barrier preventing the CO2 from contacting the atmosphere.

3. CO2 stays in the atmosphere for a long time.
Archer et al., 2009
CO2 stays in the atmosphere for a long time.

4. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

5. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

7. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

8. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

9. CO2
CaCO3
Ca2+
HCO3-
Ridgwell, Kennedy and Caldeira (2003)

10. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

11. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

12. Geological carbon cycle
Weathering of
rocks
Sediment burial
Williams and Follows (2011)

13. Carbon Cycle Time Scales
Years to centuries
CO2 taken up by biosphere
CO2 + H2O  CH2O + O2
CO2 taken up oceans
CO2 + H2O  H+ + HCO3-
Thousands of years
dissolution of carbonate minerals  oceans
CO2 + CaCO3 + H2O  Ca HCO3-
Hundreds of thousands of years
weathering of silicate rocks  carbonate rocks and sediments
CO2 + CaSiO3  CaCO3 + SiO2

14. CO2 stays in the atmosphere for a long time.
Archer et al., 2009
CO2 stays in the atmosphere for a long time.

15. If we removed all excess CO2 from the atmosphere today, that would offset only about half the warming
Cao et al 2011

16. Carbon dioxide removal proposals
Caldeira et al., 2013

17. Carbon Dioxide Removal and the Natural Carbon Cycle
Many carbon dioxide removal and storage proposals involve increasing rates of processes that already occur in the natural carbon cycle.
Removing CO2 from the atmosphere causes outgassing of CO2 from the land biosphere and ocean.
For storage times of many thousands of years or more, there must be physical or chemical barrier preventing the CO2 from contacting the atmosphere.