1. The Global Carbon Cycle
and its Relation
to Global Climate
David Archer, University of Chicago

2. Airborne fraction of fossil fuel CO2
Airborne Fraction of Carbon Released
Century timescale peak
Millennial timescale tail

3. Paleocene/Eocene Thermal Maximum Event
55 Myr Ago
A natural release
of CO2, comparable
to the potential
fossil fuel release.
Warming, with a
recovery that took
100,000 years.
Zachos et al. 2001

4. Long Tail Model Intercomparison Project
LTMIP
D. Archer, M.l Eby, V. Brovkin, A. Ridgwell, L. Cao, U. Mikolajewicz, K. Caldeira,
K. Matsumoto, G. Munhoven, A. Montenegro, Ann. Rev. Earth Sciences, 2009.

5. IPCC 2001 and earlier
Summaries for Policymakers
IPCC 2001 and earlier reports implied that
global warming would last about a century.

6. Seawater pH Chemistry
CO2 + CO3= + H2O <--> 2 HCO3-
10 100 2000 M
Concentration in seawater
CO2 uptake capacity is determined by CO3=

7. Atmosphere / Ocean Equilibrium
600 Gton C
1800 Gton C as CO3=
We expect a partitioning
of ~1:3 between air and
ocean
Gton C = 1015 g

8. Atmosphere / Ocean Equilibrium
Airborne Fraction of CO2 Slug
1000-2000 4000-5000
Gton Gton
Archer 2005 22% 33%
Lenton 2006 21-26% 34%
CLIMBER 22% 35%
Goodwin 2007 24-26% 40%
Ridgwell 2007 31%

9. Atmosphere / Ocean Equilibrium
Affected by:
changes in circulation
biology
ocean temperature
saturating the carbonate ion buffer

10. Neutralization by CaCO3
CO2 + CaCO3 + H2O ==> Ca2+ + 2 HCO3-

11. How long does it take?
Neutralization e-folding timescale
Archer 2005 5-8kyr
Lenton 2006 500 - 1000 yr
Ridgwell 2007 1-2 kyr
Tyrell 2007 2-3 kyr

12. Atm. / Ocean / CaCO3 Equilibrium
Fossil CO2
CO2 + CO3= + H2O 2 HCO3-
CaCO3 Ca2+ + CO3=

13. Atm. / Ocean / CaCO3 Equilibrium
Proportional to
pCO2 (Henry’s law). Restored by
Goes up ~ 10% of fossil CO2 CaCO3 equilibrium
release
[CO2] [CO3=] K2
-]2
=
[HCO3 K1
Increases by 2x fossil fuel release

14. The Silicate Weathering CO2 Thermostat
CO2
Weathering = function(climate)
CaO
CaCO3
Burial
Subduction
Metamorphosis

15. The long tail
1800
1600
1400
pCO2
1200
1000
800
600
400
200
0
6
5
4
°C
3
2
1
0
0 100 200 300 400 500
kyr

16. A Geochemical Joke
One gallon of gasoline
Usable energy: 2500 kcal
Unwanted greenhouse energy
over CO2 lifetime:

17. A Geochemical Joke
One gallon of gasoline
Usable energy: 2500 kcal
Unwanted greenhouse energy
over CO2 lifetime: 100,000,000,000 kcal

18. Sea Level
Sea Level, m 100
Eocene
40 Myr ago
50
Pliocene
3 Myr ago
Global Mean T, °C Today
5 10 15 20
-50
Last Glacial -100
Maximum
20 kyr ago
-150

19. Sea Level
Sea Level, m 100
Eocene
40 Myr ago
50
Pliocene
3 Myr ago
Global Mean T, °C Today
5 10 15 IPCC 20
Forecast
-50 Year 2100
-100
Last Glacial Eventual change
Maximum
20 kyr ago 100x higher than
-150
IPCC forecast for
2100

20. Conclusions
The climate impacts of fossil fuel CO2 release
will persist for millennia.
Sea level rise could ultimately be 100 times greater
than the IPCC forecast for the year 2100.
The carbon cycle on century timescales in the past
has acted as an amplifier of climate change. So far,
the carbon cycle today has been absorbing carbon
(stabilizing feedback), but this could change.

21. Intended for a “popular”-
level audience
thaw

22. Global carbon cycle
Carbon cycle science
for climate wonks

23. Understanding the forecast
Rocks-for-jocks level
undergraduate textbook

24. Open climate 101
Open access class
video lectures
on-line models
quizzes and labs
print out a useless
non-certificate

25. Climate crisis
IPCC 2007
“Unofficial Guide”
Working Groups 1
(mostly), plus 2 and 3

26. Warming papers
Classic scientific papers
(1827-2008) with snarky
commentary