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

Air

born

e F

ract

ion

of C

arbo

n R

elea

sed

Century timescale peak

Millennial timescale tail

Airborne fraction of fossil fuel CO2

Paleocene/Eocene Thermal Maximum Event 55 Myr Ago

A natural releaseof CO2, comparableto the potential fossil fuel release.

Warming, with a recovery that took100,000 years.

Zachos et al. 2001

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.

IPCC 2001 and earlier Summaries for Policymakers

IPCC 2001 and earlier reports implied that global warming would last about a century.

CO2 + CO3= + H2O <--> 2 HCO3

-

10 100 2000 M

CO2 uptake capacity is determined by CO3=

Seawater pH Chemistry

Concentration in seawater

Atmosphere / Ocean Equilibrium

600 Gton C

1800 Gton C as CO3=

Gton C = 1015 g

We expect a partitioningof ~1:3 between air andocean

Atmosphere / Ocean Equilibrium

Airborne Fraction of CO2 Slug

1000-2000Gton

4000-5000Gton

Archer 2005 22% 33%Lenton 2006 21-26% 34%CLIMBER 22% 35%Goodwin 2007 24-26% 40%Ridgwell 2007 31%

Atmosphere / Ocean Equilibrium

Affected by:changes in circulation

biologyocean temperature

saturating the carbonate ion buffer

Neutralization by CaCO3

CO2 + CaCO3 + H2O ==> Ca2+ + 2 HCO3-

How long does it take?

Neutralization e-folding timescale

Archer 2005 5-8kyrLenton 2006 500 - 1000 yrRidgwell 2007 1-2 kyrTyrell 2007 2-3 kyr

Atm. / Ocean / CaCO3 Equilibrium

CO2 + CO3= + H2O 2 HCO3

-

CaCO3 Ca2+ + CO3=

Fossil CO2

Atm. / Ocean / CaCO3 Equilibrium

[CO2] [CO3=]

[HCO3-]2

K2

K1

=

Restored by CaCO3 equilibrium

Increases by 2x fossil fuel release

Proportional to pCO2 (Henry’s law).Goes up ~ 10% of fossil CO2

release

The Silicate Weathering CO2 Thermostat

CaCO3

Burial

CO2

CaO

Subduction

Weathering = function(climate)

Metamorphosis

0200400600800

10001200

16001800

1400

0

1

2

3

4

5

6

0 100 300 500200 400

pCO

2°C

kyr

The long tail

One gallon of gasoline

Usable energy: 2500 kcal

Unwanted greenhouse energy over CO2 lifetime:

A Geochemical Joke

One gallon of gasoline

Usable energy: 2500 kcal

Unwanted greenhouse energy over CO2 lifetime: 100,000,000,000 kcal

A Geochemical Joke

Sea Level

-150

-100

-50

50

100

5 10 15 20

Global Mean T, °C

Sea Level, m

Last GlacialMaximum20 kyr ago

Eocene40 Myr ago

Today

Pliocene3 Myr ago

Sea Level

-150

-100

-50

50

100

5 10 15 20

Global Mean T, °C

Sea Level, m

Last GlacialMaximum20 kyr ago

Eocene40 Myr ago

Today

Pliocene3 Myr ago

IPCCForecast

Year 2100

Eventual change100x higher thanIPCC forecast for2100

Conclusions

The climate impacts of fossil fuel CO2 releasewill persist for millennia.

Sea level rise could ultimately be 100 times greaterthan 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.

Long thaw

Intended for a “popular”-level audience

Global carbon cycle

Carbon cycle sciencefor climate wonks

Understanding the forecast

Rocks-for-jocks levelundergraduate textbook

Open climate 101

Open access class

video lectures on-line models quizzes and labs print out a useless non-certificate

Climate crisis

IPCC 2007 “Unofficial Guide”

Working Groups 1 (mostly), plus 2 and 3

Warming papers

Classic scientific papers (1827-2008) with snarky commentary