The importance of longevity in a greenhouse gas as climate forcing

David Archer

University of Chicago

Joseph Fourier Memoires d l’Academie Royale des Sciences de l’Institute de France VIIII, 570-604 (1827)

Joseph Fourier described the greenhouse effect in 1827

(1-α) Isolar4 ε σ T

4earth

Sun Light Earth Light

Earth

Tearth = 259 K = -14° C = 6°F

Energy Balance of a Bare Rock

(1-α) Isolar4

Earth

Atmosphere

I ,up atmosphere

I ,down atmosphere

I ,up ground

Boundary to Space

Tatm = 259 K

Tearth = 303 K = 86° F

A Planet with an Atmosphere

John Tyndall, 1859

John Tyndall discovered that CO2, H2O, and CH4 aregreenhouse gases. O2 and N2 are not.

CO O

Symmetric Stretch

Asymmetric Stretch Bend

CO O

CO OCO O

Resting State

No Resting Dipole IR Inactive

2349 cm-1 660 cm-1

CO2 is a greenhouse gas

Earth’s outgoing infrared spectrum

The band saturation effect

Radiative Forcing goes as ln(CO2)

Svante Arrhenius

Svante Arrhenius calculated that doubling CO2 would warm the Earth by 4-6°C, in 1896

The water vapor feedback

Temperature+

+Water Vapor

Concentration

Water Vapor Feedback

The Runaway Greenhouse Effect

Temperature+

+Ice Melts

Ice Albedo Feedbac

The ice albedo feedback

David Keeling

David Keeling started measuring CO2 concentration in the atmosphere

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are needed to see this picture.

The biosphere breathes

Various public predictions of detectable human-caused warming by year 2000

Charney report and others

Only greenhouse gasforcing looks like therecent temperature rise.

Climate forcings

Crowley, 2000

What about phenomenaundreamed-of?

The sun is good at pushing our climate buttons.

Clouds? Humidity?

“They blame CO2 because they can’t think of anything else.”

A detective story

The Butler. Found holding a smoking gun next to the deceased. Forensics matches the gun with the bullets.

The Chauffer. In Kentucky for sister’s wedding. “Can’t think of any way he could have done it.”

To convict the Chauffer, we’d have to first unconvict the Butler.

0%

10%

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0 5000 10000 15000 20000 25000 30000 35000 40000

Ocean Invasion

Reaction with CaCO3

Year A.D.

Reaction with Igneous Rocks

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

IPCC 2001 and earlier Summaries for Policymakers

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

Everyone gets this wrong

Rutledge 2011

Ramanathan 2008

Shindell, 2012

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.

0200400600800

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0

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0 100 300 500200 400

pCO

2°C

kyr

Band saturation effect of IR absorbtion by CO2 emphasizes the tail

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

Flakiness in ocean / atmosphereequilibrium

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

Pulls the airborne fraction down to ~ 10%

The Silicate Weathering CO2 Thermostat

CaSiO2 -> Ca2+ + SiO2

Ca2+ + CO3= -> CaCO3

Burial + Subduction

Weathering = function( CO2 )

CaCO3 + SiO2 -> CaSiO2 + CO2

Volcanic CO2 degassing

CO2

>100,000 years

The Silicate Weathering CO2 Thermostat

Helps explain Carl Sagan’s “Faint Young Sun” paradox

Time scale must be longer than this

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

Methane

Methane is about here

CO2 is here

Methane is about here

CO2 is here

Methane

Methane

Earth’s temperature response toradiative forcing

Climate sensitivity: T / RF

Time scale: 10 yrsUpper 100m

DeepOcean

RF

Thermal bufferof the deepocean: Time scale 1000 yrs

Shindell, et al 2012

CO2 vs. CH4

CO2 poses a “trap” for humanity, because of the time separation of the cause and the impacts, which will continue to worsen essentially forever. It’s like an ever-intensifying curse on our descendents, or planting a cancer.

The climate impacts from CH4 peak and subside within a human timescale.

“Good” cholesterol vs. “Bad” cholesterol?

1 Trillion tons of C => 2 °C peak warming

Allen et al 2009

1 Trillion tons of C

Already released: 1/2 trillion tons 0.3 from fuels 0.2 from deforestation

Costs (cuts / year) go up if we wait

Fossil fuels are mostly coal

Coal

Oil

Gas

ConclusionsNo one has a model or theory of climate that explains the present but predicts that global warming won’t happen and be significant.

The impacts of global warming from CO2 will last for millennia (not just a few centuries).

The impacts of short-lived greenhouse gases is attenuated by the slow response time of Earth’s temperature.

Lesson from the past: Sea level is 100x more sensitive to Earth’s temperature on thousand-plus year timescales than the forecast for the year 2100.