Global Warmingin

Geologic Time

David ArcherUniversity 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

OH H

δ+δ+

2δ-

Resting State

OH H

OH H

Symmetric Stretch Bend

3657 cm-1 1594 cm-1

Water vapor is a greenhouse gas

Earth’s outgoing infrared spectrum

The band saturation effect

Svante Arrhenius

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

The water vapor feedback

Temperature+

+Water VaporConcentration

Water Vapor Feedback

Temperature+

+Ice Melts

Ice Albedo Feedback

The ice albedo feedback

Temperature Rise from 2000 to 2300, °C

Intense warming in high latitudes because of ice-albedo feedback

David Keeling

David Keeling started measuring CO2 concentration in the atmosphere

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400A

tmo

sph

eric

pC

O2

, pp

m

Mauna Loa, Hawaii

1955 1965 1975 1985 1995 2005

Year

IPCC

IPCC predicted in 1990 that global warming would rise above the noise by 2000

IPCC

IPCC in 1995 found a “discernable human influence on global climate”

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%

20%

30%

40%

50%

60%

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

What happens to fossil fuel CO2

One gallon of gasoline

Usable energy: 2500 kcal

Unwanted greenhouse energy over CO2 lifetime:

One gallon of gasoline

Usable energy: 2500 kcal

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

Avoiding Dangerous Climate Change

If the peak contains 50% of the emitted CO2, and climate sensitivity T2x = 3° C, then we could emit~ 700 Gton C and avoid warming greater than 2° C.

We have already emitted 300 Gton C.

Oil + Gas ~ 400 Gton C. Just stop burning coal.

How Long will Global Warming Last?

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

“Carbon dioxide cycles between the atmosphere, oceans andland biosphere. Its removal from the atmosphere involves arange of processes with different time scales. About 50% of a CO2 increase will be removed from the atmosphere within 30 years, and a further 30% will be removed within a few centuries. The remaining 20% may stay in the atmosphere for many thousands of years.”

IPCC 2007 Summary for Policymakers

4000-5000 Gton C Release

Peak 1 kyr 10 kyr

CLIMBER 67% 57% 26%Archer 2005 60% 33% 15%Lenton 2006 67-75% 14-16% 10-15%Ridgwell subm. 50% 34% 12%Tyrell 2007 70% 42% 21%

Atmosphere / Ocean / Weathering / CaCO3 models

Airborne Fraction

1000-2000 Gton C Release

Peak 1 kyr 10 kyr

CLIMBER 45% 31% 14%Archer 2005 58% 24% 11%Lenton 2006 50-63% 17-19% 11%

Atmosphere / Ocean / Weathering / CaCO3 models

Airborne Fraction

Warming for the Long Haul

1000 10,000years yearsfrom now from now

2000 Gton C 3° C 1.5°

5000 Gton C 5° 3°

3 °C

Year A.D.

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ther

n H

em

isph

ere

Ave

rage

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per

atur

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How much is 3 °C?

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So What Part I: Sea Level

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-100

-50

50

100Sea Level, m

Last GlacialMaximum20 kyr ago

Eocene40 Myr ago

Today

Pliocene3 Myr ago

-10 -5 0 5

Global T Change, °C

So What Part I: Sea Level

-150

-100

-50

50

100Sea Level, m

Last GlacialMaximum20 kyr ago

Eocene40 Myr ago

Today

IPCC Forecast for the year 2100

Pliocene3 Myr ago

-10 -5 0 5

Global T Change, °C

So What Part I: Sea Level

-150

-100

-50

50

100Sea Level, m

Last GlacialMaximum20 kyr ago

Eocene40 Myr ago

Today

Eventual Sea Level Rise?

Pliocene3 Myr ago

-10 -5 0 5

Global T Change, °C

Message to Florida: 20 meters would be it for ya’ll

Heat Diffuses Slowly

Ice flows if there’s water at the bed

It takes thousands of years to respondto climate changes.

Ice sheet models

Melt water carriesheat quickly

We don’t know how water gets through the ice

The real Greenlandice sheet responds in a few months.

Real ice sheets

A moulin in Greenlandwhere water submerges into the ice.

Zwalley et al (2002)

Earthquakes under Greenland ice

Ekstrom et al., 2006

Heinrich Events 30-70 kyr ago

Ice Rafted Debris (layers of rocks inocean sediments)

Ice sheet collapsed into the ocean

Raised sea level ~5 min a few centuries.

Could the Greenland ice sheet start doing this?

Meltwater Pulse 1A 14 kyr ago

1.5 to 3 Greenlandsin 1-5 centuries.

We’re not even surewhere this water came from.

5000 Gton of C release (business-as-usual to 2100 then stop)

50 m sea level rise, eventually

3.5% of the land area, home to >10% of the world’s population

Every American ultimately inundates 1000 sq. ft. of land per year.

A long-term sea level scenario

The Next Ice Age

3002001000

22°

23°

24°

25°

Intense Seasonsin the

Southern Hemisphere

Intense Seasonsin the

Northern Hemisphere

Precession Cycle

Anglefrom the Pole

to the Orbit

Obliquity Cycle

Eccentricity Cycle5% Elliptical,95% Circular

100% Circular

Thousands of Years Ago

Low

Ecce

ntric

ityW

eak

Prec

essio

n

A Threshold Model

sunlight

Interglacial Climate State

A Threshold Model

Interglacial Climate State

summer sunlight gets weak

A Threshold Model

summer sunlight gets weak

winter snow survives the summeran ice sheet is born

Glacial Climate State

A Threshold Model

sunlight gets strong again

Ice reflects light back to space

ice persists

Glacial Climate State

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Kyr Before Present

i0Trigger-minima

Red = Trigger-minima events

Dim Northern Hemisphere Sun= Growing Ice

CLIMBER Model Nucleates an Ice Sheet

Trigger

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CLIMBER model, Archer and Ganopolski, 2005

Cri

tica

l Ins

olat

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Val

ue, W

/m2

Atmospheric pCO2

If CO2 is higher,it takes a colder sunto nucleate the ice sheet.

Natural:Near miss!Wait until50 kyr

Archer and Ganopolski, 2005

1000 Gton:Wait until130 kyr fromnow

5000 Gton:No glaciationfor 400 kyr

Conclusions

Global warming is well understood, it has been detected,and the forecast for the end of the century is frightening.

CO2 emission will continue to effect climate for hundredsof thousands of years into the future.

Sea level may ultimately rise 100 times more than the forecast for the year 2100.