Global Warming in Geologic Time David Archer University of Chicago

Joseph Fourier Memoires d l’Academie Royale des Sciences de l’Institute de France VIIII, (1827) Joseph Fourier described the greenhouse effect in 1827

T earth = 259 K = -14° C = 6°F Energy Balance of a Bare Rock

T atm = 259 K T earth = 303 K = 86° F A Planet with an Atmosphere

John Tyndall, 1859 John Tyndall discovered that CO 2, H 2 O, and CH 4 are greenhouse gases. O 2 and N 2 are not.

CO O Symmetric Stretch Asymmetric StretchBend CO O C O O COO Resting State No Resting DipoleIR Inactive 2349cm 660cm CO 2 is a greenhouse gas

Water vapor is a greenhouse gas

Earth’s outgoing infrared spectrum

The band saturation effect

Svante Arrhenius Svante Arrhenius calculated that doubling CO 2 would warm the Earth by 4-6°C, in 1896

The water vapor feedback

The ice albedo feedback

Intense warming in high latitudes because of ice-albedo feedback

David Keeling David Keeling started measuring CO 2 concentration in the atmosphere

A t m o s p h e r i c p C O 2, p p m Mauna Loa, Hawaii

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 gas forcing looks like the recent temperature rise. Climate forcings Crowley, 2000

What about phenomena undreamed-of? The sun is good at pushing our climate buttons. Clouds? Humidity? “They blame CO 2 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.

Airborne Fraction of Carbon Released Century timescale peak Millennial timescale tail What happens to fossil fuel CO 2

One gallon of gasoline Usable energy: 2500 kcal Unwanted greenhouse energy over CO 2 lifetime:

One gallon of gasoline Usable energy: 2500 kcal Unwanted greenhouse energy over CO 2 lifetime:100,000,000,000 kcal

Avoiding Dangerous Climate Change If the peak contains 50% of the emitted CO 2, and climate sensitivity  T 2x = 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

Gton C Release Peak 1 kyr 10 kyr CLIMBER67%57%26% Archer %33%15% Lenton %14-16%10-15% Ridgwell subm.50%34%12% Tyrell %42%21% Atmosphere / Ocean / Weathering / CaCO 3 models Airborne Fraction

Gton C Release Peak 1 kyr 10 kyr CLIMBER45%31%14% Archer %24%11% Lenton %17-19%11% Atmosphere / Ocean / Weathering / CaCO 3 models Airborne Fraction

Warming for the Long Haul ,000 yearsyearsfrom now 2000 Gton C3° C1.5° 5000 Gton C5°3°

3 °C Year A.D. Northern Hemisphere Average Temperature How much is 3 °C?

So What Part I: Sea Level Sea Level, m Last Glacial Maximum 20kyr ago Eocene 40Myr ago Today Pliocene 3 Myr ago Global T Change, °C

So What Part I: Sea Level Sea Level, m Last Glacial Maximum 20kyr ago Eocene 40Myr ago Today IPCC Forecast for the year 2100 Pliocene 3 Myr ago Global T Change, °C

So What Part I: Sea Level Sea Level, m Last Glacial Maximum 20kyr ago Eocene 40Myr ago Today Eventual Sea Level Rise? Pliocene 3 Myr ago Global T Change, °C

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

Ice flows if there’s water at the bed It takes thousands of years to respond to climate changes. Ice sheet models

Melt water carries heat quickly We don’t know how water gets through the ice The real Greenland ice sheet responds in a few months. Real ice sheets

A moulin in Greenland where water submerges into the ice. Zwalley et al (2002)

Earthquakes under Greenland ice Ekstrom et al., 2006

Heinrich Events kyr ago Ice Rafted Debris (layers of rocks in ocean sediments) Ice sheet collapsed into the ocean Raised sea level ~5 m in a few centuries. Could the Greenland ice sheet start doing this?

Meltwater Pulse 1A 14 kyr ago 1.5 to 3 Greenlands in 1-5 centuries. We’re not even sure where 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 ° 23° 24° 25° Intense Seasons in the Southern Hemisphere Intense Seasons in the Northern Hemisphere Precession Cycle Angle from the Pole to the Orbit Obliquity Cycle Eccentricity Cycle 5% Elliptical, 95% Circular 100% Circular Thousands of Years Ago L o w E c c e n t r i c i t y W e a k P r e c e s s i o 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 summer an 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

Dim Northern Hemisphere Sun = Growing Ice

CLIMBER Model Nucleates an Ice Sheet Trigger

CLIMBER model, Archer and Ganopolski, 2005 Critical Insolation Value, W/m 2 Atmospheric pCO 2 If CO 2 is higher, it takes a colder sun to nucleate the ice sheet.

Natural: Near miss! Wait until 50 kyr Archer and Ganopolski, 2005

1000 Gton: Wait until 130 kyr from now

5000 Gton: No glaciation for 400 kyr

Conclusions Global warming is well understood, it has been detected, and the forecast for the end of the century is frightening. CO 2 emission will continue to effect climate for hundreds of thousands of years into the future. Sea level may ultimately rise 100 times more than the forecast for the year 2100.