What s up with Earth s Climate? David Archer Department of the Geophysical Sciences University of Chicago
This Sesson Began Sept. 29, 2014 Will begin again March 2015 Coursera.org
Understanding the forecast
The Long Thaw How humans are changing the next 100,000 years of Earth s climate David Archer University of Chicago
Other Good Books Six Degrees by Mark Lynas Alternative Energy Without All the Hot Air David MacKay available for free pdf download
Energy Balance of a Bare Rock Sun Light Earth Light (1- Isolar 4 T 4 earth Earth T earth = 259 K = -14 C = 6 F
A Planet with an Atmosphere Boundary to Space (1- Isolar 4 I up, atmosphere Atmosphere T atm = 259 K I down, atmosphere Iup, ground Earth T earth = 303 K = 86 F
What Makes a Greenhouse Gas? Resting State Symmetric Stretch O C O O C O No Resting Dipole IR Inactive Asymmetric Stretch Bend O C O O C O 2349 cm -1 660 cm -1
Earth s outgoing infrared spectrum CO 2 absorbs where the light is. CH 4 is off in the wing.
The band saturation effect
~40 x Steeper for CH4
Shindell Shindell et al 2012
What Happens to Methane in the Atmosphere OH. CH 4 CH 3. CO 2 ~ 10 years
Methane Dynamics in the Atmosphere
Time scale for Earth s Temperature Response Surface Ocn. ~10 yrs Deep Ocn. ~1000 yrs
Airborne Fraction of Carbon Released What Happens to Fossil Fuel CO 2 in the Atmosphere 60% 50% 40% Ocean Invasion Century timescale peak 30% 20% Reaction with CaCO3 Millennial timescale tail 10% Reaction with Igneous Rocks 0% 0 5000 10000 15000 20000 25000 30000 35000 40000 Year A.D.
Stage I: CO 2 dissolves in the oceans CO 2 + CO 3= + H 2 O <--> 2 HCO 3 - Atmospheric CO 2 ~600 Gton C We expect a partitioning of ~1:3 between air and ocean Time scale = 100 s - 1000 yrs Ocean CO 3 = ~ 1800 Gton C Gton C = 10 15 g
Stage II: CO 2 is neutralized by CaCO 3 CO 2 + CaCO 3 + H 2 O ==> Ca 2+ + 2 HCO 3 - Weathering, function of climate CaCO 3 -> Ca 2+ + CO 3 = Ca 2+ + CO 3= -> CaCO 3 Pulls the airborne fraction down to ~10% Time scale = 1000-10,000 yrs Burial, function of ph
Stage III: The CO 2 thermostat from silicate weathering CO 2 degassing from the Earth Igneous weathering = function of fresh water (hydrologic cycle) CaSiO 3 + CO 2 -> Ca 2+ + CO 3= + SiO 2 Metamorphic decarbonation Ca 2+ + CO 3= -> CaCO 3 Subduction Burial of CaCO 3
Stage III: The CO 2 thermostat from silicate weathering CO 2 concentration CO 2 flux weathering degassing 100,000 years Stabilizes Earth s climate on time scales of ~100,000 years Helps solve Sagan s faint young sun paradox Will determine the longevity of the climate impact from fossil fuel CO 2 release to the atmosphere.
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.
C Band saturation emphasizes the tail pco 2 1800 1600 1400 1200 1000 800 600 400 200 0 6 5 4 3 2 1 0 0 100 200 300 400 500 kyr
A geochemical joke One gallon of gasoline Usable energy: 2500 kcal Unwanted greenhouse energy over CO 2 lifetime:
A geochemical joke One gallon of gasoline Usable energy: Unwanted greenhouse energy over CO 2 lifetime: 2500 kcal 100,000,000,000 kcal Hahahaha
Sluglator model
Sea Level Sea Level, m 100 50 Global Mean T, C Today Pliocene 3 Myr ago Eocene 40 Myr ago 5 10 15 20-50 Last Glacial Maximum 20 kyr ago -100-150
Sea Level Sea Level, m 100 50 Global Mean T, C Today Pliocene 3 Myr ago Eocene 40 Myr ago 5 10 15 IPCC 20 Forecast -50 Year 2100 Last Glacial Maximum 20 kyr ago -100-150
Sea Level Sea Level, m 100 50 Global Mean T, C Today Eocene 40 Myr ago After a few thousand years Pliocene 3 Myr ago 5 10 15 20-50 Last Glacial Maximum 20 kyr ago -100-150
Other Slow Impacts Melt permafrost (centuries), releasing carbon Warm the deep ocean (1000 yrs) Thaw methane hydrate Decreased O 2 solubility Whatever the Glacial / Interglacial CO 2 trick was
Lower CO 2 During Ice Age
Thousands of Years Ago Orbital Forcing of Climate Intense Seasons in the Southern Hemisphere Precession Cycle Intense Seasons in the Northern Hemisphere 25 Obliquity Cycle Angle from the Pole to the Orbit 24 23 22 5% Elliptical, 95% Circular Eccentricity Cycle 100% Circular 0 100 200 300
540 520 500 480 460 440 420 400 1.4 1.2 1 0.8 0.6 0.4 0.2 Dim Northern Hemisphere Sun = Growing Ice i0 Trigger-minima Red = Trigger-minima events 0 0 100 200 300 400 500 600 700 800 KyrBefore Present
CLIMBER Model Nucleates an Ice Sheet Trigger
Critical Insolation Value, W/m 2 470 460 450 440 430 420 410 400 If CO 2 is higher, it takes a colder sun to nucleate the ice sheet. 100 200 300 400 500 600 Atmospheric pco 2 CLIMBER model, Archer and Ganopolski, 2005
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
CO 2 vs. CH 4 CO 2 poses a trap for humanity now vs. future persists essentially forever. CH 4 we emit will subside within our time except for ocean heat pollution CO 2 emissions are the main issue, CH 4 is frosting.
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
Conclusions The impacts of global warming will last for millennia (not just a few centuries). 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. Forget methane: Keep your eye on the ball, which is CO 2