Earth’s Climate History

Climate v. Weather Climate: The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region. Climate: The meteorological conditions, including temperature, precipitation, and wind, that characteristically prevail in a particular region. Weather: The state of the atmosphere at a given time and place, with respect to variables such as temperature, moisture, wind velocity, and barometric pressure. Weather: The state of the atmosphere at a given time and place, with respect to variables such as temperature, moisture, wind velocity, and barometric pressure.

Controls on Whole-Earth Climate 1. Strength of the sun 2. Earth’s position relative to the Sun (Milankovich cycles) 3. Heat from inside the Earth 4. How shiny the Earth is (Albedo) 5. Greenhouse gases

1. Strength of Sun Weak Sun Paradox Weak Sun Paradox

2. Position relative to Sun (Milankovitch Cycles)

3. Heat From Earth  Sweeping up of material close by  Heating by: 1. meteorite impact (kinetic energy) 2. gravitational compression (potential energy) 3. decay of short-lived radioactive elements.

4. “Shininess” (Albedo)

5. Greenhouse Gases

Controls on Whole-Earth Climate Which of these 5 controls on the Earth’s climate does life on Earth have any hope of influencing? Which of these 5 controls on the Earth’s climate does life on Earth have any hope of influencing? A: Albedo and A: Albedo and GHG’s. Life has affected the climate, many times...

Earth’s Climate History The extremes (Snowball and Hothouse Earth) The extremes (Snowball and Hothouse Earth) The Goldilocks state (The The Goldilocks state (The last 35 million years) Exiting Goldilocks: runaway icehouse and runaway greenhouse. Exiting Goldilocks: runaway icehouse and runaway greenhouse.

Earth History and Evolution How has Earth’s Climate changed with time? How has Earth’s Climate changed with time?

Hothouse Tropical sea surface temperatures as high as 35 o C (95 o F), compared to 28–29 o C today. Tropical sea surface temperatures as high as 35 o C (95 o F), compared to 28–29 o C today. High latitude SSTs were 20 o C (68 o F) or higher. High latitude SSTs were 20 o C (68 o F) or higher. Estimates for paleodepths greater than 1000 m range between 11 o C (51.8 o F) and 19 o C (66.2 o F). Estimates for paleodepths greater than 1000 m range between 11 o C (51.8 o F) and 19 o C (66.2 o F). Source: Bice and Norris, 2002

How hot is a Hothouse? Middle Cretaceous strata contain abundant indications of extreme global warmth... Middle Cretaceous strata contain abundant indications of extreme global warmth... –Crocodilians in the Canadian arctic –Fossil breadfruit trees in Greenland Source: Bice and Norris, 2002

Enter: Goldilocks Source: Zachos et al., 2001

The Goldilocks Metronome Lisiecki, L. E., and M. E. Raymo (2005)

2. Position relative to Sun (Milankovitch Cycles)

The Goldilocks Metronome Source: Petit et al., 1999

CO2 lead-lag Transition from cold to warm take ~5000 years. Transition from cold to warm take ~5000 years. But, for the first 800 years, temp rises without CO2 rising. Why? But, for the first 800 years, temp rises without CO2 rising. Why? CO2 is rising for the rest of that 4200 years. CO2 is rising for the rest of that 4200 years. –CO2 doesn’t trigger the warming, but it does amplify it (Models predict CO2 and other GHG’s are responsible for about ½ of the warming). Caillon et al., 2003

Goodbye Goldilocks Runaway Icehouse: Runaway Icehouse: –GHG levels drop (carbonates) –Ice extent increases the earth’s albedo to the point where we go into a snowball or slushball Earth. Runaway Greenhouse: Runaway Greenhouse: –The amount of CO2 in the atmosphere until there is enough to melt ice, and decrease albedo. –Various feedbacks speed process.

Feedbacks and ratchets Feedback: when the output of a system is fed back as an input, altering the next output. E.g. water vapor, ice, and gas solubility Feedback: when the output of a system is fed back as an input, altering the next output. E.g. water vapor, ice, and gas solubility Ratchet: You can crank it Ratchet: You can crank it one way, but you can’t crank it the other. E.g. an ice sheet.

Today’s Exit? Essential questions: Essential questions: 1.Do Greenhouse Gases trap heat? If so... 2.Are GHG concentrations rising? If so... 3.Are we causing that rise?

GHGs Do Trap Heat CO2 not the biggest greenhouse gas, water is. CO2 not the biggest greenhouse gas, water is. We can’t control water, except by controlling the others. We can’t control water, except by controlling the others. CO2, CH4, and N2O are big because they fall in gaps with water. CO2, CH4, and N2O are big because they fall in gaps with water. 1. NASA Earth Observatory 2. Fleming, J. R. (2005)

GHG Concentrations are Rising 3. The Scripps CO2 Program

Are We Causing it? : CO2 emissions estimated from the U.N. Energy Statistics Yearbook : CO2 emissions estimated from the U.N. Energy Statistics Yearbook. Before 1950: Data came from fuel-production data Before 1950: Data came from fuel-production data 4. Carbon Dioxide Information Analysis Center

Yeah, we’re causing it. We’ve emitted twice as much CO2 as is needed to account for the rise we’ve seen to 390 ppm. We’ve emitted twice as much CO2 as is needed to account for the rise we’ve seen to 390 ppm. The other half has mostly gone into the ocean. The other half has mostly gone into the ocean. 5. Sabine et al., 2004

Why does this class care? 1. It’s cool! 2. Understanding the climate is essential for understanding both Earth’s history, and the evolution of life on this planet 3. There are 5 ways to modify Earth’s average temp. 4. Life only has a chance at modifying 2 of them. 5. Humans are the most recent in a very select group of organisms that can claim to have modified the climate (joining cyanobacteria, coral, phytoplankton, and terrestrial plants).