Lecture 13

Lecture 13 - SIO 40 – Life and Climate on Earth Friday...

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SIO 40 – Life and Climate on Earth Friday Oct 30 th , 2009 Lecture 13 – Long-term climate record Photo by Gary Fleeger, PaGS. A dropstone, geological indicator of climate
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Outline The Faint Young Sun Problem Role of CO 2 , CH 4 in moderating climate Long-term climate record Snowball Earth scenario Paleozoic and Mesozoic climate patterns Role of CO 2 and continental positioning
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The Faint Young Sun Problem Sun gets brighter with age, due to conversion of hydrogen to helium Modeling Earth’s surface temperature over time based on solar luminosity and present atmosphere (upper boundary of blue band at right) indicates that Earth surface temps would have been well below freezing before about 2 billion years ago. However, geological evidence indicates that liquid water (and life) has been present on Earth’s surface since about 3.8 billion years ago. How could this be? Solar luminosity curve Today’s atmosphere No atmosphere
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Possible solutions to the Faint Young Sun Problem Geothermal heat? – only about 0.3 W/m 2 , not enough to keep more than localized areas (eg. deep-ocean vents) ice-free Lower albedo? - couldn’t have been low enough to keep Earth warm by itself Greenhouse gases? – CO 2 levels in the atmosphere could have been much higher than today, kept Earth from freezing
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Atmospheric CO 2 concentration needed to compensate for solar luminosity if CO 2 and H 2 O were the only important greenhouse gases. About 1000x our present atmospheric level of CO 2 would be needed to keep Earth from freezing with a 30% reduction in solar flux – sounds like a lot, but not so much compared to the amount of CO 2 stored in carbonate rocks on Earth.
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Kasting, Scientific American 2004 Accumulation of O 2 in the atmosphere causes loss of methane, cools climate (Huronian Glaciation, ~2.3bya) Actually, more likely that CO 2 , H 2 O and CH 4 played important roles as atmospheric greenhouse gases in very early Earth history. Adding O 2 to the mix caused some major changes….
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Mean global climate changes over Earth's history Over the past 3 billion years of Earth history,
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This note was uploaded on 10/23/2010 for the course SIO SIO 40 taught by Professor Barbeau during the Fall '10 term at UCSD.

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Lecture 13 - SIO 40 – Life and Climate on Earth Friday...

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