SIO40lecture18

SIO40lecture18 - SIO 40 Life and Climate on Earth Nov 15 2010 Lecture 18 Climate Projections Lecture Outline-Emission scenarios-Projected warming

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SIO 40 – Life and Climate on Earth Nov. 15, 2010 Lecture 18 – Climate Projections
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Lecture Outline - Emission scenarios - Projected warming trajectories - Carbon cycle feedbacks - Projected precipitation changes - Climate change and severe weather - ENSO variability - Projected sea level rise - Abrupt climate change
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Fossil fuel emission scenarios Predictions of future climate must start with some assumptions about future fossil fuel emissions. For the IPCC 4 th Assessment Report, experts developed 4 “storylines” (A1, A2, B1 and B2), each representing a group of emissions scenarios for the future. The three scenarios within the A1 storyline involve either intensive use of fossil fuels (A1FI), limited use of fossil fuels (A1T), and a scenario that assumes balanced use of both fossil and non-fossil fuels (A1B). The A2, B1 and B2 storylines make different assumptions about regionalisim, population growth, and the introduction of clean energy technologies. A1B is often used as a “middle of the road” scenario for a basis of comparison in the IPCC report. Note: since publication of the IPCC report in 2007, studies have shown that the growth rate of CO 2 emissions has tracked the most pessimistic of the IPCC scenarios (ie. the ones with the fastest rate of CO 2 emissions).
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For a given emissions scenario, various biogeochemical models are used to calculate concentrations of constituents in the atmosphere. Various radiation schemes and parametrizations are required to convert these concentrations to radiative forcing. Finally, the response of the different climate system components (atmosphere, ocean, sea ice, land surface, chemical status of atmosphere and ocean, etc.) is calculated in a comprehensive climate model. In addition, the formulation of, and interaction with, the carbon cycle in climate models introduces important feedbacks which produce additional uncertainties. From emissions scenario to temperature projection
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Temperature trajectories for different emissions scenarios For the next century, we see that aggressive reductions in emissions (eg. B1) can lead to a 1-3 ° C rise, while “middle of the road” scenarios like A1B lead to temperature increases of 1.5-4.5 ° C. Fossil fuel intensive scenarios like A1FI lead to a 2.5-6.5 ° C increase. This indicates that we are likely to experience a warming of at least 2 ° C, at a minimum. Keep in mind also that these are just global averages, certain regions may experience considerably more warming.
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The pattern of projected warming over the next century is not uniform. The greatest warming will take place over the polar latitudes of the northern hemisphere, due to positive feedbacks associated with melting sea ice. Greater warming is projected for land masses than ocean surfaces, since water tends to warm more slowly than land. This is why warming is greatest in the northern hemisphere, with its higher proportion
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This note was uploaded on 05/02/2011 for the course SIO 40 taught by Professor Barbeau,k during the Fall '08 term at UCSD.

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SIO40lecture18 - SIO 40 Life and Climate on Earth Nov 15 2010 Lecture 18 Climate Projections Lecture Outline-Emission scenarios-Projected warming

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