Lecture 18

Lecture 18 - SIO 40 Life and Climate on Earth Nov. 13, 2009...

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Unformatted text preview: SIO 40 Life and Climate on Earth Nov. 13, 2009 Lecture 18 Climate Projections Lecture Outline-Climate sensitivity- 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 Climate sensitivity To determine the potential magnitude of future global warming, scientists use estimates of climate sensitivity. Climate sensitivity is usually defined as the amount of warming (in C) that will occur in response to a doubling of atmospheric CO 2 from pre-industrial levels of 280 ppm (current CO 2 level is about 380 ppm, projected to hit 560 ppm by midway through the next century at current rates of fossil fuel consumption). Equilibrium climate sensitivity takes into account that the full amount of warming for a given increase in CO 2 may take decades to achieve due to the sluggishness of ocean warming. Top left is shown the range in climate sensitivities obtained for constraints from past climate change on various time scales. Bottom left shows the spread of results for climate sensitivity from ensembles of climate models. The global mean equilibrium warming for doubling CO 2 , is likely to lie in the range 2C to 4.5C, with a most likely value of about 3C. Equilibrium climate sensitivity is very likely larger than 1.5C. For fundamental physical reasons as well as data limitations, values substantially higher than 4.5C still cannot be excluded, but agreement with observations and proxy data is generally worse for those high values than for values in the 2C to 4.5C range. Likely ranges of climate sensitivity Fossil fuel emission scenarios redictions 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 ssumes balanced use of both fossil and non-fossil fuels (A1B). The A2, B1 and B2 storylines make ifferent 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 missions has tracked the most pessimistic of the IPCC scenarios (ie. the ones with the fastest rate of O 2 emissions). or a given emissions scenario, various biogeochemical models are used to calculate oncentrations of constituents in the atmosphere. Various radiation schemes and arametrizations are required to convert these concentrations to radiative forcing....
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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 18 - SIO 40 Life and Climate on Earth Nov. 13, 2009...

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