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by: Karlie Hayes


Karlie Hayes

GPA 3.92

J. Chiang

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About this Document

J. Chiang
Class Notes
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This 9 page Class Notes was uploaded by Karlie Hayes on Thursday October 22, 2015. The Class Notes belongs to GEOG 142 at University of California - Berkeley taught by J. Chiang in Fall. Since its upload, it has received 55 views. For similar materials see /class/226638/geog-142-university-of-california-berkeley in Geography at University of California - Berkeley.




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Date Created: 10/22/15
Lecture 1372 Global warming 11 Outline Attribution of climate change in the 20th century Prediction of future climate ifwe haVe time What do we do 5 Reading IPCC Summary for policymakers mrp WWW mm nzvllhamgvmgcalm hnn l 6 Attribution of climate change in the 20th century Attribution is the process of establishing cause and effect with some de ned leVel of con dence including an assessment 0fcompea39ng hypotheses In particular recent climate change could haVe come about because of natural forcings on climate like volcanism and solar Variations History of climate change suggests other forcings Little Ice Age La Ni a Holocene variabili midHolocene Climate Optimu Medieval Warm Period Veg long time scales Faint young sun and early earth Proterozoic snowball earths Warm Mesozoic dinosaur age Long time scales Pleistocene Glacialinterglacial cycles Abrupt change Younger Dryas lt1 OOO Shorttime scale El Ni o Southern Oscillation Forcings Less solar luminosity countered by high greenhouse gases Silicate weathering plate tectonics C02 polar ice Orbital variations NH summer insolation icealbedo CO amp cloudalbedo hermohaline shutdown more NH solar insolation NH only more sunspots less volcanoes less sunspots more volcanoes C02 and climate Pacific warm water west to east Wkened equatorial circulation ca 3 4 glacial cycles recorded in the Vostok ice core hw wwmw 139 3 7m IR Fem r1 al Na m 2m 2m in Ag 2 kw a 399 429 96 1999 H mm 1 f onus rntn Fast 62 D yealsapenmd wrunna Namely camhamzddnmam What are suns 0157 Dark areas on Sun surface Lower than norrna1 temps but compensated by bnght areas around It Hence averallauqzutix slightly ig er in periadx aihigh Summit ac vity Sunspots typrea11y have 11 year cyc e Only 0 1 d1fference between rnaxrnm of sunspot acuy1ty Volcanic effect on climate Volcanos emits sulfur dioxide 02 that is injected high in the stratosphere Volcanic aerosols affect the radiative budget volcanic aerosol forcing and hence climate In particular they act to re ect sunlight LW Th residence time of volcanic aerosols in the atmosphere is around 1 year So the climate effects of volcanism lasts for 173 years after the event All these forcings are considered in explaning climate changes in the recent and not so recent past One e ple onal Cllmate Forclnus dam new Album ac east 2 Slrmmpherle Aemsol i Ratleclwn Tmposphnnc Awucnls 4mm lnmvm Enact Ind use Forcllln Wm me was wzo Wm tam tam zauu Hg l ml chmgslgl mate am we lunausmmlanous a smmm mtomWmtmmmwmm Mm wontm u 5mm ruwc ls hascd anew 5 momml 5 me mantel ls sampled at me sam m vmswas mm 00 m Dbxwanans mrlude sea suvtxe tempemwee or the mean we amt my mm l we Hue global mm m to Na ladwwu n ll MD M the atmosriner m the lm Slmulannns me ms smmlulmus me mum oul mu m 4le1 m Imlml umluum WM e m meme 2005 B Surface Temperature Change bservalions I I un1 Models are increasingly able to simulate climate changes over the 20th century given all the external forcings on climate un3 un un 5 Run Mean 1 50 1900 1920 1940 1960 1980 200 Hansen et al Science92005 MODEL OBSERVATIONS i o 1 in 19110 1950 20m 1350 we lsso 2000 Veer vear Climate models simulate the global 9 ALL FORCINGS Annual global mean lsmpmmms W l as temperature W increase post 1950 only if 05 anthropogenic 41650 950 forcings are added a Natural forcing volcanism solar variation only b Anthropogenic forcing only c Anthropogenic forcing and natural forcing 10 Don t confuse natural forcing with natural variability Natural forcing like volcanism and solar variations are non anthropogenic climate forcings Natural variability are internal oscillations of the climate read ocean and atmosphere system in the absence of any forcings natural or anthropogenic The climate models used in the IPCC are coupled ocean atmosphere models models that simulate the atmosphere and ocean components They generally don t model changes to land vegetation and ocean biology although land hydrology is modeled It means that greenhouse gas concentrations are imposed in the models The next generation of climate models aim to incorporate land vegetation changes and the short term carbon cycle Uncertainties in attribution from IPCC 2001 The lower mid troposphere hasn t warmed over the last two decades despite the surface temperature warming Climate models predict both should warm Are climate models reliable gt MAY BE SOLVED see handout Large uncertainties in estimates of internal variability from models and observations perhaps the recent warming is natural Considerable uncertainty in reconstructions of solar and volcanic forcing which is based on proxy or limited observational data for all but the last two decades perhaps solar variability can explain Large uncertainties in anthropogenic forcing associated With effects of aerosols how certain are we of climate forcings Large differences in the response of different models to the same forcing how reliable are the models 7 Predictions for the future The IPCC made a report with different emission scenarios and have projected what will happen in the Future under widely differing circumstances SRES Special Report on Emission Scenarios In short this is what they did up to year 2100 Economic gt Emissions gt Carbon cycle gt Climate gt Climate Scenario Scenario model model Prediction Estimated CO2 emissions and 25 7 atmospheric CO2 concentrations For the next century under different scenarios cog emissions G c Modest population and economic growth a most optimistic assumes total emissions will rise 7 2500 2620 202m 2650 zo ao 2100 Gtonsyr to lt10 Gtons C yr in 2050 followed by 1300 decline to 5 Gtonsyr CO2 doubling in 100 yrs 133 b C02 emissions increase 07yr just over 13 Gtonsyr by 2100 300 1mm 002 concentration ppm in o o b l Estimated CO2 emissions and atmospheric CO2 concentrations For the next century under different scenarios More rapid population growth and economic development scenarios c Assumes energy needed comes from different sources CO2 emissions peak at 17 Gtonslyr in 2050 then slowly declines Most of our future energy will be from fossil fuels as it is today C0 emissions reach 28 Gtons Clyr by 2080 4x present values Cumulative emissions 2000 Gtons C almost half of known recoverable fossil fuel reserves CO2 doubling in 50 yrs c0Z concentration ppml l l l l 25 7 6 Q 207 v 9 157 m o O 107 7 l l l l r 2000 2020 2040 2060 2030 21 0 Year 5 130 7 1200 1100 d 970 PPM mo 7 900 7 000 700 7 600 500 A00 7 30 D r r T Y V T 1980 2000 2020 2040 2050 2080 2100 Year lb 15 lemperature change rci m l 2 a 2 C 2000 2020 2040 2060 2050 2100 Vear Hers show the range in 2100 produced ny several models Elobal temperature predictions by 2100 for each scenario Rule of thumb warming is roughly logarithmic With C02 so that an 8 23 fold increase in CO2 gives a 3 fold increase in temp


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