GEOL150_Week3_lecture3_Greenhouse - Week 3, lecture 3...

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Unformatted text preview: Week 3, lecture 3 Greenhouse Gases & Global Warming GEOl50: Climate Change University of Southern California, Los Angeles Sun Earth Gray means: “the atmosphere is in the way” Major optically active gases: Water vapor CO2 Ozone Methane •Mostly transparent to SW, but not to outgoing LW radiation Earth’s Energy Budget Albedo ~31% Earth’s surface area = 4!r 2 T = 255 K = -18oC So = 1366 W/m2 Sun Incoming solar radiation Now with an atmosphere that absorbs LW radiation : T = 287 K = 14oC Outgoing longwave radiation shadow area = !r 2 Inputs Flux (W/m2) Area Total Flux 0.69*So = 942 π R2 942*πR2 Outputs ε σT4 4πR2 = ε 4πR2 σT4 ε = Atmospheric emissivity ~ 0.6 Earth’s energy budget At equilibrium, input must equal output With a perfectly transparent atmosphere, the average temperature would be below the freezing point Thankfully, some gases (H20, CO2, etc) act as a blanket trapping heat near the surface So we can have liquid water, Life, music, etc... Therefore, we LOVE the greenhouse effect ! The Greenhouse Effect Major Greenhouse Gases (other than water) Chapter 2 Changes in Atmospheric Constituents and in Radiative Forcing Carbon Dioxide (CO2) Table 2.1. Present-day concentrations and RF for the measured LLGHGs. The changes since 1998 (the time of the TAR estimates) are also shown. Concentrationsb and their changesc Change since 1998 +13 ppm +11 ppb +5 ppb ppt –13 +4 –4 +38 0.063 0.17 0.024 0.033 0.0025 0.0031 0.0011 0.012 –5 +1 –5 +29 +93 +57 –72 –7 +234 +349 +151 +29 +36 +22 –1 Radiative Forcingd Change since 1998 (%) +13 +11 Speciesa CO2 CH4 N2O 2005 379 ± 0.65 ppm 1,774 ± 1.8 ppb 319 ± 0.12 ppb ppt 2005 (W m–2) 1.66 0.48 0.16 Methane (CH4) CFC-11 CFC-12 CFC-113 HCFC-22 HCFC-141b HCFC-142b CH3CCl3 CCl4 HFC-125 HFC-134a HFC-152a HFC-23 SF6 CF4 (PFC-14) C2F6 (PFC-116) CFCs Totalk 251 ± 0.36 538 ± 0.18 79 ± 0.064 169 ± 1.0 Source : 1I8PCC AR4, WG1, chapter 2 ± 0.068 +9 15 ± 0.13 19 ± 0.47 93 ± 0.17 +6 –47 –7 CO2 leads the pack but methane not far behind 3.7 ± 0.10e 35 ± 0.73 +2.6f +27 0.0009 0.0055 3.9 ± 0.11e +2.4f +4 0.0004 18 ± 0.12g,h 0.0033 5.6 ± 0.038i 74 ± 1.6j +1.5 0.0029 Nitrous Oxide (N2O) How do they fare compared to water vapor ? 0.0034 2.9 ± 0.025g,h +0.5 0.0008 0.268 0.039 0.320 (Note :ey all absorb LW radiation for the same reason than water) HCFCs Total +33 Montreal Gases –1 Greenhouse Effect : who dunnit ? Water vapor is (currently) the largest contributor to the greenhouse effect Therefore, why are we even worrying about CO2 ? The reasons: Residence Time Water vapor Carbon Dioxide Ozone Methane + N2O + ovlp Source: Kiehl & Trenberth BAMS 1997 Anthropogenic emissions are driving climate away from equilibrium Runaway greenhouse effect ! Water Vapor Feedback If water vapor makes the surface hot; AND Since hot temperatures mean higher moisture ...We have a classic positive feedback loop ! And like the larsen effect, it could be quite painful Runaway Greenhouse Effect On Venus, the baseline Temperature was so high that all of the liquid water evaporated Unlivable place ! e two twin sister had very different fates... All because of their distance to the Sun Key Concept : residence time (s) Mass τ= Flux (kg) (kg/s) Example: Tap Water Imagine a tap delivering water at 1.5 oz per second You have a 16oz glass. How long does it take to fill it ? Answer : 10.66s Residence Time of important trace gases Water vapor : 10 days Carbon Dioxide : 400 years Hence, whatever when we put carbon dioxide in the atmosphere, it will stay there very long “Pipeline warming, committed warming” Also, CO2 concentrations in the atmosphere are so minute in the first place (0.028% in 1750) So humans, it turns out, can compete with nature In contrast, there is ~100 times more water around, so it’s harder for us to change it Frequently Asked Question 2.1 e Forcing How do Human Activities Contribute to Climate Change Ado They CompareRadiative Perturbations nthropogenic with Natural Influences? and How Chapter 2 Human activities contribute to climate change by causing nges in Earth’s atmosphere in the amounts of greenhouse gasaerosols (small particles), and cloudiness. The largest known tribution comes from the burning of fossil fuels, which releases on dioxide gas to the atmosphere. Greenhouse gases and aeroaffect climate by altering incoming solar radiation and outg infrared (thermal) radiation that are part of Earth’s energy nce. Changing the atmospheric abundance or properties of e gases and particles can lead to a warming or cooling of the ate system. Since the start of the industrial era (about 1750), overall effect of human activities on climate has been a warminfluence. The human impact on climate during this era greatly eds that due to known changes in natural processes, such as r changes and volcanic eruptions. enhouse Gases Human activities result in emissions of four principal greense gases: carbon dioxide (CO2), methane (CH4), nitrous oxide ) and the halocarbons (a group of gases containing fluorine, rine and bromine). These gases accumulate in the atmosphere, sing concentrations tothe principal components oftime. Significclimate increases increase with the radiative forcing of ant change. All these FAQ 2.1, Figure 2. Summary of radiative forcings result have more factors that affect climate and are ll of these gasesfrom one or occurred in thethe forcings associated with (see start of theor industrial relative human activities era to the Figure natural processes as discussed in the text. The values represent in 2005 ll industrial era (about 1750). Human are attributable to human gases, ozone, water vapour, of these increases activities cause significant changes in long-lived activities. Carbon dioxide has increased from fossil fuel use in transpor- Industrial Revolution FAQ 2.1, Figure 1. Atmospheric concentrations of important long-lived greenhouse gases over the last 2,000 years. Increases since about 1750 are attributed to human activities in the industrial era. Concentration units are parts per million (ppm) or parts per billion (ppb), indicating the number of molecules of the greenhouse gas per million or billion air molecules, respectively, in an atmospheric sample. (Data combined and simplified from Chapters 6 and 2 of this report.) “Anthropos” [human] + “genic” [origin] surface albedo, aerosols and contrails. The only increase in natural forcing of any significance between 1750 and 2005 occurred in solar irradiance. Positive forcings lead to warming of climate and negative forcings lead to a cooling. The thin black line attached to each coloured bar represents the range of uncertainty for the respective • Ozone is a greenhouse gas that is continually produced and destroyed in the atmosphere by chemical reactions. In the troposphere, human activities have increased ozone through the The Keeling Curve Charles David Keeling, UCSD The long term trend since 1960 is ~ exponential What has it done to climate ? Global Warming... Global and continental temperature change models using only natural forcings models using both natural and anthropogenic forcings observations IPCC WG1 SPM Every continent and the global oceans are warming. at is impossible to explain without invoking man-made GHGs (mostly CO2) Figure SPM.4. Comparison of observed continental- and global-scale changes in surface temperature with results simulated by climate models using either natural or both natural and anthropogenic forcings. Decadal averages of observations are shown for the period 1906-2005 (black line) plotted against the centre of the decade and relative to the corresponding average for the period 1901-1950. Lines are da shed where spatial coverage is less than 50%. Blue shaded bands show the 5 to 95% range for 19 simulations from five climate models using only the natural forcings due to solar activity and volcanoes. Red shaded bands show the 5 to 95% range for 58 simulations from 14 climate models using both natural and anthropogenic forcings. {Figure 2.5} spanning many thousands of years. {2.2} Atmospheric concentrations of CO2 (379ppm) and CH4 (1774ppb) in 2005 exceed by far the natural range over the last 650,000 years. Global increases in CO2 concentrations Current Anthropogenic GHG Emissions Global anthropogenic GHG emissions 49.0 44.7 39.4 forcings would likely have produced cooling. Observed patterns of warming and their changes are simulated only by models that include anthropogenic forcings. Difficulties remain in simulating and attributing observed temperature changes at smaller than continental scales. {2.4} GtCO2-eq / yr 35.6 28.7 CO2 from fossil fuel use and other sources CH4 from agriculture, waste and energy CO2 from deforestation, decay and peat N2O from agriculture and others F-gases Figure SPM.3. (a) Global annual emissions of anthropogenic GHGs from 1970 to 2004.5 (b) Share of different anthropogenic GHGs in total emissions in 2004 in terms of carbon dioxide equivalents (CO2-eq). (c) Share of different sectors in total anthropogenic GHG emissions in 2004 in terms of CO2-eq. (Forestry includes deforestation.) {Figure 2.1} “Anthropos” [human] + “genic” [origin] 5 IPCC AR4 I ncludes only carbon dioxide (CO 2), methane (CH 4), nitrous oxide (N 2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulphurhexafluoride (SF6), whose emissions are covered by the United Nations Framework Convention on Climate Change (UNFCCC). These GHGs are weighted by their 100-year Global Warming Potentials, using values consistent with reporting under the UNFCCC. 6 Increases in GHGs tend to warm the surface while the net effect of increases in aerosols tends to cool it. The net effect due to human activities since the pre-industrial era is one of warming (+1.6 [+0.6 to +2.4] W/m2). In comparison, changes in solar irradiance are estimated to have caused a small warming effect (+0.12 [+0.06 to +0.30] W/m2). ...
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This note was uploaded on 10/04/2010 for the course GEOL 150Lxg taught by Professor Stott during the Spring '07 term at USC.

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