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ATMS 111 Quiz 1 Review Quiz #1 Review Sheet – Tuesday, July 16th Summary of Global Warming Science o CO2 concentrations have increased rapidly over the last 250 years From 280 ppm to ~394 ppm and rising Value over the last 400,000 years: 180-280 ppm Recent increase is human-caused (80% fossil fuel burning, 20% deforestation) o CO2 is a greenhouse gas, and greenhouse gases warm the planet o The Earth has warmed 0.8 C over the last 130 years Land has warmed more than ocean Northern high latitudes have warmed the most o The world is predicted to warm much more over the next 100 years Depends on how much we emit And uncertainty in climate feedbacks If no emissions control: 3-4 C additional warming is likely Basics of Climate o Earth is heated by “shortwave” radiation from the Sun 342 W/m2 50% absorbed at the surface 30% reflected back to space • Albedo measures what fraction is reflected back o Varies from 0 to 1. white = high, black = low • Clouds, ice important for albedo of Earth 20% absorbed by the atmosphere o The Earth cools by emitting “longwave” radiation out to space Greenhouse gases stop longwave radiation from escaping directly to space Greenhouse gases o The gases that make up most of the atmosphere (nitrogen, oxygen, argon) arenʼt greenhouse gases o Water vapor (aka humidity) The primary greenhouse gas: 60% of natural greenhouse effect A feedback, not a forcing o Carbon dioxide (CO2) 26% of natural greenhouse effect 63% of anthropogenic greenhouse effect (from textbook) Extremely long-lived: average lifetime is 100 years, but some remains in the atmosphere for over 1000 years o Methane (CH4) shorter-lived (8 yrs) but a more potent greenhouse gas Global warming potential (GWP) = 25 18% of anthropogenic greenhouse effect (from textbook) Produced naturally in wetlands; anthropogenic changes due to farm animals, landfills, natural gas leakage, rice Has more than doubled since preindustrial times, but isn’t increasing rapidly right now o Nitrous oxide (N2O) 1 ATMS 111 o o Quiz 1 Review GWP = 310 6% of anthropogenic greenhouse effect (from textbook) Anthropogenic emissions come from agriculture, chemical industry, deforestation Ozone (O3) As a pollutant near the surface, it’s also a greenhouse gas CFCs (Chlorofluorocarbons: ozone depleting gases) and HFCs (replacement after CFCs) 12% of anthropogenic greenhouse effect (almost all CFCs) (from textbook) CFC concentrations are decreasing (due to recognition of ozone hole problem) Some HFCs are strong greenhouse gases through (currently their emissions are small but are increasing) Climate Forcings o Measured by “radiative forcing” o A positive forcing results in warming of the climate o Longwave forcings: greenhouse gases (all the ones mentioned above except water water vapor, which is a feedback) Forcing is measured as the change in longwave radiation due to the gas, without letting global mean temperature change Current CO2 radiative forcing: 1.66 W/m2 and rising Total greenhouse gas radiative forcing: 3 W/m2 and rising o Shortwave forcings: Aerosols: small particles in the air • Most important shortwave forcing • Strong cooling influence (our best guess is around -1.2 W/m2) • caused “global dimming” • Very uncertain o Changes in the strength of the Sun solar variability is relatively small (0.2 W/m2 peak to peak) strength of sun is correlated with sunspot cycle o Land cover changes Negative shortwave forcing (clearing low-albedo forests leads to more reflection) Could also be a positive radiative forcing due to its effect on CO2 absorption o Soot on snow positive forcing - reduces albedo of snow surfaces Climate feedbacks o Positive feedbacks lead to amplification of a forcing o Negative feedbacks lead to dampening of a forcing (less temperature change for a given forcing) o Water vapor feedback: a positive feedback Warmer air can hold more moisture o Ice-albedo feedback: a positive feedback Ice/snow melts with increased temperature. Less reflection o Cloud feedbacks: an uncertain feedback o Feedbacks roughly double the amount of expected warming 2 ATMS 111 Quiz 1 Review Carbon dioxide emissions o Total emissions We emit 30 gigatonnes into the 3000 gigatonne atmospheric reservoir of CO2 Analogy: we emit 1.25” to the 10.5ʼ carbon blanket each year o Where do emissions go? Only 45% of what we emit goes into the atmosphere Around 25% goes into the ocean 30% goes into land ecosystems o Total emissions Big players are China, USA, E.U., with Russia, India, & Japan a bit behind Large population countries are higher on this list o Per capita emissions Oil-producing nations are the highest US rather high on the list too Developing nations appear lower on this list o Per economic output emissions Less developed countries appear higher on this list US is below world average on this list o Emissions sources 80% fossil fuels (mostly oil & coal), 20% deforestation Industry, buildings, transportation are main sources globally In the US, electricity and transportation are main sources Electricity is distributed: 1) transportation 2) industry 3) residential 4) commercial Extreme heat o No weather event can be attributed to global warming Have to look at averages to do attribution Weather = short term variability. Climate = average of weather Often short-term heat waves have colder areas relatively close by (because theyʼre often associated with changes in the direction of the winds) o Humidity (water vapor) Makes it feel hotter (heat index is higher for greater humidity) Also the greenhouse effect keeps nights warmer (which is particularly bad for human health) o “Dry heat” Deserts heat up much faster during the day (cool more at night) o Urban heat island effect Strongest at night Caused by buildings keeping longwave radiation in & materials staying hot Also more dark surfaces - absorb shortwave more during day o Effect of global warming Basic expectation: shifting the distribution of temperatures towards hotter everywhere • More likely hot extremes, less likely cold extremes • Many land areas are expected to dry out • These will experience more intense dry heat (especially in the daytime) • More greenhouse gases means hotter nights in locations that donʼt dry out 3 ATMS 111 Quiz 1 Review Floods and Droughts o To get rain, you need moist air and rising motion Globally, the rainy regions are where air is rising • Over warm water in the tropics (hot air rises) – also the easterly winds (trade winds) converge in the tropics, pushing air up = Intertropical Convergence Zone (ITCZ) • Monsoons: over certain land surfaces in the summer • Midlatitude weather systems have upward (rainy) and downward parts to them: midlatitude storm tracks determine where the other main rainy areas are Deserts occur where air is sinking (and away from storm tracks) o Warmer air can hold more water vapor Means rainy places will get rainier Also downpours will get stronger • Observed changes in heavy rains are suggestive but small o Many land areas especially in the subtropics will dry out (more evaporation into the warmer air) SW US, Southern Europe are examples • Shifts in rising motion can affect precipitation significantly This leads to much uncertainty in precipitation forecasts Rising motion is affected by both feedbacks & forcings (which affect where hottest temperatures are in the tropics, and also where midlatitude storms occur), also ocean currents Shifts in rising motion have been key to most dramatic changes that have been observed • Drying of Lake Chad • SW Australian drought o Flooding is affect by many factors in addition to just extreme rain events Deforestation can allow flooding to increase Soil erosion, land use, etc can also be important Floods and droughts will be among the most important impacts of global warming: hard to predict where though 4