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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)
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ATMS 111
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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
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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
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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
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