Studies of the General Circulation of the Atmosphere with a Simplified Moist GCM

Dargan M. W. FriersonDepartment of Atmospheric Sciences

Day 2: October 6, 2015ATM S 111, Global Warming: Understanding the ForecastIn the NewsIndia submits climate action planWill have 40% renewable energy by 2030Cut emissions intensity of its economy by 35% by 2030Now all major emitters have pledgedDraft of UN agreement releasedFor the Paris meeting in DecExtreme weatherHurricane Joaquin in SC, BahamasFrench Riviera flooding

NewsUW Student Chapter of the American Meteorological Society has its first meeting todayATG 610, 5-7 PMCome by if youre interested in weather, climate, and air quality

Extra credit assignment (very quick turnaround!): Send me your comments on this article by Thursday 4 PMSouth Carolina flooding is the type of event climate scientists have warned about for years by Andrew Freedmanhttp://mashable.com/2015/10/05/south-carolina-floods-global-warming/

Last timeShortwave radiation (AKA solar radiation)Radiation from the SunMostly visible lightMostly gets absorbed at the surface or reflected back to spaceLongwave radiationRadiation emitted by the EarthInfrared (invisible) radiationGreenhouse effect makes it harder for longwave radiation to escape to space

The Greenhouse EffectGreenhouse effect is intuitive if you pay attention to the weather!Cloudy nights cool less quickly

Old mariner saying: Stars bright, cold night

Energy BalanceEnergy balance occurs when heating equals coolingWhen shortwave radiation in equals longwave radiation outIf the Earth is out of energy balance, temperatures must change

OutlineWhat are the main greenhouse gases?And which are changed by human activity?Global warming potential: a way to compare how bad different gases are for the climateHow a tiny fraction of the atmosphere controls its temperatureConnections to the ozone depletion problemOzone itself and the chemicals that caused itAtmospheric compositionOur atmosphere is mostly nitrogen (N2, 78%), oxygen (O2, 21%), and argon (Ar, 0.9%)But these are not greenhouse gasesMolecules with 1 atom or 2 of the same atoms arent greenhouse gasesThe primary gases in our atmosphere are thus transparent to longwave radiation

Water vapor = 0.4% over full atmosphere (the above are dry numbers)CO2 is basically the rest (0.04%)8Greenhouse GasesPolyatomic molecules are greenhouse gasesWater vapor (H2O)Carbon dioxide (CO2)Methane (CH4)Nitrous oxide (N2O)Ozone (O3)Chlorofluorocarbons (the ozone depleting chemicals which have been banned)

The fact that they can rotate and vibrate means they can absorb the right frequencies of longwave9Greenhouse GasesAll greenhouse gases are a rather small fraction of the atmosphere!Water vapor has the highest concentration: 0.4%CO2: 0.04%Methane: 0.0002%Trace gases have a remarkable effect on the atmosphereE.g., ozone is less than 0.00001% of the atmosphere, but absorbs essentially all harmful UV-B and UV-C radiationLets discuss each gas separatelyUV-B is 350 million times stronger at TOA than the surface

10Water VaporGas form of waterAKA humidityNot the same as clouds clouds are tiny droplets of water or ice crystals suspended in airThe number one greenhouse gas!Not controlled by humans!Its a feedback not a forcing (topic of the next lecture)Observed to be increasing with global warmingCarbon DioxideCO2Its what we breathe out, what plants breathe inThe primary contributor to the anthropogenic (human-caused) greenhouse effectOver 55% of the anthropogenic greenhouse effect so farIncreases primarily due to fossil fuel burning (90%) and deforestation (10%)Preindustrial value: 280 ppmCurrent value: 400 ppm

Carbon DioxideCO2 will also be the main problem in the futureIts extremely long-lived in the atmosphereAround 50% of what we emit quickly gets taken up by the ocean or landWell discuss this more laterMost of the rest sticks around for over 100 yearsSome of what we emit will still be in the atmosphere over 1000 years from now!MethaneCH4Natural gas like in stoves/heating systemsMuch more potent on a per molecule basis than CO2Only 1.7 ppm though much smaller concentration than CO2Natural sources from marshes (swamp gas) and other wetlandsVideo of methane release from tundra lakes in Alaska & SiberiaIncreases anthropogenically due to farm animals (cow burps), landfills, coal mining, gas leakage,rice farming

Methane breaks down by reactions with hydroxyl radicals (OH) which is produced from excited atomic oxygen and water. 60% of source is anthropogenic (roughly) best guess 1/3 livestock, 1/3 energy, rest landfills, biomass burning, waste treatment

Draining fields (to aerate soil) could decrease rice emissions

There are 100M cattle in the US, 1.2B in the world. Grazing management, nutritional supplements, soil testing, and maybe even vaccines could decrease emissions from cattle.

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MethaneThe lifetime of CH4 is significantly shorter than carbon dioxideBreaks down in the atmosphere in chemical reactionsLifetime of methane is only 8 yearsMethane leveled off for a few years (droughts in high latitude wetlands?) Starting to rise again thoughIts increased to 150% preindustrial levels alreadyBig jump in 1991 due to Pinatubo (affecting photochem & OH production)In 1998 due to biomass burning (forest fires in Siberia)? Wetlands too?15Global Warming PotentialCO2 lifetime > 100 yearsMethane lifetime = 8 yearsBut methane is a much stronger greenhouse gasHow to put these on similar terms? Global warming potential (GWP)Global warming potential is how much greenhouse effect emissions of a given gas causes over a fixed amount of time (usually 100 years)Measured relative to CO2 (so CO2 = 1)Methanes global warming potential is 25Much more potent than CO2 even though it doesnt stay as long16Nitrous OxideN2OLaughing gasAlso more potent on a per molecule basis than CO2Global warming potential: 310Comes from agriculture, chemical industry, deforestationSmall concentrations of only 0.3 ppm

Application of nitrogen fertizilers is main source. More efficient fertilizer use can help (e.g., timing fertilizer application, no till, preventing soil compaction, planting N-efficient crops, etc). Also use of inorganic nitrogen fertilizers (less N2O is leaked then). 17Ozone (O3)Dont confuse ozone with global warming!The ozone depletion problem is essentially solvedAnd the ozone layer will be fully recovered in 50 years or so

Ozone (O3)Dont confuse ozone with O-ZoneOzone: O3, gas in the atmosphereO-Zone: Moldovan pop band

19OzoneOzone (O3) occurs in two places in the atmosphereIn the ozone layer very high upThis is good ozone which protects us from ultraviolet radiation & skin cancerNear the Earths surfaceBad ozone: caused by air pollutionBad ozone is a greenhouse gas, and is more potent on a per molecule basis than CO2But its very very short-livedGlobal warming potential for bad ozone is wrapped into the other gases which lead to its chemical creationChlorofluorocarbons: what caused ozone depletionGlobal warming potential for ozone is not usually calculated rather its wrapped into the GWPs of the other gases that lead to its chemical creation

CFCs & Thomas MidgleyThomas Midgley popularized chlorofluorocarbons (CFCs) in the 1920sWorked for General Motors (owned Frigidaire)CFCs first used as a coolant in refrigeratorsAlso used in air conditioners, propellant sprays, foamsMidgley was also the inventor of leaded gasolineTetraethyl lead was used as a fuel additive, only recently banned worldwideOne of the most harmful pollutants of the 20th century

CFCs and the Ozone HoleLate 1960s: James Lovelock detected CFCs all over the planetEssentially all CFCs ever emitted were still in the atmosphere!1974: Molina and Rowland postulated that CFCs could destroy the ozone layer1984: Ozone hole discovered over Antarctica! Worldwide ban came soon afterWe now have completely phased out CFCs

Mario MolinaCFCsCFCs are strong greenhouse gasesGlobal warming potentials of 5000 to 15000!Their phase-out saved significant global warming in addition to the ozone layerSlowly declining but will persist for many decadesSome replacements for CFCs (called HFCs) are strong greenhouse gases tooGlobal warming potentials of up to 15,000!

The Natural Greenhouse EffectContributions to the natural greenhouse effect: H2O (water vapor): 60%CO2 (carbon dioxide): 26%All others: 14%

The Unnatural Greenhouse EffectIncreasing levels of CO2 and other greenhouse gases leads to a stronger greenhouse effectWith more greenhouse gases, it becomes harder for outgoing radiation to escape to space

Its like this picture from before, but moreThe Unnatural Greenhouse EffectContributors to the anthropogenic greenhouse effectNumbers for the whole world up to this point: Carbon dioxide: 56%Methane: 32%CFCs, HFCs: 6%Nitrous oxide: 6%

Current US ContributionsContributors to the anthropogenic greenhouse effect for the United States (2013)CO2 = 82.5%Methane = 9.5%Nitrous oxide = 5.3%HFCs & related substances = 2.6%

http://www3.epa.gov/climatechange/science/indicators/ghg/us-ghg-emissions.html

27SummaryGreenhouse gases: Number one is water vaporNumber two is CO2Also methane, nitrous oxide, CFCsGlobal warming potential: way to compare different greenhouse gases to CO2Many other GHGs are stronger per molecule, but CO2 remains the biggest problem