"GEOG 1100 Aerosols, Dust, and GlaciersAerosols and Dust • Aerosols: liquid or solid particles small enoughto suspended indefinitely in the atmosphere • Dust: larger particles that are suspended in theatmosphere for shorter periods of time • Primary sources of aerosols: – Burning of fossil fuels – Natural and anthropogenic biomass burning – Volcanoes • Dust predominantly comes from desertsAerosol Impacts on Climate • Absorb and scatter light in the atmospherebefore it reaches the ground – Less light reaching the ground can lead to“global dimming” • Aerosols provide condensation nuclei forcloud formation • Dust and carbon particles can settle onsnow and impact snow albedo, meltingSulfate Aerosols • Sulfur dioxide is expelled into theatmosphere by fossil fuel burning(especially coal) and volcanoes • Sulfur dioxide attracts water, whichproduces tiny droplets of sulfuric acid – Sulfuric acid in the troposphere can causeacid rain – The Midwest U.S. has many coal-fired powerplants, so acid rain has been a problemdownwindSulfate Aerosols • Sulfate aerosols are very good at cooling theEarth’s surface – Increased atmospheric albedo – Higher albedo has somewhat muted temperatureincreases caused by increased greenhouse gasemissions • Volcanic eruptions can result in large amounts ofsulfates being injected into the stratosphere – Sulfate aerosols have a longer life in the stratosphere – Stratospheric aerosols can lead to short-term climatecooling – The location of the eruption is very importantSulfate Aerosols • Tambora (1815) 3 – 150 km of material erupted (largest in recorded history) – Northern hemisphere cooling of 0.5°C in the summer followingthe eruption – 1816 was called “the year without a summer”, numerous cropfailures around the world • Krakatau (1883) 3 – 21 km of material erupted – Northern hemisphere cooling of 0.3°C in the summer followingthe eruption • Pinatubo (1991) 3 – 9 km of material erupted, very high in sulfates – Northern hemisphere cooling of 0.5°C, global cooling of 0.4°CPre-eruptionImmediately after eruption1.5 years after eruptionImage taken from Space Shuttle three weeks after eruption NASASoot • Produced by biomass burning – Natural (wildfires) – Anthropogenic (forest clearing, swiddenagriculture) • Large amounts of biomass burning areoccurring in tropical rainforests in SouthAmerica, Central America, EquatorialAfrica, and IndonesiaSouthern California Fires, 2007, MODIS (NASA)Southern California Fires, 2003, MODIS (NASA)Aerosol Impacts on Climate • Direct effects: increased scattering andabsorption of incoming shortwaveradiation – Increased albedo, negative radiative forcing • Indirect effects – Impacts on number and quality ofcondensation nuclei – Impacts on albedo and duration of cloudsIPCC AR4Dust • Dust particles, larger than aerosols, can besuspended in the atmosphere for periods ofseveral days • Dust is generated from soils not covered byvegetation or water • Not all bare soils are good dust sourcesDust • Dust sources occur where: – Desert soils are disturbed or recently exposed – Smaller particles are renewed by inflow ofwater – Past lake sediments that contain anabundance of small particles • Dust is an important source of nutrients • The Sahara Desert generates some of thelargest dust plumes on Earth – Bodele Depression, ChadDustDust on Snow • Dust that falls on snow decreases thesnow’s albedo • As snow melts, dust deposited in layersaccumulates at the snow surface, furtherreducing albedo • Snow melt can occur up to a month earlierthan normalCenter for Snow and Avalanche StudiesSan Juan Mountains, May 2008, MODIS (NASA)San Juan Mountains, May 2009, MODIS (NASA)Glaciers • A glacier is a large body of ice that flowsfrom one place to another • Requires an accumulation zone wheretemperatures are low enough year-roundto keep snow and ice from melting • Where can we go to find coldtemperatures?Glaciers • Two types: – Alpine – Continental • Alpine glaciers – Form in mountains – Steep slopes – “Looks like a glacier”Continental Glaciers • Continental glaciers cover a much largerarea • Almost flat in center, steep slopes only atedges • An ice cap or ice field covers a mountainrange – Iceland – PatagoniaContinental Glaciers • Ice sheets are very large continental glaciers – Ice sheets in Greenland and Antarctica cover millionsof square kilometers each – Greenland Ice Sheet covers 80% of Greenland – East and West Antarctic Ice Sheets cover 90% ofAntarctica • Together, ice sheets cover ~10% of the Earth’ssurface • The ice sheets average 2.4 km (1.5 miles) of ice3 thickness and contain 32 million km of iceGISP2 Core Site, 3053.44 m above bedrockImportance of Glaciers • Glaciers hold 77% of Earth’s freshwater – Alpine glaciers “bank” freshwater that can bereleased slowly over long periods of time • Glaciers have a high albedo • Glaciers hold an irreplaceable record ofpast climatesHow Do Glaciers Form? • Snow must be transformed into ice tocreate a glacier • Freshly fallen snow has a very low density • Ice has a much higher densityUSDAUSDAUSDALutgens et al. 2009 Glacial Movement • Glaciers move downhill with the force of gravity • Higher friction where glacier rubs against rock • Glaciers flow most slowly along edges andbottom, most rapidly below surface and awayfrom edges • The bottom of the glacier moves by basal slip,where water lubricates the passage of ice overrock• The center of the glacier moves by plastic flow – flowing of the ice under pressureAccumulation and Ablation Zones • Accumulation zone – Higher elevations of a glacier – Little or no melting takes place at any timeduring the year – Snow can make the transition to firn, then ice • Ablation zone – Snow melts during summer, no accumulation – Ice is removed by ablation • 2 zones are separated by the firn lineLutgens et al. 2009 Positive Mass Balance • If rate of accumulation is greater than rateof ablation, mass of glacier will increase(positive mass balance) – More ice is being added to the glacier than isbeing taken away – Root causes:• Climate becomes colder, ablation decreases • Climate becomes wetter, accumulation increasesNegative Mass Balance • If rate of accumulation is less than rate ofablation, mass of glacier will decrease(negative mass balance) – More ice is being taken away from glacierthan is being added – Root causes: • Climate becomes warmer, ablation increases • Climate becomes drier, accumulation decreasesMark Dyurgerov, Institute of Arctic and Alpine Research, University of Colorado, Boulder.Mass Balance • Most alpine glaciers worldwide have anegative mass balance • Greenland Ice Sheet and West AntarcticIce Sheet have negative mass balances • East Antarctic Ice Sheet has a close-to- neutral mass balance – East Antarctica is much colder thanGreenlandMajor Impacts of Melting Glaciers • Loss of “banked” water from glacier melt • Higher sea level – Not all types of melting ice contribute to risingsea levelPast Changes in Sea Level • Sea level has been rising since 20,000years before presentRising Sea Level • Past 3,000 years: 0.1-0.2 mm per year onaverage • Past 100 years: 1.8 mm per year on average • Past 20 years: 3.1 mm per year on average • By 2100: 20-60 cm of sea level rise (2-6 mm peryear on average) – Accounts for thermal expansion, melting glaciers – Does not account for potentially increased flow ratesof glaciersImpacts of Sea Level Rise • Increased coastal flooding • Increased damage to coastal cities fromstorm events (e.g. hurricanes) • Coastal habitat loss (e.g. wetlands) • Increased intrusion of salt water intofreshwater aquifers near coasts • Displacement of populations living close tosea level – conservatively 8-9 millionpeople3 Location Volume (km ) Potential SeaLevel Rise (m) East Antarctic 26,039,200 64.80 Ice Sheet West Antarctic 3,262,000 8.06 Ice Sheet Antarctic 227,100 .46 Peninsula Greenland 2,620,000 6.55 All other glaciers 180,000 .45 Total 32,328,300 80.32"