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UW ATMS 587 - Carbon Cycle

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DARGAN M. W. FRIERSON DEPARTMENT OF ATMOSPHERIC SCIENCES DAY 9: 10/23/2013 Fundamentals of Climate Change (PCC 587): Carbon CycleOne More Important Record: CO2 ! A final important climate record: carbon dioxide levels ¡ That CO2 is rising rapidly due to human activity is equally important as the temperature rise in the whole big picture of global warming ¡ Monitored accurately at Mauna Loa Observatory, Hawaii since 1958The Mauna Loa Carbon Dioxide Record ! First reading in 1958: 316 ppm ¡ Most recent reading (last week): 391 ppm (25% increase) ! Why Mauna Loa? ¡ High mountains are away from near-surface variations ¡ Hawaii gets clean ocean air most of the timeCarbon Dioxide at Other Sites ! Other sites agree with Mauna Loa, but with different seasonality Seasonality is due to the growth of vegetation during summer, decay during winter (May has the highest CO2 concentration in the NH)Evidence of Anthropogenic Rise ! Comparisons with industrial fossil fuel usage and deforestation rates show emissions are larger than atmospheric increase ¡ 55% of emissions goes into the ocean or terrestrial biosphere, 45% stays in the atmosphere ! As with the temperature record, there is complementary evidence for anthropogenic causes of carbon dioxide rise as well…Evidence of Anthropogenic Rise ! Concentrations of oxygen have also been decreasing ¡ Oxygen is used up when fossil fuels/forests are burned ¡ If exchange with the ocean was the culprit, oxygen levels would stay the sameEvidence of Anthropogenic Rise ! Anthropogenic emissions also have different isotope concentrations ¡ Isotope: have different number of neutrons in the atom, so different weight ¡ Carbon isotopes: carbon-12, carbon-13, and carbon-14 ¡ Plants use more carbon-12 than carbon-13 as compared with the atmosphere ¡ Carbon-13 fraction has been decreasing (indicating burning of former plant/animal material is the culprit)Connection to Paleoclimate ! We also know carbon dioxide levels are higher than they’ve been in several hundred thousand years Natural variation over Ice Age Cycles: 180-280 ppm 280 180The Carbon Cycle ! Let’s discuss the various reservoirs of carbon and the fluxes among them ! The atmosphere holds around 700 gigatons of carbon ¡ 1 Gton = 1 billion (metric) tons = 10^12 kg ¡ If it were all put into a layer of pure gas at surface pressure, would be about 10 feet deep ! Note sometimes these figures are quoted for carbon dioxide instead of carbon (multiply by 3.67 to convert from C to CO2) ¡ Especially companies who claim they’re reducing their emissions use CO2 (the bigger number)Terrestrial Carbon Reservoir ! 500 Gtons carbon in living carbon on land ¡ The “terrestrial biosphere” ¡ Seasonal cycle in the terrestrial biosphere causes atmospheric CO2 seasonal cycle ! 1500 Gtons carbon in dead carbon in soilsOcean Carbon Reservoir ! 38,000 Gton inorganic carbon in the ocean ¡ Dissolved CO2, carbonic acid, etc ! 600 Gton of dead organic carbon (mostly old plant material) ! 1 Gton of living organic carbon ! Takes centuries for ocean to completely get in equilibrium with the atmosphere ¡ Water must come in contact with the surface to dissolve atmospheric carbon into itSolid Earth Carbon Reservoir ! Even bigger! But breathes even more slowly ! 1,200,000 Gton carbon in sedimentary rocks (mostly limestones) ! 5000 Gton carbon in fossil fuels ! How does carbon get into the earth? Chemical weathering ¡ Changing silicate rocks into sedimentary rocks – very slow ¡ Involves dissolving rocks via rainfall ¡ Metamorphic decarbonation is the opposite – formation of CO2 within metamorphic rocksSilicate Weathering-CO2 Thermostat ! Weathering is thought to be the primary stabilizer over very long periods of time ! More rainfall & weathering w/ high CO2, leading to more CO2 taken out of the atmosphere ¡ Safety valve on climate ! Unfortunately dissolving of rocks takes a long time!Anthropogenic Emissions ! Of CO2 emissions, around 25% goes into the ocean immediately ¡ Not necessarily a good thing -- causes ocean acidification ! 25% goes into the land currently ¡ This fraction could change… ! 50% stays in the atmosphere ¡ This is called the “airborne fraction”What if we immediately stopped emitting? ! Some carbon would likely stay in the atmosphere for thousands of years! ! Ocean uptake happens “quickly” (300 yrs) ¡ A few years for surface ocean to 300 yrs for deep ocean ! Carbonate weathering: as ocean pH recovers, more carbonate is formed & buried in deep ocean ¡ Takes 5000 yrs ! Silicate weathering takes 100,000 yrsNext: Who’s Responsible? ! How much are average emissions for: ¡ Citizen of the world ¡ Average American ¡ Nations of the world ! Which sectors do emissions come from? ¡ Transportation ¡ Electricity generation ¡ Industry ! “Carbon efficiency”How Much Carbon Dioxide Is There? ! Total amount of carbon dioxide in the atmosphere: 3000 gigatonnes ! World emissions: over 30 gigatonnes per year ¡ 1 gigatonne = 1 billion metric tons ÷ And one metric ton is a little more than a regular ton (2000 pounds)Countries by Fossil Fuel CO2 Emissions ! China: 21% ! US: 19% ! European Union: 14% ! India: 5% ! Russia: 5% ! Japan: 4% ! All others less than 3% each 2007 data (CDIAC)National Emissions ! Another way to look at national carbon dioxide emissions ¡ Area of each country is made proportional to its emissions Source of images: WorldMapperThe Developing World ! Half of the people in the world live on less than $2.50/day ! 2.1 billion live without access to electricityFuture of Emissions for Developing Nations ! In around 20 years, the developing world will surpass developed countries in CO2 emissions Advanced Developing OECD = Organization for Economic Cooperation and Development includes 30 countries, mostly industrialized Developing nations will be a massive energy market in the future… What fuels will they use? (this plot assumes no additional regulations)Emissions Numbers ! World average per capita emissions is a little less than 5 tonnes ¡ World population: 7


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