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Unformatted text preview: Carbon Sequestration and global warming Greenhouse gases prevent radiant loss of energy to space A poor understanding of stocks and flows : The concept of accumulation World and US Emissions from Fossil Fuels and Land-Use Change
Select Years (millions of metric tons of carbon per year) 1850 54 5 503 162 1900 534 181 697 247 1950 1612 692 935 -91 1960 2535 797 1302 -157 1970 3998 1160 1537 -149 1980 5177 1263 1608 -150 1990 5969 1315 2158 -110 2000 Fossil Fuel World United States Land-Use Change World United States 6385 1529 2081 -110 Eastern forests being reclaimed
Source: All data derived from Oak Ridge National Lab, Carbon Dioxide Information Analysis Center Land-use change data from "Annual Net Flux of Carbon to the Atmosphere from Land-Use Change: 1850-2000" at http://cdiac.ornl.gov/ftp/trends/landuse/houghton/houghtondata.txt Fossil fuel emissions data from "Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2000" at http://cdiac.ornl.gov/ftp/ndp030/global00.ems, and "Global CO2 Emissions from Fossil-Fuel Burning, Cement Manufacture, and Gas Flaring: 1751-2000" at http://cdiac.ornl.gov/ftp/ndp030/nation00.ems Industrialized countries agree to reduce their collective greenhouse gas emissions by 5.2% compared to the year 1990 by 2012 GHG: Carbon Dioxide Methane Nitrous Oxide Hydrofluorocarbons Perfluorocarbons Sulphur hexafluoride Because of differences in past reductions and levels of contribution of GHG countries differ in their required reductions: EU -8% USA -6% Japan -6% Russia 0% Australia +8% Mechanisms of compliance: National activities to reduce GHG emissions or to remove emissions after the fact plus: A) Emissions trading "the carbon market" B) Clean development mechanism (investing in another country to help it develop in a way that reduces their emissions) C) Joint implementation (carry out emissions reduction or emissions removal project in another country and get credit for it) The Kyoto Protocol: Major sources Fossil fuels, agriculture, and deforestation Animal respiration Major sinks Plant biomass Oceans Sediment Carbon Cycle Increasing pools of C in various terrestrial habits may help reduce increase in atmosphere Forests Sequester Carbon
In U.S studies, forests sequester 0.9 to 4.6 tons/acre/year: ca. 200 million metric tons per year Northeast Forest Carbon Stocks
Above Ground Biomass 38% Soil Organic Carbon Litter Dead Wood 38% Belowground Biomass Forms of Sequestration include: Biomass in the trunks, branches, leaves, roots, litter and under story shrubs via photosynthesis 6% 10% 8% In the Soil In Forest Products USFS predicts 90 million metric tons of Carbon in 2008 Source: Willams et al. 2000 Fast turnover, commonly practiced in plantation forestry does not sequester as much carbon on average as longer turnover or unmanaged forests Tree species differ greatly in rate at which they sequester Carbon Little continued sequestration of carbon after initial tree foundation Fast-growing trees are better in long run in sequestering carbon Poplar Oak Large variation in time during which wood products are used before disposal Landfills are a good news/bad news story Only certain fungi can degrade lignin (in wood and newsprint) - under aerobic Unfortunately, in most countries there is insufficient amount
2 of forest to act as meaningful sink for CO A good investment? Uncertain and unpredictable loss of forest mass due to fire or CO dependence of photosynthesis: Trees are C3 plants Photosynthesis Importance of rubisco in cycle Influence as a limiting factor Other limiting factors Nitrogen, phosphorous Carbon Uptake: CO and not Rubisco usually most limiting factor CO2 usually a limiting factor With increased amounts of CO2, photosynthesis increases With continued increases, RuBP (a co-substrate for Rubisco) eventually becomes the limiting factor Current levels of CO2 (370 ppm) in atmosphere are not at saturation level, (estimated to be 1000 ppm) Early Experimentation on CO Enrichment Experiments (in the `80s and `90s) were highly controlled experiments with herbaceous plants in greenhouses Single species, whole crop responses Under optimal conditions (temperature, humidity, non-limiting nutrients) Plant biomass was shown to increase significantly (30-50%) with increased CO2 Has led to use in horticulture greenhouses can easily increase CO2 levels Explanation for increased biomass: Greater concentration of CO2 allows for increased CO2 uptake with decreased water loss through transpiration Allows for smaller stomatal opening without limiting CO2 uptake This increased water availability allows for greater amounts of moisture to remain in soils aiding nutrient uptake/availability Generally, plants show more efficient utilization of nutrients, water and light Biggest increase in dry years Problems with these early experiments Grasses, crop plants are easier to work with, but their contributions to CO2 sink are not significant on global scale Only forest biomes create a significant carbon sink on a global scale Make up 80% of global plant mass Challenges of Forest Experiments
Trees are more important in sequestration, but physically harder to work with, more variable in their response, and data is harder to interpret Estimates made only of increased growth rate, not overall uptake and longterm storage of carbon Forest Stand Experiments Tested stands of trees Increased ambient air concentrations of CO2 FACE Duke Univ. and Switzerland (Korner) Free Air Carbon Enrichment (F.A.C.E) FACE plots increase the Experimental Stategies: Duke Tested stands of Loblolly pine forest Tree stands uniform age single species Used vertical pipes to increase CO2 levels to 560 ppm Switzerland Tested mixed conifer forests in Basel, Switzerland More highly varied tree species and various ages Used isotope (13C) tracking (determine fate of newly introduced CO2) Worked with forest canopy by accessing them with cranes CO enrichment resulted in: More "pumping" of carbon through forest ecosystem did not all stay in system More carbon uptake, but Faster decomposition of litter More respiration by heterotrophs in soil Beyond that, it's complicated Age, species, sink availability, nutrients, soil fauna CO Age
Young Trees respond most to increased CO2 Young trees resemble the results for grasses and crops rather than mature trees Increased growth rate, tissue accumulation, and similar use of stomatal closure No significant increase in overall growth only increase in growth/maturation rate Increased rate of life cycle Transient effect of elevated CO on growth of pine trees More cones. Stopped growing sooner. Species Foliage per unit land area, leaf duration, leaf and litter composition, growth response all varied from one species to another- sometimes with contradictory responses Nutrients Nutrient availability may be limiting when extra CO2 is present increased growth only if other nutrients not limiting Response to elevated CO is greater when N was available due to presence of legumes Mature trees tend not to increase aboveground biomass
Accumulation of nonstructural carbohydrates (NSC) such as starch, sugar in leaves can inhibit photosynthesis NSC levels increase in leaves and speed breakdown in soil Conclusions so far: It was thought that forests might could act as a increasing sink for anthropogenic CO2 emissions by increasing their biomass, but that is not the case The best way to take advantage of forest carbon sinks is to stop deforestation Reforestation partly compensates, but to a limited extent Recently replanted forest stands are a major sink in the Northern Hemisphere, but they will be less active when they reach maturity A wild idea?
Increase lignin production in trees to reduce rate at which they will be decomposed upon dying?
Others: Iron levels were much higher in the past (dust from deserts?) and were NO3 levels in Ocean Waters Could support algal growth? Add iron to ocean to overcome iron limitation of algal growth Primary productivity and chlorophyll abundance within patches of Effect on phototroph growth most pronounced in top 35 m of water Chemical forms of iron to be used (lignin acid sulfonate) different from natural forms of iron Very high rates of iron proposed Fe fertilization changes composition of the phytoplankton community Silicatious diatoms often most responsive enough silica in water to enable response to Fe? Alteration of food webs and biogeochemical cycles altered Sustained Fe fertilization might result in deep ocean hypoxia more production of CH4 and NO How much of surface phytoplankton will be deposited on ocean floor? Toxic algae preferentially respond to added Fe ...
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This note was uploaded on 01/19/2011 for the course ESPM 192 taught by Professor Lindow during the Fall '10 term at University of California, Berkeley.
- Fall '10