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February 19 Land Use and Cover Change and the Global Carbon Cycle

February 19 Land Use and Cover Change and the Global Carbon Cycle. Ecological Disturbance on a Global Scale. Global Change / Climate Change. Global Climate change which results from human activities is one of the most contentious topics in environmental science and policy

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February 19 Land Use and Cover Change and the Global Carbon Cycle

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  1. February 19Land Use and Cover Change and the Global Carbon Cycle Ecological Disturbance on a Global Scale

  2. Global Change / Climate Change • Global Climate change which results from human activities is one of the most contentious topics in environmental science and policy • There is growing agreement that: • There is a climate change occurring • That humans are the cause • The global carbon cycle is a keystone topic

  3. The carbon cycle • The carbon cycle is the canonical global change issue, especially when we want to “go beyond climate change” • think: is it the most important, in our time? • I want to use this as a good overview issue for human impacts on the planetary scale • strong geographical component • strong human component, many leads and connections to human dimensions • strong policy component • it’s a big mystery but something important to find answers to • if we cant understand something this basic we wont be able to do much else • points to all the classical issues of inquiry: measurement, models, evidence, inference, uncertainty,etc • social science needs to know this stuff

  4. The greenhouse effect • Based only on our distance from the sun, the earth should be colder by 33 degrees C. • Our planet should be a chunk of ice • But natural greenhouse gases – primarily carbon dioxide and water vapor provide for heating of the planet to a normal temperature. • But we are now introducing MORE greenhouse gases, and we don’t know what affect this will have

  5. Atmospheric Gases 78% Nitrogen 21% Oxygen <0.04% Carbon Dioxide

  6. Carbon dioxide in the atmosphere • Exists in trace quantities • This means doubling or halving can be important • Consider oxygen: if all trees were removed the oxygen concentration would decline by 300 ppm – from 209,480 to 209,180. • But an increase of 300 ppm for carbon dioxide would double it.

  7. Water vapor Methane Nitrous oxide CFC’s and other halocarbons Hydrological cycle Animal husbandry Chemical fertilizers* Refrigerants* Other Greenhouse Gases And Sources * = Long residence times and contribute to ozone depletion

  8. The greenhouse effect

  9. Global Surface Temperatures

  10. NOAA Global Flask Sampling Network

  11. 360 320 280 240 200 160 400,000 300,000 200,000 100,000 0 Atmospheric [CO2] over the last 400,000 years 2000 1750 CO2-concentration (ppm) Years before present Petit et al. (1999)

  12. Global Emissions from Land Use Change [180-200 PgC from land use change] + 90 ppm CO2 in the atmosphere [40 ppm due to changes in land use] 124 Pg emitted due to land use change 60% in tropical areas %40 in temperate areas Historically Total emissions of C [deforestation and fossil-fuel burning] 450 PgC 1 Pg C = 1,000,000,000,000,000 g C (a billion tones) From 1850 to 1990 90% due to deforestation [20% descrease Forest Area] Houghton et al. 1999, Houghton 1999, Defries et al. 1999, IPCC-TAR 2001

  13. Global Carbon Budget - The fate of CO2 Period 1990-1996 3.7 PgC/yr - Atmosphere 2.9 PgC/yr - Oceans 1.3 PgC/yr - Terrestrial Ecosystems 7.9 Pg C/yr (6.3 Pg Fossil Fuel) (1.6 Pg Land Use) After IPCC, TAR 2001

  14. Global CO2 Budgets (Pg/yr) 1980’s1990-95 Atmospheric Increase +3.3±0.1 +2.9 ±0.1 Emissions (fossil fuel, cement) +5.5 ±0.3 +6.3 ±0.4 Ocean-Atmosphere Flux -2.0 ±0.6 -2.4 ±0.5 Land-Atmosphere Flux -0.2 ±0.7 -1.0 ±0.6 Land-Use Change (80’s) +1.6 (0.5 to 2.4) Residual Terrestrial Sink - 1.8 (-3.7 to +0.4) IPCC, TAR 2001

  15. dA = F + B - O - b 1980s 3.7 = 6.3 + 1.6 - 2.9 3.7  5.0(Difference is 1.3 -- The Missing Sink) 1990s 2.9 = 6.3 + 1.6 – 2.4 2.9  5.5 (Difference is 2.6)

  16. Global Carbon Sinks resulting from land use/cover change

  17. - Atmospheric constraints of Global C sources and sinks - Location of Global C Sources and Sinks CO2 Flask Network and Inverse Modeling NOAA-CMDL 1999

  18. Inverse Model Estimates of CO2 Uptake (7 Models) IPCC, TAR, 2001

  19. Biological C Sources and Sinks - 0.7 to - 2.4 Pg C/yr + 1.6 Pg C/yr 0.0 Pg C - 1.6 Pg C/yr - 0.0 Pg C/yr

  20. Inverse Modeling Calculations of C Sources and Sinks North America: 1.6 PgC/yr Euroasia:0.5 PgC/yr Fan et al. 1998

  21. - 1.3 - 0.3 - 0.5 - 0.1 Inverse Modeling Calculations of Terrestrial Carbon Sources and Sinks Pg C/yr TM2 1985-1995 GlobalView-CO2 Ciais et al 2000

  22. Land Use/Cover Change Current Terrestrial Sinks Potential Driving Mechanisms • CO2 fertilization • Nitrogen fertilization • Climate change • Regrowth of previously harvested forests • Reforestation / Afforestation • Regrowth of previously disturbed forests • Fire, wind, insects • Fire suppression • Decreased deforestation • Improved agriculture • Sediment burial • Future: Terrestrial Carbon Management (e.g., Kyoto)

  23. Carbon Sinks Three Examples: • The Northern Hemisphere Temperate/Boreal Sink • The Eastern USA sink • China sink

  24. [Forestry Sector] 0.7 to 0.8 Pg C/yr 70% in Temperate Regions [Larger sink in Euroasia than in North America] - Forest Inventories and Land Use Change as constraints of C Sources and Sinks - 1. Northern Hemisphere Carbon Sink Late 80’s-Early 90’s 30-100% Total Sink: 0.7 to 2.4 Pg C/yr [Inverse modeling] 0.2 Pg C yr-1 in living biomass, 0.4 Pg C yr-1 in dead organic matter 0.1 Pg C yr-1 in forest products Goodel et al 2001 (in press)

  25. Asian Russia Canada Coterminous US Euro Russia Europe China Carbon Stocks in Live Forest Vegetation Over the Last Half Century 30 25 20 15 10 5 0 Live Vegetation (Pg C) 1950 1960 1970 1980 1990 2000 Goodel et al 2001 (in press)

  26. 2. Eastern United States Carbon Sink • Eastern United States (5 states) • 96% of the C sink attributed to land use change: • Forest regrowth after crop abandonment • Reduced harvesting • Fire suppression • 4% remaining attributed to: • Increasing CO2 • Nitrogen Deposition • Climate Change Caspersen et al. 2000

  27. 0.38 Pg C comes from planted forests 3. Changes in Forest Biomass C storage in China 1949-1998 Between 1940’s and 70’s, C storage declined by 0.68 Pg C due to forest exploitation policies From late 1970’s to present, C storage has increased by 0.4 Pg C due to policies of protection and timber production [+ 0.021 Pg C/yr] Fang et al. 2001

  28. Landsat TM image, Paragom.,1991, classified as forest and non-forest [Brazilian Government reporting methodology] – 62% Forest Same image, classified after ranch owners interviews: only 1/10 of the above forest was Classified as undisturbed forest by human practices – 6.2% Forest Forest Conversion: Carbon Density • Forest Impoverishment: • Surface fires • (could be responsible for doubling • C emissions during El Nino years) • Logging • (4-7% of that of forest conversion) Nepstad et al. 1999

  29. Biomass Sink Strength Forest Structure: Carbon Sink Strength time

  30. Area burned in the North America Boreal Forest Region (1940-1998) Direct C emissions from Fires in Canada (1950-1999) Kasischke and Stocks 2000 Amiro et al. 2000 Photo: M. Flannigan, Canada Carbon Source: Emissions from Forest Fires • Annual global carbon emissions from • vegetation fires • 1.6 Pg C/yr • 25% of the amount of fossil fuel emissions

  31. Annual Flux of C (TgC yr-1) Houghton et al. 2000 Carbon Sink: Fire suppression Fire exclusion has increased C storage in forests [last 100 yrs] Total Area Burned (US) Eliminating fire completely, US forest could accumulated 2.6 Pg C by 2140 Photos: M. Flannigan [Canada]

  32. Precipitation Water Availab. Air temperature Soil toxicities - + + - - N deposition Increasing CO2 - Woody Biomass Fire Harvesting Browsers + - - + + + Overgrazing + Nutrients Human population Woody Encroachment: Biophysical and land management drivers After Scholes and Hall 1996 Photo: S. Archer

  33. Maximum Potential C sequestration in the absence of fire = 2 Pg C yr-1 (upper value) Scholes and Hal 1996 Woody Encroachment Woody plant encroachment has promoted C sequestration in grassland and savanna ecosystems of N and S America, Australia, Africa, and Southeast Asia over the past century. • Estimated CO2 sink: • USA: 0.17 PgC/yr for the 1980s (Houghton et al., 1999) • Australia: 0.03 PgC/yr (Burrows, 1998) Photo: Martin 1975, Arizona 1903 & 1941

  34. Improved Agriculture Practices • High yielding plant varieties • Fertilisers • Irrigation • Residue management • Reduced tillage for erosion control has contributed to the stabilisation or enhancement of carbon stocks Donigian et al. 1994 , Lal et al. 1998, Metting et al. 1999, IPCC Land Use and Forestry 2000

  35. Bioenergy production 6 70 Woodland regeneration 5 60 50 4 No-till % Offset of 1990 European CO2 Emissions Maximum Yearly C Mitigation 40 Potential (Tg C y-1) 3 Animal manure 30 Extensification 2 Straw Incorp. 20 Sewage sludge 1 10 0 0 Land Management Change Carbon Mitigation and Offsets due to Land Management in Europe A combination of best practices could offset 0.113 Pg C/ yr. Over 100 years this is equivalent to a C offset of 11.3 Pg.

  36. In the USA: • Full adoption of best management practices • would be likely to restore soil organic carbon • levels to about 75-90% of their pre-cultivation • level, increasing 7.5-20.8 Pg C over 100 years • (0.075 to 0.208 Pg C per year).

  37. Example from the tropics

  38. Main points • Land use and management leaves a mosaic of various cover types and cover states • These systems have memory • Memory is manifested in long term sources, and sinks in regrowth and soil OM storage • Memory is also manifested in how many cycles or transitions a landscape patch has undergone alteration • Changes in stocks – changes in area, changes in density -- and changes in fluxes, which vary with time

  39. Geography and timing • Some important issues include geography and timing • Geography in the broader context to include spatial pattern • Past deforestation may currently be regenerating; in regions where current deforestation is declining and there are larger regenerating areas (reflecting a history of large deforestation rates), such asynchronies may be important. • Considerable evidence for large areas of regeneration, and for considerably variable rates of clearing

  40. Multiple changes in one landscape • The current landscape is a mosaic, or record, of current and past land use and cover changes • Variation exists at fine temporal and spatial scale • Variation exists across classes of cover (from conversion) and within classes of cover (from modification or degradation) • History has created a more complex landscape • We know nothing about the processes which form this landscapes over time, nor do we have good measures (maps) of these landscapes themselves. • Our prognostic ability is severely limited

  41. Observations: extent and density • We focus on making direct observations of changes in forest extent (both increase and decrease) and density • This can be done using annual observations from high spatial resolution remote sensing in conjunction with a coupled land use-carbon models. • This approach complements, but is more direct in determining the land use component, than use of other measures of changes in forest carbon from stand inventory data alone (Casperson et al. 2000)

  42. Inter-annual variation in rates of deforestation and regrowth

  43. Carbon flux over space

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