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Vegetation dynamics in simulations of radiatively-forced climate change

Vegetation dynamics in simulations of radiatively-forced climate change Richard A. Betts, Chris D. Jones, Peter M. Cox [ chris.d.jones@metoffice.com] Met Office Hadley Centre for Climate Prediction and Research Terrestrial Carbon Sinks Workshop, Wengen, Sept. 2002.

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Vegetation dynamics in simulations of radiatively-forced climate change

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  1. Vegetation dynamics in simulations of radiatively-forced climate change Richard A. Betts, Chris D. Jones, Peter M. Cox [chris.d.jones@metoffice.com] Met Office Hadley Centre for Climate Prediction and Research Terrestrial Carbon Sinks Workshop, Wengen, Sept. 2002

  2. Simulating global vegetation in the Hadley Centre coupled climate-carbon cycle model • Compare simulated vegetation with global observational datasets • In simulations of future global change, investigate interactions and feedbacks: • direct effects of CO2 on vegetation • biogeophysical feedbacks (through water cycle) • biogeochemical feedbacks (through carbon cycle)

  3. Hadley Centre Coupled Climate-Carbon Cycle Model (Biogeophysical) (Biogeochemical)

  4. TRIFFID vegetation model • Competition between 5 plant functional types • Broadleaf tree, Needleleaf tree, C3 grass, C4 grass, shrub • Carbon balance computed within GCM land surface scheme • Interacts with atmospheric CO2 • Vegetation distribution and leaf area determine land surface characteristics in atmosphere model

  5. TRIFFID-GCM coupling Photosynthesis, respiration, transpiration (30 minutes) Litter (1 day) Broadleaf Tree Shrub C3 Grass LAI, albedo, roughness(1 day) Soil Competition (10 days)

  6. Coverage of vegetation types, control simulation Fraction of gridbox

  7. Vegetation cover: simulated - observed (IGBP-DIS) Fraction of gridbox

  8. Surface temperature changes (K)relative to 200030-year means

  9. Precipitation changes relative to 2000mm day-130-year means 2020 2050 2080

  10. Changes in tree coverGridbox fraction

  11. What is the role of plant physiological responses to CO2? • TRIFFID includes direct effects of CO2 on vegetation • CO2 fertilization • size of stomatal openings • 3 simulations, IS92a concentration scenario • (a) CO2 exerts radiative forcing only (vegetation given constant present-day CO2) • (b) CO2 exerts radiative and physiological forcings (vegetation responds directly to rising CO2) • (c) Other GHGs included as well as CO2

  12. Broadleaf tree Net Primary Productivity(NPP) in central Africa

  13. Changes in broadleaf tree cover due to physiological responses to CO2

  14. Precipitation difference (mm day-1)due to plant physiological responses to CO2

  15. How do biogeophysical feedbacks affect Amazon drying? • Changes in land surface characteristics • albedo • moisture availability (roots, canopy) • aerodynamic roughness • 2 simulations, IS92a GHG concentration scenario (prescribed CO2 and other GHGs) • (a) Vegetation fixed at present-day state • (b) Dynamic vegetation updates land surface characteristics • NB. No direct anthropogenic deforestation- “natural” responses only

  16. Precipitation changes (mm day-1)due to biogeophysical feedbacks

  17. How do carbon cycle feedbacks affect Amazon drying and dieback? • Further simulation: fully interactive carbon cycle • IS92a emissions scenario • atmospheric CO2 calculated within GCM • (other GHGs prescribed) • vegetation and soil feedbacks on CO2 • physical and biological ocean carbon feedbacks on CO2

  18. Vegetation & soil carbon changesGtCInteractive CO2

  19. Effects of climate-carbon cycle feedbacks on atmospheric CO2 rise with CO2-climate feedbacks 1000 without CO2-climate feedbacks 800 CO2 concentrations (ppmv) 600 400 200 1900 1950 2000 2050 2100

  20. Effects of climate-carbon cycle feedbacks on land temperature rise 8 with CO2-climate feedbacks without CO2-climate feedbacks 6 4 Temperature rise (°C) 2 0 – 2 1850 1900 1950 2000 2050 2100

  21. Further precipitation changes with CO2-climate feedback(compared to prescribed CO2 dynamic veg simulation)mm day-130-year means

  22. Further changes in tree cover with CO2-climate feedbacksGridbox fraction

  23. Broadleaf tree cover (gridbox fraction) in coupled climate-carbon cycle simulation

  24. Conclusions • CO2 physiological effects enhance NPP through fertilization but also exert climatic effect • relative importance for vegetation varies from place to place • Biogeophysical feedbacks modify local climate change • enhance Amazon drying • Carbon cycle feedbacks accelerate global climate and vegetation change • enhance Amazon drying and dieback • Vegetation carbon sink may not be robust to climate change

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