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

2 Hadley Centre for Climate Prediction and Research 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 CO 2 on vegetation –biogeophysical feedbacks (through water cycle) –biogeochemical feedbacks (through carbon cycle)

3 Hadley Centre for Climate Prediction and Research Hadley Centre Coupled Climate-Carbon Cycle Model (Biogeophysical) (Biogeochemical)

4 Hadley Centre for Climate Prediction and Research 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 CO 2 Vegetation distribution and leaf area determine land surface characteristics in atmosphere model

5 Hadley Centre for Climate Prediction and Research TRIFFID-GCM coupling Photosynthesis, respiration, transpiration (30 minutes) Litter (1 day) Competition (10 days) LAI, albedo, roughness (1 day) Broadleaf Tree C3 Grass Shrub Soil

6 Hadley Centre for Climate Prediction and Research Coverage of vegetation types, control simulation Fraction of gridbox

7 Hadley Centre for Climate Prediction and Research Vegetation cover: simulated - observed (IGBP-DIS) Fraction of gridbox

8 Hadley Centre for Climate Prediction and Research Surface temperature changes (K) relative to year means

9 Hadley Centre for Climate Prediction and Research Precipitation changes relative to 2000 mm day year means

10 Hadley Centre for Climate Prediction and Research Changes in tree cover Gridbox fraction

11 Hadley Centre for Climate Prediction and Research What is the role of plant physiological responses to CO 2 ? TRIFFID includes direct effects of CO 2 on vegetation –CO 2 fertilization –size of stomatal openings 3 simulations, IS92a concentration scenario –(a) CO 2 exerts radiative forcing only (vegetation given constant present-day CO 2 ) –(b) CO 2 exerts radiative and physiological forcings (vegetation responds directly to rising CO 2 ) –(c) Other GHGs included as well as CO 2

12 Hadley Centre for Climate Prediction and Research Broadleaf tree Net Primary Productivity(NPP) in central Africa

13 Hadley Centre for Climate Prediction and Research Changes in broadleaf tree cover due to physiological responses to CO 2

14 Hadley Centre for Climate Prediction and Research Precipitation difference (mm day -1 ) due to plant physiological responses to CO 2

15 Hadley Centre for Climate Prediction and Research 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 CO 2 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 Hadley Centre for Climate Prediction and Research Precipitation changes (mm day -1 ) due to biogeophysical feedbacks

17 Hadley Centre for Climate Prediction and Research How do carbon cycle feedbacks affect Amazon drying and dieback? Further simulation: fully interactive carbon cycle IS92a emissions scenario atmospheric CO 2 calculated within GCM –(other GHGs prescribed) vegetation and soil feedbacks on CO 2 physical and biological ocean carbon feedbacks on CO 2

18 Hadley Centre for Climate Prediction and Research Vegetation & soil carbon changes GtC Interactive CO 2

19 Hadley Centre for Climate Prediction and Research Effects of climate-carbon cycle feedbacks on atmospheric CO 2 rise with CO 2 -climate feedbacks without CO 2 -climate feedbacks CO2 concentrations (ppmv)

20 Hadley Centre for Climate Prediction and Research with CO 2 -climate feedbacks without CO 2 -climate feedbacks 1850 – Temperature rise (°C) Effects of climate-carbon cycle feedbacks on land temperature rise

21 Hadley Centre for Climate Prediction and Research Further precipitation changes with CO 2 -climate feedback (compared to prescribed CO 2 dynamic veg simulation) mm day year means

22 Hadley Centre for Climate Prediction and Research Further changes in tree cover with CO 2 -climate feedbacks Gridbox fraction

23 Hadley Centre for Climate Prediction and Research Broadleaf tree cover (gridbox fraction) in coupled climate- carbon cycle simulation

24 Hadley Centre for Climate Prediction and Research Conclusions CO 2 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