Vegetation dynamics in simulations of radiativelyforced 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 1 Hadley Centre for Climate Prediction and Research

Simulating global vegetation in the Hadley Centre coupled climate-carbon cycle model n Compare simulated vegetation with global observational datasets n 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) 2 Hadley Centre for Climate Prediction and Research

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

TRIFFID vegetation model n Competition between 5 plant functional types – Broadleaf tree, Needleleaf tree, C 3 grass, C 4 grass, shrub 4 n Carbon balance computed within GCM land surface scheme n Interacts with atmospheric CO 2 n Vegetation distribution and leaf area determine land surface characteristics in atmosphere model Hadley Centre for Climate Prediction and Research

TRIFFID-GCM coupling Photosynthesis, respiration, transpiration (30 minutes) Litter (1 day) Broadleaf Tree Shrub C 3 Grass Soil Competition (10 days) 5 Hadley Centre for Climate Prediction and Research LAI, albedo, roughness (1 day)

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

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

Surface temperature changes (K) relative to 2000 30 -year means 8 Hadley Centre for Climate Prediction and Research

2020 Precipitation changes relative to 2000 mm day-1 30 -year means 2050 2080 9 Hadley Centre for Climate Prediction and Research

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

What is the role of plant physiological responses to CO 2? n TRIFFID includes direct effects of CO 2 on vegetation – CO 2 fertilization – size of stomatal openings n 3 simulations, IS 92 a 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 11 Hadley Centre for Climate Prediction and Research

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

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

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

How do biogeophysical feedbacks affect Amazon drying? n Changes in land surface characteristics – albedo – moisture availability (roots, canopy) – aerodynamic roughness n 2 simulations, IS 92 a 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 15 Hadley Centre for Climate Prediction and Research

Precipitation changes (mm day-1) due to biogeophysical feedbacks 16 Hadley Centre for Climate Prediction and Research

How do carbon cycle feedbacks affect Amazon drying and dieback? n Further simulation: fully interactive carbon cycle n IS 92 a emissions scenario n atmospheric CO 2 calculated within GCM – (other GHGs prescribed) 17 n vegetation and soil feedbacks on CO 2 n physical and biological ocean carbon feedbacks on CO 2 Hadley Centre for Climate Prediction and Research

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

Effects of climate-carbon cycle feedbacks on atmospheric CO 2 rise CO 2 concentrations (ppmv) 1000 800 600 400 200 19 with CO 2 -climate feedbacks without CO 2 -climate feedbacks 1900 Hadley Centre for Climate Prediction and Research 1950 2000 2050 2100

Effects of climate-carbon cycle feedbacks on land temperature rise 8 Temperature rise (°C) 6 with CO 2 -climate feedbacks without CO 2 -climate feedbacks 4 2 0 – 2 1850 20 1900 Hadley Centre for Climate Prediction and Research 1950 2000 2050 2100

Further precipitation changes with CO 2 climate feedback (compared to prescribed CO 2 dynamic veg simulation) mm day-1 30 -year means 21 Hadley Centre for Climate Prediction and Research

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

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

Conclusions n CO 2 physiological effects enhance NPP through fertilization but also exert climatic effect – relative importance for vegetation varies from place to place n Biogeophysical feedbacks modify local climate change – enhance Amazon drying n Carbon cycle feedbacks accelerate global climate and vegetation change – enhance Amazon drying and dieback n 24 Vegetation carbon sink may not be robust to climate change Hadley Centre for Climate Prediction and Research