The Global Carbon Cycle

Transcription

1 The Global Carbon Cycle Laurent Bopp LSCE, Paris Introduction CO2 is an important greenhouse gas Contribution to Natural Greenhouse Effect Contribution to Anthropogenic Effect 1 From NASA Website 2 Introduction Introduction CO2 and Climate have varied together in the past Past and recent variations of atmospheric CO2 3 4

2 Introduction CO2 and Climate have varied together in the past Introduction CO2 and Climate have varied together in the past Estimated from isotopic measurements in alkenones Cold From a compilation of benthic do18 records Warm Zachos et al. Science Introduction DaveSTELLA/Carbon/long_term_carbon.htm#schem atic CO2 concentration in the atmosphere seems to vary over very different time-scales from season to millions of years These variations are explained by the exchange with different reservoirs rocks, ocean, soil, biosphere and imply some very different processes Short-Term Carbon Cycle volcanism, weathering, dissolution, chemistry, photosynthesis, respiration The carbon cycles Long Term Carbon Cycle & Short Term Carbon Cycle 7 From Sarmiento and Gruber,

3 Today s Focus Short term carbon cycle (season to century) impacted by the release of long-term carbon reservoirs 1100 pp 550 pp +6,0 o Outline 1. Anthropogenic Sources of CO2 Atmospheric pco2 (ppm) 280 ppm 370 ppm 2. Observations, Trends and Budgets 3. Terrestrial and Marine Carbon Cycle : major processes 4. Coupling of the carbon cycle and the climate system ,5 o C Surface Temperature ( o C) +0,6 o C 1750 L. BOPP SOLAS Summer School Anthropogenic Sources of CO2 1. Anthropogenic Sources of CO Cumulative Emissions Products Europe USA Sectors Emissions de CO2 (1E3 tc/an) Germany France China Japan India SouthKorea A source of 6.3 GtC yr-1 in the 1990s 12

4 1. Anthropogenic Sources of CO2 : Deforestation Asie : 1.08 Am. Du sud : 0.55 Afrique : June 1975, Landsat 2 Rondônia, Brazil 22 June 1992, Landsat Anthropogenic Sources of CO2 : Deforestation 2. Observations, Trends and Budget Sink Source But very large uncertainties. New estimate based on remote sensing (de Fries et al. 2002) : GtC/yr for 90s 15 16

5 CO2 (ppm) 2. Observations, Trends and Budget 2. Observations, Trends and Budget Point Barrow (Alaska) - Maunoa Loa (Hawai) -SouthPole Observations, Trends and Budget : Global Network 2. Observations, Trends and Budget 19 20

6 2. Observations, Trends and Budget Sinks of Carbon 2. Observations, Trends and Budget Use of O2 atm. observations to constrain the carbon cycle (Keeling and Shertz, 1992) CO 2 O 2 ATMOSPHERE 21 ppm ppm O 2 /N 2 à Cape Grim et La Jolla (Bender - Keeling R.F) CO 2 àmaunaloa (Keeling C.D) Observations, Trends and BudgetC Use of O2 atm. observations to constrain the carbon cycle (Keeling and Shertz, 1992) July 1991 CO 2 = FF -Cont. -Ocean -140 FF Combustion O 2 = α FF - β Cont Observations July 1998 Jan A. July CONTINENT B OCEAN CO 2 (ppm) 23 24

7 2. Observations, Trends and Budget Atmospheric Inversions to estimate regional fluxes 2. Observations, Trends and Budget Atmospheric Inversions to estimate regional fluxes Direct Approach 3D Transport Model Concentrations Flux observations Inversion 25 Gurney et al. Transcom Project Observations, Trends and Budget : Oceanic Observations Ocean Estimations vs Inversions CO2 fluxes from oceanographic measurements (around 1million) (Takahashi et al.) Peylin et al.

8 2. Observations, Atlantic Trends and Budget : Oceanic Observations 2. Observations, Trends and Budget : Land Observations Ecosystems Estimations (based on Statistics) vs Inversions Anthropogenic Carbon in the Ocean (Sabine et al. 2004) Pacific Indian Jansen et al Observations, Trends and Budget : Land Observations Ecosystems Estimations (based on Statistics) vs Inversions 3. Terrestrial and Marine Carbon Cycle : major processes 3.1 Terrestrial Processes J: Jansen et al P: Pacala et al Northern L. BOPP SOLAS Hemisphere Summer School 2005 Sinks 31 32

9 Diversity of land ecosystems IGBP land cover map Diversity of land ecosystems Surf. Carbon Stocks 10 6 km 2 GtC Biomasse Soil Total Tropical Forests Temperate Forests Boreal Forests Savannas Grasslands Deserts Toundra Wetlands/Peatlands Agricultural land Total WBGU 1998 Deserts Wetlands Grasslands/Croplands Savannas Boreal Forests Temperate Forests Tropical Forests Ever. Needle. Forest Ever. Broad. Forest Dec.Needle. Forest Dec. Broad. Forest Mixed Forest Closed Shrublands Open Shrublands Woody Savannas Savannas Grasslands Permanent wetland Croplands Urban and built up Cropland/natural veg. Snow and Ice Bare Soil CO2 Fertilization Which processes are responsible for the terrestrial sink? CO2 fertilization Anthropogenic nitrogen deposition Climatic Variability DeLucia et al., Science, 1999 Land-use changes FACE Experiments Schlesinger et al., Nature, 2001

10 3. Terrestrial and Marine Carbon Cycle : major processes 3.2 Marine Processes Marine Carbon Cycle : Physics / Chemistry / Biology Solubility Pump Biological Pump Dissolution in cold waters of high latitudes Transfer via ocean circulation Release in warm or upwelling regions Time constants C-fixation in the euphotic layer (primary production) Most part is recycled Some part is exported beneath (export production) gas exchange ~ 1 mois transport in the ocean ~1000 ans 39 40

11 Surface Chlorophyll (SeaWiFS) Ecosystem composition bacteria pico-heterotrophs pico-autotrophs N 2 -fixers calcifiers DMS-producers mixed phytoplankton zooplankton silicifiers proto meso macro 2 examples : silicifiers / pico-autotrophs calcifiers Which processes are responsible for today s marine sink? «Despite the importance of biological processes for the ocean s natural cycle, current thinking maintains that the oceanic uptake of anthropogenic CO2 is primarily a physically and chemically controlled process surimposed on a biogically driven carbon cycle that is close to steady state» (IPCC, 2001) 43 IPCC,

12 4. Carbon-Climate Coupling in the 21 st century CO2 controls the climate 4. Carbon-Climate Coupling in the 21 st century What controls carbon uptake by the land and the oceans? CO 2 Atm CO 2 CO 2 IPCC Scenario Atm CO 2 IPCC Scenario CLIMAT CLIMAT Geochemical Impact Climate Impact 45 biosphere Ocean Carbon-Climate Coupling in the 21 st century Which processes are responsible (in the models) for the climate impact on uptakes? Land NPP decreases with decreasing water availability Heterotrophic respiration increases to temperature Ocean -> But no consensus. Large uncertainties Warming Effect : Increased T decrease CO2 solubility Dynamical Effect : Increases stratification prevents anth. CO2 penetration Biological Effects? -> Uncertainties on the dynamical effect. 47 IPCC,

13 4. Carbon-Climate Coupling in the 21 st century Coupled Carbon-Climate Simulations : Climatic Impact Fossils Fuels CLIMAT Atm CO 2 CO 2 IPCC Scenario Geochemical Impact Feedback on climate Atmospheric CO2 (ppmv) IPSL Hadley IPSL-Uncoupled Hadley-Uncoupled IPSL Hadley IPSL-Uncoupled Hadley-Uncoupled Land Flux (GtC) 280 ppmv 80 ppmv IPSL Hadley Temperature (K) Ocean Flux (GtC) IPSL Hadley IPSL-Uncoupled Hadley-Uncoupled biosphere Ocean (Cox et al, 2000)