Carbon Science Highlights 2004

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Melvyn Stokes
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1 Carbon Science Highlights 2004 THE PAST Understanding the Ice Ages THE PRESENT Observations of Atmospheric Gases Estimating CO 2 Sources and Sinks Processes Controlling CO 2 Fluxes Processes Determining U.S. Ozone Pollution THE FUTURE Ocean Model Development Land Model Development Coupled Earth System Model Development

2 We Have a Land Carbon Model that Works

3 And an Ocean Carbon Model that Works

4 Deep Dive on Thursday Afternoon Leetmaa - Understanding global environmental trends and projections Stouffer - Detection of climate change Jacobson - New carbon sink estimates Crevoisier & Gloor - Observing, diagnosing and predicting the terrestrial carbon sink Sigman & Sarmiento - Predicting the future of the ocean sink: The Southern Ocean

5 Carbon Cycle Status 2004 Where we are today Ocean - We are increasingly confident of the magnitude of the oceanic CO 2 uptake. The mechanisms are well understood. Land - Knowing the ocean CO 2 uptake allows us to estimate the total land uptake, but the spatial distribution and mechanisms are still highly contentious. We have new results on this. Major issues Land - What are the uptake mechanisms? Is there a CO 2 fertilization land sink or not? Ocean - The Southern Ocean is the key. How well do we understand it and how it will respond to climate change?

6 Growth Rate of Carbon Reservoirs

7 Carbon Sources and Sinks (Pg yr -1 ) 1990 s Fossil Fuel Emissions +6.3 ± 0.4 Atmospheric Increase -3.2 ± 0.1 NET Ocean & Land Uptake -3.1 ± 0.4

8 Oceanic Uptake Constraints ANNUAL MEAN OCEANIC UPTAKE OF ANTHROPOGENIC CARBON NORMALIZED TO (Pg C yr -1 ) Reference Method Uptake IPCC TAR [1991] Based on measured atmospheric O 2 and 1.7 ± 0.5 CO 2 New Estimates 1 Gurney, et al. [2002] Inversions based on atmospheric transport models and observed CO ± Keeling, et al. [1996], Battle, et al. [2000]*, and Bopp, et al. [2002] Based on measured atmospheric O 2 and CO 2 inventories but corrected for ocean warming and stratification 3 Takahashi, et al. [2002] Measurements of sea-air pco 2 difference and [Wanninkhof, 1992] U 2 gas exchange model Measurements of sea-air pco 2 difference and [Wanninkhof and McGillis, 1999] U 3 gas exchange model ~2.2 ± 0.7 4* McNeil, et al. [2003] Ages estimated from observed CFCÕs 2.0 ± 0.4 5* Gloor, et al. [2003] Inversions based on ocean transport 2.2 ± 0.4 models and observed DIC 6* Matsumoto, et al. Model simulations evaluated with CFCÕs 2.2 ± 0.4 [2004] and pre-bomb radiocarbon 7* Jacobson, et al. [in preparation] Joint inversion based on atmospheric and oceanic observations and models 2.2 ± 0.2 *Study carried out at Princeton/CMI

9 Land & Ocean Breakdown (Pg yr -1 ) 1990 s NET Ocean & Land Uptake -3.1 ± 0.4 Estimated Ocean Uptake Inferred Net Land Uptake -2.2 ± ± 0.5

10 The terrestrial carbon sink We have an improved estimate of the net land uptake in the 1990 s (0.9 ± 0.5). But where does land uptake occur and what is its mechanism? And what about the tropical deforestation source?

11 Carbon Sources and Sinks by Region According to IPCC TAR [2001] S. Hemis. Tropics N. Hemis. Inversions based on atmospheric CO 2 observations and models NOTE near zero land flux in Tropics and Southern Hemisphere!

12 The net southern and tropical (S&T) land flux is the result of a tropical deforestation source minus a CO 2 fertilization sink: Tropical S&T CO 2 Net S&T Deforestation - Fertilization = Land Source Sink Flux Estimates of the net S&T land flux together with independent estimates of tropical deforestation allow us to estimate the effect of CO 2 fertilization: Tropical Net S&T S&T CO 2 Deforestation - Land = Fertilization Source Flux Sink Thus the large tropical deforestation source (0.6 to 2.5 Pg C yr -1 ) and ~0 S&T land flux in the IPCC TAR imply a huge S&T CO 2 fertilization sink!

13 Only 3-4 wedges are necessary instead of 7 if CO 2 fertilization operates according to the models in the IPCC Third Assessment NOTE: 70% of the CO 2 fertilization effect is expected to be in the Tropics

14 Oceanic Carbon Observations

15 CMI s new tropical and southern land flux estimate (Jacobson, et al.) QuickTime and a TIFF (LZW) decompressor are needed to see this picture. In blue are unconstrainted atmospheric inversions In dashed green are recent atmospheric inversions with priors (the usual method used) [Gurney, et al., 2002] In red are Jacobson s new estimates from a joint atmosphere-ocean inversion NEW RESULT: an S&T source of 1.7 ± 1.0 Pg C yr 1 where IPCC shows net ~0

16 Tropical Net S&T S&T CO 2 Deforestation - Land = Fertilization Source Flux Sink 0.9 ± ± ± 1.1 (DeFries et al. 2002) 1.1 ± ± ± 1.0 (Achard et al. 2002) 1.9 ( ) ± ± 1.3 (FAO) 2.2 ± ± ± 1.3 (Houghton, 2003) Expected S&T CO 2 Fertilization Flux From IPCC Third Assessment Models: 2 ± 1

17 Implications We now have evidence that the putative tropical CO 2 fertilization sink may not exist. Added to Pacala group s prior research showing no evidence of temperate fertilization, we conclude that IPCC TAR land models have likely greatly overestimated the land sink. The fertilization land sink is worth 3 to 4 wedges (this had already been accounted for in previous CMI estimates) Cumulative Emissions Reductions Necessary to Stabilize at 500 PPM 170 Fossil Carbon Emissions Reductions (Gt/y) Year CO2 Fertilization Sink Land Use Sink

18 Importance of the Southern Ocean Models of air-sea CO 2 fluxes The ocean south of 36 S accounts for 40% of the anthropogenic CO 2 uptake The Southern Ocean accounts for >50% of the model variance Climate sensitivity studies show that the Southern Ocean is by far the most important region in determining the response of the ocean carbon sink to global warming

19 Carbon Science Plans 2005 THE PAST Understanding the influence of stratification Understanding the influence of winds THE PRESENT - Developing a Carbon Observing System Further constrain land sink distribution and mechanisms Monitor interannual variability and trends THE FUTURE - Continue development of the Earth System Model Role of the land carbon sink - CO 2 fertilization or not? Role of the ocean carbon sink - the crucial role of the Southern Ocean Simulations of the response to global warming

Observations of Growth Rate of Carbon Reservoirs. Keeling et al. (2000) & Marland et al. (2000)

Observations of Growth Rate of Carbon Reservoirs. Keeling et al. (2000) & Marland et al. (2000) Carbon Science A new synthesis of the present carbon budget. Building an earth system model for century time scale scenarios An examination of the long term consequences of continued fossil fuel use Scouts