ATOC 220 Global Carbon Cycle Recent change in atmospheric carbon The global C cycle and why is the contemporary atmospheric C increasing? How much of the excess C do the oceans and terrestrial biosphere take up? How is C ultimately removed? Nigel Roulet, Geography November 10, 2008

(Petit et al. 1999)

Why is the contemporary atmospheric carbon increasing?

Black: pre-industrial Red: + industrial era up to ~1990 Sedimentary rock 40,000,000 (CaCO 3 ) (IPCC, 2006) Global Carbon Cycle

Historical Land Use Maps (RIVM, Netherlands) Kees Klein Goldewijk (2001)

CO 2 source/sink equation 3.2 = -2.2 – IPCC 2006 best guess sink sink source source

(Sarmiento and Gruber, 2002)

atmospheric CO 2 ocean land fossil fuel emissions deforestation CO 2 flux (Pg C y -1 ) Sink Source Time (y) Perturbation of Global Carbon Budget ( ) Le Quéré, unpublished; Canadell et al. 2007, PNAS

Fossil Fuel Emissions: Actual vs. IPCC Scenarios Raupach et al 2007, PNAS & Global Carbon Project update ( ) Observed % 2007 Fossil Fuel: 8.5 Pg C

Raupach et al 2007, PNAS World F (emissions) P (population) g = G/P h = F/G Factor (relative to 1990) Emissions Population Wealth = per capita GDP Carbon intensity of GDP Drivers of Anthropogenic Emissions

Why are the oceans and terrestrial ecosystems taking up excess CO 2 ?

1. The marine biological pump Deep Ocean Ocean surface atmospheric CO 2 Phytoplankton sedimentation of organic C Bacterial decomposition CO 2 Nutrients upwelling

Ocean net primary production Global Ocean NPP ~ 50 to 60 Gt C/yr → ~ 11 buried & the rest recycled Living biomass is 3 Gt C it means the residence time of the plankton is a few weeks NPP g C/m 2 /yr

2. The solubility pump Ocean surface Atmosphere H 2 CO 3  H + + HCO 3 - HCO 3 -  H + + CO 3 2- CO 2 CO 2 + H 2 O  H 2 CO 3 bicarbonate carbonate carbonic acid

2. The solubility pump Ocean surface Atmosphere H 2 CO 3  H + + HCO 3 - HCO 3 -  H + + CO 3 2- CO 2 CO 2 + H 2 O  H 2 CO 3 bicarbonate carbonate carbonic acid

How is this CO2 removed from contact with the atmosphere?

Thermohaline circulation

CO 2 (aq) dissociates rapidly into DIC while increasing acidity: pH  K 1 K 2 CO 2 + H 2 O  HCO H +  CO H + Bjerrum Plot: pH = 8.1 T = 25 0 C, S = 35 [CO 2 ] : [HCO 3 - ] : [CO 3 = ]  0.5% : 86.5% : 13% => Buffering?? (Zeebe & Wolf-Gladrow, 2002) bicarbonatecarbonate

Ocean Acidity Observations Model analysis Calderia & Wickett

Ocean surface Atmosphere H 2 CO 3  H + + HCO 3 - CO 2 CO 2 + H 2 O  H 2 CO 3 Ca HCO 3 -  CaCO 3 + H 2 CO 3 shelled organisms The solubility pump & calcium carbonate formation

Coccolithophores (algae) planktonic produce 1.5 million tons of CaCO 3 per yr sometimes form “blooms” at the ocean surface which reflect visible light SeaWiFS image 16 July 2000

CO ~120 ~60 Gross primary production (GPP) Autotrophic Respiration (AR) Heterotrophic Respiration (HR) Net ecosystem production ( > 0) NEP = NPP - HR The ‘real’ terrestrial C cycle Store Time (longer) Disturbance ?

Forest Regrowth Pool changes were evaluated as the difference between the late 1990s and early 1980s pool estimates, pixel-by-pixel, and quoted on a per year basis. The carbon pool in the woody biomass of northern forests (1.5 billion ha) is estimated to be 61  20 Gt C during the late 1990s. Our sink estimate for the woody biomass during the 1980s and 1990s is 0.68  0.34 Gt C/yr. earth/ge.html

Why an increased uptake on land? Elevated CO 2 leading to increased NPP –Evidence suggest this might be only a few percent Response to increased nitrogen deposition –Evidence indicates that only a small fraction of added N getting into biomass: most is immobilized in soils Climate change? Forest regrowth –Most reasonable explanation Detail inventory studies in the US support this Remote sensing estimates support increase in biomass

(K.R. Gurney et al., Nature, 415:626 [2002]) What are the relative importance of the land and oceans in taking up excess CO2? Source Sink Many model inversions using lots of data

The Efficiency of Natural Sinks: Land and Ocean Fractions Land Ocean Canadell et al. 2007, PNAS Relative to annual atmospheric input

The ultimate sink – the ocean floor – slow but steady

161 Gt C 0.2 Gt C/yr = 805 years Key point It takes a very long time to get the excess carbon out of the atmosphere

So we have this all figured out!

Vulnerabilities of the Carbon-Climate-Human system Atmospheric CO 2 Fossil Fuel burning Vulnerability of C pools WARMING (+) C emissions (+) Carbon-climate System (-) Carbon-climate-human System X Energy Systems Human Actions Social Structures and Institutions Human System (+) IMPACTS - ADAPTATION (-) LUC Systems