Some questions in current climate and CO 2 studies

How big are the global land and ocean sinks? Given that they are variable, can we specify them with sufficient accuracy to be useful in Kyoto accounting What confidence can we have in predictions of their size over (say) the next 200 years? Some questions in current climate and CO 2 studies

Ocean uptake 1.9 Pg C yr -1 Fossil fuel release 5.4 Pg C yr -1 Accumulation in atmosphere 3.3 Pg C yr -1 Land uptake? (1.9 by difference) Deforestation 1.7 Pg C yr -1 ? 1980s budget of anthropogenic carbon dioxide.

The Mauna Loa atmospheric record. Late 1990s measurement network C. Dave Keeling

Fossil Fuel Emissions Well quantified from econometric data (Marland, Andres)

The total sink is known from accurate fossil fuel emission data and atmospheric accumulation rates. Two methods to separate land and ocean sinks: –Calculate ocean sink from models and obtain net land by difference (IPCC assessments 1 and 2) –Use atmospheric O 2 /N 2 measurements in the atmosphere to separate land and ocean. (IPCC assessment 3). Size of the land and ocean sinks

Comparison of North Atlantic annual average pCO 2 with multiple models.

Oxygen and CO 2 Comparison

Keelings method Diagnose size of land and ocean sinks Use known (?) molar ratios of O2 / CO2 change for Fossil fuel burning land uptake / release by vegetation Ocean uptake. Global average concentrations of O 2 vs CO 2

How well is the global ocean sink known? Estimates of the global ocean sink ReferenceSink (GtC yr -1 ) IPCC (2001) 1.7+/- 0.5 Estimate (O2- CO2 method.) OCMIP-2 Model 2.5+/- 0.4 Intercomparison (ten ocean carbon models).

Variability in the ocean and land sinks

Variation in the growth rate of atmospheric CO 2, Rate of growth is highly variable – not due to change in fossil fuel source. Variation correlates with Southern oscillation – El Ninos. Indicates the Natural sinks for atmospheric CO 2 are highly variable. Though the land sink dominates variability, ocean is also important

Estimates of the ocean sink variability

Discrimination of sources/sinks between latitude bands is relatively easy Localising sinks in the same latitude bands is subject to wide error. Fluxes over ocean basins are than easier to constrain than continental fluxes over large regions. Atmospheric Inversion calculations of CO 2 sources and sinks

North Atlantic Carbon Observing System Cruise tracks CAVASSOO 2001 – 2003 EU project Ship-of-Opportunity routes

Surface pCO 2, nutrient and surface temperature in the North Atlantic pCO 2 ( atm ) MarAprMayJunJulAugSepOct pCO 2

Comparison of recent, well-resolved data with models. Cavassoo data from I.F.M., University of Kiel (Wallace, Koertzinger et al).

Remote sensing of SST, Ocean colour to enable Interpolation/ extrapolation of surface CO2 observations

What confidence can we have in predictions of future carbon sinks?

Seasonal model-data intercomparison – Hamburg-NewYork OCMIP2 models vs dataMean of models vs data Models are forced with mean climatological data. Models: Jim Orr, LSCE And OCMIP-2 members Data: CAVASSOO, CASIX

Seasonal model-data intercomparison – Hamburg-NewYork OCMIP2 models vs dataMean of models vs data Models are forced with mean climatological data. Models: Jim Orr, LSCE And OCMIP-2 members Data: CAVASSOO, IFM group.

Possible Marine biological effects on Carbon uptake, next 100 years. Iron fertilisation -- deliberate or inadvertent NO 3 fertilisation pH change mediates against calcite- precipitating organisms Reduction in THC offset by increased efficiency of nutrient utilisation Other unforeseen ecosystem changes ProcessEffect on CO 2 uptake ?

Iron and Kyoto: At present the land is a source of iron to the ocean. Efforts to sequester carbon on land will change that source.

Ridgwell, A. J. et al, Geophys. Res. Lett. (2002)