Regional Impacts of Climate Change and Atmospheric CO 2 on Future Ocean Carbon Uptake: A Multimodel Linear Feedback Analysis (original) (raw)
Related papers
Ocean dynamics determine the response of oceanic CO2 uptake to climate change
Climate Dynamics, 2008
The increase of atmospheric CO 2 concentrations due to anthropogenic activities is substantially damped by the ocean, whose CO 2 uptake is determined by the state of the ocean, which in turn is influenced by climate change. We investigate the mechanisms of the ocean's carbon uptake within the feedback loop of atmospheric CO 2 concentration, climate change and atmosphere/ocean CO 2 flux. We evaluate two transient simulations from 1860 until 2100, performed with a version of the Max Planck Institute Earth System Model (MPI-ESM) with the carbon cycle included. In both experiments observed anthropogenic CO 2 emissions were prescribed until 2000, followed by the emissions according to the IPCC Scenario A2. In one simulation the radiative forcing of changing atmospheric CO 2 is taken into account (coupled), in the other it is suppressed (uncoupled). In both simulations, the oceanic carbon uptake increases from 1 GT C/year in 1960 to 4.5 GT C/year in 2070. Afterwards, this trend weakens in the coupled simulation, leading to a reduced uptake rate of 10% in 2100 compared to the uncoupled simulation. This includes a partial offset due to higher atmospheric CO 2 concentrations in the coupled simulation owing to reduced carbon uptake by the terrestrial biosphere. The difference of the oceanic carbon uptake between both simulations is primarily due to partial pressure difference and secondary to solubility changes. These contributions are widely offset by changes of gas transfer velocity due to sea ice melting and wind changes. The major differences appear in the Southern Ocean (-45%) and in the North Atlantic (-30%), related to reduced vertical mixing and North Atlantic meridional overturning circulation, respectively. In the polar areas, sea ice melting induces additional CO 2 uptake (+20%). Keywords Ocean carbon cycle Á Climate change Á Ocean circulation Á Climate scenarios Á Air-sea CO 2 flux Clim Dyn
Southern hemisphere ocean CO 2 uptake: reconciling atmospheric and oceanic estimates
Tellus B, 2003
Using an atmospheric inversion model we investigate the southern hemisphere ocean CO 2 uptake. From sensitivity studies that varied both the initial ocean flux distribution and the atmospheric data used in the inversion, our inversion predicted a total (ocean and land) uptake of 1.65-1.90 Gt C yr −1 . We assess the consistency between the mean southern hemisphere ocean uptake predicted by an atmospheric inversion model for the 1991-1997 period and the T99 ocean flux estimate based on observed pCO 2 in Deep-Sea Res II, 49, 1601-1622. The inversion can not match the large 1.8 Gt C yr −1 southern extratropical (20-90 • S) uptake of the T99 ocean flux estimate without producing either unreasonable land fluxes in the southern mid-latitudes or by increasing the mismatches between observed and simulated atmospheric CO 2 data. The southern extratropical uptake is redistributed between the mid and high latitudes. Our results suggest that the T99 estimate of the Southern Ocean uptake south of 50 • S is too large, and that the discrepancy reflects the inadequate representation of wintertime conditions in the T99 estimate.
The increase in atmospheric CO2 over this century depends on the evolution of the oceanic air–sea CO2 uptake, which will be driven by the combined response to rising atmospheric CO2 itself and climate change. Here, the future oceanic CO2 uptake is simulated using an ensemble of coupled climate–carbon cycle models. The models are driven by CO2 emissions from historical data and the Special Report on Emissions Scenarios (SRES) A2 high-emission scenario. A linear feedback analysis successfully separates the regional future (2010–2100) oceanic CO2 uptake into a CO2-induced component, due to rising atmospheric CO2 concentrations, and a climate-induced component, due to global warming. The models capture the observationbased magnitude and distribution of anthropogenic CO2 uptake. The distributions of the climate-induced component are broadly consistent between the models, with reduced CO2 uptake in the subpolar Southern Ocean and the equatorial regions, owing to decreased CO2 solubility; ...
Inverse estimates of anthropogenic CO 2 uptake, transport, and storage by the ocean
Global Biogeochemical Cycles, 2006
1] Regional air-sea fluxes of anthropogenic CO2 are estimated using a Green's function inversion method that combines data-based estimates of anthropogenic CO2 in the ocean with information about ocean transport and mixing from a suite of Ocean General Circulation Models (OGCMs). In order to quantify the uncertainty associated with the estimated fluxes owing to modeled transport and errors in the data, we employ 10 OGCMs and three scenarios representing biases in the data-based anthropogenic CO2 estimates. On the basis of the prescribed anthropogenic CO2 storage, we find a global uptake of 2.2 +/-0.25 Pg C yr(-1), scaled to 1995. This error estimate represents the standard deviation of the models weighted by a CFC-based model skill score, which reduces the error range and emphasizes those models that have been shown to reproduce observed tracer concentrations most accurately. The greatest anthropogenic CO2 uptake occurs in the Southern Ocean and in the tropics. The flux estimates imply vigorous northward transport in the Southern Hemisphere, northward cross-equatorial transport, and equatorward transport at eScholarship provides open access, scholarly publishing services to the University of California and delivers a dynamic research platform to scholars worldwide. high northern latitudes. Compared with forward simulations, we find substantially more uptake in the Southern Ocean, less uptake in the Pacific Ocean, and less global uptake. The large-scale spatial pattern of the estimated flux is generally insensitive to possible biases in the data and the models employed. However, the global uptake scales approximately linearly with changes in the global anthropogenic CO2 inventory. Considerable uncertainties remain in some regions, particularly the Southern Ocean. 2
Climate Dynamics, 2011
Under future scenarios of business-as-usual emissions, the ocean storage of anthropogenic carbon is 13 anticipated to decrease because of ocean chemistry constraints and positive feedbacks in the carbon-14 climate dynamics, whereas it is still unknown how the oceanic carbon cycle will respond to more 15 substantial mitigation scenarios. To evaluate the natural system response to prescribed atmospheric 16 "target" concentrations and assess the response of the ocean carbon pool to these values, 2 centennial 17 projection simulations have been performed with an Earth System Model that includes a fully coupled 18 carbon cycle, forced in one case with a mitigation scenario and the other with the SRES A1B 19 scenario. End of century ocean uptake with the mitigation scenario is projected to return to the same 20 magnitude of carbon fluxes as simulated in 1960 in the Pacific Ocean and to lower values in the 21 Atlantic. With A1B, the major ocean basins are instead projected to decrease the capacity for carbon Community Production (NCP) following changes in the subsurface equatorial circulation and 26 enhanced iron availability from extratropical regions. NCP is a proxy of the bulk organic carbon made 27 available to the higher trophic levels and potentially exportable from the surface layers. The model 28 results indicate that, besides the localized increase in the equatorial Pacific, the NCP of lower trophic 29 levels in the northern Pacific and Atlantic oceans is projected to be halved with respect to the current 30 climate under a substantial mitigation scenario at the end of the 21 st century. It is thus suggested that 31 changes due to cumulative carbon emissions up to present and the projected concentration pathways 32 of aerosol in the next decades control the evolution of surface ocean biogeochemistry in the second 33 half of this century more than the specific pathways of atmospheric CO 2 concentrations. 34 35 Keywords : Climate -Projections -Stabilisation -Ocean carbon cycle -Marine biogeochemical 36 model -PELAGOS -ENSEMBLES 37 38 39 45 and the ocean carbon pumps. These pumps (Volk and Hoffert 1985) work to maintain a higher 46 concentration of dissolved inorganic carbon (DIC) at depth than at the surface by means of biological 47 (the soft-tissue and carbonate pumps) and chemical processes (the solubility pump). The growth of 48
Global ocean carbon uptake: magnitude,variability and trends: Magnitude, variability and trends
Biogeosciences Discussions, 2012
The globally integrated sea-air anthropogenic carbon dioxide (CO 2) flux from 1990 to 2009r is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO 2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr −1. The interannual variability in the sea-air flux is largely driven by large-scale climate reorganizations and is estimated at 0.2 Pg C yr −1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr −1) decade −1 to −0.50 (Pg C yr −1) decade −1 for the two decades under investigation. The OBGCMs and the databased sea-air CO 2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO 2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.
Global ocean carbon uptake: magnitude, variability and trends
2012
The globally integrated sea-air anthropogenic carbon dioxide (CO 2) flux from 1990 to 2009r is determined from models and data-based approaches as part of the Regional Carbon Cycle Assessment and Processes (RECCAP) project. Numerical methods include ocean inverse models, atmospheric inverse models, and ocean general circulation models with parameterized biogeochemistry (OBGCMs). The median value of different approaches shows good agreement in average uptake. The best estimate of anthropogenic CO 2 uptake for the time period based on a compilation of approaches is −2.0 Pg C yr −1. The interannual variability in the sea-air flux is largely driven by large-scale climate reorganizations and is estimated at 0.2 Pg C yr −1 for the two decades with some systematic differences between approaches. The largest differences between approaches are seen in the decadal trends. The trends range from −0.13 (Pg C yr −1) decade −1 to −0.50 (Pg C yr −1) decade −1 for the two decades under investigation. The OBGCMs and the databased sea-air CO 2 flux estimates show appreciably smaller decadal trends than estimates based on changes in carbon inventory suggesting that methods capable of resolving shorter timescales are showing a slowing of the rate of ocean CO 2 uptake. RECCAP model outputs for five decades show similar differences in trends between approaches.
The role of ocean transport in the uptake of anthropogenic CO2
Biogeosciences, 2009
We compare modeled oceanic carbon uptake in response to pulse CO 2 emissions using a suite of global ocean models and Earth system models. In response to a CO 2 pulse emission of 590 Pg C (corresponding to an instantaneous doubling of atmospheric CO 2 from 278 to 556 ppm), the fraction of CO 2 emitted that is absorbed by the ocean is: 37±8%, 56±10%, and 81±4% (model mean ±2σ ) in year 30, 100, and 1000 after the emission pulse, respectively. Modeled oceanic uptake of pulse CO 2 on timescales from decades to about a century is strongly correlated with simulated presentday uptake of chlorofluorocarbons (CFCs) and CO 2 across all models, while the amount of pulse CO 2 absorbed by the ocean from a century to a millennium is strongly correlated with modeled radiocarbon in the deep Southern and Pacific Ocean. However, restricting the analysis to models that are capable of reproducing observations within uncertainty, the correlation is generally much weaker. The rates of surface-Correspondence to: L. Cao (longcao@stanford.edu) to-deep ocean transport are determined for individual models from the instantaneous doubling CO 2 simulations, and they are used to calculate oceanic CO 2 uptake in response to pulse CO 2 emissions of different sizes pulses of 1000 and 5000 Pg C. These results are compared with simulated oceanic uptake of CO 2 by a number of models simulations with the coupling of climate-ocean carbon cycle and without it. This comparison demonstrates that the impact of different ocean transport rates across models on oceanic uptake of anthropogenic CO 2 is of similar magnitude as that of climate-carbon cycle feedbacks in a single model, emphasizing the important role of ocean transport in the uptake of anthropogenic CO 2 .