Nonlinearity of Carbon Cycle Feedbacks

2011 ◽  
Vol 24 (16) ◽  
pp. 4255-4275 ◽  
Author(s):  
Kirsten Zickfeld ◽  
Michael Eby ◽  
H. Damon Matthews ◽  
Andreas Schmittner ◽  
Andrew J. Weaver
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Climate Model ◽  
Co2 Concentration ◽  
Carbon Uptake ◽  
Earth System ◽  
Carbon Sinks ◽  
Ocean Carbon ◽  
Different Response ◽  
Atmospheric Co2 Concentrations

Abstract Coupled climate–carbon models have shown the potential for large feedbacks between climate change, atmospheric CO2 concentrations, and global carbon sinks. Standard metrics of this feedback assume that the response of land and ocean carbon uptake to CO2 (concentration–carbon cycle feedback) and climate change (climate–carbon cycle feedback) combine linearly. This study explores the linearity in the carbon cycle response by analyzing simulations with an earth system model of intermediate complexity [the University of Victoria Earth System Climate Model (UVic ESCM)]. The results indicate that the concentration–carbon and climate–carbon cycle feedbacks do not combine linearly to the overall carbon cycle feedback. In this model, the carbon sinks on land and in the ocean are less efficient when exposed to the combined effect of elevated CO2 and climate change than to the linear combination of the two. The land accounts for about 80% of the nonlinearity, with the ocean accounting for the remaining 20%. On land, this nonlinearity is associated with the different response of vegetation and soil carbon uptake to climate in the presence or absence of the CO2 fertilization effect. In the ocean, the nonlinear response is caused by the interaction of changes in physical properties and anthropogenic CO2. These findings suggest that metrics of carbon cycle feedback that postulate linearity in the system’s response may not be adequate.

scholarly journals Nonlinearity of Ocean Carbon Cycle Feedbacks in CMIP5 Earth System Models

2014 ◽  
Vol 27 (11) ◽  
pp. 3869-3888 ◽  
Author(s):  
Jörg Schwinger ◽  
Jerry F. Tjiputra ◽  
Christoph Heinze ◽  
Laurent Bopp ◽  
James R. Christian ◽  
...  
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Ocean Circulation ◽  
Coupled Model ◽  
Co2 Concentration ◽  
Atmospheric Co2 ◽  
Climate Feedback ◽  
Carbon Uptake ◽  
Near Surface ◽  
Ocean Carbon

Abstract Carbon cycle feedbacks are usually categorized into carbon–concentration and carbon–climate feedbacks, which arise owing to increasing atmospheric CO2 concentration and changing physical climate. Both feedbacks are often assumed to operate independently: that is, the total feedback can be expressed as the sum of two independent carbon fluxes that are functions of atmospheric CO2 and climate change, respectively. For phase 5 of the Coupled Model Intercomparison Project (CMIP5), radiatively and biogeochemically coupled simulations have been undertaken to better understand carbon cycle feedback processes. Results show that the sum of total ocean carbon uptake in the radiatively and biogeochemically coupled experiments is consistently larger by 19–58 petagrams of carbon (Pg C) than the uptake found in the fully coupled model runs. This nonlinearity is small compared to the total ocean carbon uptake (533–676 Pg C), but it is of the same order as the carbon–climate feedback. The weakening of ocean circulation and mixing with climate change makes the largest contribution to the nonlinear carbon cycle response since carbon transport to depth is suppressed in the fully relative to the biogeochemically coupled simulations, while the radiatively coupled experiment mainly measures the loss of near-surface carbon owing to warming of the ocean. Sea ice retreat and seawater carbon chemistry contribute less to the simulated nonlinearity. The authors’ results indicate that estimates of the ocean carbon–climate feedback derived from “warming only” (radiatively coupled) simulations may underestimate the reduction of ocean carbon uptake in a warm climate high CO2 world.

scholarly journals Historical and idealized climate model experiments: an intercomparison of Earth system models of intermediate complexity

2013 ◽  
Vol 9 (3) ◽  
pp. 1111-1140 ◽  
Author(s):  
M. Eby ◽  
A. J. Weaver ◽  
K. Alexander ◽  
K. Zickfeld ◽  
A. Abe-Ouchi ◽  
...  
Keyword(s):  
Land Use ◽  
Carbon Cycle ◽  
Air Temperature ◽  
Climate Model ◽  
Surface Air Temperature ◽  
Carbon Fluxes ◽  
Carbon Uptake ◽  
Earth System ◽  
Model Experiments ◽  
Earth System Models

Abstract. Both historical and idealized climate model experiments are performed with a variety of Earth system models of intermediate complexity (EMICs) as part of a community contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report. Historical simulations start at 850 CE and continue through to 2005. The standard simulations include changes in forcing from solar luminosity, Earth's orbital configuration, CO2, additional greenhouse gases, land use, and sulphate and volcanic aerosols. In spite of very different modelled pre-industrial global surface air temperatures, overall 20th century trends in surface air temperature and carbon uptake are reasonably well simulated when compared to observed trends. Land carbon fluxes show much more variation between models than ocean carbon fluxes, and recent land fluxes appear to be slightly underestimated. It is possible that recent modelled climate trends or climate–carbon feedbacks are overestimated resulting in too much land carbon loss or that carbon uptake due to CO2 and/or nitrogen fertilization is underestimated. Several one thousand year long, idealized, 2 × and 4 × CO2 experiments are used to quantify standard model characteristics, including transient and equilibrium climate sensitivities, and climate–carbon feedbacks. The values from EMICs generally fall within the range given by general circulation models. Seven additional historical simulations, each including a single specified forcing, are used to assess the contributions of different climate forcings to the overall climate and carbon cycle response. The response of surface air temperature is the linear sum of the individual forcings, while the carbon cycle response shows a non-linear interaction between land-use change and CO2 forcings for some models. Finally, the preindustrial portions of the last millennium simulations are used to assess historical model carbon-climate feedbacks. Given the specified forcing, there is a tendency for the EMICs to underestimate the drop in surface air temperature and CO2 between the Medieval Climate Anomaly and the Little Ice Age estimated from palaeoclimate reconstructions. This in turn could be a result of unforced variability within the climate system, uncertainty in the reconstructions of temperature and CO2, errors in the reconstructions of forcing used to drive the models, or the incomplete representation of certain processes within the models. Given the forcing datasets used in this study, the models calculate significant land-use emissions over the pre-industrial period. This implies that land-use emissions might need to be taken into account, when making estimates of climate–carbon feedbacks from palaeoclimate reconstructions.

scholarly journals Twenty-First-Century Compatible CO2 Emissions and Airborne Fraction Simulated by CMIP5 Earth System Models under Four Representative Concentration Pathways

2013 ◽  
Vol 26 (13) ◽  
pp. 4398-4413 ◽  
Author(s):  
Chris Jones ◽  
Eddy Robertson ◽  
Vivek Arora ◽  
Pierre Friedlingstein ◽  
Elena Shevliakova ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Climate Models ◽  
Coupled Model ◽  
Co2 Concentration ◽  
Atmospheric Composition ◽  
System Component ◽  
Anthropogenic Emissions ◽  
Carbon Uptake ◽  
Earth System ◽  
Representative Concentration Pathways

Abstract The carbon cycle is a crucial Earth system component affecting climate and atmospheric composition. The response of natural carbon uptake to CO2 and climate change will determine anthropogenic emissions compatible with a target CO2 pathway. For phase 5 of the Coupled Model Intercomparison Project (CMIP5), four future representative concentration pathways (RCPs) have been generated by integrated assessment models (IAMs) and used as scenarios by state-of-the-art climate models, enabling quantification of compatible carbon emissions for the four scenarios by complex, process-based models. Here, the authors present results from 15 such Earth system GCMs for future changes in land and ocean carbon storage and the implications for anthropogenic emissions. The results are consistent with the underlying scenarios but show substantial model spread. Uncertainty in land carbon uptake due to differences among models is comparable with the spread across scenarios. Model estimates of historical fossil-fuel emissions agree well with reconstructions, and future projections for representative concentration pathway 2.6 (RCP2.6) and RCP4.5 are consistent with the IAMs. For high-end scenarios (RCP6.0 and RCP8.5), GCMs simulate smaller compatible emissions than the IAMs, indicating a larger climate–carbon cycle feedback in the GCMs in these scenarios. For the RCP2.6 mitigation scenario, an average reduction of 50% in emissions by 2050 from 1990 levels is required but with very large model spread (14%–96%). The models also disagree on both the requirement for sustained negative emissions to achieve the RCP2.6 CO2 concentration and the success of this scenario to restrict global warming below 2°C. All models agree that the future airborne fraction depends strongly on the emissions profile with higher airborne fraction for higher emissions scenarios.

scholarly journals Sources of Uncertainty in Future Projections of the Carbon Cycle

2016 ◽  
Vol 29 (20) ◽  
pp. 7203-7213 ◽  
Author(s):  
Alan J. Hewitt ◽  
Ben B. B. Booth ◽  
Chris D. Jones ◽  
Eddy S. Robertson ◽  
Andy J. Wiltshire ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Climate Models ◽  
Climate Model ◽  
Initial Conditions ◽  
Carbon Fluxes ◽  
Global Ocean ◽  
Lead Times ◽  
Carbon Uptake ◽  
The North ◽  
Ocean Carbon

Abstract The inclusion of carbon cycle processes within CMIP5 Earth system models provides the opportunity to explore the relative importance of differences in scenario and climate model representation to future land and ocean carbon fluxes. A two-way analysis of variance (ANOVA) approach was used to quantify the variability owing to differences between scenarios and between climate models at different lead times. For global ocean carbon fluxes, the variance attributed to differences between representative concentration pathway scenarios exceeds the variance attributed to differences between climate models by around 2025, completely dominating by 2100. This contrasts with global land carbon fluxes, where the variance attributed to differences between climate models continues to dominate beyond 2100. This suggests that modeled processes that determine ocean fluxes are currently better constrained than those of land fluxes; thus, one can be more confident in linking different future socioeconomic pathways to consequences of ocean carbon uptake than for land carbon uptake. The contribution of internal variance is negligible for ocean fluxes and small for land fluxes, indicating that there is little dependence on the initial conditions. The apparent agreement in atmosphere–ocean carbon fluxes, globally, masks strong climate model differences at a regional level. The North Atlantic and Southern Ocean are key regions, where differences in modeled processes represent an important source of variability in projected regional fluxes.

scholarly journals 23rd Century surprises: Long-term dynamics of the climate and carbon cycle under both high and net negative emissions scenarios

2021 ◽  
Author(s):  
Charles Koven ◽  
Vivek K. Arora ◽  
Patricia Cadule ◽  
Rosie A. Fisher ◽  
Chris D. Jones ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Carbon Emissions ◽  
Global Climate ◽  
Climate Projections ◽  
Earth System ◽  
Global Mean Temperature ◽  
Co2 Concentrations ◽  
Ocean Carbon ◽  
Atmospheric Co2 Concentrations ◽  
Emissions Scenario

Abstract. Future climate projections from Earth system models (ESMs) typically focus on the timescale of this century. We use a set of four ESMs and one Earth system model of intermediate complexity (EMIC) to explore the dynamics of the Earth’s climate and carbon cycles under contrasting emissions trajectories beyond this century, to the year 2300. The trajectories include a very high emissions, unmitigated fossil-fuel driven scenario, as well as a second mitigation scenario that diverges from the first scenario after 2040 and features an “overshoot”, followed by stabilization of atmospheric CO2 concentrations by means of large net-negative CO2 emissions. In both scenarios, and for all models considered here, the terrestrial system switches from being a net sink to either a neutral state or a net source of carbon, though for different reasons and centered in different geographic regions, depending on both the model and the scenario. The ocean carbon system remains a sink, albeit weakened by climate-carbon feedbacks, in all models under the high emissions scenario, and switches from sink to source in the overshoot scenario. The global mean temperature anomaly generally follows the trajectories of cumulative carbon emissions, except that 23rd-century warming continues after the cessation of carbon emissions in several models, both in the high emissions scenario and in one model in the overshoot scenario. While ocean carbon cycle responses qualitatively agree both in globally integrated and zonal-mean dynamics in both scenarios, the land models qualitatively disagree in zonal-mean dynamics, in the relative roles of vegetation and soil in driving C fluxes, in the response of the sink to CO2, and in the timing of the sink-source transition, particularly in the high emissions scenario. The lack of agreement among land models on the mechanisms and geographic patterns of carbon cycle feedbacks, alongside the potential for lagged physical climate dynamics to cause warming long after CO2 concentrations have stabilized, point to the possibility of surprises in the climate system beyond the 21st century time horizon, even under relatively mitigated global warming scenarios, which should be taken into consideration when setting global climate policy.

scholarly journals Impact of Historical Climate Change on the Southern Ocean Carbon Cycle

2008 ◽  
Vol 21 (22) ◽  
pp. 5820-5834 ◽  
Author(s):  
R. J. Matear ◽  
A. Lenton
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Carbon Uptake ◽  
Saturation State ◽  
Aragonite Saturation ◽  
Freshwater Fluxes ◽  
Anthropogenic Carbon ◽  
Natural Carbon ◽  
Ocean Carbon

Abstract Climate change over the last several decades is suggested to cause a decrease in the magnitude of the uptake of CO2 by the Southern Ocean (Le Quere et al.). In this study, the atmospheric fields from NCEP R1 for the years 1948–2003 are used to drive an ocean biogeochemical model to probe how changes in the heat and freshwater fluxes and in the winds affect the Southern Ocean’s uptake of carbon. Over this period, the model simulations herein show that the increases in heat and freshwater fluxes drive a net increase in Southern Ocean uptake (south of 40°S) while the increases in wind stresses drive a net decrease in uptake. The total Southern Ocean response is nearly identical with the simulation without climate change because the heat and freshwater flux response is approximately both equal and opposite to the wind stress response. It is also shown that any change in the Southern Ocean anthropogenic carbon uptake is always opposed by a much larger change in the natural carbon air–sea exchange. For the 1948–2003 period, the changes in the natural carbon cycle dominate the Southern Ocean carbon uptake response to climate change. However, it is shown with a simple box model that when atmospheric CO2 levels exceed the partial pressure of carbon dioxide (pCO2) of the upwelled Circumpolar Deep Water (≈450 μatm) the Southern Ocean uptake response will be dominated by the changes in anthropogenic carbon uptake. Therefore, the suggestion that the Southern Ocean carbon uptake is a positive feedback to global warming is only a transient response that will change to a negative feedback in the near future if the present climate trend continues. Associated with the increased outgassing of carbon from the natural carbon cycle was a reduction in the aragonite saturation state of the high-latitude Southern Ocean (south of 60°S). In the simulation with just wind stress changes, the reduction in the high-latitude Southern Ocean aragonite saturation state (≈0.2) was comparable to the magnitude of the decline in the aragonite saturation state over the last 4 decades because of rising atmospheric CO2 levels (≈0.2). The simulation showed that climate change could significantly impact aragonite saturation state in the Southern Ocean.

scholarly journals Earth system model simulations show different carbon cycle feedback strengths under glacial and interglacial conditions

2017 ◽  
Author(s):  
Markus Adloff ◽  
Christian H. Reick ◽  
Martin Claussen
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Co2 Concentration ◽  
System Model ◽  
Earth System ◽  
Concentration Increase ◽  
Terrestrial Carbon ◽  
Model Simulations ◽  
Fertilization Effect ◽  
Simulation Time

Abstract. In Earth system model simulations we find different carbon cycle sensitivities for recent and glacial climate. This result is obtained by comparing the transient response of the terrestrial carbon cycle to a fast and strong atmospheric CO2 concentration increase (roughly 1000ppm) in C4MIP type simulations starting from climate conditions of the Last Glacial Maximum (LGM) and from Pre-Industrial times (PI). The sensitivity β to CO2 fertilization is larger in the LGM experiment during most of the simulation time: The fertilization effect leads to a terrestrial carbon gain in the LGM experiment almost twice as large as in the PI experiment. The larger fertilization effect in the LGM experiment is caused by the stronger initial CO2 limitation of photosynthesis, implying a stronger potential for its release upon CO2 concentration increase. In contrast, the sensitivity γ to climate change induced by the radiation effect of rising CO2 is larger in the PI experiment for most of the simulation time. Yet, climate change is less pronounced in the PI experiment, resulting in only slightly higher terrestrial carbon losses than in the LGM experiment. The stronger climate sensitivity in the PI experiment results from the vastly more extratropical soil carbon under those interglacial conditions whose respiration is enhanced under climate change. Comparing the radiation and fertilization effect in a factor analysis, we find that they are almost additive, i.e. their synergy is small in the global sum of carbon changes. From this additivity, we find that the carbon cycle feedback strength is more negative in the LGM than in the PI simulations.

scholarly journals Marine biogeochemical cycling and climate-carbon cycle feedback simulated by the NUIST Earth System Model: NESM-2.0.1

2018 ◽  
Author(s):  
Yifei Dai ◽  
Long Cao ◽  
Bin Wang
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Earth System Model ◽  
Atmospheric Co2 ◽  
System Model ◽  
Co2 Uptake ◽  
Earth System ◽  
Feedback Parameter ◽  
Model Simulations ◽  
Ocean Carbon

Abstract. In this study, we evaluate the performance of Nanjing University of Information Science & Technology Earth System Model, version 2.0.1 (hereafter NESM-2.0.1). We focus on model simulated historical and future oceanic CO2 uptake, and analyze the effect of global warming on model-simulated oceanic CO2 uptake. Compared with available observations and data-based estimates, NESM-2.0.1 reproduces reasonably well large-scale ocean carbon-related fields, including nutrients (phosphate, nitrite and silicate), chlorophyll, and net primary production. However, some noticeable discrepancies between model simulations and observations are found in the deep ocean and coastal regions. Model-simulated current-day oceanic CO2 uptake compares well with data-based estimate. From pre-industrial time to 2011, modeled cumulative CO2 uptake is 144 PgC, compared with data-based estimates of 155 ± 30 PgC. Diagnosed from the end of the benchmark 1 % per year CO2 increase simulations, carbon-climate feedback parameter, which represents the sensitivity of ocean CO2 uptake to climate change, is −7.1 PgC/K; Carbon-concentration feedback parameter, which represents the sensitivity of ocean CO2 uptake to increase in atmospheric CO2 is 0.81 PgC/ppm. These two feedback parameters diagnosed from model simulations are consistent with the mean value diagnosed from the CMIP5 (Coupled Model Intercomparison Project phase 5) model simulations under the same 1 % per year CO2 simulations (−7.8 PgC/K and 0.80 PgC/ppm, respectively). Our results demonstrate that NESM-2.0.1 can be used as a useful tool in the investigation of feedback interactions between the ocean carbon cycle, atmospheric CO2, and climate change.

scholarly journals Water Mass Analysis of Effect of Climate Change on Air–Sea CO2 Fluxes: The Southern Ocean

2012 ◽  
Vol 25 (11) ◽  
pp. 3894-3908 ◽  
Author(s):  
Roland Séférian ◽  
Daniele Iudicone ◽  
Laurent Bopp ◽  
Tilla Roy ◽  
Gurvan Madec
Keyword(s):  
Climate Change ◽  
Carbon Cycle ◽  
Southern Ocean ◽  
Large Scale ◽  
Climate Model ◽  
Water Mass ◽  
Water Masses ◽  
Biogeochemical Model ◽  
Carbon Uptake ◽  
Intermediate Water

Impacts of climate change on air–sea CO2 exchange are strongly region dependent, particularly in the Southern Ocean. Yet, in the Southern Ocean the role of water masses in the uptake of anthropogenic carbon is still debated. Here, a methodology is applied that tracks the carbon flux of each Southern Ocean water mass in response to climate change. A global marine biogeochemical model was coupled to a climate model, making 140-yr Coupled Model Intercomparison Project phase 5 (CMIP5)-type simulations, where atmospheric CO2 increased by 1% yr−1 to 4 times the preindustrial concentration (4 × CO2). Impacts of atmospheric CO2 (carbon-induced sensitivity) and climate change (climate-induced sensitivity) on the water mass carbon fluxes have been isolated performing two sensitivity simulations. In the first simulation, the atmospheric CO2 influences solely the marine carbon cycle, while in the second simulation, it influences both the marine carbon cycle and earth’s climate. At 4 × CO2, the cumulative carbon uptake by the Southern Ocean reaches 278 PgC, 53% of which is taken up by modal and intermediate water masses. The carbon-induced and climate-induced sensitivities vary significantly between the water masses. The carbon-induced sensitivities enhance the carbon uptake of the water masses, particularly for the denser classes. But, enhancement strongly depends on the water mass structure. The climate-induced sensitivities either strengthen or weaken the carbon uptake and are influenced by local processes through changes in CO2 solubility and stratification, and by large-scale changes in outcrop surface (OS) areas. Changes in OS areas account for 45% of the climate-induced reduction in the Southern Ocean carbon uptake and are a key factor in understanding the future carbon uptake of the Southern Ocean.

Sign in / Sign up

Export Citation Format

Share Document