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.

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 Response of the carbon cycle to the different orbital configurations of the last 9 interglacials

2016 ◽  
Author(s):  
Nathaelle Bouttes ◽  
Didier Swingedouw ◽  
Didier Roche ◽  
Maria Sanchez-Goni ◽  
Xavier Crosta
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Ice Sheet ◽  
Atmospheric Co2 ◽  
Oceanic Circulation ◽  
Co2 Concentrations ◽  
Before And After ◽  
Ocean Carbon ◽  
Atmospheric Co2 Concentrations ◽  
The Impact

Abstract. Atmospheric CO2 levels during interglacials prior to the Mid Bruhnes Event (MBE, ~ 430 ka BP) have lower values of around 40 ppm than after the MBE. The reasons for this difference remain unclear. A recent hypothesis proposed that changes in oceanic circulation, in response to differences in external forcing before and after the MBE, might have increased the ocean carbon storage and thus explained the lower CO2. Nevertheless, no quantitative estimate of this hypothesis has been produced up to now. Here we use an intermediate complexity model including the carbon cycle to evaluate the response of the carbon reservoirs in the atmosphere, ocean and land in response to the changes of orbital forcings and atmospheric CO2 concentrations over the nine last interglacials. We show that the ocean takes up more carbon during pre-MBE interglacials in agreement with data, but the impact on atmospheric CO2 is limited to a few ppm. Terrestrial biosphere is simulated to be less developed in pre-MBE interglacials, which reduces the storage of carbon on land and increases atmospheric CO2. Accounting for different simulated ice sheet extents modifies the vegetation cover and temperature, and thus the carbon reservoir distribution. Overall, atmospheric CO2 is slightly smaller in these pre-MBE simulated interglacials including ice sheet variations, but the magnitude is still far too small. These results suggest a possible mis-representation of some key processes in the model, such as the magnitude of ocean circulation changes, or the lack of crucial mechanisms or internal feedbacks, such as those related to permafrost, that could explain the lower atmospheric CO2 concentrations during pre-MBE interglacials.

scholarly journals Analytically tractable climate–carbon cycle feedbacks under 21st century anthropogenic forcing

2018 ◽  
Vol 9 (2) ◽  
pp. 507-523 ◽  
Author(s):  
Steven J. Lade ◽  
Jonathan F. Donges ◽  
Ingo Fetzer ◽  
John M. Anderies ◽  
Christian Beer ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Global Climate ◽  
Future Climate Change ◽  
Earth System ◽  
Co2 Solubility ◽  
Carbon Cycle Model ◽  
Ocean Climate ◽  
System Models ◽  
Analytical Expressions ◽  
Earth System Models

Abstract. Changes to climate–carbon cycle feedbacks may significantly affect the Earth system's response to greenhouse gas emissions. These feedbacks are usually analysed from numerical output of complex and arguably opaque Earth system models. Here, we construct a stylised global climate–carbon cycle model, test its output against comprehensive Earth system models, and investigate the strengths of its climate–carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon cycle feedbacks and the operation of the carbon cycle. Specific results include that different feedback formalisms measure fundamentally the same climate–carbon cycle processes; temperature dependence of the solubility pump, biological pump, and CO2 solubility all contribute approximately equally to the ocean climate–carbon feedback; and concentration–carbon feedbacks may be more sensitive to future climate change than climate–carbon feedbacks. Simple models such as that developed here also provide workbenches for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the planetary boundaries, that are currently too uncertain to be included in comprehensive Earth system models.

scholarly journals Analytically tractable climate-carbon cycle feedbacks under 21st century anthropogenic forcing

2017 ◽  
Author(s):  
Steven J. Lade ◽  
Jonathan F. Donges ◽  
Ingo Fetzer ◽  
John M. Anderies ◽  
Christian Beer ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Model Test ◽  
Global Climate ◽  
Earth System ◽  
Planetary Boundaries ◽  
Cycle Model ◽  
Carbon Cycle Model ◽  
The Earth ◽  
Analytical Expressions ◽  
Earth System Models

Abstract. Changes to climate-carbon cycle feedbacks may significantly affect the Earth System’s response to greenhouse gas emissions. These feedbacks are usually analysed from numerical output of complex and arguably opaque Earth System Models (ESMs). Here, we construct a stylized global climate-carbon cycle model, test its output against complex ESMs, and investigate the strengths of its climate-carbon cycle feedbacks analytically. The analytical expressions we obtain aid understanding of carbon-cycle feedbacks and the operation of the carbon cycle. We use our results to analytically study the relative strengths of different climate-carbon cycle feedbacks and how they may change in the future, as well as to compare different feedback formalisms. Simple models such as that developed here also provide workbenches for simple but mechanistically based explorations of Earth system processes, such as interactions and feedbacks between the Planetary Boundaries, that are currently too uncertain to be included in complex ESMs.

Physical Climate Response to a Reduction of Anthropogenic Climate Forcing

2010 ◽  
Vol 14 (7) ◽  
pp. 1-11 ◽  
Author(s):  
Arindam Samanta ◽  
Bruce T. Anderson ◽  
Sangram Ganguly ◽  
Yuri Knyazikhin ◽  
Ramakrishna R. Nemani ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Thermohaline Circulation ◽  
Climate Model ◽  
Global Climate ◽  
Ghg Emissions ◽  
Climate System ◽  
Initial Increase ◽  
Earth System ◽  
Human Welfare ◽  
Co2 Concentrations

Abstract Recent research indicates that the warming of the climate system resulting from increased greenhouse gas (GHG) emissions over the next century will persist for many centuries after the cessation of these emissions, principally because of the persistence of elevated atmospheric carbon dioxide (CO2) concentrations and their attendant radiative forcing. However, it is unknown whether the responses of other components of the climate system—including those related to Greenland and Antarctic ice cover, the Atlantic thermohaline circulation, the West African monsoon, and ecosystem and human welfare—would be reversed even if atmospheric CO2 concentrations were to recover to 1990 levels. Here, using a simple set of experiments employing a current-generation numerical climate model, the authors examine the response of the physical climate system to decreasing CO2 concentrations following an initial increase. Results indicate that many characteristics of the climate system, including global temperatures, precipitation, soil moisture, and sea ice, recover as CO2 concentrations decrease. However, other components of the Earth system may still exhibit nonlinear hysteresis. In these experiments, for instance, increases in stratospheric water vapor, which initially result from increased CO2 concentrations, remain present even as CO2 concentrations recover. These results suggest that identification of additional threshold behaviors in response to human-induced global climate change should focus on subcomponents of the full Earth system, including cryosphere, biosphere, and chemistry.

scholarly journals Impact of an extremely large magnitude volcanic eruption on the global climate and carbon cycle estimated from ensemble Earth System Model simulations

2012 ◽  
Vol 9 (7) ◽  
pp. 8693-8732 ◽  
Author(s):  
J. Segschneider ◽  
A. Beitsch ◽  
C. Timmreck ◽  
V. Brovkin ◽  
T. Ilyina ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Carbon Content ◽  
Volcanic Eruption ◽  
Global Climate ◽  
Earth System Model ◽  
System Model ◽  
Carbon Pools ◽  
Earth System ◽  
Ensemble Mean ◽  
Atmospheric Carbon

Abstract. The response of the global climate-carbon cycle system to an extremely large Northern Hemisphere mid latitude volcanic eruption is investigated using ensemble integrations with the comprehensive Earth System Model MPI-ESM. The model includes dynamical compartments of the atmosphere and ocean and interactive modules of the terrestrial biosphere as well as ocean biogeochemistry. The MPI-ESM was forced with anomalies of aerosol optical depth and effective radius of aerosol particles corresponding to a super eruption of the Yellowstone volcanic system. The model experiment consists of an ensemble of fifteen model integrations that are started at different pre-ENSO states of a contol experiment and run for 200 yr after the volcanic eruption. The climate response to the volcanic eruption is a maximum global monthly mean surface air temperature cooling of 3.8 K for the ensemble mean and from 3.3 K to 4.3 K for individual ensemble members. Atmospheric pCO2 decreases by a maximum of 5 ppm for the ensemble mean and by 3 ppm to 7 ppm for individual ensemble members approximately 6 yr after the eruption. The atmospheric carbon content only very slowly returns to near pre-eruption level at year 200 after the eruption. The ocean takes up carbon shortly after the eruption in response to the cooling, changed wind fields, and ice cover. This physics driven uptake is weakly counteracted by a reduction of the biological export production mainly in the tropical Pacific. The land vegetation pool shows a distinct loss of carbon in the initial years after the eruption which has not been present in simulations of smaller scale eruptions. The gain of the soil carbon pool determines the amplitude of the CO2 perturbation and the long term behaviour of the overall system: an initial gain caused by reduced soil respiration is followed by a rather slow return towards pre-eruption levels. During this phase, the ocean compensates partly for the reduced atmospheric carbon content in response to the land's gain. In summary, we find that the volcanic eruption has long lasting effects on the carbon cycle: after 200 yr, the ocean and the land carbon pools are still different from the pre-eruption state, and the land carbon pools (vegetation and soil) show some long lasting local anomalies that are only partly visible in the global signal.

Showcasing the compact Earth system model OSCAR v3.1 with CMIP6 simulations

2021 ◽  
Author(s):  
Yann Quilcaille ◽  
Thomas Gasser
Keyword(s):  
Carbon Cycle ◽  
Atmospheric Chemistry ◽  
Coupled Model ◽  
Climate Feedback ◽  
Large Set ◽  
Earth System ◽  
Ocean Carbon Cycle ◽  
Intercomparison Project ◽  
Reduced Complexity ◽  
Ocean Carbon

<p>While Earth system models (ESM) provide spatially detailed process-based outputs, they present heavy computational costs. Reduced complexity models such as OSCAR are calibrated on those complex models and provide an alternative with faster calculations but lower resolutions. Yet, reduced-complexity models need to be evaluated and validated. We diagnose the newest version of OSCAR (v3.1) using observations and results from ESMs and the current Coupled Model Intercomparison Project 6. A total of 99 experiments are selected for simulation with OSCAR v3.1 in a probabilistic framework, reaching a total of 567,700,000 simulated years. Here, we showcase these results. A first highlight of this exercise is the unstability of the model for high-warming scenarios, which we attribute to the ocean carbon cycle module. The diverging runs caused by this unstability were discarded in the post-processing. The ensuing main results were further obtained by weighting each physical parametrizations based on their performance to replicate a set of observations. Overall, OSCAR v3.1 qualitively behaves like complex ESMs, for all aspects of the Earth system, although we observe a number of quantitative differences with state-of-the-art models. Some specific features of OSCAR contribute in these differences, such as its fully interactive atmospheric chemistry and endogenous calculations of biomass burning, wetlands and permafrost emissions. Nevertheless, the low sensitivity of the land carbon cycle to climate change, the unstability of the ocean carbon cycle, the seemingly over-constrained climate module, and the strong climate feedback over short-lived species, all call for an improvement of these aspects in OSCAR. Beyond providing a key diagnosis of the model in the context of the reduced-complexity models intercomparison project (RCMIP), this work is also meant to help with the upcoming calibration of OSCAR on CMIP6 results, and to provide a large set of CMIP6 simulations all run consistently with a probalistic model.</p>

scholarly journals Evaluation of NorESM-OC (versions 1 and 1.2), the ocean carbon-cycle stand-alone configuration of the Norwegian Earth System Model (NorESM1)

2016 ◽  
Author(s):  
J. Schwinger ◽  
N. Goris ◽  
J. Tjiputra ◽  
I. Kriest ◽  
M. Bentsen ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Deep Ocean ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Atmospheric Forcing ◽  
Ocean Carbon Cycle ◽  
Data Set ◽  
Model Version ◽  
Ocean Carbon

Abstract. Idealised and hindcast simulations performed with the stand-alone ocean carbon-cycle configuration of the Norwegian Earth System Model (NorESM-OC) are described and evaluated. We present simulation results of two different model versions at different grid resolutions and using two different atmospheric forcing data sets. Model version NorESM-OC1 corresponds to the version that is included in the fully coupled model NorESM-ME1, which participated in CMIP5. The main update between NorESM-OC1 and NorESM-OC1.2 is the addition of two new options for the treatment of sinking particles. We find that using a constant sinking speed, which has been the standard in NorESM's ocean carbon cycle module HAMOCC (HAMburg Ocean Carbon Cycle model) does not transport enough particulate organic carbon (POC) into the deep ocean below approximately 2000 m depth. The two newly implemented parameterisations, a particle aggregation scheme with prognostic sinking speed, and a simpler scheme prescribing a linear increase of sinking speed with depth, provide better agreement with observed POC fluxes. Additionally, reduced deep ocean biases of oxygen and remineralised phosphate indicate a better performance of the new parameterisations. For model version 1.2, a re-tuning of the ecosystem parameterisation has been performed, which (i) reduces previously too high primary production in high latitudes, (ii) consequently improves model results for surface nutrients, and (iii) reduces alkalinity and dissolved inorganic carbon biases at low latitudes. We use hindcast simulations with prescribed observed and constant (pre-industrial) atmospheric CO2 concentrations to derive the past and contemporary ocean carbon sink. For the period 1990–1999 we find an average ocean carbon uptake ranging from 2.01 to 2.58 Pg C yr-1 depending on model version, grid resolution and atmospheric forcing data set.

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