Emergent constraints on climate‐carbon cycle feedbacks in the CMIP5 Earth system models

Wenzel, Sabrina; Cox, Peter M.; Eyring, Veronika; Friedlingstein, Pierre

doi:10.1002/2013jg002591

Cited by 148 publications

(200 citation statements)

References 72 publications

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“…This propagation of the twentieth-century bias is consistent with the CMIP5 multi-model mean and has motivated attempts to reduce such biases by using observational constraints for ocean ventilation (Matsumoto et al, 2004), the tropical land carbon storage sensitivity to temperature variations Wenzel et al, 2014;Wang et al, 2014), and the oceanic and terrestrial carbon fluxes . CESM with CLM4, however, shows very little sensitivity to tropical land carbon, in part due to the inclusion of an interactive nitrogen cycle, which -through enhanced photosynthetic uptake due to nitrogen fertilization -tends to counteract accelerated soil decomposition from warming (Lawrence et al, 2012;Wenzel et al, 2014). Together with the underestimated oceanic uptake, this leads to the roughly 20 % larger airborne fraction in CESM as compared to what is actually prescribed as atmospheric concentration in the radiative code according to the RCP8.5.…”

Section: Carbon Cyclementioning

confidence: 65%

Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

et al. 2015

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Abstract. Under the protocols of phase 3 of the Paleoclimate Modelling Intercomparison Project, a number of simulations were produced that provide a range of potential climate evolutions from the last millennium to the end of the current century. Here, we present the first simulation with the Community Earth System Model (CESM), which includes an interactive carbon cycle, that covers the last millennium. The simulation is continued to the end of the twenty-first century. Besides state-of-the-art forcing reconstructions, we apply a modified reconstruction of total solar irradiance to shed light on the issue of forcing uncertainty in the context of the last millennium. Nevertheless, we find that structural uncertainties between different models can still dominate over forcing uncertainty for quantities such as hemispheric temperatures or the land and ocean carbon cycle response. Compared to other model simulations, we find forced decadal-scale variability to occur mainly after volcanic eruptions, while during other periods internal variability masks potentially forced signals and calls for larger ensembles in paleoclimate modeling studies. At the same time, we were not able to attribute millennial temperature trends to orbital forcing, as has been suggested recently. The climate-carbon-cycle sensitivity in CESM during the last millennium is estimated to be between 1.0 and 2.1 ppm • C −1 . However, the dependence of this sensitivity on the exact time period and scale illustrates the prevailing challenge of deriving robust constraints on this quantity from paleoclimate proxies. In particular, the response of the land carbon cycle to volcanic forcing shows fundamental differences between different models. In CESM the tropical land dictates the response to volcanoes, with a distinct behavior for large and moderate eruptions. Under anthropogenic emissions, global land and ocean carbon uptake rates emerge from the envelope of interannual natural variability by about year 1947 and 1877, respectively, as simulated for the last millennium.

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Section: Carbon Cyclementioning

confidence: 65%

Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

et al. 2015

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“…Recent studies showed the potential of observed interannual CO 2 variability to constrain the future tropical land carbon cycle sensitivity to climate change Wenzel et al, 2014).…”

Section: Evaluation Of Global Carbon Cycle Modelsmentioning

confidence: 99%

C4MIP – The Coupled Climate–Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6

et al. 2016

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Abstract. Coordinated experimental design and implementation has become a cornerstone of global climate modelling. Model Intercomparison Projects (MIPs) enable systematic and robust analysis of results across many models, by reducing the influence of ad hoc differences in model set-up or experimental boundary conditions. As it enters its 6th phase, the Coupled Model Intercomparison Project (CMIP6) has grown significantly in scope with the design and documentation of individual simulations delegated to individual climate science communities.The Coupled Climate-Carbon Cycle Model Intercomparison Project (C4MIP) takes responsibility for design, documentation, and analysis of carbon cycle feedbacks and interactions in climate simulations. These feedbacks are potentially large and play a leading-order contribution in determining the atmospheric composition in response to human emissions of CO 2 and in the setting of emissions targets to stabilize climate or avoid dangerous climate change. For over a decade, C4MIP has coordinated coupled climate-carbon cycle simulations, and in this paper we describe the C4MIP simulations that will be formally part of CMIP6. While the climate-carbon cycle community has created this experimental design, the simulations also fit within the wider CMIP activity, conform to some common standards including documentation and diagnostic requests, and are designed to complement the CMIP core experiments known as the Diagnostic, Evaluation and Characterization of Klima (DECK).C4MIP has three key strands of scientific motivation and the requested simulations are designed to satisfy their needs: (1) pre-industrial and historical simulations (formally part of the common set of CMIP6 experiments) to enable model evaluation, (2) idealized coupled and partially coupled simulations with 1 % per year increases in CO 2 to enable diagnosis of feedback strength and its components, (3) future scenario simulations to project how the Earth system will rePublished by Copernicus Publications on behalf of the European Geosciences Union. This paper documents in detail these simulations, explains their rationale and planned analysis, and describes how to set up and run the simulations. Particular attention is paid to boundary conditions, input data, and requested output diagnostics. It is important that modelling groups participating in C4MIP adhere as closely as possible to this experimental design.

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“…Skill score metrics, which can be used to rank models according to their ability to reproduce physical and biogeochemical variables simultaneously, may become a valuable tool for future simulations. A simplified short-cut method in order to assess the quality of future projections of Earth system models is the emergent constraint approach Hoffman et al, 2014;Wenzel et al, 2014). In this approach, an interrelation is sought between a specific Earth system sensitivity as resulting across an ensemble of comparable models and a corresponding observational trend or variability (see also Flato et al, 2013).…”

Section: Integrative Modelling and Combination With Measurementsmentioning

confidence: 99%

The ocean carbon sink – impacts, vulnerabilities and challenges

et al. 2015

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Abstract. Carbon dioxide (CO 2 ) is, next to water vapour, considered to be the most important natural greenhouse gas on Earth. Rapidly rising atmospheric CO 2 concentrations caused by human actions such as fossil fuel burning, land-use change or cement production over the past 250 years have given cause for concern that changes in Earth's climate system may progress at a much faster pace and larger extent than during the past 20 000 years. Investigating global carbon cycle pathways and finding suitable adaptation and mitigation strategies has, therefore, become of major concern in many research fields. The oceans have a key role in regulating atmospheric CO 2 concentrations and currently take up about 25 % of annual anthropogenic carbon emissions to the atmosphere. Questions that yet need to be answered are what the carbon uptake kinetics of the oceans will be in the future and how the increase in oceanic carbon inventory will affect its ecosystems and their services. This requires comprehensive investigations, including high-quality ocean carbon measurements on different spatial and temporal scales, the management of data in sophisticated databases, the application of Earth system models to provide future projections for given emission scenarios as well as a global synthesis and outreach to policy makers. In this paper, the current understanding of the ocean as an important carbon sink is reviewed with respect to these topics. Emphasis is placed on the complex interplay of different physical, chemical and biological processes that yield both positive and negative air-sea flux values for natural and anthropogenic CO 2 as well as on increased CO 2 (uptake) as the regulating force of the radiative warming of the atmosphere and the gradual acidification of the oceans. Major future ocean carbon challenges in the fields of ocean observations, modelling and process research as well as the relevance of other biogeochemical cycles and greenhouse gases are discussed.Published by Copernicus Publications on behalf of the European Geosciences Union.

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Emergent constraints on climate‐carbon cycle feedbacks in the CMIP5 Earth system models

Cited by 148 publications

References 72 publications

Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

Climate and carbon cycle dynamics in a CESM simulation from 850 to 2100 CE

C4MIP – The Coupled Climate–Carbon Cycle Model Intercomparison Project: experimental protocol for CMIP6

The ocean carbon sink – impacts, vulnerabilities and challenges

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