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-estimate projections and uncertainty ranges for emission scenarios, there are two major sources of uncertainty that need to be taken into account. The first relates to physical processes and feedbacks, and the uncertainty they induce on climate response for a given greenhouse gas (GHG) concentration and aerosol forcing in terms of the global-mean temperature response, and regional climate change; while the second relates to carbon cycle processes and feedbacks, with the associated uncertainty on the relationship
-estimate projections and uncertainty ranges for emission scenarios, there are two major sources of uncertainty that need to be taken into account. The first relates to physical processes and feedbacks, and the uncertainty they induce on climate response for a given greenhouse gas (GHG) concentration and aerosol forcing in terms of the global-mean temperature response, and regional climate change; while the second relates to carbon cycle processes and feedbacks, with the associated uncertainty on the relationship
. 2009 ). The first attempts to quantify these feedbacks were made decades ago (e.g., Eriksson 1963 ; Siegenthaler and Oeschger 1978 ), and the first three-dimensional atmosphere–ocean modeling experiments including both the carbon–concentration and the carbon–climate feedback were devised by Maier-Reimer et al. (1996) , Sarmiento and Le Quéré (1996) , and Matear and Hirst (1999) . With the advent of earth system models with fully coupled land and ocean carbon cycle modules, it became possible
. 2009 ). The first attempts to quantify these feedbacks were made decades ago (e.g., Eriksson 1963 ; Siegenthaler and Oeschger 1978 ), and the first three-dimensional atmosphere–ocean modeling experiments including both the carbon–concentration and the carbon–climate feedback were devised by Maier-Reimer et al. (1996) , Sarmiento and Le Quéré (1996) , and Matear and Hirst (1999) . With the advent of earth system models with fully coupled land and ocean carbon cycle modules, it became possible
does not have a uniformly accepted definition, models that couple a prognostic carbon cycle model to a climate model are generally agreed to qualify as Earth system models. These models can predict atmospheric CO 2 , allowing for internally consistent feedbacks between the varying model climate and atmospheric CO 2 . This is in contrast to traditional climate models that use prescribed atmospheric CO 2 trajectories that are produced by an independent, and typically reduced-complexity, model. Usage
does not have a uniformly accepted definition, models that couple a prognostic carbon cycle model to a climate model are generally agreed to qualify as Earth system models. These models can predict atmospheric CO 2 , allowing for internally consistent feedbacks between the varying model climate and atmospheric CO 2 . This is in contrast to traditional climate models that use prescribed atmospheric CO 2 trajectories that are produced by an independent, and typically reduced-complexity, model. Usage
1. Introduction Anthropogenic CO 2 emissions ( C E ) induce feedbacks between the global carbon cycle and the climate system (hereafter carbon cycle feedbacks) by perturbing the efficiency of atmospheric CO 2 uptake and storage by the ocean (Δ C O ; Sarmiento et al. 1998 ) and land (Δ C L ; Cao and Woodward 1998 ) reservoirs and causing the atmospheric carbon reservoir (Δ C A ) to rise faster or slower than expected from anthropogenic CO 2 emissions alone ( Sarmiento et al. 1995 ; Cox et
1. Introduction Anthropogenic CO 2 emissions ( C E ) induce feedbacks between the global carbon cycle and the climate system (hereafter carbon cycle feedbacks) by perturbing the efficiency of atmospheric CO 2 uptake and storage by the ocean (Δ C O ; Sarmiento et al. 1998 ) and land (Δ C L ; Cao and Woodward 1998 ) reservoirs and causing the atmospheric carbon reservoir (Δ C A ) to rise faster or slower than expected from anthropogenic CO 2 emissions alone ( Sarmiento et al. 1995 ; Cox et
1. Introduction The global carbon cycle consists of the combined interactions among a series of carbon reservoirs in the earth system (such as CO 2 in the atmosphere, soil organic carbon and vegetation, and carbonate and phytoplankton in the ocean) and all the fluxes and feedbacks that regulate dynamics in the sizes of these reservoirs. Most of the sensitivity and uncertainty in coupled carbon–climate projections lie in the terrestrial (rather than oceanic) carbon cycle (e.g., Zeng et al
1. Introduction The global carbon cycle consists of the combined interactions among a series of carbon reservoirs in the earth system (such as CO 2 in the atmosphere, soil organic carbon and vegetation, and carbonate and phytoplankton in the ocean) and all the fluxes and feedbacks that regulate dynamics in the sizes of these reservoirs. Most of the sensitivity and uncertainty in coupled carbon–climate projections lie in the terrestrial (rather than oceanic) carbon cycle (e.g., Zeng et al
1. Introduction The global carbon cycle is a crucial component of future climate change, closely linking anthropogenic CO 2 emissions with future changes in atmospheric CO 2 concentration and hence climate ( Denman et al. 2007 ; Ciais et al. 2013 ). Inclusion of the carbon cycle as an interactive component in comprehensive Earth system models (ESMs) has grown since early coupled studies ( Cox et al. 2000 ) and intercomparisons such as the Coupled Carbon Cycle–Climate Model Intercomparison
1. Introduction The global carbon cycle is a crucial component of future climate change, closely linking anthropogenic CO 2 emissions with future changes in atmospheric CO 2 concentration and hence climate ( Denman et al. 2007 ; Ciais et al. 2013 ). Inclusion of the carbon cycle as an interactive component in comprehensive Earth system models (ESMs) has grown since early coupled studies ( Cox et al. 2000 ) and intercomparisons such as the Coupled Carbon Cycle–Climate Model Intercomparison
and climate. The methane-induced changes in the Earth system can qualitatively be understood as described above but have not yet been quantified. For the study of changes in the Earth system, a numerical model that simulates the coupling of atmosphere–ocean general circulation, atmospheric chemistry, and the carbon cycle is useful because of the consistent interaction between geophysical and biogeochemical processes. With regard to a massive methane release event, although atmosphere–ocean models
and climate. The methane-induced changes in the Earth system can qualitatively be understood as described above but have not yet been quantified. For the study of changes in the Earth system, a numerical model that simulates the coupling of atmosphere–ocean general circulation, atmospheric chemistry, and the carbon cycle is useful because of the consistent interaction between geophysical and biogeochemical processes. With regard to a massive methane release event, although atmosphere–ocean models
patterns and trends from the remote sensing record in the context of more comprehensive simulations of the terrestrial carbon cycle. The Western Arctic Linkage Experiment (WALE) was initiated to investigate the role of northern terrestrial ecosystems in the larger Arctic system response to global change through model and satellite remote sensing analyses of regional carbon, water, and energy cycles (McGuire et al., see WALE Special Theme). The objectives of the current investigation are to assess
patterns and trends from the remote sensing record in the context of more comprehensive simulations of the terrestrial carbon cycle. The Western Arctic Linkage Experiment (WALE) was initiated to investigate the role of northern terrestrial ecosystems in the larger Arctic system response to global change through model and satellite remote sensing analyses of regional carbon, water, and energy cycles (McGuire et al., see WALE Special Theme). The objectives of the current investigation are to assess
climate change. Perturbations to the carbon cycle will change the storage of carbon on land and in the ocean, constituting a feedback on the atmospheric CO 2 concentration. Because of their potential importance for future climate change, representations of the relevant processes are being incorporated into AOGCMs. Simulated carbon cycle changes exhibit a large spread, indicating systematic uncertainty in the models ( Friedlingstein et al. 2006 ; Meehl et al. 2007 ; Plattner et al. 2008 ). As with
climate change. Perturbations to the carbon cycle will change the storage of carbon on land and in the ocean, constituting a feedback on the atmospheric CO 2 concentration. Because of their potential importance for future climate change, representations of the relevant processes are being incorporated into AOGCMs. Simulated carbon cycle changes exhibit a large spread, indicating systematic uncertainty in the models ( Friedlingstein et al. 2006 ; Meehl et al. 2007 ; Plattner et al. 2008 ). As with
, daily surface in situ records of atmospheric CO 2 concentrations in Barrow (now known as Utqiaġvik), Alaska (AK), from 1974 to 2014 was used to estimate the atmospheric CO 2 drawdown rate (CDR) over spring and summer. The CDR is used as a proxy for the strength of NHL seasonal net CO 2 uptake, given that the atmospheric CO 2 seasonal cycle at Barrow is mainly driven by the seasonal changes in the imbalance between terrestrial carbon uptake and release in northern middle and high latitudes
, daily surface in situ records of atmospheric CO 2 concentrations in Barrow (now known as Utqiaġvik), Alaska (AK), from 1974 to 2014 was used to estimate the atmospheric CO 2 drawdown rate (CDR) over spring and summer. The CDR is used as a proxy for the strength of NHL seasonal net CO 2 uptake, given that the atmospheric CO 2 seasonal cycle at Barrow is mainly driven by the seasonal changes in the imbalance between terrestrial carbon uptake and release in northern middle and high latitudes
