Uncertainty in remaining carbon budgets increases with less ambitious targets

2020 ◽  
Author(s):  
Endre Falck Mentzoni ◽  
Andreas Johansen ◽  
Andreas Rostrup Martinsen ◽  
Kristoffer Rypdal ◽  
Martin Rypdal
Keyword(s):  
Radiative Forcing ◽  
Carbon Budget ◽  
Climate Models ◽  
Temperature Response ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Carbon Budgets ◽  
Cumulative Emission ◽  
Internal Climate Variability ◽  
Earth System Models

<blockquote> <div dir="ltr"> <div> <p><span lang="en-US">In this work, we present estimates and uncertainties of the remaining carbon budget for a range of different global temperature targets. To model how atmospheric CO2 and methane concentrations depend on emissions, we use impulse response functions estimated from emission-pulse experiments in Earth System Models (ESMs). We use box-model ESM emulators to model the temperature response to radiative forcing and analyze a range of emission scenarios from Integrated Assessment Models. Taking into account uncertainties in the approximately linear relationship between cumulative emission and peak temperature, as well as internal climate variability and uncertainties in the carbon and climate models, we estimate the remaining carbon budgets for varying targets. The results show that the carbon-budget-uncertainties increase significantly with less ambitious targets.</span></p> </div> </div> </blockquote>

scholarly journals Simple emission metrics for climate impacts

2013 ◽  
Vol 4 (1) ◽  
pp. 145-170 ◽  
Author(s):  
B. Aamaas ◽  
G. P. Peters ◽  
J. S. Fuglestvedt
Keyword(s):  
Temperature Change ◽  
Radiative Forcing ◽  
Time Horizon ◽  
Climate Models ◽  
Climate Impacts ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Emission Scenarios ◽  
Radiative Efficiency ◽  
Analytical Expressions

Abstract. In the context of climate change, emissions of different species (e.g., carbon dioxide and methane) are not directly comparable since they have different radiative efficiencies and lifetimes. Since comparisons via detailed climate models are computationally expensive and complex, emission metrics were developed to allow a simple and straightforward comparison of the estimated climate impacts of emissions of different species. Emission metrics are not unique and variety of different emission metrics has been proposed, with key choices being the climate impacts and time horizon to use for comparisons. In this paper, we present analytical expressions and describe how to calculate common emission metrics for different species. We include the climate metrics radiative forcing, integrated radiative forcing, temperature change and integrated temperature change in both absolute form and normalised to a reference gas. We consider pulse emissions, sustained emissions and emission scenarios. The species are separated into three types: CO2 which has a complex decay over time, species with a simple exponential decay, and ozone precursors (NOx, CO, VOC) which indirectly effect climate via various chemical interactions. We also discuss deriving Impulse Response Functions, radiative efficiency, regional dependencies, consistency within and between metrics and uncertainties. We perform various applications to highlight key applications of emission metrics, which show that emissions of CO2 are important regardless of what metric and time horizon is used, but that the importance of short lived climate forcers varies greatly depending on the metric choices made. Further, the ranking of countries by emissions changes very little with different metrics despite large differences in metric values, except for the shortest time horizons (GWP20).

scholarly journals A synthesis of climate-based emission metrics with applications

2012 ◽  
Vol 3 (2) ◽  
pp. 871-934 ◽  
Author(s):  
B. Aamaas ◽  
G. P. Peters ◽  
J. S. Fuglestvedt
Keyword(s):  
Temperature Change ◽  
Radiative Forcing ◽  
Time Horizon ◽  
Climate Models ◽  
Climate Impacts ◽  
Impulse Response Functions ◽  
Response Functions ◽  
Emission Scenarios ◽  
Time Horizons ◽  
Analytical Expressions

Abstract. In the context of climate change, emissions of different species (e.g. carbon dioxide and methane) are not directly comparable since they have different radiative efficiencies and lifetimes. Since comparisons via detailed climate models are computationally expensive and complex, emission metrics were developed to allow a simple and straight forward comparison of the estimated climate impacts of the emissions of different species. Because emission metrics depend on a variety of choices, a variety of different metrics may be used and with different time-horizons. In this paper, we present analytical expressions and describe how to calculate common emission metrics for different species. We include the climate metrics radiative forcing, integrated radiative forcing, temperature change, and integrated temperature change in both absolute form and normalized to a reference gas. We consider pulse emissions, sustained emissions, and emission scenarios. The species are separated into three types: species with a simple exponential decay, CO2 which has a complex decay over time, and ozone pre-cursors (NOx, CO, VOC). Related issues are also discussed, such as deriving Impulse Response Functions, simple modifications to metrics, and regional dependencies. We perform various applications to highlight key applications of simple emission metrics, which show that emissions of CO2 are important regardless of what metric and time horizon is used, but that the importance of SLCFs varies greatly depending on the metric choices made.

scholarly journals Changes in the width of the tropical belt due to simple radiative forcing changes in the GeoMIP simulations

2016 ◽  
Vol 16 (15) ◽  
pp. 10083-10095 ◽  
Author(s):  
Nicholas A. Davis ◽  
Dian J. Seidel ◽  
Thomas Birner ◽  
Sean M. Davis ◽  
Simone Tilmes
Keyword(s):  
Carbon Dioxide ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Models ◽  
Temperature Response ◽  
Austral Summer ◽  
Hadley Cell ◽  
Solar Constant ◽  
Cell Width ◽  
Climate Forcings

Abstract. Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of Earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidence stabilizes the atmosphere and suppresses precipitation. Understanding the primary drivers of tropical expansion is hampered by the myriad forcing agents in most model projections of future climate. While many previous studies have examined the response of idealized models to simplified climate forcings and the response of comprehensive climate models to more complex climate forcings, few have examined how comprehensive climate models respond to simplified climate forcings. To shed light on robust processes associated with tropical expansion, here we examine how the tropical belt width, as measured by the Hadley cell edges, responds to simplified forcings in the Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt expands in response to a quadrupling of atmospheric carbon dioxide concentrations and contracts in response to a reduction in the solar constant, with a range of a factor of 3 in the response among nine models. Models with more surface warming and an overall stronger temperature response to quadrupled carbon dioxide exhibit greater tropical expansion, a robust result in spite of inter-model differences in the mean Hadley cell width, parameterizations, and numerical schemes. Under a scenario where the solar constant is reduced to offset an instantaneous quadrupling of carbon dioxide, the Hadley cells remain at their preindustrial width, despite the residual stratospheric cooling associated with elevated carbon dioxide levels. Quadrupled carbon dioxide produces greater tropical belt expansion in the Southern Hemisphere than in the Northern Hemisphere. This expansion is strongest in austral summer and autumn. Ozone depletion has been argued to cause this pattern of changes in observations and model experiments, but the results here indicate that seasonally and hemispherically asymmetric tropical expansion can be a basic response of the general circulation to climate forcings.

scholarly journals Emergent Scale Invariance and Climate Sensitivity

Climate ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 93 ◽  
Author(s):  
Martin Rypdal ◽  
Hege-Beate Fredriksen ◽  
Eirik Myrvoll-Nilsen ◽  
Kristoffer Rypdal ◽  
Sigrunn Sørbye
Keyword(s):  
Climate Sensitivity ◽  
Scale Invariance ◽  
Radiative Forcing ◽  
Temperature Response ◽  
Temperature Record ◽  
Radiative Balance ◽  
Global Surface ◽  
Earth System Models ◽  
Climate Responses ◽  
Best Estimates

Earth’s global surface temperature shows variability on an extended range of temporal scales and satisfies an emergent scaling symmetry. Recent studies indicate that scale invariance is not only a feature of the observed temperature fluctuations, but an inherent property of the temperature response to radiative forcing, and a principle that links the fast and slow climate responses. It provides a bridge between the decadal- and centennial-scale fluctuations in the instrumental temperature record, and the millennial-scale equilibration following perturbations in the radiative balance. In particular, the emergent scale invariance makes it possible to infer equilibrium climate sensitivity (ECS) from the observed relation between radiative forcing and global temperature in the instrumental era. This is verified in ensembles of Earth system models (ESMs), where the inferred values of ECS correlate strongly to estimates from idealized model runs. For the range of forcing data explored in this paper, the method gives best estimates of ECS between 1.8 and 3.7 K, but statistical uncertainties in the best estimates themselves will provide a wider likely range of the ECS.

scholarly journals GIR v1.0.0: a generalised impulse-response model for climate uncertainty and future scenario exploration

2020 ◽  
Author(s):  
Nicholas James Leach ◽  
Zebedee Nicholls ◽  
Stuart Jenkins ◽  
Christopher J. Smith ◽  
John Lynch ◽  
...  
Keyword(s):  
Greenhouse Gas ◽  
Impulse Response ◽  
Radiative Forcing ◽  
Climate Models ◽  
Temperature Response ◽  
Structural Complexity ◽  
Common Denominator ◽  
Response Model ◽  
State Dependent ◽  
Effective Radiative Forcing

Abstract. Here we present a Generalised Impulse Response (GIR) model for use in probabilistic future climate and scenario exploration, integrated assessment, policy analysis and teaching. This model is based on a set of only six equations, which correspond to the standard Impulse Response model used for greenhouse gas metric calculations by the IPCC, plus one physically-motivated additional equation to represent state-dependent feedbacks on the response timescales of each greenhouse gas cycle. These six equations are simple and transparent enough to be easily understood and implemented in other models without reliance on the original source code, but flexible enough to reproduce observed well-mixed greenhouse gas (GHG) concentrations and atmospheric lifetimes, best-estimate effective radiative forcing, and temperature response. We describe the assumptions and methods used in selecting the default parameters, but emphasize that other methods would be equally valid: our focus here is on identifying a minimum level of structural complexity. The tunable nature of the model lends it to use as a fully transparent emulator of complex Earth System Models, such as those participating in CMIP6, while also reproducing the behaviour of other simple climate models. We argue that this GIR model is adequate to reproduce the global temperature response to global emissions and effective radiative forcing, and that it should be used as a lowest-common denominator to provide consistency and continuity between different climate assessments. The model design is such that it can be written in tabular data analysis software, such as Excel, increasing the potential user base considerably.

Probabilistic climate projections with Minimal CMIP Emulator (MCE)

2021 ◽  
Author(s):  
Junichi Tsutsui
Keyword(s):  
Climate Sensitivity ◽  
Radiative Forcing ◽  
Climate Models ◽  
Model Parameters ◽  
Climate Projections ◽  
Second Phase ◽  
Impulse Response Functions ◽  
Model Intercomparison ◽  
Probabilistic Climate Projections ◽  
Intercomparison Project

<p>One of the key applications of simple climate models is probabilistic climate projections to assess a variety of emission scenarios in terms of their compatibility with global warming mitigation goals. The second phase of the Reduced Complexity Model Intercomparison Project (RCMIP) compares nine participating models for their probabilistic projection methods through scenario experiments, focusing on consistency with given constraints for climate indicators including radiative forcing, carbon budget, warming trends, and climate sensitivity. The MCE is one of the nine models, recently developed by the author, and has produced results that well match the ranges of the constraints. The model is based on impulse response functions and parameterized physics of effective radiative forcing and carbon uptake over ocean and land. Perturbed model parameters are generated from statistical models and constrained with a Metropolis-Hastings independence sampler. A parameter subset associated with CO<sub>2</sub>-induced warming is assured to have a covariance structure as diagnosed from complex climate models of the Coupled Model Intercomparison Project (CMIP). The model's simplicity and the successful results imply that a method with less complicated structures and fewer control parameters has an advantage when building reasonable perturbed ensembles in a transparent way despite less capacity to emulate detailed Earth system components. Experimental results for future scenarios show that the climate sensitivity of CMIP models is overestimated overall, suggesting that probabilistic climate projections need to be constrained with observed warming trends.</p>

scholarly journals Mechanisms for European summer temperature response to solar forcing over the last millennium

2012 ◽  
Vol 8 (2) ◽  
pp. 1301-1318
Author(s):  
D. Swingedouw ◽  
L. Terray ◽  
J. Servonnat ◽  
J. Guiot
Keyword(s):  
Central Europe ◽  
Radiative Forcing ◽  
Climate Models ◽  
Temperature Response ◽  
Mediterranean Area ◽  
Summer Temperature ◽  
Last Millennium ◽  
Solar Forcing ◽  
The Mediterranean ◽  
Spatio Temporal

Abstract. A simulation of the last millennium is compared to a recent spatio-temporal reconstruction of summer temperature over Europe. The focus is on the response to solar forcing over the pre-industrial era. Although the correlation between solar forcing and the reconstruction remains small, the spatial regression over solar forcing shows statistically significant regions. The meridional pattern of this regression is found to be similar in the model and in the reconstruction. This pattern exhibits a large warming over Northern and Mediterranean Europe and a lesser amplitude response over Central Europe. The mechanisms explaining this pattern in the simulation are mainly related to evapotranspiration fluxes. It is shown that the evapotranspiration is larger in summer over Central Europe when solar forcing increases, while it decreases over the Mediterranean area. The explanation for the evapotranspiration increase over Central Europe is found in the increase of winter precipitation there, leading to a soil moisture increase in spring. As a consequence, the evapotranspiration is larger in summer, which leads to an increase in cloud cover over this region, reducing the surface shortwave flux there and leading to less warming. Over the Mediterranean area, the surface shortwave flux increases with solar forcing, the soil becomes dryer and the evapotranspiration is reduced in summer leading to a larger increase in temperature. This effect appears to be overestimated in the model as compared to the reconstruction. Finally, the warming of Northern Europe is related to the albedo feedback due to sea-ice cover retreat with increasing solar forcing. These results show that the last millennium can be useful to evaluate the sensitivity of climate models to radiative forcing changes, using spatio-temporal reconstruction of climate.

scholarly journals HIRM v1.0: A hybrid impulse response model for climate modeling and uncertainty analyses

2020 ◽  
Author(s):  
Kalyn Dorheim ◽  
Steven Smith ◽  
Ben Bond-Lamberty
Keyword(s):  
Impulse Response ◽  
Radiative Forcing ◽  
Climate Models ◽  
Climate Model ◽  
Computational Cost ◽  
Global Temperature ◽  
Impulse Response Functions ◽  
Response Model ◽  
Modeling Framework ◽  
Uncertainty Analyses

Abstract. Simple climate models (SCMs) are frequently used in research and decision-making communities because of their flexibility, tractability, and low computational cost. SCMs can be idealized, flexibly representing major climate dynamics as impulse response functions, or process-based, using explicit equations to model possibly nonlinear climate and earth system dynamics. Each of these approaches has strengths and limitations. Here we present and test a hybrid impulse response modeling framework (HIRM) that combines the strengths of process-based SCMs in an idealized impulse response model, with HIRM’s input derived from the output of a process-based model. This structure allows it to capture the crucial nonlinear dynamics frequently encountered in going from greenhouse gas emissions to atmospheric concentration to radiative forcing to climate change. As a test, the HIRM framework was configured to emulate total temperature of the simple climate model Hector 2.0 under the four Representative Concentration Pathways and the temperature response of an abrupt four times CO2 concentration step. HIRM was able to reproduce near-term and long-term Hector global temperature with a high degree of fidelity. Additionally, we conducted two case studies to demonstrate potential applications for this hybrid model: examining the effect of aerosol forcing uncertainty on global temperature, and incorporating more process-based representations of black carbon into a SCM. The open-source HIRM framework has a range of applications including complex climate model emulation, uncertainty analyses of radiative forcing, attribution studies, and climate model development.

scholarly journals Changes in theWidth of the Tropical Belt due to Simple Radiative Forcing Changes in the GeoMIP Simulations

2016 ◽  
Author(s):  
Nicholas Davis ◽  
Dian J. Seidel ◽  
Thomas Birner ◽  
Sean M. Davis ◽  
Simone Tilmes
Keyword(s):  
Carbon Dioxide ◽  
Radiative Forcing ◽  
General Circulation ◽  
Climate Models ◽  
Temperature Response ◽  
Austral Summer ◽  
Hadley Cell ◽  
Solar Constant ◽  
Cell Width ◽  
Climate Forcings

Abstract. Model simulations of future climates predict a poleward expansion of subtropical arid climates at the edges of earth's tropical belt, which would have significant environmental and societal impacts. This expansion may be related to the poleward shift of the Hadley cell edges, where subsidence stabilizes the atmosphere and suppresses precipitation. Understanding the primary drivers of tropical expansion is hampered by the myriad forcing agents in most model projections of future climate. While many previous studies have examined the response of idealized models to simplified climate forcings and the response of comprehensive climate models to more complex climate forcings, none have examined how comprehensive climate models respond to simplified climate forcings. To shed light on robust processes associated with tropical expansion, here we examine how the tropical belt width, as measured by the Hadley cell edges, responds to simplified forcings in the Geoengineering Model Intercomparison Project (GeoMIP). The tropical belt expands in response to a quadrupling of atmospheric carbon dioxide concentrations and contracts in response to a reduction in the solar constant, with a range of a factor of three in the response among nine models. Models with more surface warming and an overall stronger temperature response to quadrupled carbon dioxide exhibit greater tropical expansion, a robust result in spite of intermodel differences in the mean Hadley cell width, parameterizations, and numerical schemes. Under a scenario where the solar constant is reduced to offset an instantaneous quadrupling of carbon dioxide, the Hadley cells remain at their preindustrial width, despite the residual stratospheric cooling associated with elevated carbon dioxide levels. Quadrupled carbon dioxide produces greater tropical belt expansion in the Southern Hemisphere than in the Northern Hemisphere. This expansion is strongest in austral summer and autumn. Ozone depletion has been argued to cause this pattern of changes in observations and model experiments, but the results here indicate that seasonally- and hemispherically-asymmetric tropical expansion can be a basic response of the general circulation to climate forcings.

scholarly journals Evaluation of the absolute regional temperature potential

2012 ◽  
Vol 12 (17) ◽  
pp. 7955-7960 ◽  
Author(s):  
D. T. Shindell
Keyword(s):  
Radiative Forcing ◽  
Large Scale ◽  
Climate Models ◽  
Climate Model ◽  
Temperature Response ◽  
The Arctic ◽  
Large Set ◽  
Temperature Potential ◽  
Regional Temperature ◽  
The Absolute

Abstract. The Absolute Regional Temperature Potential (ARTP) is one of the few climate metrics that provides estimates of impacts at a sub-global scale. The ARTP presented here gives the time-dependent temperature response in four latitude bands (90–28° S, 28° S–28° N, 28–60° N and 60–90° N) as a function of emissions based on the forcing in those bands caused by the emissions. It is based on a large set of simulations performed with a single atmosphere-ocean climate model to derive regional forcing/response relationships. Here I evaluate the robustness of those relationships using the forcing/response portion of the ARTP to estimate regional temperature responses to the historic aerosol forcing in three independent climate models. These ARTP results are in good accord with the actual responses in those models. Nearly all ARTP estimates fall within ±20% of the actual responses, though there are some exceptions for 90–28° S and the Arctic, and in the latter the ARTP may vary with forcing agent. However, for the tropics and the Northern Hemisphere mid-latitudes in particular, the ±20% range appears to be roughly consistent with the 95% confidence interval. Land areas within these two bands respond 39–45% and 9–39% more than the latitude band as a whole. The ARTP, presented here in a slightly revised form, thus appears to provide a relatively robust estimate for the responses of large-scale latitude bands and land areas within those bands to inhomogeneous radiative forcing and thus potentially to emissions as well. Hence this metric could allow rapid evaluation of the effects of emissions policies at a finer scale than global metrics without requiring use of a full climate model.

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