scholarly journals If Anthropogenic CO2 Emissions Cease, Will Atmospheric CO2 Concentration Continue to Increase?

2013 ◽  
Vol 26 (23) ◽  
pp. 9563-9576 ◽  
Author(s):  
Andrew H. MacDougall ◽  
Michael Eby ◽  
Andrew J. Weaver
Keyword(s):  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Climate Model ◽  
Carbon Sources ◽  
Co2 Concentration ◽  
Earth System ◽  
Terrestrial Source ◽  
The University ◽  
Aerosol Emissions ◽  
Over Time

If anthropogenic CO2 emissions were to suddenly cease, the evolution of the atmospheric CO2 concentration would depend on the magnitude and sign of natural carbon sources and sinks. Experiments using Earth system models indicate that the overall carbon sinks dominate, such that upon the cessation of anthropogenic emissions, atmospheric CO2 levels decrease over time. However, these models have typically neglected the permafrost carbon pool, which has the potential to introduce an additional terrestrial source of carbon to the atmosphere. Here, the authors use the University of Victoria Earth System Climate Model (UVic ESCM), which has recently been expanded to include permafrost carbon stocks and exchanges with the atmosphere. In a scenario of zeroed CO2 and sulfate aerosol emissions, whether the warming induced by specified constant concentrations of non-CO2 greenhouse gases could slow the CO2 decline following zero emissions or even reverse this trend and cause CO2 to increase over time is assessed. It is found that a radiative forcing from non-CO2 gases of approximately 0.6 W m−2 results in a near balance of CO2 emissions from the terrestrial biosphere and uptake of CO2 by the oceans, resulting in near-constant atmospheric CO2 concentrations for at least a century after emissions are eliminated. At higher values of non-CO2 radiative forcing, CO2 concentrations increase over time, regardless of when emissions cease during the twenty-first century. Given that the present-day radiative forcing from non-CO2 greenhouse gases is about 0.95 W m−2, the results suggest that if all CO2 and aerosols emissions were eliminated without also decreasing non-CO2 greenhouse gas emissions CO2 levels would increase over time, resulting in a small increase in climate warming associated with this positive permafrost–carbon feedback.

Sensitivity of an Earth system climate model to idealized radiative forcing

2012 ◽  
Vol 39 (10) ◽  
pp. n/a-n/a ◽  
Author(s):  
Timothy Andrews ◽  
Mark A. Ringer ◽  
Marie Doutriaux-Boucher ◽  
Mark J. Webb ◽  
William J. Collins
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Earth System

Investigating model nudging as a novel technique to isolate aerosol radiative adjustment mechanisms

2021 ◽  
Author(s):  
Max Coleman ◽  
William Collins ◽  
Keith Shine ◽  
Nicolas Bellouin ◽  
Fiona O'Connor
Keyword(s):  
Black Carbon ◽  
Radiative Forcing ◽  
Potential Temperature ◽  
Atmospheric Temperature ◽  
Earth System Model ◽  
System Model ◽  
Earth System ◽  
Aerosol Emission ◽  
Aerosol Emissions ◽  
Adjustment Mechanisms

<p>We investigate a novel use of model nudging to interrogate radiative rapid adjustment mechanisms and their magnitudes in response to aerosol emission perturbations in an earth system model. The radiative effects of a forcing agent can be quantified using the effective radiative forcing (ERF). ERF is the sum of the instantaneous radiative forcing, and radiative adjustments – changes in the atmosphere’s state in response to the initial forcing agent that cause a further radiative forcing. Radiative adjustments are particularly important for aerosols, which affect clouds both via microphysical interactions and changes in circulation, stratification and convection. Understanding the different adjustment mechanisms and their contribution to the total ERF of different aerosol emissions is necessary to better understand how their ERF may change with future changes in anthropogenic aerosol emissions. In this work we investigate radiative adjustments resulting from changes in atmospheric temperature (and the resulting changes in stratification and convection) due to anthropogenic sulphate and black carbon aerosol forcing.</p><p>We have conducted multiple global atmosphere-only time-slice experiments using the UK Earth System Model (UKESM1). Each experiment has either control, black carbon perturbed, or sulphur dioxide perturbed emissions; and either no nudging, nudged horizontal winds (uv), or nudged horizontal winds and potential temperature (uvθ). The difference between nudged uvθ minus nudged uv simulations determines the atmospheric temperature related adjustments arising from the aerosol perturbation. We have also conducted repeats of each simulation, varying the nudging setup to test sensitivity to different nudging parameters.</p><p>We find that nudging horizontal winds affects the resulting ERF very little, whereas nudging potential temperature as well can cause a significant difference from the non-nudged experiments, primarily in the cloud radiative effect. However, this difference is sensitive to the strength of the nudging applied, for which we consider the most appropriate value.</p>

scholarly journals Effective radiative forcing in the aerosol–climate model CAM5.3-MARC-ARG

2018 ◽  
Author(s):  
Benjamin S. Grandey ◽  
Daniel Rothenberg ◽  
Alexander Avramov ◽  
Qinjian Jin ◽  
Hsiang-He Lee ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Climate Model ◽  
Regional Distribution ◽  
Radiative Effect ◽  
Mixing State ◽  
Anthropogenic Aerosols ◽  
Effective Radiative Forcing ◽  
Aerosol Module ◽  
Aerosol Emissions ◽  
Global Mean

Abstract. We quantify the effective radiative forcing (ERF) of anthropogenic aerosols modelled by the aerosol–climate model CAM5.3-MARC-ARG. CAM5.3-MARC-ARG is a new configuration of the Community Atmosphere Model version 5.3 (CAM5.3) in which the default aerosol module has been replaced by the two-Moment, Multi-Modal, Mixing-state-resolving Aerosol model for Research of Climate (MARC). CAM5.3-MARC-ARG uses the default ARG aerosol activation scheme, consistent with the default configuration of CAM5.3. We compute differences between simulations using year-1850 aerosol emissions and simulations using year-2000 aerosol emissions in order to assess the radiative effects of anthropogenic aerosols. We compare the aerosol column burdens, cloud properties, and radiative effects produced by CAM5.3-MARC-ARG with those produced by the default configuration of CAM5.3, which uses the modal aerosol module with three log-normal modes (MAM3). Compared with MAM3, we find that MARC produces stronger cooling via the direct radiative effect, stronger cooling via the surface albedo radiative effect, and stronger warming via the cloud longwave radiative effect. The global mean cloud shortwave radiative effect is similar between MARC and MAM3, although the regional distributions differ. Overall, MARC produces a global mean net ERF of −1.75 ± 0.04 W m−2, which is stronger than the global mean net ERF of −1.57 ± 0.04 W m−2 produced by MAM3. The regional distribution of ERF also differs between MARC and MAM3, largely due to differences in the regional distribution of the cloud shortwave radiative effect. We conclude that the specific representation of aerosols in global climate models, including aerosol mixing state, has important implications for climate modelling.

scholarly journals The Key Role of Ozone-Depleting Substances in Weakening the Walker Circulation in the Second Half of the Twentieth Century

2019 ◽  
Vol 32 (5) ◽  
pp. 1411-1418 ◽  
Author(s):  
Lorenzo M. Polvani ◽  
Katinka Bellomo
Keyword(s):  
Twentieth Century ◽  
Pacific Ocean ◽  
Greenhouse Gases ◽  
Radiative Forcing ◽  
Climate Model ◽  
Walker Circulation ◽  
Surface Warming ◽  
Ozone Depleting Substances ◽  
The Antarctic ◽  
The Walker Circulation

It is widely appreciated that ozone-depleting substances (ODS), which have led to the formation of the Antarctic ozone hole, are also powerful greenhouse gases. In this study, we explore the consequence of the surface warming caused by ODS in the second half of the twentieth century over the Indo-Pacific Ocean, using the Whole Atmosphere Chemistry Climate Model (version 4). By contrasting two ensembles of chemistry–climate model integrations (with and without ODS forcing) over the period 1955–2005, we show that the additional greenhouse effect of ODS is crucial to producing a statistically significant weakening of the Walker circulation in our model over that period. When ODS concentrations are held fixed at 1955 levels, the forcing of the other well-mixed greenhouse gases alone leads to a strengthening—rather than weakening—of the Walker circulation because their warming effect is not sufficiently strong. Without increasing ODS, a surface warming delay in the eastern tropical Pacific Ocean leads to an increase in the sea surface temperature gradient between the eastern and western Pacific, with an associated strengthening of the Walker circulation. When increasing ODS are added, the considerably larger total radiative forcing produces a much faster warming in the eastern Pacific, causing the sign of the trend to reverse and the Walker circulation to weaken. Our modeling result suggests that ODS may have been key players in the observed weakening of the Walker circulation over the second half of the twentieth century.

scholarly journals Global warming projections derived from an observation-based minimal model

2016 ◽  
Vol 7 (1) ◽  
pp. 51-70 ◽  
Author(s):  
K. Rypdal
Keyword(s):  
Global Warming ◽  
Conceptual Model ◽  
Radiative Forcing ◽  
Climate Model ◽  
Co2 Concentration ◽  
Observation Data ◽  
Policy Makers ◽  
Global Emission ◽  
Inertia Parameters ◽  
Intercomparison Project

Abstract. A simple conceptual model for the global mean surface temperature (GMST) response to CO2 emissions is presented and analysed. It consists of linear long-memory models for the GMST anomaly response ΔT to radiative forcing and the atmospheric CO2-concentration response ΔC to emission rate. The responses are connected by the standard logarithmic relation between CO2 concentration and its radiative forcing. The model depends on two sensitivity parameters, αT and αC, and two "inertia parameters," the memory exponents βT and βC. Based on observation data, and constrained by results from the Climate Model Intercomparison Project Phase 5 (CMIP5), the likely values and range of these parameters are estimated, and projections of future warming for the parameters in this range are computed for various idealised, but instructive, emission scenarios. It is concluded that delays in the initiation of an effective global emission reduction regime is the single most important factor that influences the magnitude of global warming over the next 2 centuries. The most important aspect of this study is the simplicity and transparency of the conceptual model, which makes it a useful tool for communicating the issue to non-climatologists, students, policy makers, and the general public.

scholarly journals Solar irradiance reduction to counteract radiative forcing from a quadrupling of CO<sub>2</sub>: climate responses simulated by four earth system models

2012 ◽  
Vol 3 (1) ◽  
pp. 63-78 ◽  
Author(s):  
H. Schmidt ◽  
K. Alterskjær ◽  
D. Bou Karam ◽  
O. Boucher ◽  
A. Jones ◽  
...  
Keyword(s):  
Radiative Forcing ◽  
Surface Air Temperature ◽  
Co2 Concentration ◽  
Northern Eurasia ◽  
Earth System ◽  
Model Intercomparison ◽  
Regional Patterns ◽  
System Models ◽  
Eu Project ◽  
Earth System Models

Abstract. In this study we compare the response of four state-of-the-art Earth system models to climate engineering under scenario G1 of two model intercomparison projects: GeoMIP (Geoengineering Model Intercomparison Project) and IMPLICC (EU project "Implications and risks of engineering solar radiation to limit climate change"). In G1, the radiative forcing from an instantaneous quadrupling of the CO2 concentration, starting from the preindustrial level, is balanced by a reduction of the solar constant. Model responses to the two counteracting forcings in G1 are compared to the preindustrial climate in terms of global means and regional patterns and their robustness. While the global mean surface air temperature in G1 remains almost unchanged compared to the control simulation, the meridional temperature gradient is reduced in all models. Another robust response is the global reduction of precipitation with strong effects in particular over North and South America and northern Eurasia. In comparison to the climate response to a quadrupling of CO2 alone, the temperature responses are small in experiment G1. Precipitation responses are, however, in many regions of comparable magnitude but globally of opposite sign.

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 A new method to diagnose the contribution of anthropogenic activities to temperature: temperature tagging

2013 ◽  
Vol 6 (2) ◽  
pp. 417-427 ◽  
Author(s):  
V. Grewe
Keyword(s):  
Greenhouse Gases ◽  
Surface Temperature ◽  
Greenhouse Effect ◽  
Climate Model ◽  
Co2 Concentration ◽  
Base Case ◽  
Atmospheric Absorption ◽  
The Difference ◽  
The Impact ◽  
Longwave Flux

Abstract. This study presents a new methodology, called temperature tagging. It keeps track of the contributions of individual processes to temperature within a climate model simulation. As a first step and as a test bed, a simple box climate model is regarded. The model consists of an atmosphere, which absorbs and emits radiation, and of a surface, which reflects, absorbs and emits radiation. The tagging methodology is used to investigate the impact of the atmosphere on surface temperature. Four processes are investigated in more detail and their contribution to the surface temperature quantified: (i) shortwave influx and shortwave atmospheric absorption ("sw"), (ii) longwave atmospheric absorption due to non-CO2 greenhouse gases ("nC"), (iii) due to a base case CO2 concentration ("bC"), and (iv) due to an enhanced CO2 concentration ("eC"). The differential equation for the temperature in the box climate model is decomposed into four equations for the tagged temperatures. This method is applied to investigate the contribution of longwave absorption to the surface temperature (greenhouse effect), which is calculated to be 68 K. This estimate contrasts an alternative calculation of the greenhouse effect of slightly more than 30 K based on the difference of the surface temperature with and without an atmosphere. The difference of the two estimates is due to a shortwave cooling effect and a reduced contribution of the shortwave to the total downward flux: the shortwave absorption of the atmosphere results in a reduced net shortwave flux at the surface of 192 W m−2, leading to a cooling of the surface by 14 K. Introducing an atmosphere results in a downward longwave flux at the surface due to atmospheric absorption of 189 W m−2, which roughly equals the net shortwave flux of 192 W m−2. This longwave flux is a result of both the radiation due to atmospheric temperatures and its longwave absorption. Hence the longwave absorption roughly accounts for 91 W m−2 out of a total of 381 W m−2 (roughly 25%) and therefore accounts for a temperature change of 68 K. In a second experiment, the CO2 concentration is doubled, which leads to an increase in surface temperature of 1.2 K, resulting from a temperature increase due to CO2 of 1.9 K, due to non-CO2 greenhouse gases of 0.6 K and a cooling of 1.3 K due to a reduced importance of the solar heating for the surface and atmospheric temperatures. These two experiments show the feasibility of temperature tagging and its potential as a diagnostic for climate simulations.

scholarly journals A dynamic marine iron cycle module coupled to the University of Victoria Earth System Model: the Kiel Marine Biogeochemical Model 2 (KMBM2) for UVic 2.9

2014 ◽  
Vol 7 (6) ◽  
pp. 8505-8563 ◽  
Author(s):  
L. Nickelsen ◽  
D. P. Keller ◽  
A. Oschlies
Keyword(s):  
Climate Model ◽  
Iron Concentration ◽  
Biogeochemical Model ◽  
Change Scenario ◽  
Earth System ◽  
Iron Release ◽  
Iron Cycle ◽  
Biogeochemical Models ◽  
Sensitivity Studies ◽  
The University

Abstract. Marine biological production and the associated biotic uptake of carbon in many ocean regions depend on the availability of nutrients in the euphotic zone. While large areas are limited by nitrogen and/or phosphorus, the micronutrient iron is considered the main limiting nutrient in the North Pacific, equatorial Pacific and Southern Ocean. Changes in iron availability via changes in atmospheric dust input are discussed to play an important role in glacial/interglacial cycles via climate feedbacks caused by changes in biological ocean carbon sequestration. Although many aspects of the iron cycle remain unknown, its incorporation into marine biogeochemical models is needed to test our current understanding and better constrain its role in the Earth system. In the University of Victoria Earth System Climate Model (UVic) iron limitation in the ocean was, until now, simulated pragmatically with an iron concentration masking scheme that did not allow a consistent interactive response to perturbations of ocean biogeochemistry or iron cycling sensitivity studies. Here, we replace the iron masking scheme with a dynamic iron cycle and compare the results to available observations and the previous marine biogeochemical model. Sensitivity studies are also conducted with the new model to test the importance of considering the variable solubility of iron in dust deposition, the importance of considering high resolution bathymetry for the sediment release of iron, the effect of scaling the sedimentary iron release with temperature and the sensitivity of the iron cycle to a climate change scenario.

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