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Gunnar Myhre - One of the best experts on this subject based on the ideXlab platform.
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Effective Radiative Forcing and adjustments in CMIP6 models
Atmospheric Chemistry and Physics, 2020Co-Authors: Christopher J. Smith, Gunnar Myhre, Olivier Boucher, William J. Collins, Ryan J. Kramer, Kari Alterskjær, Adriana Sima, Jean-louis Dufresne, Pierre Nabat, Martine MichouAbstract:The effective Radiative Forcing, which includes the instantaneous Forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective Radiative Forcing and adjustments in 17 contemporary climate models that are participating in the Coupled Model Intercomparison Project (CMIP6) and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global-mean anthropogenic Forcing relative to pre-industrial (1850) levels from climate models stands at 2.00 (±0.23) W m−2, comprised of 1.81 (±0.09) W m−2 from CO2, 1.08 (± 0.21) W m−2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m−2 from aerosols and −0.09 (±0.13) W m−2 from land use change. Quoted uncertainties are 1 standard deviation across model best estimates, and 90 % confidence in the reported Forcings, due to internal variability, is typically within 0.1 W m−2. The majority of the remaining 0.21 W m−2 is likely to be from ozone. In most cases, the largest contributors to the spread in effective Radiative Forcing (ERF) is from the instantaneous Radiative Forcing (IRF) and from cloud responses, particularly aerosol–cloud interactions to aerosol Forcing. As determined in previous studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted Radiative Forcing is approximately equal to ERF for greenhouse gas Forcing but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol Forcing ranges from −0.63 to −1.37 W m−2, exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO2 Forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol Forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol Forcing and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol Forcing to recreate observed historical warming.
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Effective Radiative Forcing and adjustments in CMIP6 models
Atmospheric Chemistry and Physics, 2020Co-Authors: Christopher Smith, Gunnar Myhre, Olivier Boucher, Kari Alterskjær, Adriana Sima, Jean-louis Dufresne, Pierre Nabat, Ryan Kramer, William Collins, Martine MichouAbstract:The effective Radiative Forcing, which includes the instantaneous Forcing plus adjustments from the atmosphere and surface, has emerged as the key metric of evaluating human and natural influence on the climate. We evaluate effective Radiative Forcing and adjustments in 17 contemporary climate models that are participating in CMIP6 and have contributed to the Radiative Forcing Model Intercomparison Project (RFMIP). Present-day (2014) global mean anthropogenic Forcing relative to pre-industrial (1850) from climate models stands at 2.00 (± 0.23) W m −2 , comprised of 1.81 (± 0.09) W m −2 from CO 2 , 5 1.08 (± 0.21) W m −2 from other well-mixed greenhouse gases, −1.01 (± 0.23) W m −2 from aerosols and −0.09 (± 0.13) W 1 m −2 from land use change. Quoted uncertainties are one standard deviation across model best estimates, and 90% confidence in the reported Forcings, due to internal variability, is typically within 0.1 W m −2. The majority of the remaining 0.21 W m −2 is likely to be from ozone. In most cases, the largest contributors to the spread in ERF is from the instantaneous Radiative Forcing (IRF) and from cloud responses, particularly aerosol-cloud interactions to aerosol Forcing. As determined in previous 10 studies, cancellation of tropospheric and surface adjustments means that the stratospherically adjusted Radiative Forcing is approximately equal to ERF for greenhouse gas Forcing, but not for aerosols, and consequentially, not for the anthropogenic total. The spread of aerosol Forcing ranges from −0.63 to −1.37 W m −2 , exhibiting a less negative mean and narrower range compared to 10 CMIP5 models. The spread in 4×CO 2 Forcing has also narrowed in CMIP6 compared to 13 CMIP5 models. Aerosol Forcing is uncorrelated with climate sensitivity. Therefore, there is no evidence to suggest that the increasing spread 15 in climate sensitivity in CMIP6 models, particularly related to high-sensitivity models, is a consequence of a stronger negative present-day aerosol Forcing, and little evidence that modelling groups are systematically tuning climate sensitivity or aerosol Forcing to recreate observed historical warming.
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Radiative Forcing of Climate: The Historical Evolution of the Radiative Forcing Concept, the Forcing Agents and their Quantification, and Applications
Meteorological Monographs, 2019Co-Authors: Venkatachalam Ramaswamy, Gunnar Myhre, Jim Haywood, Keith P. Shine, William D. Collins, Judith Lean, Natalie M. Mahowald, Vaishali Naik, Brian J. Soden, G. StenchikovAbstract:AbstractWe describe the historical evolution of the conceptualization, formulation, quantification, application, and utilization of “Radiative Forcing” (RF) of Earth’s climate. Basic theories of sh...
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Resolving uncertainties in the Radiative Forcing of HFC-134a
2005Co-Authors: Piers M. Forster, Gunnar Myhre, James B. Burkholder, Cathy Clerbaux, Pierre-françois Coheur, Mitra Dutta, L. K. Gohar, Michael D. Hurley, Robert W. Portmann, Keith P. ShineAbstract:HFC-134a (CF3CH2F) is the most rapidly growing hydrofluorocarbon in terms of atmospheric abundance. It is currently used in a large number of household refrigerators and air-conditioning systems and its concentration in the atmosphere is forecast to increase substantially over the next 50–100 years. Previous estimates of its Radiative Forcing per unit concentration have differed significantly 25%. This paper uses a two-step approach to resolve this discrepancy. In the first step six independent absorption cross section datasets are analysed. We find that, for the integrated cross section in the spectral bands that contribute most to the Radiative Forcing, the differences between the various datasets are typically smaller than 5% and that the dependence on pressure and temperature is not significant. A “recommended'' HFC-134a infrared absorption spectrum was obtained based on the average band intensities of the strongest bands. In the second step, the “recommended'' HFC-134a spectrum was used in six different Radiative transfer models to calculate the HFC-134a Radiative Forcing efficiency. The clear-sky instantaneous Radiative Forcing, using a single global and annual mean profile, differed by 8%, between the 6 models, and the latitudinally-resolved adjusted cloudy sky Radiative Forcing estimates differed by a similar amount. We calculate that the Radiative Forcing efficiency of HFC-134a is
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Resolution of the uncertainties in the Radiative Forcing of HFC-134a
Journal of Quantitative Spectroscopy and Radiative Transfer, 2005Co-Authors: Piers M. Forster, Gunnar Myhre, James B. Burkholder, Cathy Clerbaux, Pierre-françois Coheur, Mitra Dutta, L. K. Gohar, Michael D. Hurley, Robert W. Portmann, Keith P. ShineAbstract:Abstract HFC-134a (CF 3 CH 2 F) is the most rapidly growing hydrofluorocarbon in terms of atmospheric abundance. It is currently used in a large number of household refrigerators and air-conditioning systems and its concentration in the atmosphere is forecast to increase substantially over the next 50–100 years. Previous estimates of its Radiative Forcing per unit concentration have differed significantly ∼ 25%. This paper uses a two-step approach to resolve this discrepancy. In the first step six independent absorption cross section datasets are analysed. We find that, for the integrated cross section in the spectral bands that contribute most to the Radiative Forcing, the differences between the various datasets are typically smaller than 5% and that the dependence on pressure and temperature is not significant. A “recommended'' HFC-134a infrared absorption spectrum was obtained based on the average band intensities of the strongest bands. In the second step, the “recommended'' HFC-134a spectrum was used in six different Radiative transfer models to calculate the HFC-134a Radiative Forcing efficiency. The clear-sky instantaneous Radiative Forcing, using a single global and annual mean profile, differed by 8%, between the 6 models, and the latitudinally-resolved adjusted cloudy sky Radiative Forcing estimates differed by a similar amount. We calculate that the Radiative Forcing efficiency of HFC-134a is 0.16 ± 0.02 Wm - 2 ppbv - 1 .
Frode Stordal - One of the best experts on this subject based on the ideXlab platform.
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Uncertainties in the Radiative Forcing Due to Sulfate Aerosols
Journal of the Atmospheric Sciences, 2004Co-Authors: Gunnar Myhre, Frode Stordal, Tore F. Berglen, Jostein K. Sundet, Ivar S A IsaksenAbstract:Radiative transfer calculations based on a new sulfate distribution from a chemistry-transport model simulation have been performed. A wide range of sensitivity experiments have been performed to illustrate the large uncertainty in the Radiative Forcing due to sulfate aerosols. The most important factors seem to be processes involved in the mixing of sulfate aerosols with other particles and uncertainties in the relative humidities. These factors can explain much of the large range in previous estimates of the Radiative Forcing due to sulfate aerosols reflected, for example, in the Intergovernmental Panel on Climate Change estimate. Included in this study is a simple subgrid-scale parameterization of relative humidity to investigate a potentially large uncertainty in the Radiative Forcing due to sulfate aerosol.
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Global sensitivity experiments of the Radiative Forcing due to mineral aerosols
Journal of Geophysical Research: Atmospheres, 2001Co-Authors: Gunnar Myhre, Frode StordalAbstract:The Radiative effects of mineral dust in the atmosphere are uncertain. Further, the human contribution to the mineral aerosol concentration is difficult to quantify. We have performed several global sensitivity experiments to investigate the Radiative Forcing due to mineral dust. Two global data sets of mineral aerosol distribution are used. Radiative transfer schemes for thermal infrared and solar radiation are used in the calculations. We have investigated the sensitivity of the global Radiative Forcing to the spatial distribution of the aerosols, including the altitude, the size distribution, and optical parameters. Our strongest emphasis has been on the size distribution of the mineral aerosol, for which we have found a strong sensitivity. A range of −0.7 Wm−2 to 0.5 Wm−2 is estimated for the human influence on the global Radiative Forcing due to mineral aerosols. We find it almost as probable with a positive Radiative Forcing as with a negative Forcing. Even if the global mean Radiative Forcing is small, there are large contributions of different sign in certain regions.
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Historical evolution of Radiative Forcing of climate
Atmospheric Environment, 2001Co-Authors: Gunnar Myhre, Arne Myhre, Frode StordalAbstract:Abstract We have compiled the evolution of the Radiative Forcing for several mechanisms based on our Radiative transfer models using a variety of information sources to establish time histories. The anthropogenic Forcing mechanisms considered are well-mixed greenhouse gases, ozone, and tropospheric aerosols (direct and indirect effect). The natural Forcing mechanisms taken into account are the Radiative effects of solar irradiance variation and particles of volcanic origin. In general there has been an increase in the Radiative Forcing during the 20th century. The exception is a decline in the Radiative Forcing in the 1945–1970 period. We have found that the evolution of anthropogenic particle emissions in the same period may have been a major cause of this decline in the Forcing. We have discussed uncertainties in the various Forcings and their evolution. The uncertainties are large for many Forcing mechanisms, especially the impact of anthropogenic aerosols. In particular the indirect effect of aerosols on clouds is difficult to quantify. Several evolutions of their effect may have been possible, strongly influencing the evolution of the total anthropogenic Radiative Forcing.
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Radiative Forcing due to changes in tropospheric ozone in the period 1980 to 1996
Journal of Geophysical Research, 2000Co-Authors: Gunnar Myhre, SigrÙn Karlsdottir, Ivar S A Isaksen, Frode StordalAbstract:Radiative Forcing calculations of changes in tropospheric ozone in the period 1980 to 1996 are performed. The tropospheric ozone changes used in this study are from a chemistry transport model [Karlsdottir et al., this issue]. For the Radiative transfer calculations, schemes for thermal infrared radiation and shortwave radiation are used. Effects of reduced stratospheric ozone and emissions of tropospheric ozone precursors on the changes in tropospheric ozone are taken into account. Large positive Radiative Forcing is estimated over Southeast Asia, due to emissions of ozone precursors. Effects of decreased stratospheric ozone have reduced the Radiative Forcing due to change in tropospheric ozone from 1980 to 1996, particularly at high latitudes where the Radiative Forcing is negative.
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new estimates of Radiative Forcing due to well mixed greenhouse gases
Geophysical Research Letters, 1998Co-Authors: Gunnar Myhre, Keith P. Shine, E J Highwood, Frode StordalAbstract:We have performed new calculations of the Radiative Forcing due to changes in the concentrations of the most important well mixed greenhouse gases (WMGG) since pre-industrial time. Three Radiative transfer models are used. The Radiative Forcing due to CO2, including shortwave absorption, is 15% lower than the previous IPCC estimate. The Radiative Forcing due to all the WMGG is calculated to 2.25 Wm−2, which we estimate to be accurate to within about 5%. The importance of the CFCs is increased by about 20% relative to the total effect of all WMGG compared to previous estimates. We present updates to simple Forcing-concentration relationships previously used by IPCC.
Keith P. Shine - One of the best experts on this subject based on the ideXlab platform.
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Radiative Forcing of climate change from the Copernicus reanalysis of atmospheric composition
Earth System Science Data, 2020Co-Authors: Nicolas Bellouin, Piers M. Forster, Keith P. Shine, Will Davies, Johannes Quaas, Johannes Mülmenstädt, Chris Smith, Lindsay Lee, Leighton Regayre, Guy BrasseurAbstract:Abstract. Radiative Forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different Forcing agents, has involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly and spatially resolved global distributions of Radiative Forcing consistently for six of the largest Forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol–radiation interactions, and aerosol–cloud interactions. These Radiative-Forcing estimates account for adjustments in stratospheric temperatures but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2017, stratospherically adjusted Radiative Forcing of carbon dioxide has averaged +1.89 W m−2 (5 %–95 % confidence interval: 1.50 to 2.29 W m−2) relative to 1750 and increased at a rate of 18 % per decade. The corresponding values for methane are +0.46 (0.36 to 0.56) W m−2 and 4 % per decade but with a clear acceleration since 2007. Ozone Radiative-Forcing averages +0.32 (0 to 0.64) W m−2, almost entirely contributed by tropospheric ozone since stratospheric ozone Radiative Forcing is only +0.003 W m−2. Aerosol Radiative-Forcing averages −1.25 (−1.98 to −0.52) W m−2, with aerosol–radiation interactions contributing −0.56 W m−2 and aerosol–cloud interactions contributing −0.69 W m−2 to the global average. Both have been relatively stable since 2003. Taking the six Forcing agents together, there is no indication of a sustained slowdown or acceleration in the rate of increase in anthropogenic Radiative Forcing over the period. These ongoing Radiative-Forcing estimates will monitor the impact on the Earth's energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in Radiative Forcing before being clear in the temperature record. In addition, this Radiative-Forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020b).
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Radiative Forcing of climate change from the Copernicus reanalysis of atmospheric composition
2020Co-Authors: Nicolas Bellouin, Piers M. Forster, Keith P. Shine, Christopher J. Smith, Will Davies, Johannes Quaas, Johannes Mülmenstädt, Lindsay Lee, Leighton Regayre, Guy BrasseurAbstract:Abstract. Radiative Forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different Forcing agents, involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly- and spatially-resolved global distributions of Radiative Forcing consistently for six of the largest Forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol-radiation interactions, and aerosol-cloud interactions. These Radiative Forcing estimates account for adjustments in stratospheric temperatures, but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2016, stratospherically adjusted Radiative Forcing of carbon dioxide has averaged +1.84 W m−2 (5–95% confidence interval: 1.46 to 2.22 W m−2) relative to 1750 and increased at a rate of 17 % per decade. The corresponding values for methane are +0.45 (0.35 to 0.55) W m−2 and 3 % per decade, but with a clear acceleration since 2007. Ozone Radiative Forcing averages +0.32 (0 to 0.64) W m−2 and aerosol Radiative Forcing averages −1.37 (−2.17 to −0.57) W m−2. Both have been relatively stable since 2003. Taking the six Forcing agents together, there no indication of a slowdown or acceleration in the rate of increase in anthropogenic Radiative Forcing over the period. These ongoing Radiative Forcing estimates will monitor the impact on the Earth’s energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in Radiative Forcing before being clear in the temperature record. In addition, this Radiative Forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020).
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Radiative Forcing of Climate: The Historical Evolution of the Radiative Forcing Concept, the Forcing Agents and their Quantification, and Applications
Meteorological Monographs, 2019Co-Authors: Venkatachalam Ramaswamy, Gunnar Myhre, Jim Haywood, Keith P. Shine, William D. Collins, Judith Lean, Natalie M. Mahowald, Vaishali Naik, Brian J. Soden, G. StenchikovAbstract:AbstractWe describe the historical evolution of the conceptualization, formulation, quantification, application, and utilization of “Radiative Forcing” (RF) of Earth’s climate. Basic theories of sh...
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Encyclopedia of Aerospace Engineering - Radiative Forcing and Climate Change
Encyclopedia of Aerospace Engineering, 2015Co-Authors: Keith P. ShineAbstract:Aviation causes climate change as a result of its emissions of CO2, oxides of nitrogen, aerosols, and water vapor. One simple method of quantifying the climate impact of past emissions is Radiative Forcing. The Radiative Forcing due to changes in CO2 is best characterized, but there are formidable difficulties in estimating the non-CO2 Forcings – this is particularly the case for possible aviation-induced changes in cloudiness (AIC). The most recent comprehensive assessment gave a best estimate of the 2005 total Radiative Forcing due to aviation of about 55–78 mW m−2 depending on whether AIC was included or not, with an uncertainty of at least a factor of 2. The aviation CO2 Radiative Forcing represents about 1.6% of the total CO2 Forcing from all human activities. It is estimated that, including the non-CO2 effects, aviation contributes between 1.3 and 14% of the total Radiative Forcing due to all human activities. Alternative methods for comparing the future impact of present-day aviation emissions are presented – the perception of the relative importance of the non-CO2 emissions, relative to CO2, depends considerably on the chosen method and the parameters chosen within those methods. Keywords: carbon dioxide; climate change; global temperature change potential; global warming potential; Radiative Forcing
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Resolving uncertainties in the Radiative Forcing of HFC-134a
2005Co-Authors: Piers M. Forster, Gunnar Myhre, James B. Burkholder, Cathy Clerbaux, Pierre-françois Coheur, Mitra Dutta, L. K. Gohar, Michael D. Hurley, Robert W. Portmann, Keith P. ShineAbstract:HFC-134a (CF3CH2F) is the most rapidly growing hydrofluorocarbon in terms of atmospheric abundance. It is currently used in a large number of household refrigerators and air-conditioning systems and its concentration in the atmosphere is forecast to increase substantially over the next 50–100 years. Previous estimates of its Radiative Forcing per unit concentration have differed significantly 25%. This paper uses a two-step approach to resolve this discrepancy. In the first step six independent absorption cross section datasets are analysed. We find that, for the integrated cross section in the spectral bands that contribute most to the Radiative Forcing, the differences between the various datasets are typically smaller than 5% and that the dependence on pressure and temperature is not significant. A “recommended'' HFC-134a infrared absorption spectrum was obtained based on the average band intensities of the strongest bands. In the second step, the “recommended'' HFC-134a spectrum was used in six different Radiative transfer models to calculate the HFC-134a Radiative Forcing efficiency. The clear-sky instantaneous Radiative Forcing, using a single global and annual mean profile, differed by 8%, between the 6 models, and the latitudinally-resolved adjusted cloudy sky Radiative Forcing estimates differed by a similar amount. We calculate that the Radiative Forcing efficiency of HFC-134a is
Nicolas Bellouin - One of the best experts on this subject based on the ideXlab platform.
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Radiative Forcing of climate change from the Copernicus reanalysis of atmospheric composition
Earth System Science Data, 2020Co-Authors: Nicolas Bellouin, Piers M. Forster, Keith P. Shine, Will Davies, Johannes Quaas, Johannes Mülmenstädt, Chris Smith, Lindsay Lee, Leighton Regayre, Guy BrasseurAbstract:Abstract. Radiative Forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different Forcing agents, has involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly and spatially resolved global distributions of Radiative Forcing consistently for six of the largest Forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol–radiation interactions, and aerosol–cloud interactions. These Radiative-Forcing estimates account for adjustments in stratospheric temperatures but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2017, stratospherically adjusted Radiative Forcing of carbon dioxide has averaged +1.89 W m−2 (5 %–95 % confidence interval: 1.50 to 2.29 W m−2) relative to 1750 and increased at a rate of 18 % per decade. The corresponding values for methane are +0.46 (0.36 to 0.56) W m−2 and 4 % per decade but with a clear acceleration since 2007. Ozone Radiative-Forcing averages +0.32 (0 to 0.64) W m−2, almost entirely contributed by tropospheric ozone since stratospheric ozone Radiative Forcing is only +0.003 W m−2. Aerosol Radiative-Forcing averages −1.25 (−1.98 to −0.52) W m−2, with aerosol–radiation interactions contributing −0.56 W m−2 and aerosol–cloud interactions contributing −0.69 W m−2 to the global average. Both have been relatively stable since 2003. Taking the six Forcing agents together, there is no indication of a sustained slowdown or acceleration in the rate of increase in anthropogenic Radiative Forcing over the period. These ongoing Radiative-Forcing estimates will monitor the impact on the Earth's energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in Radiative Forcing before being clear in the temperature record. In addition, this Radiative-Forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020b).
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Bounding global aerosol Radiative Forcing of climate change
2020Co-Authors: Nicolas BellouinAbstract:<p>Aerosol Radiative Forcing plays an important role in the attribution of past climate changes, estimates of future allowable carbon emissions, and the assessment of potential geoengineering solutions. Substantial progress made over the past 40 years in observing, understanding, and modelling aerosol processes helped quantify aerosol Radiative Forcing, but uncertainties remain large.</p><p>In spring 2018, under the auspices of the World Climate Research Programme's Grand Science Challenge on Clouds, Circulation and Climate Sensitivity, thirty-six experts gathered to take a fresh and comprehensive look at present understanding of aerosol Radiative Forcing and identify prospects for progress on some of the most pressing open questions. The outcome of that meeting is a review paper, Bellouin et al. (2019), accepted for publication in Reviews of Geophysics. This review provides a new range of aerosol Radiative Forcing over the industrial era based on multiple, traceable and arguable lines of evidence, including modelling approaches, theoretical considerations, and observations. A substantial achievement is to focus on lines of evidence rather than a survey of past results or expert judgement, and to make the open questions much more specific.</p><p>This talk will present the key messages and arguments of the review and identify work that show promise for improving the quantification of aerosol Radiative Forcing.</p>
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bounding global aerosol Radiative Forcing of climate change
Reviews of Geophysics, 2020Co-Authors: Nicolas Bellouin, Olivier Boucher, Johannes Quaas, E Gryspeerdt, S. Kinne, P. Stier, K. Carslaw, M Christensen, Duncan Watsonparris, A.-l DaniauAbstract:Aerosols interact with radiation and clouds. Substantial progress made over the past 40 years in observing, understanding, and modeling these processes helped quantify the imbalance in the Earth’s radiation budget caused by anthropogenic aerosols, called aerosol Radiative Forcing, but uncertainties remain large. This review provides a new range of aerosol Radiative Forcing over the industrial era based on multiple, traceable and arguable lines of evidence, including modelling approaches, theoretical considerations, and observations. Improved understanding of aerosol absorption and the causes of trends in surface Radiative fluxes constrain the Forcing from aerosol-radiation interactions. A robust theoretical foundation and convincing evidence constrain the Forcing caused by aerosol-driven increases in liquid cloud droplet number concentration. However, the influence of anthropogenic aerosols on cloud liquid water content and cloud fraction is less clear, and the influence on mixed-phase and ice clouds remains poorly constrained. Observed changes in surface temperature and Radiative fluxes provide additional constraints. These multiple lines of evidence lead to a 68% confidence interval for the total aerosol effective Radiative Forcing of −1.60 to −0.65 W m−2, or −2.0 to −0.4 W m−2 with a 90% likelihood. Those intervals are of similar width to the last Intergovernmental Panel on Climate Change assessment but shifted towards more negative values. The uncertainty will narrow in the future by continuing to critically combine multiple lines of evidence, especially those addressing industrial-era changes in aerosol sources and aerosol effects on liquid cloud amount and on ice clouds.
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Radiative Forcing of climate change from the Copernicus reanalysis of atmospheric composition
2020Co-Authors: Nicolas Bellouin, Piers M. Forster, Keith P. Shine, Christopher J. Smith, Will Davies, Johannes Quaas, Johannes Mülmenstädt, Lindsay Lee, Leighton Regayre, Guy BrasseurAbstract:Abstract. Radiative Forcing provides an important basis for understanding and predicting global climate changes, but its quantification has historically been done independently for different Forcing agents, involved observations to varying degrees, and studies have not always included a detailed analysis of uncertainties. The Copernicus Atmosphere Monitoring Service reanalysis is an optimal combination of modelling and observations of atmospheric composition. It provides a unique opportunity to rely on observations to quantify the monthly- and spatially-resolved global distributions of Radiative Forcing consistently for six of the largest Forcing agents: carbon dioxide, methane, tropospheric ozone, stratospheric ozone, aerosol-radiation interactions, and aerosol-cloud interactions. These Radiative Forcing estimates account for adjustments in stratospheric temperatures, but do not account for rapid adjustments in the troposphere. On a global average and over the period 2003–2016, stratospherically adjusted Radiative Forcing of carbon dioxide has averaged +1.84 W m−2 (5–95% confidence interval: 1.46 to 2.22 W m−2) relative to 1750 and increased at a rate of 17 % per decade. The corresponding values for methane are +0.45 (0.35 to 0.55) W m−2 and 3 % per decade, but with a clear acceleration since 2007. Ozone Radiative Forcing averages +0.32 (0 to 0.64) W m−2 and aerosol Radiative Forcing averages −1.37 (−2.17 to −0.57) W m−2. Both have been relatively stable since 2003. Taking the six Forcing agents together, there no indication of a slowdown or acceleration in the rate of increase in anthropogenic Radiative Forcing over the period. These ongoing Radiative Forcing estimates will monitor the impact on the Earth’s energy budget of the dramatic emission reductions towards net-zero that are needed to limit surface temperature warming to the Paris Agreement temperature targets. Indeed, such impacts should be clearly manifested in Radiative Forcing before being clear in the temperature record. In addition, this Radiative Forcing dataset can provide the input distributions needed by researchers involved in monitoring of climate change, detection and attribution, interannual to decadal prediction, and integrated assessment modelling. The data generated by this work are available at https://doi.org/10.24380/ads.1hj3y896 (Bellouin et al., 2020).
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Regional and seasonal Radiative Forcing by perturbations to aerosol and ozone precursor emissions
Atmospheric Chemistry and Physics, 2016Co-Authors: Nicolas Bellouin, Laura Baker, Øivind Hodnebrog, Dirk Olivié, Ribu Cherian, Claire Macintosh, Bjørn Hallvard Samset, A. R. Esteve, Borgar Aamaas, Johannes QuaasAbstract:Abstract. Predictions of temperature and precipitation responses to changes in the anthropogenic emissions of climate forcers require the quantification of the Radiative Forcing exerted by those changes. This task is particularly difficult for near-term climate forcers like aerosols, methane, and ozone precursors because their short atmospheric lifetimes cause regionally and temporally inhomogeneous Radiative Forcings. This study quantifies specific Radiative Forcing, defined as the Radiative Forcing per unit change in mass emitted, for eight near-term climate forcers as a function of their source regions and the season of emission by using dedicated simulations by four general circulation and chemistry-transport models. Although differences in the representation of atmospheric chemistry and Radiative processes in different models impede the creation of a uniform dataset, four distinct findings can be highlighted. Firstly, specific Radiative Forcing for sulfur dioxide and organic carbon are stronger when aerosol–cloud interactions are taken into account. Secondly, there is a lack of agreement on the sign of the specific Radiative Forcing of volatile organic compound perturbations, suggesting they are better avoided in climate mitigation strategies. Thirdly, the strong seasonalities of the specific Radiative Forcing of most forcers allow strategies to minimise positive Radiative Forcing based on the timing of emissions. Finally, European and shipping emissions exert stronger aerosol specific Radiative Forcings compared to East Asia where the baseline is more polluted. This study can therefore form the basis for further refining climate mitigation options based on regional and seasonal controls on emissions. For example, reducing summertime emissions of black carbon and wintertime emissions of sulfur dioxide in the more polluted regions is a possible way to improve air quality without weakening the negative Radiative Forcing of aerosols.
Ivar S A Isaksen - One of the best experts on this subject based on the ideXlab platform.
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Uncertainties in the Radiative Forcing Due to Sulfate Aerosols
Journal of the Atmospheric Sciences, 2004Co-Authors: Gunnar Myhre, Frode Stordal, Tore F. Berglen, Jostein K. Sundet, Ivar S A IsaksenAbstract:Radiative transfer calculations based on a new sulfate distribution from a chemistry-transport model simulation have been performed. A wide range of sensitivity experiments have been performed to illustrate the large uncertainty in the Radiative Forcing due to sulfate aerosols. The most important factors seem to be processes involved in the mixing of sulfate aerosols with other particles and uncertainties in the relative humidities. These factors can explain much of the large range in previous estimates of the Radiative Forcing due to sulfate aerosols reflected, for example, in the Intergovernmental Panel on Climate Change estimate. Included in this study is a simple subgrid-scale parameterization of relative humidity to investigate a potentially large uncertainty in the Radiative Forcing due to sulfate aerosol.
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Radiative Forcing due to changes in tropospheric ozone in the period 1980 to 1996
Journal of Geophysical Research, 2000Co-Authors: Gunnar Myhre, SigrÙn Karlsdottir, Ivar S A Isaksen, Frode StordalAbstract:Radiative Forcing calculations of changes in tropospheric ozone in the period 1980 to 1996 are performed. The tropospheric ozone changes used in this study are from a chemistry transport model [Karlsdottir et al., this issue]. For the Radiative transfer calculations, schemes for thermal infrared radiation and shortwave radiation are used. Effects of reduced stratospheric ozone and emissions of tropospheric ozone precursors on the changes in tropospheric ozone are taken into account. Large positive Radiative Forcing is estimated over Southeast Asia, due to emissions of ozone precursors. Effects of decreased stratospheric ozone have reduced the Radiative Forcing due to change in tropospheric ozone from 1980 to 1996, particularly at high latitudes where the Radiative Forcing is negative.
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Estimation of the direct Radiative Forcing due to sulfate and soot aerosols
Tellus B: Chemical and Physical Meteorology, 1998Co-Authors: Gunnar Myhre, Frode Stordal, Knut Restad, Ivar S A IsaksenAbstract:The direct Radiative Forcings due to tropospheric sulfate and fossil fuel soot aerosols are calculated. The change in the atmospheric sulfate since preindustrial time is taken from a recent three-dimensional chemistry transport model calculation. A multistream Radiative transfer code and observed atmospheric input data is used. The direct Radiative Forcing due to sulfate is calculated to – 0.32 W/m 2 . Our results for global and annual mean Radiative Forcing have been compared with results from other model studies.We have assumed a linear relationship between the concentration of fossil fuel soot and sulfate aerosols. The resulting Radiative Forcing due to soot particles is 0.16 W/m2. Two types of mixtures of sulfate and soot are further assumed. The calculated single scattering albedo is compared to observations. DOI: 10.1034/j.1600-0889.1998.t01-4-00005.x
