ORCID Profile
0000-0003-2699-929X
Current Organisations
Met Office
,
University of Leeds
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Publisher: Copernicus GmbH
Date: 25-01-2020
Abstract: 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 0.24380/ads.1hj3y896 (Bellouin et al., 2020).
Publisher: Copernicus GmbH
Date: 04-06-2018
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-2401
Abstract: & & Monsoon biases are long-standing and an important problem to solve because nearly half of the world& #8217 s population is affected by monsoon precipitation and circulation. The effect of local and remote circulation biases on Asian monsoon biases is studied with dynamical nudging using the latest version of the atmospheric component of the HadGEM3 model. Constraining the large-scale circulation substantially reduces oceanic biases in precipitation and circulation, particularly over the extra-tropics. Tropical wet biases may become even stronger because of unconstrained convection. By contrast, model biases over land are less sensitive to nudging due to the prominent role of local planetary boundary layer processes in modulating the low-level circulation. Nudging reduces the seasonal excess (deficit) precipitation over India in winter (summer) by reducing the local cyclonic (anti-cyclonic) biases. Constraining the circulation outside Asia demonstrates that the wet (dry) biases are mostly remotely (locally) controlled in winter (summer) over India. The monsoon biases over China show small changes with nudging, suggesting they are more thermodynamically driven. Monsoon variability is improved over India but not over China in nudged simulations. Despite the remaining errors in nudged simulations, our study suggests that nudging serves as a useful tool to disentangle the contribution of regional and remote circulation in generating the monsoon responses.& &
Publisher: Copernicus GmbH
Date: 03-2018
Publisher: Copernicus GmbH
Date: 24-11-2022
Publisher: Copernicus GmbH
Date: 04-03-2021
DOI: 10.5194/EGUSPHERE-EGU21-8499
Abstract: & & & & The change in planetary albedo due to aerosol-cloud interactions (aci) during the industrial era is the leading source of uncertainty in inferring& Earth's& climate sensitivity to increased greenhouse gases from the historical record. Examining pristine environments such as the Southern Ocean (SO) helps us to understand the pre-industrial state and constrain the change in cloud brightness over the industrial period associated with aci. This study presents two methods of utilizing observations of pristine environments to examine climate models and our understanding of the pre-industrial state.& & & / & & & & & First, cloud droplet number concentration (& em& N& sub& d& /sub& & /em& ) is used as an indicator of aci. Global climate models (GCMs) show that the& hemispheric contrast& in liquid cloud & em& N& sub& d& /sub& & /em& between the& ristine SO& and the polluted& Northern Hemisphere observed in the present-day can be used& strong& & /strong& as& a proxy for the increase& in & em& N& sub& d& /sub& & /em& from& the pre-industrial. A hemispheric difference constraint& developed from MODIS satellite observations indicates that pre-industrial& & em& N& sub& d& /sub& & /em& may have been higher than previously thought and provides an estimate of radiative forcing associated with aci between -1.2 and -0.6 Wm& sup& -2& /sup& . Comparisons with MODIS & em& N& sub& d & & /sub& & /em& highlight significant GCM discrepancies in pristine, biologically active regions.& & & / & & & & & Second, aerosol and cloud microphysical observations from a recent SO aircraft c aign are used to identify two potentially important mechanisms that are incomplete or missing in GCMs: i) production of new aerosol particles through synoptic uplift, and ii) buffering of & em& N& sub& d& /sub& & /em& against precipitation removal by small, Aitken mode aerosols entrained from the free troposphere. The latter may significantly contribute to the high, summertime SO & em& N& sub& d& /sub& & /em& levels which persist despite precipitation depletion associated with mid-latitude storm systems. Observational comparisons with nudged Community Atmosphere Model version 6 (CAM6) hindcasts show low-biased SO & em& N& sub& d & & /sub& & /em& is linked to under-production of free-tropospheric Aitken aerosol which drives low-biases in cloud condensation nuclei number and likely discrepancies in composition. These results have important implications for the ability of current GCMs to capture aci in pristine environments.& & & / &
Publisher: Copernicus GmbH
Date: 04-12-2019
Abstract: Abstract. Aerosol measurements over the Southern Ocean are used to constrain aerosol-cloud interaction radiative forcing uncertainty in a global climate model. Aerosol forcing uncertainty is quantified using one million climate model variants that s le the uncertainty in nearly 30 model parameters. Ship-based measurements of cloud condensation nuclei, particle number concentrations and sulfate mass concentrations from the Antarctic Circumnavigation Expedition: Study of Preindustrial-like Aerosols and Their Climate Effects (ACE-SPACE) are used to identify observationally implausible variants and thereby reduce the spread in the simulated forcing. Southern Ocean measurements strongly constrain natural aerosol emissions: default sea spray emissions in the model need to be increased by around a factor of 3 to be consistent with measurements. Aerosol forcing uncertainty is reduced by around 7 % using these measurements, which is comparable to the 8 % reduction achieved using an extensive set of over 9000 predominantly Northern Hemisphere measurements. The radiative forcing due to aerosol–cloud interactions (RFaci) is constrained to −2.61 to −1.10 W m−2 (95 % confidence) and the effective radiative forcing from aerosol-cloud interactions (ERFaci) is constrained to −2.43 to −0.54 W m−2. When Southern Ocean and Northern Hemisphere measurements are combined, the uncertainty in RFaci is reduced by 21 % and the strongest 20 % of forcing values are ruled out as implausible. In this combined constraint the observationally plausible RFaci is around 0.17 W m−2 weaker (less negative) with credible values ranging from −2.51 to −1.17 W m−2 and from −2.18 to −1.46 W m−2 when using one standard deviation to quantify the uncertainty. The Southern Ocean and Northern Hemisphere measurement datasets are complementary because they constrain different processes. These results highlight the value of remote marine aerosol measurements.
Publisher: Copernicus GmbH
Date: 07-12-2017
DOI: 10.5194/GMD-2017-266
Abstract: Abstract. Simple climate models can be valuable if they are able to replicate aspects of complex fully coupled earth system models. Larger ensembles can be produced, enabling a probabilistic view of future climate change. A simple emissions-based climate model, FAIR, is presented which calculates atmospheric concentrations of greenhouse gases and effective radiative forcing (ERF) from greenhouse gases, aerosols, ozone precursors and other agents. The ERFs are integrated into global mean surface temperature change. Model runs are constrained to observed temperature change from 1880 to 2016 and produce a range of future projections under the Representative Concentration Pathway (RCP) scenarios. For the historical period the ERF time series in FAIR emulates the results in the IPCC Fifth Assessment Report (AR5), whereas for RCP historical and future scenarios, the greenhouse gas concentrations in FAIR closely track the observations and projections in the RCPs. The constrained estimates of equilibrium climate sensitivity (ECS) of 2.79 (1.97 to 4.08) K, transient climate response (TCR) of 1.47 (1.03 to 2.23) K and transient climate response to cumulative CO2 emissions (TCRE) of 1.43 (1.01 to 2.16) K (1000 GtC)−1 (median and 5–95 % credible intervals) are in good agreement, with tighter uncertainty bounds, than AR5 (1.5 to 4.5 K, 1.0 to 2.5 K, and 0.8 to 2.5 K respectively). The ranges of future projections of temperature and ranges of estimates of ECS, TCR and TCRE are moderately sensitive to the historical temperature dataset used to constrain, prior distributions of ECS/TCR parameters, aerosol radiative forcing relationship and ERF from a doubling of CO2. Taking these sensitivities into account, there is no evidence to suggest that the median and credible range of observationally constrained TCR or ECS differ from climate model-derived estimates. However, the range of temperature projections under the RCP scenarios for 2081–2100 in the constrained FAIR model ensemble are lower than the emissions-based estimates reported in AR5.
Publisher: Copernicus GmbH
Date: 11-09-2018
DOI: 10.5194/ACP-18-13031-2018
Abstract: Abstract. Observational constraint of simulated aerosol and cloud properties is an essential part of building trustworthy climate models for calculating aerosol radiative forcing. Models are usually tuned to achieve good agreement with observations, but tuning produces just one of many potential variants of a model, so the model uncertainty cannot be determined. Here we estimate the uncertainty in aerosol effective radiative forcing (ERF) in a tuned climate model by constraining 4 million variants of the HadGEM3-UKCA aerosol–climate model to match nine common observations (top-of-atmosphere shortwave flux, aerosol optical depth, PM2.5, cloud condensation nuclei at 0.2 % supersaturation (CCN0.2), and concentrations of sulfate, black carbon and organic carbon, as well as decadal trends in aerosol optical depth and surface shortwave radiation.) The model uncertainty is calculated by using a perturbed parameter ensemble that s les 27 uncertainties in both the aerosol model and the physical climate model, and we use synthetic observations generated from the model itself to determine the potential of each observational type to constrain this uncertainty. Focusing over Europe in July, we show that the aerosol ERF uncertainty can be reduced by about 30 % by constraining it to the nine observations, demonstrating that producing climate models with an observationally plausible “base state” can contribute to narrowing the uncertainty in aerosol ERF. However, the uncertainty in the aerosol ERF after observational constraint is large compared to the typical spread of a multi-model ensemble. Our results therefore raise questions about whether the underlying multi-model uncertainty would be larger if similar approaches as adopted here were applied more widely. The approach presented in this study could be used to identify the most effective observations for model constraint. It is hoped that aerosol ERF uncertainty can be further reduced by introducing process-related constraints however, any such results will be robust only if the enormous number of potential model variants is explored.
Publisher: Copernicus GmbH
Date: 29-05-2020
Publisher: American Geophysical Union (AGU)
Date: 25-04-2020
DOI: 10.1029/2020GL087141
Publisher: Copernicus GmbH
Date: 29-05-2020
Publisher: Copernicus GmbH
Date: 16-02-2023
Publisher: American Geophysical Union (AGU)
Date: 18-01-2019
DOI: 10.1029/2018JD028675
Publisher: Copernicus GmbH
Date: 16-02-2023
DOI: 10.5194/EGUSPHERE-2023-77
Abstract: Abstract. Aerosol radiative forcing uncertainty affects estimates of climate sensitivity and limits model skill at making climate projections. Efforts to improve the representations of physical processes in climate models, including extensive comparisons with observations, have not significantly constrained the range of possible aerosol forcing values. A far stronger constraint, in particular for the lower (most-negative) bound, can be achieved using global mean energy-balance arguments based on observed changes in historical temperature. Here, we show that structural deficiencies in a climate model, revealed as inconsistencies among observationally constrained cloud properties in the model, limit the effectiveness of observational constraint of the uncertain physical processes. We s le uncertainty in 37 model parameters related to aerosols, clouds and radiation in a perturbed parameter ensemble of the UK Earth System Model and evaluate 1 million model variants (different parameter settings from Gaussian Process emulators) against satellite-derived observations over several cloudy regions. We show that it is possible to reduce the parametric uncertainty in global mean aerosol forcing by more than 50 %, constraining it to a range in close agreement with energy-balance constraints (around −1.3 to −0.1 W m−2). However, our analysis of a very large set of model variants exposes model internal inconsistencies that would not be apparent in a small set of model simulations. Incorporating observations associated with these inconsistencies weakens the forcing constraint because they require a wider range of parameter values to accommodate conflicting information. Our estimated aerosol forcing range is the maximum feasible constraint using our structurally imperfect model and the chosen observations. Structural model developments targeted at the identified inconsistencies would enable a larger set of observations to be used for constraint, which would then narrow the uncertainty further. Such an approach provides a rigorous pathway to improved model realism and reduced uncertainty that has so far not been achieved through the normal model development approach.
Publisher: Copernicus GmbH
Date: 08-08-2023
Abstract: Abstract. Aerosol radiative forcing uncertainty affects estimates of climate sensitivity and limits model skill in terms of making climate projections. Efforts to improve the representations of physical processes in climate models, including extensive comparisons with observations, have not significantly constrained the range of possible aerosol forcing values. A far stronger constraint, in particular for the lower (most-negative) bound, can be achieved using global mean energy balance arguments based on observed changes in historical temperature. Here, we show that structural deficiencies in a climate model, revealed as inconsistencies among observationally constrained cloud properties in the model, limit the effectiveness of observational constraint of the uncertain physical processes. We s le the uncertainty in 37 model parameters related to aerosols, clouds, and radiation in a perturbed parameter ensemble of the UK Earth System Model and evaluate 1 million model variants (different parameter settings from Gaussian process emulators) against satellite-derived observations over several cloudy regions. Our analysis of a very large set of model variants exposes model internal inconsistencies that would not be apparent in a small set of model simulations, of an order that may be evaluated during model-tuning efforts. Incorporating observations associated with these inconsistencies weakens any forcing constraint because they require a wider range of parameter values to accommodate conflicting information. We show that, by neglecting variables associated with these inconsistencies, it is possible to reduce the parametric uncertainty in global mean aerosol forcing by more than 50 %, constraining it to a range (around −1.3 to −0.1 W m−2) in close agreement with energy balance constraints. Our estimated aerosol forcing range is the maximum feasible constraint using our structurally imperfect model and the chosen observations. Structural model developments targeted at the identified inconsistencies would enable a larger set of observations to be used for constraint, which would then very likely narrow the uncertainty further and possibly alter the central estimate. Such an approach provides a rigorous pathway to improved model realism and reduced uncertainty that has so far not been achieved through the normal model development approach.
Publisher: Copernicus GmbH
Date: 23-03-2022
DOI: 10.5194/ESD-2022-11
Abstract: Abstract. An observed southward shift in tropical rainfall over land between 1950 and 1985, followed by a weaker recovery post 1985, has been attributed to anthropogenic aerosol radiative forcing and cooling of the Northern Hemisphere relative to the Southern Hemisphere. We might therefore expect models that have a strong historic hemispheric contrast in aerosol forcing to simulate a further northward tropical rainfall shift in the near-term future when anthropogenic aerosol emission reductions will predominantly warm the Northern Hemisphere. We investigate this paradigm using a perturbed parameter ensemble (PPE) of transient coupled ocean-atmosphere climate simulations that span a range of aerosol radiative forcing comparable to multi-model studies. In the 20th century, in our single-model ensemble, we find no relationship between the magnitude of pre-industrial to 1975 inter-hemispheric anthropogenic aerosol radiative forcing and tropical precipitation shifts. Instead, tropical precipitation shifts are associated with major volcanic eruptions and are strongly affected by internal variability. However, we do find a relationship between the magnitude of pre-industrial to 2005 inter-hemispheric anthropogenic aerosol radiative forcing and future tropical precipitation shifts over 2006 to 2060 under scenario RCP8.5. Our results suggest that projections of tropical precipitation shifts will be improved by reducing aerosol radiative forcing uncertainty, but predictive gains may be offset by temporary shifts in tropical precipitation caused by future major volcanic eruptions.
Publisher: Copernicus GmbH
Date: 21-11-2019
Publisher: IOP Publishing
Date: 10-2017
Publisher: American Meteorological Society
Date: 11-2019
Abstract: Uncertainty in radiative forcing caused by aerosol–cloud interactions is about twice as large as for CO 2 and remains the least well understood anthropogenic contribution to climate change. A major cause of uncertainty is the poorly quantified state of aerosols in the pristine preindustrial atmosphere, which defines the baseline against which anthropogenic effects are calculated. The Southern Ocean is one of the few remaining near-pristine aerosol environments on Earth, but there are very few measurements to help evaluate models. The Antarctic Circumnavigation Expedition: Study of Preindustrial-like Aerosols and their Climate Effects (ACE-SPACE) took place between December 2016 and March 2017 and covered the entire Southern Ocean region (Indian, Pacific, and Atlantic Oceans length of ship track ,000 km) including previously unexplored areas. In situ measurements covered aerosol characteristics [e.g., chemical composition, size distributions, and cloud condensation nuclei (CCN) number concentrations], trace gases, and meteorological variables. Remote sensing observations of cloud properties, the physical and microbial ocean state, and back trajectory analyses are used to interpret the in situ data. The contribution of sea spray to CCN in the westerly wind belt can be larger than 50%. The abundance of methanesulfonic acid indicates local and regional microbial influence on CCN abundance in Antarctic coastal waters and in the open ocean. We use the in situ data to evaluate simulated CCN concentrations from a global aerosol model. The extensive, available ACE-SPACE dataset ( ommunities/spi-ace?page=1& size=20 ) provides an unprecedented opportunity to evaluate models and to reduce the uncertainty in radiative forcing associated with the natural processes of aerosol emission, formation, transport, and processing occurring over the pristine Southern Ocean.
Publisher: Copernicus GmbH
Date: 11-04-2023
Publisher: American Geophysical Union (AGU)
Date: 11-2019
DOI: 10.1029/2019MS001628
Abstract: Tropospheric aerosol radiative forcing has persisted for many years as one of the major causes of uncertainty in global climate model simulations. To s le the range of plausible aerosol and atmospheric states and perform robust statistical analyses of the radiative forcing, it is important to account for the combined effects of many sources of model uncertainty, which is rarely done due to the high computational cost. This paper describes the designs of two ensembles of the Met Office Hadley Centre Global Environment Model‐U.K. Chemistry and Aerosol global climate model and provides the first analyses of the uncertainties in aerosol radiative forcing and their causes. The first ensemble was designed to comprehensively s le uncertainty in the aerosol state, while the other s les additional uncertainties in the physical model related to clouds, humidity, and radiation, thereby allowing an analysis of uncertainty in the aerosol effective radiative forcing. Each ensemble consists of around 200 simulations of the preindustrial and present‐day atmospheres. The uncertainty in aerosol radiative forcing in our ensembles is comparable to the range of estimates from multimodel intercomparison projects. The mean aerosol effective radiative forcing is −1.45 W/m 2 (credible interval of −2.07 to −0.81 W/m 2 ), which encompasses but is more negative than the −1.17 W/m 2 in the 2013 Atmospheric Chemistry and Climate Model Intercomparison Project and −0.90 W/m 2 in the Intergovernmental Panel on Climate Change Fifth Assessment Report. The ensembles can be used to reduce aerosol radiative forcing uncertainty by challenging them with multiple measurements as well as to isolate potential causes of multimodel differences.
Publisher: Copernicus GmbH
Date: 11-04-2023
DOI: 10.5194/EGUSPHERE-2023-604
Abstract: Abstract. Anthropogenic emissions of aerosols and precursor compounds are known to significantly affect the energy balance of the Earth-atmosphere system, alter the formation of clouds and precipitation, and have substantial impact on human health and the environment. Global models are an essential tool for examining the impacts of these emissions. In this study, we examine the sensitivity of model results to the assumed height of SO2 injection, seasonality of SO2 and BC emissions, and the assumed fraction of SO2 emissions that is injected into the atmosphere as SO4 in 11 climate and chemistry models, including both chemical transport models and the atmospheric component of Earth system models. We find a large variation in atmospheric lifetime across models for SO2, SO4, and BC, with a particularly large relative variation for SO2, which indicates that fundamental aspects of atmospheric sulfur chemistry remain uncertain. Of the perturbations examined in this study, the assumed height of SO2 injection had the largest overall impacts, particularly on global mean net radiative flux (maximum difference of -0.35 W m-2), SO2 lifetime over northern hemisphere land (maximum difference of 0.8 days), surface SO2 concentration (up to 59 % decrease), and surface sulfate concentration (up to 23 % increase). Emitting SO2 at height consistently increased SO2 and SO4 column burdens and shortwave cooling, with varying magnitudes, but had inconsistent effects across models on the sign of the change in implied cloud forcing. The assumed SO4 emission fraction also had a significant impact on net radiative flux and surface sulfate concentration. Because these properties are not standardized across models this is a source of inter-model ersity typically neglected in model intercomparisons. These results imply a need to assure that anthropogenic emission injection height and SO4 emission fraction are accurately and consistently represented in global models.
Publisher: Copernicus GmbH
Date: 04-12-2019
Publisher: Copernicus GmbH
Date: 21-11-2019
DOI: 10.5194/ACP-2019-834
Abstract: Abstract. The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol–climate model. The study uses 1 million variants of the HadGEM3-UKCA climate model that s le 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulphate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ± 1σ (standard deviation) range of global annual mean direct radiative forcing, RFari, is reduced by 33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI) is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual mean aerosol–cloud radiative forcing, RFaci, the ± 1σ range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by 6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined representativeness error associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For ex le, constraints using either sulphate or PM2.5 measurements in idually result in RFari ± 1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be over-confident.
Publisher: American Geophysical Union (AGU)
Date: 16-12-2014
DOI: 10.1002/2014GL062029
Publisher: Copernicus GmbH
Date: 18-06-2018
Abstract: Abstract. Simple climate models can be valuable if they are able to replicate aspects of complex fully coupled earth system models. Larger ensembles can be produced, enabling a probabilistic view of future climate change. A simple emissions-based climate model, FAIR, is presented, which calculates atmospheric concentrations of greenhouse gases and effective radiative forcing (ERF) from greenhouse gases, aerosols, ozone and other agents. Model runs are constrained to observed temperature change from 1880 to 2016 and produce a range of future projections under the Representative Concentration Pathway (RCP) scenarios. The constrained estimates of equilibrium climate sensitivity (ECS), transient climate response (TCR) and transient climate response to cumulative CO2 emissions (TCRE) are 2.86 (2.01 to 4.22) K, 1.53 (1.05 to 2.41) K and 1.40 (0.96 to 2.23) K (1000 GtC)−1 (median and 5–95 % credible intervals). These are in good agreement with the likely Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) range, noting that AR5 estimates were derived from a combination of climate models, observations and expert judgement. The ranges of future projections of temperature and ranges of estimates of ECS, TCR and TCRE are somewhat sensitive to the prior distributions of ECS∕TCR parameters but less sensitive to the ERF from a doubling of CO2 or the observational temperature dataset used to constrain the ensemble. Taking these sensitivities into account, there is no evidence to suggest that the median and credible range of observationally constrained TCR or ECS differ from climate model-derived estimates. The range of temperature projections under RCP8.5 for 2081–2100 in the constrained FAIR model ensemble is lower than the emissions-based estimate reported in AR5 by half a degree, owing to differences in forcing assumptions and ECS∕TCR distributions.
Publisher: Copernicus GmbH
Date: 03-2018
DOI: 10.5194/ACP-2018-175
Abstract: Abstract. Changes in aerosols cause a change in net top-of-the-atmosphere (ToA) short-wave and long-wave radiative fluxes, rapid adjustments in clouds, water vapour and temperature, and cause an effective radiative forcing (ERF) of the planetary energy budget. The erse sources of model uncertainty and the computational cost of running climate models make it difficult to isolate the main causes of aerosol ERF uncertainty and to understand how observations can be used to constrain it. We explore the aerosol ERF uncertainty by using fast model emulators to generate a very large set of aerosol-climate model variants that span the model uncertainty due to twenty-seven parameters related to atmospheric and aerosol processes. Sensitivity analyses shows that the uncertainty in the ToA flux is dominated (around 80 %) by uncertainties in the physical atmosphere model, particularly parameters that affect cloud reflectivity. However, uncertainty in the change in ToA flux caused by aerosol emissions over the industrial period (the aerosol ERF) is controlled by a combination of uncertainties in aerosol (around 60 %) and physical atmosphere (around 40 %) parameters. Four of the atmospheric and aerosol parameters that cause uncertainty in short-wave ToA flux (mostly parameters that directly scale cloud reflectivity, cloud water content or cloud droplet concentrations) also account for around 60% of the aerosol ERF uncertainty. The common causes of uncertainty mean that constraining the modelled planetary brightness to tightly match satellite observations changes the lower 95 % credible aerosol ERF value from −2.65 Wm−2 to −2.37 Wm−2. This suggests the strongest forcings (below around −2.4 Wm−2) are inconsistent with observations. These results show that, regardless of the fact that the ToA flux is an order of magnitude larger than the aerosol ERF, the observed flux can constrain the uncertainty in ERF because their values are connected by constrainable process parameters. The key to reducing the aerosol ERF uncertainty further will be to identify observations that can additionally constrain in idual parameter ranges and/or combined parameter effects, which can be achieved through sensitivity analysis of perturbed parameter ensembles.
Publisher: Springer Science and Business Media LLC
Date: 03-2017
Publisher: Copernicus GmbH
Date: 07-03-2018
DOI: 10.5194/ACP-2018-174
Abstract: Abstract. Observational constraint of simulated aerosol and cloud properties is an essential part of building trustworthy climate models for calculating aerosol radiative forcing. Models are usually tuned to achieve good agreement with observations, but tuning produces just one of many potential variants of a model, so the model uncertainty cannot be determined. Here we estimate the uncertainty in aerosol effective radiative forcing (ERF) in a tuned climate model by constraining 4 million variants of the HadGEM3-UKCA aerosol-climate model to match nine common observations (top-of-atmosphere shortwave flux, aerosol optical depth, PM2.5, cloud condensation nuclei, concentrations of sulphate, black carbon and organic carbon, as well as decadal trends in aerosol optical depth and surface shortwave radiation.) The model uncertainty is calculated by using a perturbed parameter ensemble that s les twenty-seven uncertainties in both the aerosol model and the physical climate model. Focusing over Europe, we show that the aerosol ERF uncertainty can be reduced by about 30 % by constraining it to the nine observations, demonstrating that producing climate models with an observationally plausible base state can contribute to narrowing the uncertainty in aerosol ERF. However, the uncertainty in the aerosol ERF after observational constraint is large compared to the typical spread of a multi-model ensemble. Our results therefore raise questions about whether the underlying multi-model uncertainty would be larger if similar approaches as adopted here were applied more widely. It is hoped that aerosol ERF uncertainty can be further reduced by introducing process-related constraints, however, any such results will be robust only if the enormous number of potential model variants is explored.
Publisher: American Meteorological Society
Date: 09-2015
Abstract: Regional patterns of aerosol radiative forcing are important for understanding climate change on decadal time scales. Uncertainty in aerosol forcing is likely to vary regionally and seasonally because of the short aerosol lifetime and heterogeneous emissions. Here the sensitivity of regional aerosol cloud albedo effect (CAE) forcing to 31 aerosol process parameters and emission fluxes is quantified between 1978 and 2008. The effects of parametric uncertainties on calculations of the balance of incoming and outgoing radiation are found to be spatially and temporally dependent. Regional uncertainty contributions of opposite sign cancel in global-mean forcing calculations, masking the regional importance of some parameters. Parameters that contribute little to uncertainty in Earth’s global energy balance during recent decades make significant contributions to regional forcing variance. Aerosol forcing sensitivities are quantified within 11 climatically important regions, where surface temperatures are thought to influence large-scale climate effects. Substantial simulated uncertainty in CAE forcing in the eastern Pacific leaves open the possibility that apparent shifts in the mean ENSO state may result from a forced aerosol signal on multidecadal time scales. A likely negative aerosol CAE forcing in the tropical North Atlantic calls into question the relationship between Northern Hemisphere aerosol emission reductions and CAE forcing of sea surface temperatures in the main Atlantic hurricane development region on decadal time scales. Simulated CAE forcing uncertainty is large in the North Pacific, suggesting that the role of the CAE in altering Pacific tropical storm frequency and intensity is also highly uncertain.
Publisher: American Geophysical Union (AGU)
Date: 20-07-2021
DOI: 10.1029/2020JD034342
Abstract: Monsoon precipitation affects nearly half of the world's population, but monsoon biases are a long‐standing problem in climate simulations. We apply dynamical nudging either globally or regionally to demonstrate the role of regional and remote circulation in generating Asian monsoon biases in an atmospheric general circulation model. Monsoon precipitation biases are substantially reduced in response to global nudging but may also be exacerbated over the warm oceanic equatorial areas because of unconstrained sub‐grid convection. Regional nudging over Asia appears to be more efficient than nudging outside Asia in reducing seasonal precipitation biases over eastern China and India. This suggests a predominant role of local circulation anomalies in generating monsoon precipitation errors in these regions. An exception is the summer precipitation bias over eastern China, which is more strongly controlled by remote circulation. Besides seasonal mean rainfall, nudging can also improve the simulated interannual and intraseasonal precipitation variability over the subtropics. This results in a better skill in reproducing the observed El Niño teleconnections to India and China and the monsoon onset date. Improved understanding of the origin of Asian monsoon biases and the contribution from regional and remote circulation advances our knowledge of the interplay between the Asian monsoon and large‐scale circulation, which can be beneficial to the simulation and interpretation of monsoon projections.
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-13286
Abstract: & & Increasing anthropogenic aerosol emissions have been attributed as the main driver of an observed southward shift in tropical precipitation between the 1950s and 1980s. In the near-term future, anthropogenic aerosol emissions will decline which could drive a northward shift in tropical precipitation over the coming decades. We use a perturbed parameter ensemble (PPE) of transient coupled-ocean atmosphere simulations that span a range of aerosol radiative forcing to investigate the role of aerosol radiative forcing uncertainty on tropical precipitation shifts in the 20& sup& th& /sup& and 21& sup& st& /sup& centuries. We find no relationship between the strength of the hemispheric contrast in pre-industrial to 1975 anthropogenic aerosol radiative forcing and tropical precipitation shifts during the 20& sup& th& /sup& century. This result is in contrary to that from CMIP5, and we suspect internal variability plays a large role in why we do not see the expected relationship in our PPE. Tropical precipitation shifts are associated with major volcanic eruptions over the 20& sup& th& /sup& century. However, we do find a relationship between the hemispheric contrast in pre-industrial to 2005 anthropogenic aerosol radiative forcing and the magnitude of future tropical precipitation shifts over 2006 to 2060 under scenario RCP8.5. Overall, our results suggest that reduction in aerosol radiative forcing uncertainty would improve projections of future precipitation shifts, but any predictive gains would be offset if future major volcanic eruptions temporarily shift tropical precipitation.& &
Publisher: Copernicus GmbH
Date: 13-07-2018
Abstract: Abstract. Changes in aerosols cause a change in net top-of-the-atmosphere (ToA) short-wave and long-wave radiative fluxes rapid adjustments in clouds, water vapour and temperature and an effective radiative forcing (ERF) of the planetary energy budget. The erse sources of model uncertainty and the computational cost of running climate models make it difficult to isolate the main causes of aerosol ERF uncertainty and to understand how observations can be used to constrain it. We explore the aerosol ERF uncertainty by using fast model emulators to generate a very large set of aerosol–climate model variants that span the model uncertainty due to 27 parameters related to atmospheric and aerosol processes. Sensitivity analyses shows that the uncertainty in the ToA flux is dominated (around 80 %) by uncertainties in the physical atmosphere model, particularly parameters that affect cloud reflectivity. However, uncertainty in the change in ToA flux caused by aerosol emissions over the industrial period (the aerosol ERF) is controlled by a combination of uncertainties in aerosol (around 60 %) and physical atmosphere (around 40 %) parameters. Four atmospheric and aerosol parameters account for around 80 % of the uncertainty in short-wave ToA flux (mostly parameters that directly scale cloud reflectivity, cloud water content or cloud droplet concentrations), and these parameters also account for around 60 % of the aerosol ERF uncertainty. The common causes of uncertainty mean that constraining the modelled planetary brightness to tightly match satellite observations changes the lower 95 % credible aerosol ERF value from −2.65 to −2.37 W m−2. This suggests the strongest forcings (below around −2.4 W m−2) are inconsistent with observations. These results show that, regardless of the fact that the ToA flux is 2 orders of magnitude larger than the aerosol ERF, the observed flux can constrain the uncertainty in ERF because their values are connected by constrainable process parameters. The key to reducing the aerosol ERF uncertainty further will be to identify observations that can additionally constrain in idual parameter ranges and/or combined parameter effects, which can be achieved through sensitivity analysis of perturbed parameter ensembles.
Publisher: IOP Publishing
Date: 07-09-2020
Publisher: Wiley
Date: 30-01-2020
Publisher: Copernicus GmbH
Date: 23-03-2022
Publisher: Copernicus GmbH
Date: 28-03-2022
DOI: 10.5194/EGUSPHERE-EGU22-12007
Abstract: & & & span xml:lang=& quot EN-US& quot data-contrast=& quot auto& quot & & span data-ccp-parastyle-defn='{& quot ObjectId& quot :& quot c112871-d111-4339-b713-ce16d1de72eb124& quot ,& quot ClassId& quot :1073872969,& quot Properties& quot :[469775450,& quot Text body& quot ,201340122,& quot & quot ,134233614,& quot true& quot ,469778129,& quot Textbody& quot ,335559740,& quot & quot ,201341983,& quot & quot ,335559739,& quot & quot ,469778324,& quot Normal& quot ]}'& The transition from stratocumulus& /span& & span& to& /span& & span& cumulus clouds that takes place & /span& & span& as air is advected from the subtropics towards the equator causes a decrease in cloud radiative effect& /span& & span& , with cloud fraction halving from start to finish. & /span& & span& The transition is initiated by & /span& & span& increas& /span& & span& ing sea surface temperatures& /span& & span& , and & /span& & span& it is widely agreed that & /span& & span& the lower tropospheric stability plays a key role in the tim& /span& & span& ing of the transition.& /span& & span& In this work, we study the relative importance of five atmospheric initial cond& /span& & span& itions& /span& & span& :& /span& & span& specific humidity in the boundary layer and free troposphere, free tropospheric potential temperature, inversion height and initial aerosol distribution. & /span& & span& We& /span& & span& simulate& /span& & span& a & /span& & span& Lagrangian& /span& & span& trajectory of a stratocumulus-to-cumulus transition, & /span& & /span& & span xml:lang=& quot EN-GB& quot data-contrast=& quot none& quot & & span& using the Met Office/NERC cloud model coupled with a & /span& & span& bulk microphysics scheme and a radiation scheme. & /span& & span& From this base simulation we & /span& & span& make 60 perturbations to simulate the transition under different combinations of & /span& & span& the & /span& & span& atmospheric & /span& & span& initial & /span& & span& conditions& /span& & span& mentioned& /span& & span& . & /span& & /span& & span xml:lang=& quot EN-US& quot data-contrast=& quot auto& quot & & span& Additionally, we include a model parameter from the & /span& & span& Khairoutdinov& /span& & span& and Kogan & /span& & span& autoconversion& /span& & span& arameterisation& /span& & span& from 2000.& /span& & /span& & span xml:lang=& quot EN-GB& quot data-contrast=& quot none& quot & & span& We discuss here the relative importance of these so-called parameters, in particular the role of aerosol, and we explore whether a much faster transition by drizzle takes place in simulations with lower aerosol concentrations.& /span& & /span& & span& & & /span& & &
Publisher: Copernicus GmbH
Date: 13-08-2020
Abstract: Abstract. The effect of observational constraint on the ranges of uncertain physical and chemical process parameters was explored in a global aerosol–climate model. The study uses 1 million variants of the Hadley Centre General Environment Model version 3 (HadGEM3) that s le 26 sources of uncertainty, together with over 9000 monthly aggregated grid-box measurements of aerosol optical depth, PM2.5, particle number concentrations, sulfate and organic mass concentrations. Despite many compensating effects in the model, the procedure constrains the probability distributions of parameters related to secondary organic aerosol, anthropogenic SO2 emissions, residential emissions, sea spray emissions, dry deposition rates of SO2 and aerosols, new particle formation, cloud droplet pH and the diameter of primary combustion particles. Observational constraint rules out nearly 98 % of the model variants. On constraint, the ±1σ (standard deviation) range of global annual mean direct radiative forcing (RFari) is reduced by 33 % to −0.14 to −0.26 W m−2, and the 95 % credible interval (CI) is reduced by 34 % to −0.1 to −0.32 W m−2. For the global annual mean aerosol–cloud radiative forcing, RFaci, the ±1σ range is reduced by 7 % to −1.66 to −2.48 W m−2, and the 95 % CI by 6 % to −1.28 to −2.88 W m−2. The tightness of the constraint is limited by parameter cancellation effects (model equifinality) as well as the large and poorly defined “representativeness error” associated with comparing point measurements with a global model. The constraint could also be narrowed if model structural errors that prevent simultaneous agreement with different measurement types in multiple locations and seasons could be improved. For ex le, constraints using either sulfate or PM2.5 measurements in idually result in RFari±1σ ranges that only just overlap, which shows that emergent constraints based on one measurement type may be overconfident.
Publisher: Copernicus GmbH
Date: 28-08-2020
DOI: 10.5194/ACP-20-10063-2020
Abstract: Abstract. Aerosol measurements over the Southern Ocean are used to constrain aerosol–cloud interaction radiative forcing (RFaci) uncertainty in a global climate model. Forcing uncertainty is quantified using 1 million climate model variants that s le the uncertainty in nearly 30 model parameters. Measurements of cloud condensation nuclei and other aerosol properties from an Antarctic circumnavigation expedition strongly constrain natural aerosol emissions: default sea spray emissions need to be increased by around a factor of 3 to be consistent with measurements. Forcing uncertainty is reduced by around 7 % using this set of several hundred measurements, which is comparable to the 8 % reduction achieved using a erse and extensive set of over 9000 predominantly Northern Hemisphere measurements. When Southern Ocean and Northern Hemisphere measurements are combined, uncertainty in RFaci is reduced by 21 %, and the strongest 20 % of forcing values are ruled out as implausible. In this combined constraint, observationally plausible RFaci is around 0.17 W m−2 weaker (less negative) with 95 % credible values ranging from −2.51 to −1.17 W m−2 (standard deviation of −2.18 to −1.46 W m−2). The Southern Ocean and Northern Hemisphere measurement datasets are complementary because they constrain different processes. These results highlight the value of remote marine aerosol measurements.
Publisher: American Meteorological Society
Date: 09-2017
DOI: 10.1175/BAMS-D-15-00317.1
Abstract: The largest uncertainty in the historical radiative forcing of climate is caused by changes in aerosol particles due to anthropogenic activity. Sophisticated aerosol microphysics processes have been included in many climate models in an effort to reduce the uncertainty. However, the models are very challenging to evaluate and constrain because they require extensive in situ measurements of the particle size distribution, number concentration, and chemical composition that are not available from global satellite observations. The Global Aerosol Synthesis and Science Project (GASSP) aims to improve the robustness of global aerosol models by combining new methodologies for quantifying model uncertainty, to create an extensive global dataset of aerosol in situ microphysical and chemical measurements, and to develop new ways to assess the uncertainty associated with comparing sparse point measurements with low-resolution models. GASSP has assembled over 45,000 hours of measurements from ships and aircraft as well as data from over 350 ground stations. The measurements have been harmonized into a standardized format that is easily used by modelers and nonspecialist users. Available measurements are extensive, but they are biased to polluted regions of the Northern Hemisphere, leaving large pristine regions and many continental areas poorly s led. The aerosol radiative forcing uncertainty can be reduced using a rigorous model–data synthesis approach. Nevertheless, our research highlights significant remaining challenges because of the difficulty of constraining many interwoven model uncertainties simultaneously. Although the physical realism of global aerosol models still needs to be improved, the uncertainty in aerosol radiative forcing will be reduced most effectively by systematically and rigorously constraining the models using extensive syntheses of measurements.
Publisher: Copernicus GmbH
Date: 24-11-2022
DOI: 10.5194/EGUSPHERE-2022-1330
Abstract: Abstract. Aerosol radiative forcing uncertainty affects estimates of climate sensitivity and limits model skill at making climate projections. Efforts to improve the representations of physical processes in climate models, including extensive comparisons with observations, have not significantly constrained the range of possible aerosol forcing values. A far stronger constraint, in particular for the lower (most-negative) bound, can be achieved using global mean energy-balance arguments based on observed changes in historical temperature. Here, we show that structural deficiencies in a climate model, revealed as inconsistencies among observationally constrained cloud properties, limit the effectiveness of observational constraint of the uncertain physical processes. We s le uncertainty in 37 model parameters related to aerosols, clouds and radiation in a perturbed parameter ensemble of the UK Earth System Model and evaluate one million model variants (different parameter settings from Gaussian Process emulators) against satellite-derived observations over several cloudy regions. We show it is possible to reduce the parametric uncertainty in global mean aerosol forcing by more than 50 % to a range in close agreement with energy-balance constraints (around -1.3 to -0.1 W m-2). However, incorporating observations associated with model inconsistencies weakens the constraint because the inconsistencies introduce conflicting information about relationships between model parameter values and aerosol forcing. Our estimated aerosol forcing range is the maximum feasible constraint using these observations and our structurally imperfect model. Structural model developments, targeted at the inconsistencies identified here, would enable a larger set of observations to be used for constraint, which would then narrow the uncertainty further.
Publisher: Proceedings of the National Academy of Sciences
Date: 27-07-2020
Abstract: Enhancement of aerosol that can nucleate cloud droplets increases the droplet number concentration and albedo of clouds. This increases the amount of sunlight reflected to space. Uncertainty in how aerosol−cloud interactions over the industrial period have increased planetary albedo by this mechanism leads to significant uncertainty in climate projections. Our work presents a method for observationally constraining the change in albedo due to anthropogenic aerosol emissions: a hemispheric difference in remotely sensed cloud droplet number between the pristine Southern Ocean (a preindustrial proxy) and the polluted Northern Hemisphere. Application of this constraint to climate models reduces the range of estimated albedo change since industrialization and suggests current models underpredict cloud droplet number concentration in the preindustrial era.
Publisher: Copernicus GmbH
Date: 26-08-2022
Abstract: Abstract. An observed southward shift in tropical rainfall over land between 1950 and 1985, followed by a weaker recovery post-1985, has been attributed to anthropogenic aerosol radiative forcing and cooling of the Northern Hemisphere relative to the Southern Hemisphere. We might therefore expect models that have a strong historic hemispheric contrast in aerosol forcing to simulate a further northward tropical rainfall shift in the near-term future when anthropogenic aerosol emission reductions will predominantly warm the Northern Hemisphere. We investigate this paradigm using a perturbed parameter ensemble (PPE) of transient coupled ocean–atmosphere climate simulations that span a range of aerosol radiative forcing comparable to multi-model studies. In the 20th century, in our single-model ensemble, we find no relationship between the magnitude of pre-industrial to 1975 inter-hemispheric anthropogenic aerosol radiative forcing and tropical precipitation shifts. Instead, tropical precipitation shifts are associated with major volcanic eruptions and are strongly affected by internal variability. However, we do find a relationship between the magnitude of pre-industrial to 2005 inter-hemispheric anthropogenic aerosol radiative forcing and future tropical precipitation shifts over 2006 to 2060 under scenario RCP8.5. Our results suggest that projections of tropical precipitation shifts will be improved by reducing aerosol radiative forcing uncertainty, but predictive gains may be offset by temporary shifts in tropical precipitation caused by future major volcanic eruptions.
Publisher: Springer Science and Business Media LLC
Date: 06-05-2021
Publisher: Springer Science and Business Media LLC
Date: 11-2013
DOI: 10.1038/NATURE12674
Abstract: The effect of anthropogenic aerosols on cloud droplet concentrations and radiative properties is the source of one of the largest uncertainties in the radiative forcing of climate over the industrial period. This uncertainty affects our ability to estimate how sensitive the climate is to greenhouse gas emissions. Here we perform a sensitivity analysis on a global model to quantify the uncertainty in cloud radiative forcing over the industrial period caused by uncertainties in aerosol emissions and processes. Our results show that 45 per cent of the variance of aerosol forcing since about 1750 arises from uncertainties in natural emissions of volcanic sulphur dioxide, marine dimethylsulphide, biogenic volatile organic carbon, biomass burning and sea spray. Only 34 per cent of the variance is associated with anthropogenic emissions. The results point to the importance of understanding pristine pre-industrial-like environments, with natural aerosols only, and suggest that improved measurements and evaluation of simulated aerosols in polluted present-day conditions will not necessarily result in commensurate reductions in the uncertainty of forcing estimates.
Publisher: Copernicus GmbH
Date: 23-03-2020
DOI: 10.5194/EGUSPHERE-EGU2020-10202
Abstract: & & Anthropogenic aerosol emissions over the industrial period have caused a negative but highly uncertain radiative forcing. This negative radiative forcing has had a cooling effect mainly over the northern hemisphere, affecting the atmospheric interhemispheric energy balance. Consequently aerosols have been linked to observed dynamical responses over the industrial period that depend on the atmospheric interhemispheric energy balance, such as changes in the position of the Intertropical Convergence Zone (ITCZ) and resultant tropical precipitation shifts. However, over the course of the 21& sup& st& /sup& century anthropogenic aerosol emissions are predicted to decline. The reduction in anthropogenic aerosol emissions will cause a positive radiative forcing relative to present day, creating a warming effect in the northern hemisphere. Hence, if the strength of aerosol radiative forcing modulates the magnitude of shifts in the ITCZ, then the large uncertainty in aerosol radiative forcing will limit our understanding of how tropical precipitation will shift in the near-term future.& & & & We use a perturbed parameter ensemble (PPE) of a global coupled climate model to investigate the link between aerosol radiative forcing and ITCZ and tropical rainfall shifts in the near-term future. The PPE consists of 20 simulations of the UK Met Office& #8217 s GC3.05 model with parameters perturbed from a range of model schemes. The ensemble was designed to s le uncertainties in future changes, and as a result spans a range of aerosol radiative forcings.& & & & The PPE reveals both northward and southwards shifts in the ITCZ position across the ensemble in the latter half of the 20& sup& th& /sup& century and first half of the 21& sup& st& /sup& century, as well as changes in width and intensity of the ITCZ. We find a correlation between the shift in the ITCZ position and the magnitude of aerosol radiative forcing and AOD trends. However, the correlations in our ensemble are not as strong as those cited in previous studies that use multi-model ensembles. The potential causes of this difference are investigated. We also compare our model output to aerosol, cloud and radiation observations in attempt to identify the most plausible future aerosol-driven climate responses.& &
Publisher: Copernicus GmbH
Date: 16-07-2020
DOI: 10.5194/ESSD-12-1649-2020
Abstract: 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 0.24380/ads.1hj3y896 (Bellouin et al., 2020b).
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Leighton Regayre.