Evaluation of climate model aerosol trends with ground-based observations over the last two decades – an AeroCom and CMIP6 analysis

Mortier, Augustin; Gliß, Jonas; Schulz, Mıchael; Aas, Wenche; Andrews, Elisabeth; Bian, Huisheng; Chin, Mian; Ginoux, Paul; Hand, J. L.; Holben, B. N.; Zhang, Hua; Kipling, Zak; Kirkevåg, Alf; Laj, Paolo; Lurton, Thibault; Myhre, Gunnar; Neubauer, David; Olivié, Dirk; Salzen, Knut von; Tilmes, Simon

doi:10.5194/acp-2019-1203

Cited by 4 publications

(8 citation statements)

References 32 publications

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“…S22), potentially due to land-use vegetation change as UKESM1-0-LL has dynamic vegetation coupled to BVOC emissions (Table S1 in the Supplement). This could also reduce PM 2.5 concentrations over this region because monoterpene emissions are the main precursor to SOA formation in UKESM1-0-LL (Mulcahy et al, 2020).…”

Section: Surface Pm 25mentioning

confidence: 99%

Historical and future changes in air pollutants from CMIP6 models

et al. 2020

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Abstract. Poor air quality is currently responsible for large impacts on human health across the world. In addition, the air pollutants ozone (O3) and particulate matter less than 2.5 µm in diameter (PM2.5) are also radiatively active in the atmosphere and can influence Earth's climate. It is important to understand the effect of air quality and climate mitigation measures over the historical period and in different future scenarios to ascertain any impacts from air pollutants on both climate and human health. The Coupled Model Intercomparison Project Phase 6 (CMIP6) presents an opportunity to analyse the change in air pollutants simulated by the current generation of climate and Earth system models that include a representation of chemistry and aerosols (particulate matter). The shared socio-economic pathways (SSPs) used within CMIP6 encompass a wide range of trajectories in precursor emissions and climate change, allowing for an improved analysis of future changes to air pollutants. Firstly, we conduct an evaluation of the available CMIP6 models against surface observations of O3 and PM2.5. CMIP6 models consistently overestimate observed surface O3 concentrations across most regions and in most seasons by up to 16 ppb, with a large diversity in simulated values over Northern Hemisphere continental regions. Conversely, observed surface PM2.5 concentrations are consistently underestimated in CMIP6 models by up to 10 µg m−3, particularly for the Northern Hemisphere winter months, with the largest model diversity near natural emission source regions. The biases in CMIP6 models when compared to observations of O3 and PM2.5 are similar to those found in previous studies. Over the historical period (1850–2014) large increases in both surface O3 and PM2.5 are simulated by the CMIP6 models across all regions, particularly over the mid to late 20th century, when anthropogenic emissions increase markedly. Large regional historical changes are simulated for both pollutants across East and South Asia with an annual mean increase of up to 40 ppb for O3 and 12 µg m−3 for PM2.5. In future scenarios containing strong air quality and climate mitigation measures (ssp126), annual mean concentrations of air pollutants are substantially reduced across all regions by up to 15 ppb for O3 and 12 µg m−3 for PM2.5. However, for scenarios that encompass weak action on mitigating climate and reducing air pollutant emissions (ssp370), annual mean increases in both surface O3 (up 10 ppb) and PM2.5 (up to 8 µg m−3) are simulated across most regions, although, for regions like North America and Europe small reductions in PM2.5 are simulated due to the regional reduction in precursor emissions in this scenario. A comparison of simulated regional changes in both surface O3 and PM2.5 from individual CMIP6 models highlights important regional differences due to the simulated interaction of aerosols, chemistry, climate and natural emission sources within models. The projection of regional air pollutant concentrations from the latest climate and Earth system models used within CMIP6 shows that the particular future trajectory of climate and air quality mitigation measures could have important consequences for regional air quality, human health and near-term climate. Differences between individual models emphasise the importance of understanding how future Earth system feedbacks influence natural emission sources, e.g. response of biogenic emissions under climate change.

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Section: Surface Pm 25mentioning

confidence: 99%

Historical and future changes in air pollutants from CMIP6 models

et al. 2020

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“…It also provides an overview of the variability of the variables, and of some additional derived variables from the collection of data for the reference year 2017. The present paper is jointly written with companion papers, three of which (Collaud Coen et al, 2020a;Gliß et al, 2020 andMortier et al, 2020) are in review in 2020 in parallel with this paper. Gliß et al (2020) and Mortier et al (2020) also belong to the Ae-roCom initiative for IPCC.…”

Section: Scope Of the Papermentioning

confidence: 99%

“…The present paper is jointly written with companion papers, three of which (Collaud Coen et al, 2020a;Gliß et al, 2020 andMortier et al, 2020) are in review in 2020 in parallel with this paper. Gliß et al (2020) and Mortier et al (2020) also belong to the Ae-roCom initiative for IPCC. The papers are the following.…”

Section: Scope Of the Papermentioning

confidence: 99%

“…-Additional papers are in preparation to analyse the variability of physical properties and to investigate the variability of carbonaceous aerosol using continuous observations worldwide. Some preliminary information on trends and comparisons with models that are further developed in Collaud Coen et al (2020a), Gliß et al (2020) and Mortier et al (2020) are presented in this paper. Additional manuscripts are in preparation to further investigate variability of the optical and physical properties.…”

Section: Scope Of the Papermentioning

confidence: 99%

“…The recent generation of AeroCom models has been asked to provide additional diagnostics on dry scattering and absorption coefficients at ground level. These are currently being analysed by the two companion papers of Gliß et al (2020) and Mortier et al (2020) using 14 model simulations of present-day (2010 emissions and meteorology) to construct an ensemble mean AeroCom model and aerosol information extracted from SARGAN surface sites. For a detailed analysis of comparison for variability and trends, readers can refer to the two companion papers.…”

Section: Comparison With Aerocom Model Outputs For Optical Propertiesmentioning

confidence: 99%

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A global analysis of climate-relevant aerosol properties retrieved from the network of GAW near-surface observatories

Laj¹,

Bigi²,

Coen³

et al. 2020

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<p>Aerosol particles are essential constituents of the Earth&#8217;s atmosphere, impacting the earth radiation balance directly by scattering and absorbing solar radiation, and indirectly by acting as cloud condensation nuclei. In contrast to most greenhouse gases, aerosol particles have short atmospheric residence time resulting in a highly heterogeneous distribution in space and time. There is a clear need to document this variability at regional scale through observations involving, in particular, the in-situ near-surface segment of the atmospheric observations system. This paper will provide the widest effort so far to document variability of climate-relevant in-situ aerosol properties (namely wavelength dependent particle light scattering and absorption coefficients, particle number concentration and particle number size distribution) from all sites connected to the Global Atmosphere Watch network. High quality data from more than 90 stations worldwide have been collected and controlled for quality and are reported for a reference year in 2017, providing a very extended and robust view of the variability of these variables worldwide. The range of variability observed worldwide for light scattering and absorption coefficients, single scattering albedo and particle number concentration are presented together with preliminary information on their long-term trends and comparison with model simulation for the different stations. The scope of the present paper is also to provide the necessary suite of information including data provision procedures, quality control and analysis, data policy and usage of the ground-based aerosol measurements network. It delivers to users of the World Data Centre on Aerosol, the required confidence in data products in the form of a fully-characterized value chain, including uncertainty estimation and requirements for contributing to the global climate monitoring system.</p>

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Multidecadal trend analysis of in situ aerosol radiative properties around the world

et al. 2020

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Abstract. In order to assess the evolution of aerosol parameters affecting climate change, a long-term trend analysis of aerosol optical properties was performed on time series from 52 stations situated across five continents. The time series of measured scattering, backscattering and absorption coefficients as well as the derived single scattering albedo, backscattering fraction, scattering and absorption Ångström exponents covered at least 10 years and up to 40 years for some stations. The non-parametric seasonal Mann–Kendall (MK) statistical test associated with several pre-whitening methods and with Sen's slope was used as the main trend analysis method. Comparisons with general least mean square associated with autoregressive bootstrap (GLS/ARB) and with standard least mean square analysis (LMS) enabled confirmation of the detected MK statistically significant trends and the assessment of advantages and limitations of each method. Currently, scattering and backscattering coefficient trends are mostly decreasing in Europe and North America and are not statistically significant in Asia, while polar stations exhibit a mix of increasing and decreasing trends. A few increasing trends are also found at some stations in North America and Australia. Absorption coefficient time series also exhibit primarily decreasing trends. For single scattering albedo, 52 % of the sites exhibit statistically significant positive trends, mostly in Asia, eastern/northern Europe and the Arctic, 22 % of sites exhibit statistically significant negative trends, mostly in central Europe and central North America, while the remaining 26 % of sites have trends which are not statistically significant. In addition to evaluating trends for the overall time series, the evolution of the trends in sequential 10-year segments was also analyzed. For scattering and backscattering, statistically significant increasing 10-year trends are primarily found for earlier periods (10-year trends ending in 2010–2015) for polar stations and Mauna Loa. For most of the stations, the present-day statistically significant decreasing 10-year trends of the single scattering albedo were preceded by not statistically significant and statistically significant increasing 10-year trends. The effect of air pollution abatement policies in continental North America is very obvious in the 10-year trends of the scattering coefficient – there is a shift to statistically significant negative trends in 2009–2012 for all stations in the eastern and central USA. This long-term trend analysis of aerosol radiative properties with a broad spatial coverage provides insight into potential aerosol effects on climate changes.

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Evaluation of climate model aerosol trends with ground-based observations over the last two decades – an AeroCom and CMIP6 analysis

Cited by 4 publications

References 32 publications

Historical and future changes in air pollutants from CMIP6 models

Historical and future changes in air pollutants from CMIP6 models

A global analysis of climate-relevant aerosol properties retrieved from the network of GAW near-surface observatories

Multidecadal trend analysis of in situ aerosol radiative properties around the world

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