Tropospheric ozone in CMIP6 simulations Griffiths, Paul T; Murray, Lee T; Zeng, Guang ...
Atmospheric chemistry and physics,
03/2021, Letnik:
21, Številka:
5
Journal Article
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The evolution of tropospheric ozone from 1850 to 2100 has been studied using data from Phase 6 of the Coupled Model Intercomparison Project (CMIP6). We evaluate long-term changes using coupled ...atmosphere–ocean chemistry–climate models, focusing on the CMIP Historical and ScenarioMIP ssp370 experiments, for which detailed tropospheric-ozone diagnostics were archived. The model ensemble has been evaluated against a suite of surface, sonde and satellite observations of the past several decades and found to reproduce well the salient spatial, seasonal and decadal variability and trends. The multi-model mean tropospheric-ozone burden increases from 247 ± 36 Tg in 1850 to a mean value of 356 ± 31 Tg for the period 2005–2014, an increase of 44 %. Modelled present-day values agree well with previous determinations (ACCENT: 336 ± 27 Tg; Atmospheric Chemistry and Climate Model Intercomparison Project, ACCMIP: 337 ± 23 Tg; Tropospheric Ozone Assessment Report, TOAR: 340 ± 34 Tg). In the ssp370 experiments, the ozone burden increases to 416 ± 35 Tg by 2100. The ozone budget has been examined over the same period using lumped ozone production (PO3) and loss (LO3) diagnostics. Both ozone production and chemical loss terms increase steadily over the period 1850 to 2100, with net chemical production (PO3-LO3) reaching a maximum around the year 2000. The residual term, which contains contributions from stratosphere–troposphere transport reaches a minimum around the same time before recovering in the 21st century, while dry deposition increases steadily over the period 1850–2100. Differences between the model residual terms are explained in terms of variation in tropopause height and stratospheric ozone burden.
Biogenic volatile organic compounds (BVOCs) affect climate via changes to aerosols, aerosol-cloud interactions (ACI), ozone and methane. BVOCs exhibit dependence on climate (causing a feedback) and ...land use but there remains uncertainty in their net climatic impact. One factor is the description of BVOC chemistry. Here, using the earth-system model UKESM1, we quantify chemistry's influence by comparing the response to doubling BVOC emissions in the pre-industrial with standard and state-of-science chemistry. The net forcing (feedback) is positive: ozone and methane increases and ACI changes outweigh enhanced aerosol scattering. Contrary to prior studies, the ACI response is driven by cloud droplet number concentration (CDNC) reductions from suppression of gas-phase SO
oxidation. With state-of-science chemistry the feedback is 43% smaller as lower oxidant depletion yields smaller methane increases and CDNC decreases. This illustrates chemistry's significant influence on BVOC's climatic impact and the more complex pathways by which BVOCs influence climate than currently recognised.
Long-term exposure to ambient ozone (O3) can lead to a series of chronic diseases and associated premature deaths, and thus population-level environmental health studies hanker after the ...high-resolution surface O3 concentration database. In response to this demand, we innovatively construct a space–time Bayesian neural network parametric regressor to fuse TOAR historical observations, CMIP6 multimodel simulation ensemble, population distributions, land cover properties, and emission inventories altogether and downscale to 10 km × 10 km spatial resolution with high methodological reliability (R 2 = 0.89–0.97, RMSE = 1.97–3.42 ppbV), fair prediction accuracy (R 2 = 0.69–0.77, RMSE = 5.63–7.97 ppbV), and commendable spatiotemporal extrapolation capabilities (R 2 = 0.62–0.76, RMSE = 5.38–11.7 ppbV). Based on our predictions in 8-h maximum daily average metric, the rural-site surface O3 are 15.1±7.4 ppbV higher than urban globally averaged across 30 historical years during 1990–2019, with developing countries being of the most evident differences. The globe-wide urban surface O3 are climbing by 1.9±2.3 ppbV per decade, except for the decreasing trends in eastern United States. On the other hand, the global rural surface O3 tend to be relatively stable, except for the rising tendencies in China and India. Using CMIP6 model simulations directly without urban–rural differentiation will lead to underestimations of population O3 exposure by 2.0±0.8 ppbV averaged over each historical year. Our original Bayesian neural network framework contributes to the deep-learning-driven environmental studies methodologically by providing a brand-new feasible way to realize data fusion and downscaling, which maintains high interpretability by conforming to the principles of spatial statistics without compromising the prediction accuracy. Moreover, the 30-year highly spatial resolved monthly surface O3 database with multiple metrics fills in the literature gap for long-term surface O3 exposure tracing.
Forestation is widely proposed for carbon dioxide (CO
) removal, but its impact on climate through changes to atmospheric composition and surface albedo remains relatively unexplored. We assessed ...these responses using two Earth system models by comparing a scenario with extensive global forest expansion in suitable regions to other plausible futures. We found that forestation increased aerosol scattering and the greenhouse gases methane and ozone following increased biogenic organic emissions. Additionally, forestation decreased surface albedo, which yielded a positive radiative forcing (i.e., warming). This offset up to a third of the negative forcing from the additional CO
removal under a 4°C warming scenario. However, when forestation was pursued alongside other strategies that achieve the 2°C Paris Agreement target, the offsetting positive forcing was smaller, highlighting the urgency for simultaneous emission reductions.
Editor’s summaryForestation is considered a good way to sequester atmospheric carbon dioxide and cool climate, but its impact on climate is more complex than just its effects through carbon capture. ...Weber et al. explored the impacts of forestation on climate by quantifying its influence on surface albedo and atmospheric composition (see the Perspective by Hayman). They found that the combination of decreased reflection and increased aerosol scattering of incident sunlight offsets about one-third of the cooling by carbon dioxide removal that forestation produces. —H. Jesse Smith
We present an assessment of the impacts on atmospheric composition and radiative forcing of short-lived pollutants following worldwide decrease in anthropogenic activity and emissions comparable to ...what has occurred in response to the COVID-19 pandemic, using the global composition-climate model UKCA. Changes in emissions reduce tropospheric hydroxyl radical and ozone burdens, increasing methane lifetime. Reduced SO emissions and oxidising capacity lead to a decrease in the sulphate aerosol burden and increase in aerosol particle size, with accompanying reductions to cloud droplet number concentration. However, large reductions in black carbon emissions increase the albedo of aerosols. Overall, the changes in ozone and aerosol direct effects (neglecting aerosol-cloud interactions) result in an instantaneous radiative forcing of -31 to -74 mWm . Upon cessation of emission reductions the short-lived climate forcers rapidly return to pre-COVID levels, meaning these changes are unlikely to have lasting impacts on climate assuming emissions return to pre-intervention levels.
We document the implementation of the Common Representative
Intermediates Mechanism version 2, reduction 5 (CRIv2-R5)
into the United Kingdom Chemistry and Aerosol model
(UKCA) version 10.9. The ...mechanism is merged with the
stratospheric chemistry already used by the StratTrop mechanism,
as used in UKCA and the UK Earth System Model (UKESM1),
to create a new CRI-Strat mechanism. CRI-Strat simulates a
more comprehensive treatment of non-methane volatile organic
compounds (NMVOCs) and provides traceability with the Master
Chemical Mechanism (MCM). In total, CRI-Strat simulates the
chemistry of 233 species competing in 613 reactions (compared
to 87 species and 305 reactions in the existing StratTrop
mechanism). However, while more than twice as complex than
StratTrop, the new mechanism is only 75% more computationally
expensive. CRI-Strat is evaluated against an array of
in situ and remote sensing observations and simulations
using the StratTrop mechanism in the UKCA model. It is found
to increase production of ozone near the surface, leading to
higher ozone concentrations compared to surface observations.
However, ozone loss is also greater in CRI-Strat, leading to
less ozone away from emission sources and a similar tropospheric
ozone burden compared to StratTrop. CRI-Strat also produces more
carbon monoxide than StratTrop, particularly downwind of biogenic
VOC emission sources, but has lower burdens of nitrogen oxides
as more is converted into reservoir species. The changes to
tropospheric ozone and nitrogen budgets are sensitive to the
treatment of NMVOC emissions, highlighting the need to reduce
uncertainty in these emissions to improve representation
of tropospheric chemical composition.
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