Multimodel ensemble simulations of present-day and near-future tropospheric ozone

Journal of Geophysical Research Atmospheres (Impact Factor: 3.43). 04/2006; 111:D08301. DOI: 10.1029/2005JD006338
Source: OAI


Global tropospheric ozone distributions, budgets, and radiative forcings from an ensemble of 26 state-of-the-art atmospheric chemistry models have been intercompared and synthesized as part of a wider study into both the air quality and climate roles of ozone. Results from three 2030 emissions scenarios, broadly representing “optimistic,” “likely,” and “pessimistic” options, are compared to a base year 2000 simulation. This base case realistically represents the current global distribution of tropospheric ozone. A further set of simulations considers the influence of climate change over the same time period by forcing the central emissions scenario with a surface warming of around 0.7K. The use of a large multimodel ensemble allows us to identify key areas of uncertainty and improves the robustness of the results. Ensemble mean changes in tropospheric ozone burden between 2000 and 2030 for the 3 scenarios range from a 5% decrease, through a 6% increase, to a 15% increase. The intermodel uncertainty (±1 standard deviation) associated with these values is about ±25%. Model outliers have no significant influence on the ensemble mean results. Combining ozone and methane changes, the three scenarios produce radiative forcings of −50, 180, and 300 mW m−2, compared to a CO2 forcing over the same time period of 800–1100 mW m−2. These values indicate the importance of air pollution emissions in short- to medium-term climate forcing and the potential for stringent/lax control measures to improve/worsen future climate forcing. The model sensitivity of ozone to imposed climate change varies between models but modulates zonal mean mixing ratios by ±5 ppbv via a variety of feedback mechanisms, in particular those involving water vapor and stratosphere-troposphere exchange. This level of climate change also reduces the methane lifetime by around 4%. The ensemble mean year 2000 tropospheric ozone budget indicates chemical production, chemical destruction, dry deposition and stratospheric input fluxes of 5100, 4650, 1000, and 550 Tg(O3) yr−1, respectively. These values are significantly different to the mean budget documented by the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report (TAR). The mean ozone burden (340 Tg(O3)) is 10% larger than the IPCC TAR estimate, while the mean ozone lifetime (22 days) is 10% shorter. Results from individual models show a correlation between ozone burden and lifetime, and each model's ozone burden and lifetime respond in similar ways across the emissions scenarios. The response to climate change is much less consistent. Models show more variability in the tropics compared to midlatitudes. Some of the most uncertain areas of the models include treatments of deep tropical convection, including lightning NO x production; isoprene emissions from vegetation and isoprene's degradation chemistry; stratosphere-troposphere exchange; biomass burning; and water vapor concentrations.

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    • "As soon as variations occur, they have to detect the stress and turn on a whole battery of mechanisms leading to acclimation. Nowadays, due to anthropic activities, ozone (O 3 ) is a more and more widespread pollutant with concentration peaks usually occurring in spring and summer, and a constant increase of its ground levels since the pre-industrial period (Stevenson et al., 2006). O 3 affects plants in different manners, depending on its concentration (Renaut et al., 2009). "
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    • "Among all explanations, it is crucial to note that the present findings underline a potential global warming-related ecotoxicological risk for aquatic organisms, mainly derived from the toxicity variations of single or more complex mixtures of environmental pollutants. Therefore, this study supports the growing body of evidence that rising temperatures will have broad negative impacts on the distribution and toxicity of environmental contaminants (Macdonald et al., 2003, 2005; Knowlton et al., 2004; Knowlton and Kinney, 2004; Dentener et al., 2006; Stevenson et al., 2006; Bell et al., 2007; Buckman et al., 2007; Patra et al., 2007; Schiedek et al., 2007; Noyes et al., 2009). Further implementations in terms of experimental studies and modelling are needed to test various scenarios concerning transport , transfer, bioavailability as well as the final fate of all environmentally relevant pollutants, assessing the impacts on fitness and population/ecosystem effects on key species (Wu, 1995; Vaughan and Smith, 1996; Mezcua et al., 2006; Sarmah et al., 2006). "

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    • "The increase was, however, somewhat slower during the 1990s in comparison with the 1970s and 1980s. The rise of the background ozone levels in the future was also predicted by Stevenson et al. (2006) by as much as 5 to 16 %. The expected rise of the ozone levels in the region was one of the arguments for starting the TOR-subproject of EUROTRAC in 1988. "
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