Olivier Dessens

Impact of perturbations to nitrogen oxide emissions from global aviation

The atmospheric response to perturbations in NO x emissions from global air traffic is investigated by performing a coherent set of sensitivity experiments. The importance of cruise altitude, size of the emission perturbation and geographical distribution of emissions is systematically analyzed using two global chemistry transport models and an off-line radiative transfer model. NO x emissions from a contemporary aircraft inventory have been used to assess the impact of global air traffic on ozone and methane. In further experiments the NO x emissions are perturbed, in turn, in 16 cruise altitude bands between 5 and 15 km altitude. In the p-TOMCAT model we diagnose an annual mean ozone increase of up to 6 ppbv and a decrease in the methane lifetime of 3% due to global air traffic in 2002. Associated radiative forcings of 30 mWm−2 for ozone and −19 mWm−2 for methane are diagnosed; a simple method is used to estimate the forcing due to the methane-induced ozone change and this yields an additional −11 mWm−2. Results show that up to the tropopause, ozone production efficiency and resulting impacts increase per emitted mass of NO x with the altitude of the perturbation. Between 11 and 15 km we find that the geographical location of the NO x emissions plays a crucial role in the potential O3 impact and lifetime change of CH4. We show that changes in flight routing in this altitude range can have significant consequences for O3 and CH4 concentrations. Overall, we demonstrate a linear relationship in the atmospheric response to small emission changes which can be used to predict the importance of perturbations about the reference aircraft emissions profile, provided the geographical distribution of the emissions is not altered significantly.

China’s air pollution reduction efforts may result in an increase in surface ozone levels in highly polluted areas

Abstract China, as a fast growing fossil-fuel-based economy, experiences increasing levels of air pollution. To tackle air pollution, China has taken the first steps by setting emission–reduction targets for nitrogen oxides (NOx) and sulphur dioxide (SO2) in the 11th and 12th Five Year Plans. This paper uses two models—the Energy–Environment–Economy Model at the Global level (E3MG) and the global Chemistry Transport Model pTOMCAT—to test the effects of these policies. If the policy targets are met, then the maximum values of 32 % and 45 % reductions below ‘business as usual’ in the monthly mean NOx and SO2 concentrations, respectively, will be achieved in 2015. However, a decrease in NOx concentrations in some highly polluted areas of East, North-East and South-East China can lead to up to a 10% increase in the monthly mean concentrations in surface ozone in 2015. Our study demonstrates an urgent need for the more detailed analysis of the impacts and designs of air pollution reduction guidelines for China.

A change in the calculated impact of supersonic aircraft NOx emissions on the atmosphere

New model calculations suggest that the potential impact on the atmosphere of a future fleet of supersonic aircraft, for the year 2015, is highly dependent upon the amount of nitrogen oxides (NO x ) emitted from the fleet. This result contrasts with the IPCC assessment which suggested that the impact of supersonic aircraft on the atmosphere was primarily through the role of water vapour emissions both on atmospheric ozone and climate change. These new findings are extremely important for atmospheric scientists, the aviation industry and policy makers, highlighting the importance of further development of low NO x combustors for supersonic aircraft, an aspect which has been largely ignored following the IPCC Special Report.

Climate change impacts on the energy system: a review of trends and gaps

Major transformation of the global energy system is required for climate change mitigation. However, energy demand patterns and supply systems are themselves subject to climate change impacts. These impacts will variously help and hinder mitigation and adaptation efforts, so it is vital they are well understood and incorporated into models used to study energy system decarbonisation pathways. To assess the current state of understanding of this topic and identify research priorities, this paper critically reviews the literature on the impacts of climate change on the energy supply system, summarising the regional coverage of studies, trends in their results and sources of disagreement. We then examine the ways in which these impacts have been represented in integrated assessment models of the electricity or energy system.Studies tend to agree broadly on impacts for wind, solar and thermal power stations. Projections for impacts on hydropower and bioenergy resources are more varied. Key uncertainties and gaps remain due to the variation between climate projections, modelling limitations and the regional bias of research interests. Priorities for future research include the following: further regional impact studies for developing countries; studies examining impacts of the changing variability of renewable resources, extreme weather events and combined hazards; inclusion of multiple climate feedback mechanisms in IAMs, accounting for adaptation options and climate model uncertainty.