Health Climate Change impacts report card technical paper 3: Climate Change Impacts on Human Health through its effect on Air Quality

The World Health Organization has recently reported that evidence has strengthened for adverse health effects of the surface pollutants ozone (O3) and particulate matter (PM). In Europe, emissions controls have resulted in declining trends of many emitted species. However, due to the complexities of the processes linking emissions and air quality, reductions in local or regional emissions do not always produce a corresponding fall in atmospheric concentrations. Hence, it is not possible to clearly attribute effects of emissions relative to effects of meteorology and climate on air quality, or to identify how health burdens have changed in recent decades, due to observable climate change. There is considerable literature, including the Intergovernmental Panel on Climate Change’s (IPCC) 5th assessment report (AR5) that assigns confidence statements (as given below) to their findings, on the effects of climate change on O3 but far fewer studies on the effects of climate change on PM concentrations. This leads to low confidence in the overall impact of climate change on PM2.5. A number of studies have examined future climate and emissions changes and there is consensus that the impact of emission changes on air quality in the near-term will outweigh that due to climate change (medium confidence). Under the IPCC AR5 Representative Concentration Pathways (RCPs), O3 averaged over Europe is expected to decrease under all scenarios due to higher water vapour concentrations, except under RCP8.5 when high methane (CH4) emissions offset this decrease (high confidence). In polluted areas with high levels of nitrogen oxides (NOx), elevated surface temperatures are likely to enhance chemical reaction rates and increase emissions, increasing mean surface O3 (medium confidence).Air pollution episodes are associated with stagnation events and sometimes heat waves. Air quality during the 2003 heatwave over Europe has been examined in numerous studies and mechanisms for enhancing O3 have been identified. Anthropogenic climate change has increased the near-term risk of heat waves (high confidence). However, projections of changes in stagnation events associated with winter and summer air pollution episodes remain highly uncertain. A number of modelling studies suggest that uniformly elevated temperatures due to climate change will also increase peak O3 and PM concentrations (medium confidence), but there is large variability in the patterns and incidences of these events across the studies.Recent studies have sought to evaluate changes in future air pollution impacts on human health. However, besides considerable uncertainty because of the multitude of mechanisms by which changes in emissions and in climate can influence O3 and PM concentrations there is also uncertainty in risk estimates to apply- including their spatial and temporal variations. For O3, the unresolved issue of a threshold concentration below which no adverse effects occur is highly important for determining human health burdens.