Continued reductions in air pollution and greenhouse gas (GHG) emissions are essential, as they pose serious threats to both people’s health and the environment across the world. Air quality and climate policies can provide mutual benefits: climate change mitigation actions can help reduce air pollution, and clean air measures can help reduce GHG emissions leading to reductions in global warming. There can also be trade-offs, if reducing a particular pollutant emission leads to additional atmospheric warming rather than cooling.
Furthermore, air pollution and climate change influence each other through complex interactions in the atmosphere. Increasing levels of GHGs alter the energy balance between the atmosphere and the Earth’s surface which, in turn, can lead to temperature changes that change the chemical composition of the atmosphere. Direct emissions of air pollutants (e.g. black carbon), or those formed from emissions such as sulfate and ozone, can also influence this energy balance. Thus, climate change and air pollution management have consequences for each other.
Given that emissions are linked to air quality and climate change, this thematic issue presents recent research that investigates the trade-offs and co-benefits that may be gained from reducing both long-lived GHGs, responsible for climate change, and air pollutants, responsible for adverse impacts on human health, ecosystems and the climate.
Although reducing particulate matter (PM) has clear health benefits, understanding the impact of this reduction on climate change is essential if mutual benefits for climate and health are to be delivered. The overall impacts of reductions are complex because PM is made up of many different chemical components with different physical properies, some of which lead to warming of temperatures (e.g. black carbon) by absorbing heat from the sun, whilst others (e.g. sulfates) bring about cooling effects by reflecting sunlight.
Several studies suggest that, in addition to health benefits, reducing black carbon sources would lead to cooling of global temperatures (see: ‘Reducing black carbon emissions benefits both climate and health’ download article (PDF)). On the other hand, other studies point out that reducing air pollution could worsen climate change in the short-term by contributing to an increase in global temperatures (see: ‘Do climate policies need a ‘pollution safety margin’?’ download article (PDF)). This is still an area of active research with many uncertainties to resolve.
Poor air quality is also caused by emissions of nitrogen oxides, methane and other volatile organic compounds that combine in the lower atmosphere to produce ozone. Ground-level ozone is a serious pollutant, which at high levels, damages human health and vegetation, including crop yields. In addition, ozone is a short-lived GHG contributing to climate change.
Changing environmental conditions, including rising temperatures caused by climate change, are expected to increase concentrations of ground-level ozone. Policies and management strategies to reduce ozone levels must be designed in light of evidence that there is a ‘climate penalty’ since increased temperatures make it more difficult to reach targets for ozone (and PM) in summertime. In particular, policies must incorporate evidence of how climate change is likely to affect different regions of Europe, if they are to be effective. The article, ‘How climate change could affect European ozone pollution’ download article (PDF), reports on research which suggests that climate change will lead to higher ozone levels across southern Europe this century.
The health costs of ozone pollution are likely to worsen under climate change. The impacts of climate change on air quality, ozone levels and ill-health are presented in ‘Climate impacts on air pollution could increase respiratory disease’ download article (PDF).
A reduction in pollutant emissions that produce ozone would not only improve public health but would also provide climate benefits. Integrating climate change and air quality policies would be the most effective approach.
One article, ‘Integrated climate change and air pollution strategies: a winning combination’ download article (PDF), compares the costs and benefits of implementing reductions in local air pollution and climate change actions separately or in combination. The message, again, is that simultaneous achievements in welfare and climate change are possible when decision-makers integrate both sets of policies.
Designing policies to combat future climate change is complicated by the many uncertainties associated with predicting the complex interactions governing long-term changes in climate and air pollutants. A recent study, detailed in ‘Unravelling the complex chemistry of the atmosphere’ download article (PDF), has reviewed progress in understanding the interactions between atmospheric chemical composition and climate. Continued and improved networks of measurements that provide long-term data are essential to gain a more robust understanding about past and present changes in concentrations of air pollutants and GHGs.
Such networks include surface, aircraft and satellite monitoring. Aircraft experiments combined with analysis using numerical models have proved to be particularly useful in advancing our knowledge about key chemical and physical processes in the atmosphere. There is also a clear need for improved emission inventories that track changing sources of air pollutants and GHGs over a wide range of locations and from year to year.
Ongoing research can provide opportunities for decision makers to choose policies that not only reduce GHGs but improve air quality and meet health goals.