Air pollution affects the regional and global climate both directly and indirectly. Ozone in the lower layers of the atmosphere contributes to global warming even more than some greenhouse gases included in the Kyoto Protocol, and particulate matter in the atmosphere has a significant impact on climate.
However, black carbon, or soot particles, has a warming effect, while other particles, for instance sulphates and nitrates, have a cooling effect on climate. The current high levels of sulphates and nitrates therefore mask the effects of climate change to some degree. Cuts in sulphur and nitrogen emissions that are necessary to protect public health and the environment may actually mean that the impact on climate caused by greenhouse gases shows more quickly.
On the other hand, measures to cut black carbon emissions will be beneficial on two counts, protecting both human health locally as well as the regional and global climate.
Methane emissions have grown
Methane, one of the Kyoto Protocol greenhouse gases, has a direct negative impact on climate and also contributes to ground-level ozone levels. Methane emissions have grown rapidly since pre-industrial times. Cutting these emissions will reduce ozone levels, which are damaging to health and the ecosystem, and lessen the extent of climate change.
While indications of the climate impact of increasing greenhouse gas concentrations can already be seen in the rise of mean temperatures and the increase in the number of extreme climate-related events, most effects are likely to happen over the next 50–100 years.
Some gases, like carbon dioxide, stay in the atmosphere for a very long time, which is why it takes a few decades before we begin to see the effects of measures to reduce emissions. In contrast, ozone, black carbon and methane can be controlled in such a way that the effects are visible much sooner (10–15 years). Cutting these pollutants can thus help reduce some climate effects while waiting for longer-term measures to pay off.