GEO-5 Chapter 2: Atmosphere

The global atmosphere is at a critical stage, particularly in relation to climate change. There is considerable scientific evidence of the causes and solutions that could protect human health and ecosystems, and effective action has resulted in the achievement of some internationally agreed goals. The phase-out of ozone-depleting substances and lead in petrol by implementing relatively simple and cost-effective solutions demonstrates that, when most major stakeholders agree, significant progress is possible.

Progress in achieving environmental goals for particulate matter (PM) and tropospheric ozone is mixed, despite the high levels of concern about their impacts, as solutions are complex and can be costly. Much of the developed world has successfully reduced concentrations of indoor and outdoor PM, sulphur and nitrogen compounds to levels close to or within World Health Organization guidelines. However, more remains to be done. Concern is high in Africa, Asia and Latin America, where levels of PM in many cities remain far in excess of the guidelines. Existing solutions can be relatively costly and the time it will take to meet guideline or target concentrations will depend on the priority given to the issue. Tropospheric ozone also remains a significant problem and is proving difficult to address despite some progress with regard to peak concentrations in Europe and North America.

Climate change is the most important atmospheric issue. While there is considerable concern about this complex problem, progress has been slow due to varying levels of motivation and because some low-carbon technological solutions are considered expensive. Despite attempts to develop low-carbon economies in a number of countries, atmospheric concentrations of greenhouse gases continue to increase to levels likely to push global temperatures beyond the internationally agreed limit of 2°C above the pre-industrial average temperature. Application of current low-carbon technologies and existing policy options would reduce the risks posed by climate change, but a gap of several billion tonnes of carbon dioxide (CO₂) equivalent remains between present emission reduction pledges and those necessary to reach climate targets.

Complementary strategies to address short-lived climate forcers (SLCFs) – black carbon, methane and tropospheric ozone – could, if implemented widely, significantly reduce the rate of temperature increase in the near term while delivering substantial co-benefits for human health and food security. Given that policy tools and technological solutions already exist, progress in reducing SLCFs could be rapid. Nevertheless, this has to be seen as a complementary strategy to the reductions in anthropogenic CO₂ emissions necessary to protect the Earth from exceeding the 2°C limit.

Climate change, air quality and stratospheric ozone depletion are increasingly seen as closely related issues but governments are not addressing them in an integrated manner. An integrated approach to atmospheric protection could support economic development and, by addressing key sectors, policy makers could accomplish multiple goals. Addressing sources of pollution can affect the different gases and particles they emit and deliver multiple climate and air quality benefits. The challenge is to find those solutions that maximize the benefits and lend themselves to widespread implementation.

Investment in achieving atmospheric goals is expected to be cost-effective. The benefits of these policies include reducing anthropogenic radiative forcing, saving millions of lives and significantly enhancing quality of life. Achievement of these benefits and climate and air quality goals requires widespread implementation of currently available technology and proven policy – but it is likely that transformative changes affecting major drivers of emissions are required as well.

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