Table of Contents 1 Chapter 2: Atmosphere 2 Main messages 3 Introduction 4 Drivers of Change and Pressures 4.1 Production, consumption and population growth 4.2 Sectors and technology 4.2.1 Transport 4.2.2 Industry 4.2.3 Energy 4.2.4 Land-use practices 4.2.5 Urban settlements 4.2.6 Technological innovation 5 Environmental Trends and Responses 5.1 Air Pollution 5.1.1 Atmospheric emissions and air pollution trends 5.1.2 Effects of air pollution 5.1.3 Managing air pollution 5.1.4 Transport emissions 5.1.5 Industrial and energy sector emissions 5.1.6 Indoor air quality 6 Climate Change 6.1 Greenhouse gas concentrations and anthropogenic warming 6.2 Effects of climate change 6.3 Managing climate change 7 Stratospheric Ozone Depletion 7.1 The ozone layer 7.2 Effects of stratospheric ozone depletion 7.3 Managing stratospheric ozone depletion 8 Challenges and Opportunities 8.1 Two decades of mixed progress 8.2 Comparing the responses to different atmospheric environment issues 8.3 Reducing emissions of chemicals with long residence times in the atmosphere 8.4 Opportunities to deal with atmospheric environment challenges 9 Contributors 10 Notes

---

---

Chapter 2: Atmosphere

Main messages

A series of major atmospheric environment issues face the world, with both short- and long-term challenges, that are already affecting human health and well-being. Impacts are changing in their nature, scope and regional distribution, and there is a mixture of both worrying developments and substantial progress.

Climate change is a major global challenge. Impacts are already evident, and changes in water availability, food security and sea-level rise are projected to dramatically affect many millions of people. Anthropogenic greenhouse gas (GHG) emissions (principally CO₂) are the main drivers of change. There is now visible and unequivocal evidence of climate change impacts. There is confirmation that the Earth’s average temperature has increased by approximately 0.74°C over the past century. The impacts of this warming include sea-level rise and increasing frequency and intensity of heat waves, storms, floods and droughts. The best estimate for warming over this century is projected by the Intergovernmental Panel on Climate Change (IPCC) to be between a further 1.8 and 4°C. This will intensify the impacts, leading to potentially massive consequences, especially for the most vulnerable, poor and disadvantaged people on the planet. There is increasing concern about the likelihood of changes in rainfall patterns and water availability, thereby affecting food security. Major changes are projected for regions, such as Africa, that are least able to cope. Sea-level rise threatens millions of people and major economic centres in coastal areas and the very existence of small island states. Adaptation to anticipated climate change is now a global priority.

To prevent future severe impacts from climate change, drastic steps are necessary to reduce emissions from energy, transport, forest and agricultural sectors. There has been a remarkable lack of urgency in tackling GHG emissions during most of the past two decades. Since the 1987 report of the World Commission on Environment and Development (Brundtland Commission), there has been a sharp and continuing rise in the emissions. There is an agreement in force, the Kyoto Protocol, but the global response is far from adequate. Recent studies show that the total cost of measures to mitigate climate change would be a small fraction of the global economy. Mainstreaming climate concerns in development planning is urgent, especially in sectors such as energy, transport, agriculture, forests and infrastructure development, at both policy and implementation levels. Likewise, policies facilitating adaptation to climate change in vulnerable sectors, such as agriculture, are crucial to minimize adverse impacts. Transformations in social and economic structures, with broad stakeholder participation toward low carbon societies, are critical.

More than 2 million people globally are estimated to die prematurely each year due to indoor and outdoor air pollution. Although air quality has improved dramatically in some cities, many areas still suffer from excessive air pollution. The situation on air pollution is mixed, with some successes in both developed and developing countries, but major problems remain. Air pollution has decreased in some cities in different parts of the world through a combination of technology improvement and policy measures. However, increasing human activity is offsetting some of the gains. Transport demand increases every year, and is responsible for a substantial part of both anthropogenic GHG emissions and health effects due to air pollution. Many people, especially in Asia where the most polluted cities are now found, still suffer from very high levels of pollutants in the air they breathe, particularly from very fine particulate matter, the main air pollutant affecting human health. This is also related to the massive industrial expansion in many Asian cities that are producing goods for the global economy. This pollution also reduces visibility by creating urban and regional haze. Many poor communities are still dependent on traditional biomass and coal for cooking. The health of women and children in particular suffers as a result of indoor air pollution, and a total of 1.6 million people are estimated to die prematurely each year. Many air pollutants, including sulphur and nitrogen oxides, accelerate damage to materials, including historic buildings. Long-range transport of a variety of air pollutants remains an issue of concern for human and ecosystem health, and for the provision of ecosystem services. Tropospheric (ground-level) ozone is increasing throughout the northern hemisphere, and is a regional pollutant affecting human health and crop yields. Persistent organic pollutants from industrial economies accumulate in the Arctic, affecting people not responsible for the emissions.

The “hole” over the Antarctic in the stratospheric ozone layer that gives protection from harmful ultraviolet radiation is now the largest ever. Emissions of ozone-depleting substances (ODS) have decreased over the last 20 years, yet the concern about the state of stratospheric ozone still persists. On the positive side, precautionary action on stratospheric ozone depletion was taken by some industrialized countries before the impacts were evident. Their leadership was key to making the reductions in the manufacture and consumption of ODS a global success story. Although emissions of ODS have decreased over the last 20 years, it is estimated that the ozone layer over the Antarctic will not fully recover until between 2060 and 2075, assuming full Montreal Protocol compliance.

Rapid growth in energy demand, transport and other forms of consumption continue to result in air pollution, and are responsible for unprecedented absolute growth in anthropogenic GHG emissions. Since the Brundtland Commission emphasized the urgent need for addressing these problems, the situation has changed, in some cases for the better, but in others for the worse. A number of pressures are still building, driving up the emissions. The population is increasing, and people use more and more fossil fuel-based energy, consume more goods and travel further, increasingly using cars as their favourite transport mode. Aviation is growing rapidly and increased trade, as part of the globalized economy, leads to growth in the transport of goods by sea, where fuel quality and emissions are currently not strictly regulated. These pressures are being somewhat offset by increases in efficiency and/or from implementation of new or improved technology.

Measures to address harmful emissions are available and cost-effective, but require leadership and collaboration. Existing mechanisms to tackle ODS are adequate, while air quality management in many parts of the world requires the strengthening of institutional, human and financial resources for implementation. Where air pollution has been reduced, the economic benefits associated with reduced impacts have far outweighed the costs of action. For climate change, more innovative and equitable approaches for mitigation and adaptation are crucial, and will require systemic changes in consumption and production patterns. Many policies and technologies required to address emissions of GHGs and air pollutants are currently available and are cost-effective. Some nations have started to implement changes. While additional research and assessment efforts should continue, dynamic leadership and international collaboration, including technological transfer and effective financial mechanisms, are required to accelerate policy implementation around the world. The long-term risks from emissions of substances with long residence times, especially those that are also GHGs, should strongly encourage the use of a precautionary approach now.

Introduction

In 1987 the World Commission on Environment and Development (WCED), also known as the Brundtland Commission, recognized problems of regional air pollution, with its impacts on environmental and cultural values (see Chapter 1). It stated that burning fossil fuels gives rise to carbon dioxide (CO₂) emissions, and that the consequent greenhouse effect “may by early next century have increased average global temperatures enough to shift agricultural production areas, raise sea levels to flood coastal cities and disrupt national economies.” It also said that “Other industrial gases threaten the planet’s protective ozone shield,” and “Industry and agriculture put toxic substances into the human food chain,” highlighting the lack of an approach to effective chemicals management.

Key conclusions of Our Common Future, the Brundtland Commission report, were that while economic activity, industrial production and consumption have profound environmental impacts, “poverty is a major cause-and-effect of global environmental problems.” Human well-being, especially poverty and equity, are affected by all of the atmospheric environment issues addressed in this chapter. It is clear that air pollution from human activities constitutes one of the most important environmental issues affecting development across the world. Climate change threatens coastal areas, as well as the food security and livelihoods of people in the most vulnerable regions. Indoor air pollution, from burning biomass or coal for cooking, particularly affects women and young children. Outdoor air pollution in cities or near major industries disproportionately kills or harms the health of poorer people. Tackling emissions will contribute to the attainment of the Millennium Development Goals ^[26], especially the goals of eradicating hunger, ensuring good health for all and ensuring environmental sustainability.

Atmospheric environment issues are complex. Different primary pollutants emitted, and secondary pollutants formed in the atmosphere, have very different residence times, and are transported to varying distances, and this affects the scale at which their impact is felt (see Figure 2.1). Those substances that have very short residence times affect indoor and local air quality. Substances with residence times of days to weeks give rise to local and regional problems, those with residence times from weeks to months give rise to continental and hemispheric problems, and those with residence times of years give rise to global problems. Some greenhouse gases may last up to 50,000 years in the atmosphere.

There is now a consensus amongst the vast majority of scientists that anthropogenic emissions of greenhouse gases, of which CO₂ and methane are the most significant, are already causing climate change. The global emissions are still increasing and the impact will be felt by all regions of the world, with changing weather patterns and sea-level rise affecting coastal human settlements, disease patterns, food production and ecosystem services.

Air pollution is still leading to the premature death of a large number of people. Although the air quality of some cities has improved dramatically over the last 20 years, mainly in the richer nations, the air quality of many cities in developing nations has deteriorated to extremely poor levels. Even in richer countries, in recent years, improvements in levels of particulate matter and tropospheric ozone have stagnated, and further measures are needed. Regional air pollution problems of acidification have been reduced in Europe and North America, but are now a growing policy focus in parts of Asia, where acidic deposition has increased. Tropospheric (ground-level) ozone pollution causes significant reductions in crop yield and quality. The transfer of pollutants across the northern hemisphere, especially tropospheric ozone, is becoming an increasingly important issue. Despite efforts to tackle air pollution since 1987, emissions of various air pollutants to the atmosphere are still having dramatic impacts on human health, economies and livelihoods, as well as on ecosystem integrity and productivity.

Emissions of ozone-depleting substances (ODS), such as chlorofluorocarbons, lead to thinning of the stratospheric ozone layer, resulting in increased ultraviolet (UV-B) radiation reaching the Earth’s surface. The ozone hole, or seasonal ozone depletion over the Antarctic, still occurs. Increasing UV-B radiation affects skin cancer rates, eyes and immune systems, thus having important public health implications^[27]. There are concerns about the UV-B effect on ecosystems, for example through impacts on phytoplankton and marine food webs^[28].

Since 1987, it has become clear that there are high levels of persistent organic pollutants (POPs) and mercury in food chains, with the potential to affect the health of humans and wildlife, especially species higher in food chains. POPs represent a global problem. Some have low residence times in the atmosphere, but are re-volatilized, and can migrate over long distances and persist in the environment. Many POPs are transported through the atmosphere, but their impacts are mediated by aquatic and land-based food chains (see Chapters 3 and 4) and accumulated in Polar Regions (see Chapter 6).

Drivers of Change and Pressures

Atmospheric composition is affected by virtually all human activities. Population increases, income growth and the global liberalization of trade in goods-and services all stimulate an increase in energy and transport demand. These are drivers of emissions of substances into the atmosphere and, as many cost-benefit studies have shown^[29], the costs to our collective well-being often outweigh the individual benefits of the high-consumption lifestyles people have or aspire to (see Chapter 1). In many cases, emissions result from satisfying the wants of a rising affluent class rather than from fulfilling basic needs (see Box 2.1). Significant downward pressure on emissions has come from increases in efficiency and/or from implementation of new or improved technology.

Box 2.1 Energy use in the context of Millennium Development Goals (MDGs)[30]

Currently, access to energy for heating, cooking, transport and electricity is considered a basic human right. Various studies have investigated the consequences of meeting the minimum standards set out in the MDGs, and found that the total amount of primary energy required to meet the minimum standards is negligible on the global scale. Electricity for lighting (in homes, schools and rural health facilities), liquefied petroleum gas (LPG) for cooking fuel (for 1.7 billion urban and rural dwellers), and diesel used in cars and buses for transport (for 1.5 million rural communities) would require less than 1 per cent of total annual global energy demand, and would generate less than 1 per cent of current annual global CO2 emissions. This shows that energy services could be provided to meet the MDGs without significantly increasing the global energy sector’s environmental impacts.

The developed world is still the main per capita user of fossil fuel, and often exports long-lived, outdated and polluting technology to developing countries. The wealthier nations also “transfer” pollution by purchasing goods that are produced in a less environmentally friendly manner in lower-income countries. As a consequence, vulnerable communities in developing countries are most exposed to the adverse health effects caused by air pollution (see Chapters 6, 7 and 10).

Due to inertia in economic, social, cultural and institutional systems, transitions to more sustainable modes of production and consumption are slow and cumbersome. Typically, it takes 30–50 years or more before such changes are fully implemented, although the first improvements can be seen at a much earlier stage (see Box 2.2). Understanding how policy decisions will affect economic activities, and their associated emissions and impacts can facilitate early warning signals and timely actions. Table 2.1 presents the main drivers affecting the atmosphere.

Production, consumption and population growth

Ultimately, the drivers for atmospheric environment impacts are the increasing scale and changing form of human activity. The increasing population on the planet contributes to the scale of activity but, of even greater importance, the continuing expansion of the global economy has led to massive increases in production and consumption (see Chapter 1), indirectly or directly causing emissions to the atmosphere.

Box 2.2 Examples of inertia in drivers[31]

Energy supply The energy sector requires massive investments in infrastructure to meet projected demand. The International Energy Agency (IEA) estimates that the investments will total around US$20 trillion from 2005 to 2030, or US$800 billion/year, with the electricity sector absorbing the majority of this investment. Developing countries, where energy demand is expected to increase quickly, will require about half of such investments. Often, these investments are long term. Nuclear plants, for example, are designed for a lifetime of 50 years or more. Decisions made today will have effects well into our future. Transport Production of road vehicles, aircraft and ships are all examples of steadily growing mature markets. It will take time for new concepts, such as hybrid or hydrogen fuel cell cars, or high-speed magnetic trains, to massively penetrate markets. Technology barriers and standards, cost reductions, new production plants and, finally, market penetration are all challenging obstacles. Old production facilities often remain operational until they are economically outdated, and the lifetime of a new car is well over a decade. The penetration time of a new technology, such as the hydrogen fuel cell car will, even under the most optimistic projections, take at least 40 years.

Since the Brundtland Commission report, the Earth’s population has risen by almost 30 per cent (see Chapter 1), with regional increases ranging from 5.1 per cent in Europe to 57.2 per cent in Africa^[32]. Global economic output (measured in purchasing power parity or PPP) has increased by 76 per cent, almost doubling the average per capita gross national income from about US$3 300 to US$6 400. This average increase in per capita income masks large regional variations, ranging from virtual stagnation in Africa to a doubling in some countries in Asia and the Pacific. Over the same period, urban populations have risen to include half of humanity. Although the rate of population growth is expected to continue to slow, the world population is still expected to be 27 per cent above current levels by 2030^[33]. Nearly all population growth expected for the world in that period will be concentrated in urban areas (see Chapter 1).

In line with population and GDP growth, there is an increase in production and consumption. Energy use has been partly decoupled from the growth of GDP (see Figure 2.2), due to increased efficiency in energy and electricity production, improved production processes and a reduction in material intensity. Nevertheless, the major proportion of pollutant emissions result from energy-related activities, especially from the use of fossil fuel. The global primary energy supply has increased by 4 percent/ year between 1987 and 2004^[34] since Brundtland, and fossil fuels still supply over 80 per cent of our energy needs (see Figure 2.3). The contribution of non-biomass renewable energy sources (solar, wind, tidal, hydro and geothermal) to the total global energy supply has increased very slowly, from 2.4 percent in 1987 to 2.7 percent in 2004^[35] (see Chapter 5).

The energy intensity of our society (defined as energy use per unit of GDP in PPP units) has decreased since Brundtland by an average of 1.3 percent per year (see Figure 2.2). However, the impact of total GDP growth on energy use has outweighed these mitigating efficiency improvements.

Manufacturing processes can also cause direct emissions, such as CO₂ from steel and cement production, SO₂ from copper, lead, nickel and zinc production, NO_X from nitric acid production, CFCs from refrigeration and air conditioning, SF₆ from electricity equipment use, and perfluorocarbons (PFCs) from the electronic industry and aluminium production.

Humanity’s footprint on the planet has grown correspondingly larger. Natural resource demands have expanded, the burden on the environment has grown heavier, and this trend looks set to continue although there have been shifts in the sources of the pressures. The share of total GDP of the agriculture and industry sectors has decreased from 5.3 and 34.2 percent in 1987 to 4 and 28 percent of GDP in 2004^[36]. The transport sector has shown a consistently high growth rate over the same period, with a 46.5 percent increase in energy used globally by road transport between 1987 and 2004^[37]. Reducing the impacts of these major drivers of atmospheric pollution will involve multiple transitions in sectors such as energy, transport, agricultural land use and urban infrastructure. The right mix of appropriate government regulation, greater use of energy saving technologies and behavioural change can substantially reduce CO₂ emissions from the building sector, which accounts for 30–40 percent of global energy use. An aggressive energy efficiency policy in this sector might deliver billions of tonnes of emission reductions annually^[38].

Increasing demand for such products and services as refrigeration, air-conditioning, foams, aerosol sprays, industrial solvents and fire suppressants led to increasing production of a variety of chemicals. Some of them, after being released into the atmosphere, can rise into the stratosphere, where they break apart, releasing chlorine or bromine atoms, which can destroy ozone molecules. Though the physical volume of emissions of ozone-depleting substances has never been very large in comparison to other anthropogenic emissions to the atmosphere, the risks associated with potential impacts are enormous. Fortunately, the response to this problem has been a success story.

Sectors and technology

Transport

The relatively high growth in passenger car sales reveals that people put a high preference on car ownership as they become more affluent (see Figure 2.4). Moreover, there has been a shift to heavier cars, equipped with an increasing number of energy demanding features (for example air conditioning and power windows), which add to a greater than expected growth in energy use by the transport sector.

Atmospheric emissions from the transport sector depend upon several factors, such as vehicle fleet size, age, technology, fuel quality, vehicle kilometres travelled and driving modes. The low fleet turnover rate, especially for diesel-powered vehicles, and the export of older vehicles from rich to poor countries, slows progress in curbing emissions in developing countries. In some parts of Asia, a majority of road vehicles consist of two- and three-wheelers powered by small engines. They provide mobility for millions of families. Although inexpensive, and with lower fuel consumption than cars or light trucks on a per vehicle basis, they contribute disproportionately to particulate, hydrocarbon and carbon monoxide emissions^[39].

Shifting from public transport systems to private car use increases congestion and atmospheric emissions. Poor urban land-use planning, which leads to high levels of urban sprawl (spreading the urban population over a larger area), results in more car travel (see Figure 2.5) and higher energy consumption. The lack of adequate infrastructure for walking and cycling, which are the most environmentally-friendly transport modes, also contributes to increased vehicle use. Figure 2.6 shows the relative space required to accommodate people driving cars, using buses or cycling, with clear implications for transport strategy and planning.

Air transport is one the fastest rising transport modes, with an 80 per cent increase in kilometres flown between 1990 and 2003^[40]. This dramatic increase was driven by growing affluence, more airports, the rise in low-cost airlines and the promotion of overseas tourism. Economic efficiency is driving improvements in energy efficiency, and new commercial aircraft are claimed to use up to 20 percent less fuel than those sold 10 years ago^[41]. Shipping has also grown remarkably since Brundtland, mirroring the increase in global trade. It has risen from 4 billion tonnes in 1990 to 7.1 billion tonnes total goods loaded in 2005^[42]. Improvements in the environmental performance of the shipping industry have been less pronounced than for air transport.

Industry

The shift in the regional character of industrial production, which has decreased in developed countries and increased in the developing world, can be illustrated by the changes in secondary energy use by the industrial sector. In the United States, increased energy use in the transport and service sectors has been partially counterbalanced by the decrease (0.48 tonne oil equivalent/capita) in the industrial sector. In contrast, in Asia and the Pacific, and Latin America and the Caribbean, there has been an increase in per capita energy use in all sectors^[43].

Atmospheric emissions from large stationary sources in developed countries have been reduced by using cleaner fuels, end-of-pipe controls, relocating or shutting down high-emitting sources and promoting more efficient energy use. In many developing countries such measures have not been fully implemented, but have the potential to rapidly reduce emissions. If 20 percent of energy was saved in existing energy generation and industrial facilities in developing countries through use of currently available technologies, the increase in CO₂ emissions from developing countries from 2000 to 2020 would only be about half of what it otherwise be^[44]. Industrial sources that use obsolete technology, lack emission controls and are not subject to effective enforcement measures, contribute significantly to the emission load. In general, the implementation of governmental regulations has stimulated the use of technologies that often reduce costs, and result in greater benefits than originally foreseen.

Emissions from small factories and commercial sources are much more difficult to control. Enforcement of compliance with emission standards is politically difficult and expensive. Technology solutions are more challenging, and there is no simple way to check that best management practices are being used.

Energy

In the industrialized world, large power plants are confronted with increasingly tight environmental standards. A wide range of options for the production of clean energy exists, and has started to penetrate the market, often stimulated by government subsidies. High growth rates in clean energy options since 1987 have been observed, especially for solar and wind energy. Energy supply from wind power increased 15 times by 2004, with an average growth of approximately 30 percent per year, although its share in global electricity supply is still very small at about 0.5 percent in 2004^[45].

Energy efficiency improvements and energy conservation are given high priority in the energy development strategies of many countries, including developing countries. High efficiency and clean technology will be crucial to achieve a low-emission development path, combined with security of supply. Among the factors that define the level of emissions are fuel quality, technology, emission control measures, and operation and maintenance practices. Energy security considerations and fuel costs often determine the choice of fuels, such as coal and nuclear (see Chapter 7). Thermal power plants burning coal are major air pollution sources, and emit higher levels of many pollutants than gas-fired power plants to produce the same amount of energy. Clean energy sources, such as geothermal, wind energy and solar power, are still underutilized. With the recent high oil prices, more efficient power plants have become more cost-effective, but still require substantial investment in infrastructure. Many countries in, for example, sub-Saharan Africa, cannot cope with the rising energy demand, and continue to rely on obsolete, low-efficiency power plants that emit high levels of pollutants.

Land-use practices

In rural areas, customary land-use practices also drive atmospheric emissions. The clearance of forested land, and its subsequent use for cattle and crop production, releases carbon stored in the trees and soils, and depletes its potential as a CO₂ sink (see Chapter 3). It may also increase methane, ammonia and nitrogen oxide emissions. Deforestation is known to contribute as much as 20–25 percent to annual atmospheric emissions of CO₂^[46]. Normal agricultural land-use practices, such as burning crop residues and other intentional fires, increase emissions of CO₂, particulate matter and other pollutants^[47]. Wildfires and forest fires used for land clearance also release very high levels of particulates. The Southeast Asian haze of 1997, produced by land clearance, cost the people of that region an estimated US$1.4 billion, mostly in short-term health costs^[48]. Since 1987, there has been little progress in mitigating these unwanted effects. Fine dust particles from the ground are also a major concern in arid or semi-arid areas subject to seasonal or periodic high winds.

Urban settlements

Emissions in densely populated areas tend to be higher due to the total level of emission-related activity, even though the per capita emissions are reduced by higher efficiency and shorter travel distances using personal transport (see Figure 2.5). In combination with low dispersion conditions, this results in exposure of large populations to poor air quality. Urbanization, seen in such forms as urban population growth in Latin America, Asia and Africa, and urban sprawl in North America and Europe, is continuing as a result of a combination of social and economic drivers. Urban areas concentrate energy demands for transport, heating, cooking, air conditioning, lighting and housing. Despite the obvious opportunities that cities offer, such as their economic and cultural benefits, they are often associated with problems that are aggravated by large increases in population and limited financial means, which force city authorities to accept unsustainable short-term solutions. For example, there is pressure to use land reserved as green areas and for future public transport systems for houses, offices, industrial complexes or other uses with a high economic value. Moreover, cities create heat islands that alter regional meteorological conditions and affect atmospheric chemistry and climate. Reversing the trend of unsustainable development is a challenge for many city authorities.

Technological innovation

Technological innovation, coupled with technology transfer and deployment, is essential for reducing emissions. A broad portfolio of technologies is necessary, as no single technology will be adequate to achieve the desired level of emissions. Desulphurization technologies, low nitrogen combustors and end-of pipe particulate capture devices are examples of technologies that have contributed considerably to SO₂, NO_X and PM emission reduction. A number of technologies may play key roles in reducing GHG emissions. They include those for improved energy efficiency, renewable energy, integrated gasification combined cycle (IGCC), clean coal, nuclear and carbon sequestration^[49].

A “technology push” approach, based on large-scale research and technology deployment programmes and new breakthrough technologies, is needed to achieve deeper GHG emission cuts in the long run (2050 and beyond).

In addition to government and private sector investment in technology research and development, regulations for energy, environment and health are key drivers for stimulating the deployment of cleaner technologies in developing countries. It is also important to lower the risk of locking in more CO₂-intensive energy technologies in developing countries.

Environmental Trends and Responses

In this chapter, three major atmosphere-related environmental issues are analysed in detail: air pollution, climate change and stratospheric ozone depletion. For each issue the changes in the environmental state are related to the impacts on both the environment and on human well-being for the period since 1987. This is followed by descriptions of what has been done to curb emissions. Table 2.2 below summarizes the interconnections between changes in the atmosphere and human well-being, including changes in state of the atmosphere, the mechanisms through which impacts occur and changes in well-being over time.

Air Pollution

Human and environmental exposure to air pollution is a major challenge, and an issue of global concern for public health. The World Health Organization (WHO) estimated that about 2.4 million people die prematurely every year due to fine particles^[50]. This includes about 800,000 deaths due to outdoor urban PM₁₀ (see Box 2.3 for an explanation), and 1.6 million due to indoor PM₁₀, even though the study did not include all mortality causes likely to be related to air pollution. Figure 2.7 shows the annual mortality that is attributable to outdoor PM₁₀ for different world regions. The highest number of estimated annual premature deaths occurs in developing countries of Asia and the Pacific^[51].

Beside effects on human health, air pollution has adverse impacts on crop yields, forest growth, ecosystem structure and function, materials and visibility. Once released into the atmosphere, air pollutants can be carried by winds, mix with other pollutants, undergo chemical transformations and eventually be deposited on various surfaces (see Box 2.3).

Atmospheric emissions and air pollution trends

Emissions in the various regions show different trends for SO₂ and NO_x (see Figure 2.8). There have been decreases in the national emissions in the more affluent countries of Europe and North America since 1987. More recently Europe is as concerned with unregulated sulphur emissions from international shipping as it is with the regulated land-based sources^[52]. For the industrializing nations of Asia, emissions have increased, sometimes dramatically, over the last two decades. There are no aggregate data for regions after 2000, and therefore recent changes in emissions of developing countries are not displayed, especially in Asia. For instance, from 2000 to 2005 the Chinese SO₂ emissions increased by approximately 28 per cent^[53], and satellite data suggest that NO_X emissions in China have grown by 50 per cent between 1996 and 2003^[54]. The main result is that global emissions of SO₂ and NO_X are increasing with respect to 1990 levels. In Africa, and in Latin America and the Caribbean, small increases have been reported.

In many large cities in developing countries, current air pollution concentrations are very high, especially for PM₁₀ (see Figures 2.9 and 2.10). However, pollutant levels are decreasing, usually because of controls on emission sources, changing fuel use patterns, and closures of obsolete industrial facilities. For lead, the trends are decreasing, and ambient levels in most cities are currently below the WHO guideline^[55]. In general, PM₁₀ and SO₂ levels have been decreasing, although levels of PM₁₀ are still many times higher than the WHO guideline in many developing countries, and SO₂ levels are above the WHO guideline in a number of cities and differences are considerable in different regions. Most large cities exceed the WHO guideline for NO₂, and the levels are not showing any significant decreases.

Box 2.3 Features of different air pollutants [56]

Six common pollutants – suspended particulate matter (SPM), sulphur dioxide (SO2), nitrogen dioxide (NO2), carbon monoxide (CO), tropospheric ozone (O3) and lead (Pb) – harm human health, and are used as indicators of air quality by regulatory agencies. They are known as criteria pollutants, for which health-based ambient air quality guidelines have been recommended by WHO. PM is distinguished as different inhalable fractions that are classified as coarse and fine particulates with aerodynamic diameters below 10 μm (PM10) and 2.5 μm (PM2.5) respectively. Air pollutants may be considered primary – emitted directly into the air – or secondary pollutants that are formed in the air by chemical and/or photochemical reactions on primary pollutants. The formation of secondary pollutants, such as tropospheric ozone and secondary aerosols, from primary pollutants such as SO2, NOX, NH3 and volatile organic compounds (VOCs) is strongly dependent on climate and atmospheric composition. Due to atmospheric transport, their impacts can occur far from their sources. The major chemical components of PM are sulphate, nitrate, ammonium, organic carbon, elemental carbon and soil dust (consisting of several mineral elements). Other important primary pollutants include heavy metals, such as mercury, cadmium and arsenic; VOCs, such as benzene, toluene, ethylbenzene and xylenes; polycyclic aromatic hydrocarbons (PAHs); and some persistent organic pollutants (POPs), such as dioxins and furans. These air pollutants result from the burning of fossil fuels, biomass and solid waste. Ammonia (NH3) is emitted primarily from agricultural sources.

Modelling indicates the highest levels of tropospheric ozone – a major component of photochemical smog – are in a subtropical belt that includes southeastern parts of North America, southern Europe, northern Africa, the Arabian Peninsula, and the southern and northeastern parts of Asia (see Figure 2.11). However, there is currently a lack of rural measurements in Asia, Africa and Latin America that could validate these results. There is a trend of rising annual mean tropospheric ozone concentrations across the northern hemisphere^[57] that implies that several regions may need to cooperate to address the problem.

In addition, clouds of tiny aerosol particles from emissions hang over a number of regions (known as Atmospheric Brown Clouds). These seasonal layers of haze reduce the amount of sunlight that can reach the Earth’s surface, which has potential direct and indirect impacts on the water cycle, agriculture and human health^[58]. The aerosols and other particulate air pollutants in the atmosphere absorb solar energy and reflect sunlight back into space^[59].

Effects of air pollution

Air pollution is one of the major environmental factors causing adverse impacts on human health, crops, ecosystems and materials, with priorities varying among regions (see Box 2.4). Both indoor and outdoor air pollution are associated with a broad range of acute and chronic impacts on health, with the specific type of the impact depending on the characteristics of the pollutant. The developing nations of northeast, southeast and southern Asia are estimated to suffer about two-thirds of the world’s premature deaths due to indoor and outdoor air pollution^[60].

The most important air pollutant from a disease perspective is fine particulate matter. WHO estimated that particulates (see Box 2.5) in urban areas worldwide cause about 2 per cent of mortality from cardiopulmonary disease in adults, 5 per cent of mortality from cancers of the trachea, bronchus and lung, and about 1 per cent of mortality from acute respiratory infections in children, amounting to about 1 per cent of premature deaths in the world each year^[61]. In addition, the WHO estimated that indoor smoke from solid fuel causes about one-third of lower respiratory infections, about one-fifth of chronic obstructive pulmonary disease, and approximately 1 per cent of cancers of the trachea, bronchus and lung^[62]. Figure 2.12 presents global estimates of the burden of disease attributable to indoor and urban PM₁₀ pollution.

Box 2.4 Key air pollution issues differ around the world

(See graphs presented throughout this chapter and Chapter 6 for details) Africa, Asia and the Pacific, Latin America and the Caribbean and West Asia The highest priority issue for these regions is the effect of indoor and outdoor particulates on human health, especially for women and young children exposed to indoor smoke when cooking. The widespread use of poor quality fuels for industrial processes and transport represent a critical outdoor urban air pollution issue for the regions’ policy-makers, especially in Asia and the Pacific. Food security issues caused by growing levels of tropospheric ozone represent future challenges for parts of the regions. The risks of acidic deposition are not yet well understood, but acidification already is a policy focus in parts of Asia and the Pacific. Europe and North America The priority issues for these regions are impacts of fine particulates and tropospheric ozone on human health and agricultural productivity, and the effects of nitrogen deposition on natural ecosystems. The effects of SO2 and coarse particles emissions, and acidic deposition are well understood in these regions. They have been generally successfully addressed and are of decreasing importance (see Chapter 3).

The health impacts of air pollution are closely linked with poverty and gender issues. Women in poor families bear a disproportionate burden of the impacts of air pollution due to their greater exposure to smoke from poor quality fuel for cooking. In general, the poor are more exposed to air pollution due to the location of their residences and workplaces, and their increased susceptibility due to such factors as poor nutrition and medical care^[63].

Air pollution also adversely affects agriculture. Measurable, regional-scale impacts on crop yields caused by tropospheric ozone have been estimated to cause economic losses for 23 arable crops in Europe in the range US$5.72–12 billion/year^[64]. There is evidence of significant adverse effects on staple crops in some developing countries, such as India, Pakistan and China, which are now starting to deal with this issue^[65] (see also the example in Figure 2.13).

In 1987 the regional impacts of acid rain caused by sulphur and nitrogen deposition were of major importance in Europe and North America, causing lake acidification and forest decline, mainly due to soil acidification. More recently, such declines have also been documented in Mexico and China, and are probably occurring in many other countries^[66]. There is recent evidence that emission controls led to a reversal of freshwater acidification^[67], and the dire warnings related to widespread forest decline across Europe and North America at the time of the Brundtland Commission have not materialized. There is now a risk of acidification in other areas of the world, particularly Asia^[68] (see Chapter 3 and 6).

Box 2.5 The health impacts of fine particles[69]

The health impacts of particles depend considerably on their physical and chemical characteristics. Particle size is important, as this influences how easily and deeply the particles get into the lungs. The ability of the body to protect itself against inhaled particles, and the susceptibility of individuals to particles are closely linked with particle size and chemical composition. Particles larger than 10 μm in diameter generally do not penetrate into the lungs, and have a short residence time in the atmosphere. As a consequence, epidemiological evidence generally links PM10 and PM2.5 particles with adverse effects on health. There has been more interest recently in ultrafine particles (those having a diameter less than 0.1 μm), because poorly soluble ultrafine particles can move from the lung to the blood, and then to other parts of the body. Scientists know that chemical composition and size of particles are often linked to health effects, and that particle number and surface area are also important factors in assessing the health effects of particles. However, there is little detailed understanding yet of the specific chemical components of particles responsible for adverse health outcomes.

Over recent decades the eutrophying effect of nitrogen deposition has also caused significant loss of biodiversity in some sensitive, nutrient limited ecosystems, such as heaths, bogs and mires in northern Europe and North America^[70]. Nitrogen deposition has been recognized within the Convention on Biological Diversity as a significant driver of species loss. Several major global biodiversity hot spots have been identified as being at significant risk because of nitrogen deposition^[71] (see Chapters 4, 5 and 6).

The built environment is affected by air pollution in several ways. Soot particles and dust from transport are deposited on monuments and buildings, SO₂ and acid deposition induces corrosion of stone and metal structures and ozone attacks many synthetic materials, decreasing their useful life, and degrading their appearance. All these effects impose significant costs for maintenance and replacement. In addition, fine particles in urban environments typically reduce visibility by one order of magnitude^[72].

Persistent organic pollutants (POPs) and mercury have emerged as important issues since 1987. These toxic substances become volatile when emitted to the environment, and can then be transported over long distances. When pollutants are persistent, concentrations will build up in the environment, causing a risk of bioaccumulation in food chains. Many POPs are now found around the globe, even far from their sources. In the Arctic environment, harmful health effects have been observed in northern wildlife, and the pollution threatens the integrity of traditional food systems and the health of indigenous peoples (see Chapter 6).

Managing air pollution

Progress in managing air pollution presents a mixed picture. Urban air pollution remains a critical issue, affecting people’s health in many developing countries, although progress is evident in high-income countries. Some regional air pollution issues, such as acid rain, have been successfully addressed in Europe, but they pose a threat in parts of Asia. Tropospheric ozone has emerged as a particularly intractable problem, mainly in the northern hemisphere, where it affects crops and health. Burning biomass fuels indoors in developing regions imposes an enormous health burden on poor families, especially women and young children. Action in developing countries has been inadequate to date, but there remains an opportunity to improve health and reduce premature mortality.

The considerable progress that has been made in preventing and controlling air pollution in many parts of the world has been achieved largely through command-and-control measures, both at the national and regional levels. At the national level, many countries have clean air legislation that set emission and ambient air quality standards to protect public health and the environment. At the regional level, examples include the Convention on Long-Range Transboundary Air Pollution^[73], the Canada-U.S. Air Quality Agreement^[74] and European Union legislation^[75]. Other emerging regional intergovernmental agreements include the ASEAN Haze Agreement ^[76], the Malé Declaration on the Control and Prevention of Air Pollution in South Asia^[77], and the Air Pollution Information Network for Africa (APINA), a regional science-policy network. At the global level, the Stockholm Convention on Persistent Organic Pollutants^[78] regulates the use and emission of certain pollutants (POPs). Although the Brundtland Commission highlighted the issue of mercury in the environment, no global agreement to limit mercury contamination has been reached. There has been a global mercury programme operational since 2001, and changes in technology and the use of alternative compounds seem to have reduced emissions^[79].

Transport emissions

Fuel and vehicle technologies have improved substantially during the last two decades, driven both by technological and legislative developments. Vehicle emissions have been partially controlled by the removal of lead from gasoline, requirements for catalytic converters, improved evaporative emission controls, fuel improvements, on-board diagnostic systems and other measures. Diesel vehicle emissions have been reduced by improved engine design and, for some vehicles, particle traps. Widespread use of particle traps will await reductions of sulphur in diesel fuel to below 15 ppm. Current diesel fuel sulphur levels differ considerably among regions (see Figure 2.14). Reducing sulphur in gasoline to low levels enables use of more effective catalytic converters, thus leading to improved emission control. Hybrid gasoline-electric vehicles, which tend to be more fuel efficient in urban traffic than gasoline-only vehicles, have been introduced in many developed countries, but their use is still very limited.

Most developed countries have made substantial progress in reducing per vehicle emissions, and many middle-income countries have implemented significant measures to control vehicle emissions. In addition to improved vehicle technologies, effective vehicle inspection and maintenance programmes have helped to control vehicle emissions and enforce emission standards^[80]. However, progress in some low-income countries has been slow. Developing countries will not achieve benefits of advanced emission control technologies unless they implement cleaner fuel options.

In some Asian countries motorized two- and three-wheeled vehicles contribute disproportionately to emissions. However, regulations in some nations are reducing emissions from these vehicles. The shift from two-cycle to four-cycle engines, and the introduction of emission standards that effectively ban the sale of new vehicles powered by two-cycle engines will, in time, lead to a significant improvement in vehicle emissions^[81].

Mass transport is an important alternative to private vehicles, and has been successfully implemented in many cities by using light rail, underground and rapid bus transit systems^[82]. Fuel switching from diesel to compressed natural gas has been implemented for public transport vehicles in cities such as Delhi and Cairo, leading to reductions in emissions of particulate matter and SO₂. In many countries, widespread use of mass transport continues to be hampered, however, by inefficiency and negative perceptions.

Industrial and energy sector emissions

In many developed countries emissions from large industrial sources have been controlled by fuel changes and emission control laws. The reduction of SO₂ emissions in Europe and North America has been one of the success stories of recent decades. Agreements such as the 1979 UNECE Convention on Long-Range Transboundary Air Pollution played an important role in this success. The ECE convention adopted the concept of critical loads (thresholds in the environment) in 1988 and, in 1999, the Gothenburg Protocol set targets for national emissions of SO₂, NO_X, NH_x and VOCs. In Europe, SO₂ has been reduced considerably, partly due to these agreements. It is also the result of policies calling for cleaner fuels, flue gas desulphurization and new industrial processes. Emissions also fell as the result because of the demise of many heavy industries, particularly in Eastern Europe and the former Soviet Union. However, SO₂ emissions have increased in many developing country regions.

Stricter environmental regulation and economic instruments, such as emissions trading, have triggered the introduction of cleaner technologies, and promoted further technological innovation.

Economic policies send important signals to producers and consumers. For example, Europe is shifting from taxing labour to taxing energy use to better reflect the impacts of emissions^[83]. Other successful examples include cap-and-trade policies in the United States to reduce SO₂ emissions from power plants^[84]. International use of such economic instruments is growing^[85]. Many cleaner technologies and cleaner production options are mature and commercially available, but there is great need for global cooperation regarding technology transfer to make them more widely available.

Indoor air quality

With some 1.6 million people dying prematurely each year from exposure to polluted indoor air ^[86], many developing countries in Africa, Asia and Latin America have attempted to address the emissions from the burning of biomass fuels and coal indoors. Responses include providing households with improved stoves, cleaner fuels, such as electricity, gas and kerosene, and information and education to make people aware of the impacts of smoke on the health of those exposed, especially women and young children. A modest shift from solid biomass fuels, such as wood, dung and agricultural residues, to cleaner fuels has been achieved, and governments have supported such measures, but further progress along such lines is urgently necessary if any major advances are to be realized^[87].

Climate Change

The trend of global warming is virtually certain, with 11 of the last 12 years (1995–2006) ranking among the 12 warmest years since 1850, from which time there has been systematic temperature keeping^[88]. The evidence of this warming includes a number of shrinking mountain glaciers^[89], thawing permafrost^[90], earlier breakup of river and lake ice, lengthening of mid- to high-latitude growing seasons, shifts of plant, insect and animal ranges, earlier tree flowering, insect emergence and egg laying in birds^[91], changes in precipitation patterns and ocean currents^[92], and, possibly, increasing intensity and lifetimes of tropical storms in some regions^[93].

Poor communities are most directly dependent for their livelihoods on a stable and hospitable climate. In developing countries the poor, often relying on rain-fed subsistence agriculture and gathered natural resources, are deeply dependent on climate patterns, such as the monsoons, and are most vulnerable to the devastation of extreme weather events, such as hurricanes. Vulnerable communities already suffer from climate variability, for example due to increasing frequency of droughts in Africa^[94] and, as was demonstrated by the effects of Hurricane Katrina in 2005, and by the European heat wave of 2003, it is the poor or vulnerable who suffer most from weather extremes, even within relatively affluent societies.

While the Earth’s climate has varied throughout the prehistoric ages, the last few decades have witnessed a global climate disruption that is unprecedented over the recent millennia, a period of relative climatic stability during which civilization emerged^[95]. Some regions, particularly the Arctic, will be more affected by climate change than others closer to the equator (see Polar Regions section of Chapter 6). In many regions, the agricultural sector will be particularly affected. The combination of high temperatures and decreased soil moisture projected for parts of Africa will be particularly hard to adapt to. With the majority of the world’s population struggling to meet basic development needs, such as those identified in the Millennium Development Goals, humanity can ill afford this additional burden of climate change impacts^[96].

Greenhouse gas concentrations and anthropogenic warming

The greatest direct human pressure on the climate system arises from the emission of greenhouse gases, chief of which is CO₂, mainly originating from fossil fuel consumption. Since the dawn of the industrial age, the concentrations of these gases have been steadily increasing in the atmosphere. Figure 2.15 shows the atmospheric concentration of CO₂ over the past 10,000 years. The unprecedented recent rise has resulted in a current level of 380 parts per million, much higher than the pre-industrial (18th century) level of 280 ppm. Since 1987, annual global emissions of CO₂ from fossil fuel combustion have risen by about one-third (see Figure 2.16), and the present per capita emissions clearly illustrate large differences among regions (see Figure 2.17).

There has also been a sharp rise in the amount of methane, another major greenhouse gas, with an atmospheric level 150 per cent above that of the 19th century^[97]. Examination of ice cores has revealed that levels of CO₂ and methane are now far outside their ranges of natural variability over the preceding 500,000 years^[98].

There are other atmospheric pollutants that affect the planet’s heat balance. They include industrial gases, such as sulphur hexafluoride, hydrofluorocarbons and perfluorocarbons; several ozone-depleting gases that are regulated under the Montreal Protocol; tropospheric ozone; nitrous oxide; particulates; and sulphur- and carbon-based aerosols from burning fossil fuels and biomass. Elemental carbon aerosols (soot or “black carbon”) contribute to global warming by absorbing short-wave radiation, while also contributing to local air pollution. Removing such pollutants will be beneficial both with respect to climate change and health effects. Sulphur-based aerosol pollutants, on the other hand, cool the planet through their influence on the formation of clouds, and by scattering incoming sunlight, and are thus currently “shielding” the planet from the full warming effect of greenhouse gas emissions^[99]. In the future, the policy measures needed to reduce public health problems and local environmental impacts associated with sulphur-based pollutants will weaken this unintended but fortunate shielding.

The Earth’s surface temperature has increased by approximately 0.74°C since 1906, and there is very high confidence among scientists that the globally averaged net effect of human activities since 1750 has been one of warming^[100]. The warming of the last few decades is exceptionally rapid in comparison to the changes in climate during the past two millennia. It is very likely that the present temperature has not been exceeded during this period. Earlier discrepancies between surface temperature measurements and satellite measurements have been largely resolved^[101]. Model calculations including both natural and anthropogenic drivers give quite good agreement with the observed changes since the beginning of the industrial age (see Figure 2.18). Most of the warming over the last century has occurred in recent decades, and this more rapid warming cannot be accounted for by changes in solar radiation or any other effects related to the sun that have been examined^[102].

The climate system possesses intrinsic positive and negative feedback mechanisms that are generally beyond society’s control. The net effect of warming is a strong positive feedback^[103], with several processes within the Earth’s complex climate system (see Figure 2.19 for the stocks and flows of carbon on a global scale) acting to accelerate warming once it starts (see Box 2.6 below). The magnitude of such feedbacks is the subject of intense study. What is known is that the Earth’s climate has entered a state that has no parallel in the recent prehistory. The cumulative result of these feedbacks will be far greater than the “direct” warming caused by the increase in greenhouse gas emissions alone.

Effects of climate change

Spells of very high temperatures appear to be increasing as global temperatures increase. A notable recent case is the exceptional heat wave experienced in much of Europe in the summer of 2003, with over 30,000 estimated premature deaths from heat stress and associated air pollution^[104]. In the Arctic, average temperatures are rising almost twice as rapidly as in the rest of the world. Widespread melting of glaciers and sea ice, and rising permafrost temperatures present further evidence of strong Arctic warming. Since 1979, satellite observation has allowed scientists to carefully track the extent of seasonal melting of the surface of the Greenland Ice Sheet (see Figure 2.20). There is now also evidence of widespread melting of permafrost, both in Alaska and Siberia, which is expected to increase the release of methane from frozen hydrates, giving rise to a significant positive feedback (see Box 2. 6 above and the Polar Regions section in Chapter 6). This phenomenon has a precedent, as a vast amount of methane was emitted some 55 million years ago, and was associated with a temperature increase of 5–7°C^[105]. It took approximately 140,000 years from the start of the emission period to return to a “normal” situation. Trends in global patterns^[106] reveal increased variance in precipitation everywhere: wet areas are becoming wetter, and dry and arid areas are becoming dryer. It is notable that the regions with the lowest contribution to anthropogenic GHG emissions, such as Africa, are those projected to be most vulnerable to their negative consequences, especially in the form of water stress^[107] (see Chapters 4 and 6).

Box 2.6 Positive feedbacks in the Earth system[108]

A first important positive feedback is the increase in the amount of water vapour in the atmosphere that will result from higher air and ocean temperatures. The ability of air to hold moisture increases exponentially with temperature, so a warming atmosphere will contain more water vapour, which in turn will enhance the greenhouse effect. Recent observations confirm that the atmosphere water vapour concentration increases with a warming planet. Another important feedback is the loss of snow and sea ice that results from rising temperatures, exposing land and sea areas that are less reflective, and hence more effective at absorbing the sun’s heat. Over the last few decades, there is a documented decline in alpine glaciers, Himalayan glaciers and Arctic sea ice, (see Chapters 3 and 6). A third feedback is the melting of permafrost in boreal regions, resulting in the release of methane, a potent greenhouse gas, and CO2 from soil organic matter. Recent studies in Siberia, North America and elsewhere have documented the melting of permafrost. A fourth important feedback is the release of carbon from ecosystems due to changing climatic conditions. The dieback of high-carbon ecosystems, such as the Amazon, due to changes in regional precipitation patterns, has been predicted from some models, but it has not yet been observed. Laboratory studies have indicated accelerated decomposition of soil organic matter in temperate forests and grasslands due to temperature and precipitation changes, or the CO2-induced enhancement of decomposition by mycorrhizae.

There is observational evidence for an increase of intense tropical cyclone activity in the North Atlantic since about 1970, correlated with increases in tropical sea surface temperatures. There are also suggestions of more intense tropical cyclone activity in some other regions, where concerns over data quality are greater^[109]. The number of the most intense tropical storms (Class 4 and 5) has nearly doubled over the past 35 years, increasing in every ocean basin. This is consistent with model results that suggest this trend will continue in a warming world^[110]. If correct, this would suggest an increasing frequency in the future of devastatingly intense hurricanes, such as Katrina (in 2005) and Mitch (in 1998), and cyclones such as the super cyclone of Orissa in India in 1999. However, there has been recent