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A startling UNEP study claims that a blanket of pollution three kilometres thick is threatening the food security and health of millions
 About 60 per cent of the world's population of 6000 million lives in Asia. The recent decades witnessed impressive economic development in the region. Fuelled by growing population, globalisation and the information technology revolution, this development has resulted in higher demands for energy, mobility and communications. The scope and magnitude of the environmental consequences of these demands are far reaching, especially with respect to air pollution at local and regional levels. The problem of air pollution is no longer confined only at local scale. The new scenario encompasses complex interlinkages of several issues, including air pollution, haze, smog, ozone and global warming. The most visible impact of air pollution is the haze, a brownish layer of pollutants and particles from biomass burning and industrial emissions that pervades many regions in Asia. A recent international study, the Indian Ocean Experiment (INDOEX), has revealed that this haze is transported far beyond the source region, particularly during December to April. The INDOEX findings pertain mainly to the period from December to April referred to in this report as the dry season. The seasonal is the 'winter monsoon ' or the 'north east monsoon'.
 This UNEP report is the first comprehensive study of the South Asian haze and its impact on climate. It is largely based on the studies of the INDOEX science team of over 200 scientists from Europe, India and USA. It provides a summary of the large brownish haze layer and its impact on the radiative heating of the atmosphere and the surface for South Asia and the adjacent Indian Ocean during the INDOEX campaign. It also discusses preliminary findings with respect to the impact of this haze on regional temperatures, precipitation, agriculture and health.
The INDOEX campaign began in 1995 with ship observations and culminated in a major field campaign launched from the Maldives during January to April of 1999,with ships, aircraft, satellites and surface observations. An aerosol-chemistry-climate observatory was established on an island in the Maldives. The government of the Maldives, which also provided generous logistic support, received the field operations and this observatory enthusiastically. The discovery during INDOEX of the so-called South Asian haze is clear evidence of the magnitude of the aerosol pollution problem. Three dimensional aerosol-assimilation models reveal this haze to extend over South, Southeast and East Asia. At present, biomass burning and fossil fuel burning are the major sources of air pollution. Due to lack of observations of emissions at the source regions in South Asia, it was infeasible to determine with confidence the relative contribution of biomass and fossil fuel burning to the observed haze. But our tentative conclusion is that biomass burning plays a major role in gaseous pollution (such as carbon monoxide), while fossil fuel combustion and biomass burning contribute to particulate (aerosol) pollution. The affected region is the most densely populated in the world characterised by a monsoon climate, high levels of pollution, and increasing problems of water stress, agricultural productivity and health. The haze can impact all of these aspects directly. It can also impact them indirectly through its effects on atmospheric and surface temperatures and the hydrologic cycle. Its most direct effect, as documented during INDOEX, is a significant reduction in the solar radiation reaching the surface; a 50 to 100per cent increase in solar heating of the lower atmosphere. Possible direct effects also include a reduction in the precipitation efficiency by inhibiting the formation of larger raindrop size particles; reduction in agricultural productivity by reducing available sunlight for photosynthesis; and adverse health effects. The direct effects are restricted mainly to the regions beneath the haze layer (south Asia in this case). Indirect effects of the haze include cooling of the land surface; increase in the frequency and strength of the thermal inversion that can trap more pollution; perturbation of the winter time rainfall patterns; and an overall reduction in the average tropical (20 ° N to 20 ° S) evaporation and precipitation. The impact of these pollution particles on the hydrological cycle of the tropics and the sub-tropics has implications to water availability and quality, which are the major environmental concerns for this century. The aerosol effects on surface temperature and hydrological cycle are of opposite sign to that of greenhouse gases (GHG). While GHGs warm the surface and increase rainfall, aerosols exert a cooling and drying effect. In this regard, it is significant that most regions in Asia experienced a decreasing trend in precipitation since the 1960s. The agricultural impact of aerosol-induced drying, coupled with the reduction in photo-synthetically active solar radiation, is of major concern to Asia, the largest agricultural continent with 60 to 90 per cent of the world's agricultural population (Fu et al, 1998) and producer of 80 to 90 per cent of the world's rice. In what follows, we summarise the specific details of our findings. First, we would like to note the following important caveats. The findings in this report regarding the climate impacts of the haze are based on limited sets of modelling studies. For example, the studies do not include the effects of increase in greenhouse gases. While definitive conclusions cannot be drawn from these studies, these studies illustrate the potential importance of the haze to the region's climate, water budget and agriculture and also illustrate the great need for further studies of this important environmental problem facing most of the Asian region. We are at the very early stages of our understanding of regional climate changes, in particular, how regionally and seasonally concentrated climate forcing terms (e.g. the haze forcing) influence regional and global climate. The climate change problem is made considerably complex because aerosols can directly alter the hydrological cycle (by suppressing evaporation and rainfall), which in turn can feedback on temperatures since latent heat released in rainfall regulates the general circulation and the wind patterns around the globe. We are probably at least a decade or more away from comprehending these effects quantitatively. In spite of these reservations, we have used sensitivity studies with three-dimensional models (the same models used for global warming studies) to make quantitative estimates. However these models are global models with coarse horizontal resolution and regional climate studies require a factor of 5 to 10 higher spatial resolution to resolve important monsoon features. Quantitative estimates of rainfall changes cited in this report merely indicate possibilities and such estimates may be revised substantially along with improvement in understanding of the haze phenomenon. Another major limitation of our report is that it is restricted primarily to the dry season, from December to April. The vertical and horizontal distribution of aerosols during May to November are not known, excepting over the oceans where satellite data give the column integrated optical depths, and furthermore the anthropogenic contribution is not known over the oceans or the land. Composition of the Pollution "Cloud " and Haze
Emission Strength: For the INDOEX region, the fossil energy related CO 2 per capita is nearly an order of magnitude lower than in North America and Europe, but the emissions are growing at a rate 5-6 times larger. The CO emissions, however, are comparable. India emits about 110 Tg/yr (tera (10 12) grams per year) compared with about 107 Tg/yr from North America. Although simultaneous emissions of NO x lead to enhanced ozone, and thereby OH, concentrations, altogether it is likely that hydroxyl (OH) concentrations are reduced because of the reaction of OH with CO. Because almost all of the gases that are emitted to the atmosphere by human activities and natural processes are removed by reaction with OH, and OH can be reduced furthermore by the presence of the haze layer, the air pollution in South and Southeast Asia does negatively impact on the self-cleaning (oxidation) efficiency of the atmosphere, on regional and on global scales. SO 2 emissions (which are converted to sulfate aerosols) are 5 Tg/yr of sulfur for India, 28 Tg/yr for China and 25 Tg/yr for North America. Emission sources of other aerosol components such as organics, black carbon, fly ash and dust are very poorly characterised. For black carbon, available estimates suggest that the Asian region may contribute about 30 to 50 per cent of the total world emissions. Composition: Direct chemical measurements were used to show that anthropogenic sources contribute as much as 75 per cent to the observed haze. The sub micrometer anthropogenic aerosol typically has a chemical composition (by mass) of 10-15 per cent black carbon, 26 per cent organic, 32 per cent sulfate, 10 per cent mineral dust, 5 per cent fly ash, and smaller fractions of various other chemicals. Over the Indian Ocean, hundreds to a thousand kilometres downwind of the sources, aerosol mass loading was comparable to suburban air pollution in North America and Europe. Aerosol optical depth in visible wavelengths varies from about 0.05 in the Southern Indian Ocean (typical of unpolluted air) to between 0.4 and 0.7 (very polluted) north of the equator over the Arabian Sea and the Bay of Bengal. Over adjacent continental areas, optical depths are even larger. Several three-dimensional aerosol-assimilation models were used to extend the experiment domain to reveal that the time-mean optical depth exceeds 0.4,indicating heavy aerosol pollution, over central and northern Asia, portions of Southeast Asia and eastern China. Impacts on the Climate System
Radiative Forcing: The impacts of the South Asian haze are listed below. This aerosol haze causes a reduction in the spatial and temporal mean solar energy at the earth's surface by about14 Wm -2 , about 10per cent of natural levels, and an additional heating of the planetary boundary layers by about 14 Wm -2 (doubling the lower atmosphere solar heating). These values should be compared with the greenhouse forcing (from the pre-industrial to the present) of about 1 Wm -2 at the surface and 1.6 Wm -2 heating of the atmosphere. The result is a solar radiative disturbance over a substantial fraction of South Asia during the dry winter monsoon period (January -April), about an order of magnitude larger than that coming from CO 2 and the other "greenhouse gases ". These INDOEX findings have been extensively reported in peer-reviewed international publications including three special issues of American and Indian journals that were dedicated to INDOEX. Temperature Effects: The impact of INDOEX aerosols on the climate of South Asian region is estimated to be substantial. The panel initiated a series of sensitivity studies with three-dimensional climate models (with and without interactive oceans) in collaboration with the National Centre for Atmospheric Research (J T Kiehl, J J Hack and W M Washington). As of publication of this report, general circulation model (GCM) studies with fixed ocean temperature (referred as GCM-FO for fixed ocean temperature) and a mixed layer slab ocean (GCM-MO for mixed layer ocean) have been completed and sent for publication (Chung et al., 2002 and Kiehl et al.,2000). We have also completed simulations of the haze effects with a fully coupled ocean model (referred as GCM-CO) and preliminary analysis supports the temperature changes derived from the simpler models. In spite of the fact that the top-of-atmosphere (TOA) direct radiative forcing is nearly zero; the computed surface cooling is substantial, thus demonstrating the importance of the surface forcing. All three, GCM-FO, -MO and -CO, models indicate an overall decrease of surface air temperature over the Indian subcontinent, the Indo-China region and eastern China during January to March. The seasonal and land surface averaged temperature change is about -0.5K (GCM-FO and -MO). The estimated winter/spring (January to April) cooling due to the haze is comparable to the estimated (by GCM-CO) greenhouse warming. There is strong observational support for this model result. For example, the surface temperatures (averaged over the Indian sub-continent) during June to December show a strong warming trend (very similar to the global average warming trend) where as during January to April, the surface temperatures show practically zero trend from 1950 to 2000, thus supporting our finding that the cooling by the absorbing haze has nearly cancelled the GHG warming. In contrast, in the lower troposphere (1 to 3 km), there is local heating by about 0.5 K. The surface cooling accompanied by atmospheric warming stabilises the boundary layer, which can lead to more trapping of pollution and increased lifetimes of the haze. Implications to the Role of Black Carbon: The large surface cooling, in spite of the substantial increase in solar heating of the lower atmosphere by black carbon is significant, particularly in view of its potential policy implications. The first implication is that the TOA forcing, by itself, is not sufficient to judge the climate impacts of aerosols, at least, regionally. The regional surface temperature changes, even its sign, depend on the sign and magnitude of the surface forcing. Since absorption of solar radiation by absorbing aerosols (black carbon, fly ash and dust) contributes about 75 per cent of the reduction in solar radiation at the surface, these absorbing aerosols lead to surface cooling (and not a warming), at least over South Asia and the tropical Indian Ocean region. This deduction raises the disturbing possibility that a reduction in the haze (motivated by air quality and health concerns) may significantly amplify global warming over Asia, at least during the dry season. Hydrological Cycle: The haze has been found to substantially perturb the hydrological cycle. Introduction of the haze in the GCM results in a reduction in the tropical (20 ° N to 20 ° S) mean evaporation and precipitation by about 1 to 2 per cent. Regional precipitation patterns in the GCM-FO and GCM-MO versions of the model changed significantly. Model simulations with the haze show significant redistribution of rainfall with large increases (20 to 40 per cent) in some regions, which in turn are compensated by comparable decreases in other regions. For example, the GCM-FO simulations suggest that, while the rainfall in the near equatorial rainfall regime may increase and the enhanced activity may extend farther northward up to the southern fringe of the peninsular India, there may be corresponding decrease over the sub-tropical belt over NW India, Pakistan, Afghanistan, and the adjoining western central Asian region (not unlike the observed trends of the last 4 decades). This is possible through the enhancement of the ascending branch of the regional Hadley cell and its descending branch over the sub-tropics. Winter precipitation over NW India contributes 20-40 per cent of the annual rainfall and over northern Pakistan, Afghanistan, and adjoining central western Asia; its contribution is even 50-70 per cent of the annual. Such a reduction in rainfall is very likely to cause water stress as the winter precipitation is through snowfall and the decreased snow melting in summer would deplete the water resources over the region of impact. Even the man-made irrigation resources in the affected region would suffer due to reduced snowmelt. Reduction in irrigation water is likely to cause long-term impact on agricultural production though in the wheat model used this aspect has not been explicitly considered as winter-spring wheat is mostly (over 80 per cent) irrigated over the region. The results could be taken as possibilities as the models have the capabilities to simulate the winter climate well. However they are not certainties as the natural climate system on the regional scale could be impacted through other natural variability 's and human-induced activities, such as the green house gases warming. Although the model results are still preliminary, having neglected, for instance, the effects of growing concentrations of the greenhouse gases and feedbacks with the ocean whose temperatures were kept constant, they clearly indicate that the effects of anthropogenic aerosol can be large on regional scales. Agriculture Impacts
Haze can impact agriculture productivity in a variety of direct and indirect ways. Direct Effects: 1) Reduction of total solar radiation (sum of direct and diffused) in the photo-synthetically active part of the spectrum (0.4 to 0.7 micron) reduces photosynthesis, which in turn leads to a reduction in productivity. 2) Settling of aerosol particles (eg fly ash, black carbon and dust) on the plants can shield the leaves from solar radiation. 3) In addition, aerosol deposition can increase acidity and cause plant damage. Indirect Effects: 1) Changes in surface temperature can directly impact the growing season. In the tropics, a surface cooling (such as expected from aerosols) can extend the growing season (while a greenhouse warming can shrink it). 2) Changes in rainfall or surface evaporation can have a large impact. In this report we have accounted only for the direct effect of solar reduction that too using just one crop model developed by the Indian Agriculture Research Institute of India. The major effect was found for rice productivity (the dominant winter time crop grown South India) and a negligible decrease for productivity of winter wheat. When the haze effects on surface solar radiation were included in the crop model, rice productivity decreases by about 5 to 10 per cent. A more realistic picture would emerge when these studies are coupled with GCM scenarios with changing concentrations of greenhouse gases and aerosols. Health Effects
There is now a growing body of literature linking air pollution with short and long term effects on human health. Populations at risk from inhaled particles are those most susceptible to pulmonary and heart diseases, infants and elderly people. A 1997 joint study of the World Health Organisation (WHO), the World Resources Institute (WRI) and the US Environmental Protection Agency (EPA) estimated that nearly 700,000 deaths worldwide are related to air pollution and that this number can escalate to 8 million deaths by 2020 (Working Group,1997). Occurrences of respiratory diseases in South Asia resulting from air pollution both indoors and outdoors, is estimated to be quite substantial. In each of the 23 cities with a million plus population in India, air pollution levels exceed WHO standards. It has been estimated that in India alone about 500,000 premature deaths are caused by indoor pollution, for mothers and their children who are under 5 years of age (Smith,2000). Serious respiratory disease related problems have been identified for both indoor and outdoor pollution in Calcutta, Delhi, Lucknow, Bombay, Ahmedabad, and several countries in East Asia including China, Thailand and Korea. There is still inadequate knowledge of the relative effectiveness of sub micron particles compared with larger particles, or the specific roles of black carbon and organic carbon. Such studies need to be performed in the future. Summary
Some of the results listed in this report are preliminary in nature but do indicate possibilities of substantial changes in climate scenario and impacts even when GHGs are considered .In spite of the advances by INDOEX, significant scientific uncertainties remain. First, we need to estimate the haze amount and its radiative forcing during May to December. We need studies with coupled ocean-atmosphere models to address the following questions: How does the solar heating in the haze affect the monsoon rainfall? How does the reduction of solar energy to the surface affect the water budget and soil moisture? Does the haze amplify or ameliorate the warming due to greenhouse gases? How does air pollution from Asia affect the worldwide concentrations of ozone and other pollutants? On the policy side, the evidence of long- range transport of the haze complicates potential prescriptions for dealing with the problem, as responses must be coordinated among sovereign nations. It is also important to note that the same actions that can reduce the build-up of GHGs in burning of fossil fuels can also contribute to reduction of particulate matter. It is our perception that air pollution ranks among the top environmental issues in the region largely due to its potential effects on health, agriculture and water budget. A survey conducted by the Asian Development Bank a few years ago found that senior environmental policymakers in the region share this perception. As early as 1992,the World Bank, in its annual World Development Report, highlighted the health threat posed by particulate air pollution. With respect to health effects, indoor air pollution is just as important, an issue not considered in the report. Lastly, there are consequences for the hydrological cycle, climate and the global ozone budget. It is of great interest and relevance to note the enormous range of scales we have to deal with in the study of air pollution and its effects on the environment, ranging from the severe health effects caused by indoor pollution, to those of urban and rural pollution, the impact of the aerosol on regional and even global climate. The climate effects of urban air pollution can no longer be considered as negligible. We conclude this report by suggesting a strategy for understanding the air pollution issue in this broader context and help policymakers arrive at informed decisions. The entire report can be downloaded at http://www.rrcap.unep.org/ |
