A UNEP report seeks, in an unsubstantiated manner, to link the Asian Brown Cloud, a relatively localised pollution cloud, to serious local and global changes in weather patterns and even to long-term climatic impacts.
THE decade after the Earth Summit at Rio de Janeiro in 1992 has witnessed a general failure on the part of the developed economies to meet their obligations towards implementation of Agenda 21, the centrepiece of the Rio Declaration on Environment and Development. The rejection last year by the United States of the Kyoto Protocol on climate change symbolised the lack of commitment amongst developed countries to end the unsustainable levels of energy consumption that they have been guilty of.
The Protocol required significant reductions in the emissions of greenhouse gases (GHGs), carbondioxide (CO2) in particular, which have been directly linked to global warming. The US is responsible for 33 per cent of global GHG emissions and 25 per cent of global CO2 emissions. The fossil-fuel-related CO2 release per capita in Asia is about an order of magnitude less than in North America and Europe. One of the chief reasons for the rejection of the Kyoto Protocol by U.S. President George W. Bush was that, while it mandated reductions on countries sucha as the U.S., it did not impose any reductions on major population concentrations such as China and India.
On the eve of the World Summit for Sustainable Development (WSSD), this premise was sought to be turned on its head through a report of the United Nations Environment Programme (UNEP) on what has been termed the Asian Brown Cloud (ABC), the apparent haze due to the thick brown blanket caused by polluting aerosols fine particles of a micrometre or less in size being sent into the atmosphere by burning fossil fuels, industrial pollutants and vehicular emissions by the populous regions of South Asia. The report sought to link this relatively localised pollution haze to serious local and global changes in weather patterns over decadal scales and even to long-term climatic impacts. According to the report, this could be comparable to, if not greater than, the effects due to GHGs. It was as if the charge made against the developed world by the developing countries was being thrown back at them.
The report was prepared on behalf of the UNEP by the Centre for Clouds, Chemistry and Climate (C4). The ABC team comprises three UNEP scientists headed by Klaus Toepfer, the UNEP Executive Director, and three C4 scientists headed by V. Ramanathan of Scripps Institute of Oceanography, La Jolla, U.S.
The UNEP press release of August 12, a fortnight before the WSSD got under way, stated the following rather ominously: ``A vast blanket of pollution stretching across South Asia is damaging agriculture, modifying rainfall patterns including those of the mighty monsoon and putting hundreds of thousands of people at risk.'' This definitive sounding alarm bell was followed by a carefully worded qualifying statement: ``Vital follow-up studies are needed to unravel the precise role this 3 km deep pollution blanket may be having on the region's climate and the world's.''
Releasing the report on ABC in London, Toepfer added: ``The haze is the result of forest fires, the burning of agricultural wastes, dramatic increases in the burning of fossil fuels in vehicles, industries and power stations and emissions from millions of inefficient cookers, burning of wood, cowdung and other biofuels...These initial findings clearly indicate that this growing cocktail of soot, particles, aerosols and other pollutants are becoming a major environmental hazard for Asia. There are also global implications not least because a pollution parcel like this... can travel half way round the globe within a week.''
On August 24, shortly before the Indian delegation was scheduled to leave for Johannesburg, Union Minister for Environment and Forests T.R. Baalu met a cross-section of scientists, following which the government rejected the UNEP report and stated that there was no scientific basis for the alarmist proclamation by Toepfer. At Johannesburg, after meeting Toepfer, Baalu said: ``I can say that the UNEP chief was a little inconvenienced by our denial. He has agreed that it required better investigation and more thorough study before these drastic and alarming predictions were made.''
Indeed, the government's rejection was not just a knee-jerk reaction, confronted all of a sudden as it was by this unexpected charge on the eve of the WSSD. It was a well-considered rejection of what seemed to be a politically motivated interpretation of scientific data.
THERE is no denying the presence of the pollution haze over the Asian region; it is evident from satellite imagery. Nor is it anyone's case, least of all the government's, that the growing pollution and the consequent aerosol loading that causes this need not be controlled. Indeed, laws and regulations are being put in place for controlling particulate emissions from vehicles.
The denial stems from the environmental politics that seems to dictate the unscientific extrapolations and conclusions, pointing to meteorological and climatological implications on the local, regional as well as global scale not to mention the undercurrent of internationally negotiated asymmetric controls that are being imposed.
``The results presented in the report do not support this suggestion about the impact of aerosols on climate and agriculture,'' points out Sulochana Gadgil of the Centre for Atmospheric and Oceanic Sciences (CAOS), Indian Institute of Science (IISc), who was one of the peer reviewers of the UNEP report. ``The model simulations show no perceptible impact on the monsoon systems of Asia, as is being claimed. In fact, the simulations seem to show enhanced rainfall,'' she points out.
The UNEP report is based on the studies of the Indian Ocean Experiment (INDOEX), a joint campaign by over 200 scientists from Europe, India and the U.S., between 1995 and 1999, using data collected from ships, aircraft, balloons, satellites and surface observations. As part of INDOEX, an aerosol-chemistry-climate observatory too was established on an island in the Maldives. The report is claimed to be the first comprehensive study of the South Asian haze and its impact on climate. It also discusses the impact of the haze on regional temperatures, precipitation, agriculture and health.
The INDOEX findings pertain mainly to the period from January to March, which the report refers to as the dry season. The term Asian Brown Cloud was coined by the leaders of INDOEX to describe the brown haze occurring during this period over the South Asian region and the tropical Indian Ocean, Arabian Sea and the Bay of Bengal. This wintertime haze appears brown when seen from aircraft or space because a substantial component of it is composed of man-made (or anthropogenic) particles such as soot.
However, as J. Srinivasan (a member of the INDOEX team) and Gadgil of CAOS point out in a recent paper in Current Science, the use of the term cloud for what is actually a haze is a misnomer. Haze consists of a combination of water droplets and minute particles less than a micrometre in size whereas cloud contains liquid water condensed from water vapour in the atmosphere with the typical size of droplets being 10 micrometre to one millimetre. ``The word `cloud' may have been used to suggest that it is much denser than haze,'' they point out.
But the term `Asian Brown Cloud' gives the wrong impression of the Asian region choking under a thick and permanent blanket of dirty atmosphere. Further, the haze is not a permanent feature of the atmosphere of the Asian region. It occurs only during the season following the southwest and northeast monsoon.
``Even during January-March there is considerable variation from year to year in the intensity of the haze,'' Srinivasan and Gadgil point out. According to them, the intensity happened to peak in 1999 because of unusual atmospheric circulation pattern during that year. Also, the brown haze is not a feature of the Asian region alone. It is a characteristic of most big cities in North America, Europe and other parts of the world. Haze over adjacent oceans is also not exclusive to Asia. A thick plume of haze emanating from the east coast of the U.S. and extending over more than 1,000 km over the Atlantic was seen on May 4, 2002, according to the Srinivasan-Gadgil paper.
THE political implications of the INDOEX findings for the countries of the Asian region were apparent in February 2001, when a sub-group of scientists from the INDOEX team, which ironically included three Indian scientists, published a paper titled `The Indian Ocean Experiment: Widespread Air Pollution from South and South East Asia' in the journal Science. It included two of the three C4 scientists in the ABC team, V. Ramanathan and P.J. Crutzen of the Max Planck Institute for Chemistry, Munich.
The paper used data on long-range transport of air pollution from South and Southeast Asia towards the Indian Ocean during the ``dry'' months, from January to March 1999. The study had observed that there existed high pollution levels over the entire northern Indian Ocean extending up to the Intertropical Convergence Zone (ITCZ), the meteorological system located at around 6 S that is involved in the monsoon, implying that during the dry season haze is transported far beyond the source region. Arguing that agricultural burning, biofuel use, fossil fuel combustion and biomass burning caused high aerosol loading and enhanced carbon monoxide concentrations, the paper concluded that growing pollution in the South Asian region gave rise to ``extensive air quality degradation with local, regional and global implications, including a reduction in the oxidising power of the atmosphere.'' It called for international measures to control this increasing pollution that ``will continue to grow into a global plume across the developed and the developing world,'' _ an unwarranted remark in a scientific work that is not without uncertainties and assumptions. It is this premise that the UNEP report too attempts to establish despite the study's limitations.
Interestingly, while certain important caveats are spelt out in the executive summary of the report, the main report, the UNEP press release and Toepfer's remarks give the impression of the results of the study being definitive which they certainly are not. ``The findings in this report,'' says the summary, ``regarding the climatic impacts of the haze are based on limited sets of modelling studies. For example, the studies do not include the effects of increase in GHGs. While definitive conclusions cannot be drawn from these studies, they 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 most important problem facing most of the Asian region.'' According to the report, anthropogenic sources contribute as much as 75 per cent to the observed haze. Typically the sub-micrometre anthropogenic aerosol in the INDOEX region is stated to be composed of (by mass): 10-15 per cent black carbon (BC), 26 per cent organic carbon (OC), 32 per cent sulphate, 10 per cent mineral dust, 5 per cent fly ash and smaller fractions of other chemicals.
Unlike the long-lived GHGs, which are distributed uniformly over the globe, aerosol lifetimes are only a week or less, resulting in substantial spatial and temporal variations with peak concentrations near the source. Natural aerosols in the INDOEX region would be predominantly dust, desert sands and sea salt. The level and composition of aerosols vary considerably across seasons and from year to year. The aerosol content builds up during October, peaks during February and March, decreases in May and June and decreases even further during July to September.
The basic physical process by which aerosols are believed to influence the weather and climate is believed to be as follows. Aerosols increase the reflection of solar radiation to space through a variety of complex radiative and microphysical processes. They also absorb radiation and this solar absorption within the atmosphere, together with reflection of solar radiation to space, greatly reduces the solar radiation reaching the earth's surface. Aerosols can influence climate indirectly through their important role as cloud condensation nuclei (CCN).
Increase in aerosols leads to an increase in the droplet number concentration. The increase in the number of drops results in an increased reflection of solar radiation from clouds into space, leading to overall cooling. If the condensed moisture within the cloud is not altered by an increase in aerosols, the droplet size will decrease because of the increase in the number concentration. This would lead to a decrease in precipitation, the report argues. In addition, this could lead to an increase in the cloud lifetime and in turn the amount of clouds resulting in a further increase in the reflection of solar radiation into space.
The key findings of the UNEP study are the following. The 3-km thick blanket of pollution is reducing amounts of solar radiation hitting the earth's surface by as much as 10 to 15 per cent. The heat-absorbing properties, predominantly due to BC and OC, are warming the lower parts of the atmosphere by 50 to 100 per cent.
The combination of these two results in a disturbance of the solar radiance over a substantial part of South Asia which is an order of magnitude larger than that due to CO2 and other GHGs. According to the report, the estimated winter-spring cooling due to ABC is comparable to the warming due to GHGs and the time-series data over the past 50 years show that the two cancel each other during this season. However, the warming of the lower atmosphere locally by about 0.5 can lead to more trapping of pollution and increased lifetime of haze, the report says.
More important, according to the report, the phenomenon has the effect of substantially perturbing the hydrological cycle. The study has observed a one to two per cent reduction in tropical (20 N -20 S) mean evaporation (essentially owing to the surface cooling) and a consequent fall in precipitation. Model simulations with haze show a significant redistribution of winter-spring rainfall with large (20-40 per cent) increases in the northeastern and eastern regions of Asia which is compensated by a corresponding drop in the northwestern parts.
This is argued to be the cause for the droughts in northwestern India, Pakistan and West Asia and the increased rainfall in northeastern India, Nepal and Bangladesh. However, the report has added a caveat to the prognosis that the results are not certainties because regional scale climate system could be impacted through other natural variabilities and human-induced activities such as global warming.
According to Srinivasan and Gadgil, decrease in solar radiation reaching the surface of the ocean due to aerosols observed during INDOEX was 29 watt/sq m. This, as well as the other characteristic features in the two cases, they point out, are comparable to the decrease (of 26 watt/sq m) observed over the Atlantic due to aerosols from the east coast of the U.S. In the case of the Amazon haze due to aerosols from forest fires, reduction in solar radiation reaching the surface was 34 watt/sq m. They also point out that aerosols are also good absorbers of infrared (IR) radiation and hence the IR radiation emitted by the ocean surface will be absorbed by aerosols and re-emitted to the ocean surface thus off-setting the reduction in the direct sunlight reaching the surface. In effect, they say, the decrease would only be of the order of 10-15 watt/sq m and the impact of this on evaporation from oceans will not be significant. The suggestion that this would lead to significant reduction in rainfall has, therefore, no scientific basis, say Srinivasan and Gadgil.
AN important point is the fact that the simulations on precipitation carried out using various global circulation models (GCMs) for the report are for rainfall during January-March, which is outside the southwest monsoon and the northeast monsoon seasons, during which periods regions in India get all their rainfall. Average rainfall during January-March is only 10 cm. Therefore, even if there is a large reduction in rainfall during this period, it does not alter the total monsoon precipitation in the Indian region in a major way.
But the simulation results presented (as plots) in the report indicate a substantial increase in precipitation over the Indian peninsula and the large region over the ocean where the brown haze was observed. There is only a slight decrease in rainfall over northwestern India. In any case, the GCMs used do not reproduce the normal monsoon correctly and so the results of the simulation exercise that use them in order to assess the impact of aerosols would be suspect, the Srinivasan-Gadgil paper points out.
``During this period, the overall effect is an enhancement of rainfall due to aerosols, perhaps because the warming of the atmosphere more than compensated for the cooling of the surface,'' points out Gadgil. ``Given the large increase in precipitation over the region of enhanced aerosols, it is difficult to understand the reduction of precipitation as is being claimed,'' she adds. ``
Further, while the report claims that the role of aerosols during the wet season (June-October) is currently unknown, there have been measurements of aerosols from several stations for over a decade and data show that summer monsoon washes out most of the aerosols. So the impact of aerosols during the actual monsoon period will be much less,'' she argues. Given this, the argument that the haze was responsible for the failure of this year's monsoon does not hold.
A recent work by Srinivasan and S.K. Satheesh of the CAOS has highlighted the importance of aerosols transported from the Arabian and Saharan regions (mostly natural dust), which, along with locally produced sea-salt aerosols constitute a very significant fraction of aerosols over the Arabian Sea during April-May. They argue that this could have a stronger impact on the weather systems of the season, the monsoon in particular, than anthropogenic aerosols from south and southeast Asia. Clearly, there are still a host of uncertainties in understanding the impact of aerosols on the weather and climate of the region. The alarmist prognosis on rainfall would, therefore, appear to be premature if not wrong and unjustified.
The report finds a major impact on the productivity of rice (the dominant winter crop in South India) _ a decrease by 5-10 per cent _ and a negligible decrease in the productivity of winter wheat. But a closer look at the results of simulation using the one crop model called WTGROWS (developed by the Indian Agricultural Research Institute and described in terms of diagrams and graphs) in the report, show that there is hardly any impact of aerosols on the crops studied, namely rice, sugarcane and wheat. The observations of the report on agriculture is therefore misleading.
The implication of the ABC on a global scale is argued, as Toepfer has, on the grounds of transportation and dispersal of the aerosol cloud from South Asia over thousands of kilometres in the seven days of the aerosol's lifetime in the atmosphere. But as Gadgil points out, if the aerosol is hygroscopic such as sulphate, nitrate and so on, then the residence time would be even less and most of the aerosols will be lost and the air mass will contain only whatever is collected on the way and not the original ``parcel of pollution''. Hence the remote effect of ABC is not likely to extend beyond the West Pacific, she says.
It is apparent, therefore, that much of what has been claimed as impacts of the ABC in the UNEP press release and in Toepfer's remarks require a great deal of scientific validation before they can be accepted. The timing of the UNEP report would seem to have been driven more by environmental politics than by science.
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