Global Climate Change & Bangladesh....

Greenhouse Effect: The Science                                                                                  The temperature of a greenhouse is raised by using a shield through which solar radiation is allowed to enter but the consequential heat is prevented from escaping. In a roughly analogous manner, certain trace gases in the atmosphere notably carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂0), water vapour, ozone (O₃) and the chloroflrocarbons (CFCs) are transparent to high energy solar radiation, having short-wave length, but absorb long-wave terrestial radiation, thus trapping heat in the lower atmosphere. The global atmospheric concentrations of these trace gases have been increasing, largely due to human activities, and likely to increase substantially in the future. The result is in theory, warming of the Earth's surface and lower atmosphere.

The phenomenon has become known as the "Greenhouse Effect" in popular terminology, and its consequential effect is known as "Global Warming". The gases responsible for this are known as Greenhouse Gases (GHGs). The magnitude of this warming would depend on the rate of increase in the concentration of greenhouse gases in the atmosphere, the radioactive properties of the gases involved and the complex feed-back processes in the earth-atmosphere system.

There exists a delicate balance between earth's hot equatorial climate, cold polar long regions, wind and rainfall patterns. With an increased load of GHGs into the atmosphere and its consequential effect, a new pattern of temperature, wind and rainfall distribution would result. It is believed that the new climate patterns would be significantly different compared to that being observed in different parts of the world.

GHGs and Their Global Emissions

The concentrations of GHGs in the atmosphere are believed to have changed naturally on ice-age time scales, and have been increasing since pre-industrial times due to anthropogenic activities. Table-1 summarises the present and pre-industrial abundances, current rates of change and the atmospheric lifetimes of GHGs. influenced by anthropogenic activities. The abundance of the GHGs were relatively constant for over a thousand years prior to the industrial
revolution. However, with increasing population atmospheric GHG concentrations increased significantly. Evidences from air trapped in Antarctic and Greenland ice shows that there have been major increases in the concentrations of radiatively active gases since the beginning of the industrial revolution (Barnola et at., 1987; Chappellaz et at., 1990).

The important issue in the emission of GHGs is the large gap between the developed and the developing countries. The rich developed countries are emitting GHGs as a result of their wasteful consumption pattern and reckless lifestyle. On the other hand activities of vast population living in poor developing countries also contributing to the GHG load. The per capita GHG emission by industrialised countries is about 6 times the world average emissions, while
GHG emissions from USA alone accounts for 20% of the total global emissions.

Countries like Bangladesh are not big GHG emitters. Unfortunately, as predicted by the national and international research communities involved in climate change impact assessments, poor countries such as Bangladesh would be the worst victims of climate change and sea level rise.

Sea Level Rise

One of the most important consequences of an increase in mean global temperatures will be a possible rise in the sea level around the planet. The reasons for this rise in sea level include:

• The expansion of the ocean's volume when water temperatures increase. Although small, such thermal expansion can translate to a considerable rise in mean sea levels.

• Mountain glacier melt will also contribute a sizeable amount of water to the oceans, which will also contribute to sea level rise. It should be noted that such mountain glaciers melt will not only contribute to sea level rise once the water reaches the sea, but will also contribute to sea level rise once the water reaches the sea, but will also contribute to increased flooding in floodplains.

• Meltwater from the land is expected to be the third component.

In addition to the rise in sea level due to increased temperatures, as described above, the land surface of the planet is also undergoing changes in elevation due to a number of factors, including tectonic changes, sedimentation etc.

Climate Change and Concern of Bangladesh

Bangladesh, .one of the most densely populated countries in the world. With over 755 people per square Km has a per capita income only about US$235. Over 40% of the population live in poverty. With its high population density, low level of development, and low lying deltaic mass, Bangladesh has already been facing a number of natural and man made problems. Natural hazards like cyclones, floods, droughts and socio-economic problems such as poverty, low literacy, poor health delivery systems, high unemployment are some of them. In the future Bangladesh .may also have to face adverse impact of development across Its border -Which among other things, are expected to have reduced availability of water during the dry season and has to deal with impacts of climate change and sea level rise. To better prepare the country for dealing with these impacts pragmatic planning is needed based on authentic data and analyses from scientific studies.

Carbon di-oxide emissions

The commercial energy in Bangladesh is supplied from the following sources:

i) Natural gas (Indigeneous)
ii) Petroleum

a) Imported petroleum products
b) Imported crude oil
c) Local crude oil from Haripur Oil Field

iii) Coal, primarily imported, and
iv) Hydropower

Among these, the last one is not used for estimation of any carbon di-oxide emission, The carbon di-oxide emission from the consumption of the rest, all fossil fuels, has been calculated using the 6-step methodology. The estimates are summarised in Table-4,

From these estimates, one reaches the following conclusions:

• The total carbon dioxide released from all primary fossil fuel use in Bangladesh amounted to 13,443 Gg in 1990.

• The corresponding value of carbon (oxidized) amounted to 3,666 Gg in the base year.

• On a per capita basis the above values of carbon dioxide and carbon emission (1990 population being 109 million) amounted to just about 123,3 and 33.6 Kgs respectively.

• Biomass combustion caused an annual release of 61283.7 Gg of CO2 in 1990. The emission from agricultural residues contributed to about 59% of total emissions from biomass energy combustion. As indicated earlier, however, emission from biomass combustion has not been considered for estimating total carbon di-oxide emission.

Emission Sources

Emission from energy production

In Bangladesh, natural gas is the only indigenous source of commercial energy, excepting a little oil discovered in 1987 and coal which remain yet to be mined. Hence natural gas production is the only source from which methane emission needs to be considered, The natural gas companies reported the following two types of natural gas losses during production and distribution:

Venting and flaring losses                   6.983 MMCF/Yr.
Transmission and distribution losses 305.010 MMCF/Yr.
Total                                             311.993 MMCF/Yr.

Corrected for average methane content of Bangladesh natural gas (96%), the total loss equalled 299.51 MMCF/Yr. Converted into weight, it is estimated that about 6.1 Gg of methane (CH4) gas is emitted due to energy (natural gas) production.

Table- 2 : CO₂ emissions from primary energy sources in Bangladesh

Emission from Landfills

Very little quantitative information exists in Bangladesh on municipal waste. The Study Team could obtain some information only from Dhaka City and some fragmented information on other principal towns. In Dhaka, the following information could be collected, but again in a fragmentary manner:

Municipal solid waste generated
Municipal waste used for landfilling
Total area landfilled

Quite obviously, the available information were incomplete and inadequate. Accordingly, expert judgement and conjectures had to be used in interpreting these information. Be that as it may, the methane emission from six (6) major urban areas of Bangladesh (the capital city of Dhaka, port cities Chittagong and Khulna and three other district towns - Rajshahi, Sylhet and Mymensingh) from land fills has been estimated at about 73.6 Gg per year.

Emissions from Agriculture, Livestock and Waste Water

This section deals with methane emission from various non-energy sources such as flooded rice fields, enteric fermentation in livestock, manure management and anaerobic waste water treatment in municipalities. The general methodology and approach and the default values provided in the given workbooks are modified as deemed necessary to better represent country specific situations. For example, for a variety of reasons, the methane flux in Bangladesh rice cultivation is expected to be significantly lower than in other countries. The rationale for using such country specific values for the calculations are given in details in the relevant final report.

Emission from rice fields

There is a high degree of uncertainty in the global flux measurements in case of methane, particularly from rice fields. Experiments have shown that the Methane flux from flooded rice fields varies with soil type, temperature, redox potential, and acidity/alkalinity of the soil; the type, timing, application method and amount of fertiliser applied; water management technique; and cultivar type (Schutz et al.,1990; Matthews et al., 1991). A range (i.e., 0.19 - 0.69 gCH4fm2/day) for daily emission fluxes, based on the field experiments (Schutz et al., 1989), has been recommended as default values by the OECD report (OECD, 1991) for estimating national CH4 emissions from flooded rice fields. This range, however, has been scaled down on the basis of several criteria applicable to Bangladesh situation. The modified fluxes may be found in the Final Report of the Emission Study.

In estimating methane emission from flooded rice fields the harvested area for each of the major rice varieties are estimated in the first step. This is done by subtracting the area under non-irrigated uplands from the gross harvested area for each of the varieties. Depending on the local agricultural practice and water regime management during rice cultivation, the length of continuously and intermittently flooded days are derived from existing database of Bangladesh Agriculture Research Council.

Emission factors are derived by scaling down the range 0.19 to 0.69 gim2/day (Schutz et ai, 1989) to suit to local conditions and practices in the country. However, this has been done on the basis of expert judgement and needs to be verified through experiments in future.

The lower bound estimates show that Bangladesh emits about 257 Gg of CH4 from flooded rice fields. The upper bound estimate is 622 Gg of CH4. Considering the median values, it is estimated that rice cultivation emits about 468 Gg of methane gas per year. HYV Boro rice (which is dependent on irrigation) contributes about 42% to the methane emission from rice fields followed by HYV transplanted Aman (about 31 %).

Emission from livestock

Bangladesh has one of the highest densities of livestock population per unit of land in the world. But the country does not have any pastoral land dedicated only to grazing. Animals feed themselves by scavenging in and around the cultivated lands and homesteads. Partly, they are also fed with rice straws and husks. On the whole there is a feed shortage. This is reflected in the poor health condition of the animals. Due to lack of adequate nutrition, the animals are under-weight. The average body weight of cattle is only 200-250 Kg for local breeds and 300-450 Kg for improved breeds. These figures are quite low compared to those elsewhere. As expected, the low body-weights result in low level of CH4 emission by enteric fermentation from
livestock sector in Bangladesh. It is estimated that about 446.8 Gg of methane is emitted from enteric fermentation of livestock, 67.5% of which is contributed by non-dairy cattle.

For estimation of methane emission due to manure management, use has been made O.f the default methane emission values by livestock types, as presented in the GHG Emission Inventory Workbook (ICF Inc., 1995). It is estimated that 73.07 Gg of methane is emitted from manure management  a large fraction of which comes from non-dairy cattle.

Emission from waste water treatment

Traditionally waste water from households, be it in the rural or in the urban areas, is ultimately discharged in the open space or in the water bodies. There is only one exception to this traditional practice in the capital city Dhaka. There is a waste water treatment plant adjacent to
Dhaka which treats waste water from municipal sources, but the treatment is not anaerobic. Therefore, waste water from domestic sources in Bangladesh do not emit any significant amount of methane gas.

Industries also discharge huge quantities of waste water into surface water systems. In most cases such waste water is not treated before being discharged. Only recently a few of these industries have taken measures to treat the waste water before releasing it to the nearby surface water system. But there is no systematic database regarding the actual amount of industrial waste water being treated anaerobically. Therefore, methane emission from industrial waste water could not be estimated.

Emissions from Land Use Change and Open Bio-mass Burning

Land use change is often considered to be a major source of GHGs, particularly of CO2, in developing countries. Usually, when forest land is cleared for agricultural or other purposes by felling trees, a part of the carbon locked in them is released as parts of the trees are used as fuel wood, the land clearing takes place through slash and burning and because the soil is disturbed which also release the carbon locked therein. On the other hand if the area under forest or tree cover increases there is likely to be a net sink effect.

Forest area characteristics

The forest area includes officially classified and unclassified state forest land, homestead forest land in rural areas, tea and rubber gardens etc. The private forest areas are tree covered while much of the state forest land is barren of tree vegetation. Still, there are 835,000 ha of state forest land having reasonable vegetation; over in the better quality natural forest areas and bamboo areas and plantations, excluding the parks and sanctuaries. This good quality forest area accounts for 5.8% of the total land in Bangladesh. Apart from the different kinds of forest areas, there are other areas in the country where afforestation has taken place in recent years, especially along the newly built embankments and road sides.

Non-CO2 emissions from Bio-mass Burning

In rural Bangladesh a portion of the above ground bio-mass is left in the fields after each harvest. A fraction of the bio- mass is mulched during the field preparation for the next crop and in some areas farmers amass the dried bio-mass to make a small heap and deliberately set them afire. This open air burning results into emission of gases such as CO2, CO, CH4, N20 and NOx.

Since the major crop in Bangladesh is rice, estimation for emission of non-CO2 gases was done in terms of field burning of paddy-straw only. The amount of CO2 released was not estimated assuming that it would be balanced by locking of carbon by growing plants during the next cropping season. It is found that about 695.4 Gg carbon and about 9.7 Gg nitrogen is being released annually from field burning of bio-mass sources.

Also, as discussed earlier, the major source of rural energy in Bangladesh is the bio-mass source which provides rice straws, husks, dung, twigs and leaves, baggage, jute sticks, fuel-wood etc. It is estimated that traditional bio-mass fuel combustion in open air releases about 189.5 Gg methane gas, 2339.9 Gg of carbon monoxide gas, 2.4 Gg of N20 and 85.9 Gg of NOx gas.

Summary of Total Emissions

Collecting all the results mentioned so far, one may arrive at an aggregate emission figure as shown in Table-5. The estimates indicate that on the basis of global warming potentials, more than one-half is due to methane while about 30% is contributed by CO2 from fossil fuel burning.

Source : Global Climate Change : Bangladesh Episode, 1997, DOE, MoEF-GOB.