CNG produces a lower level of greenhouse gases and is an environmentally cleaner alternative to petrol. Dhaka's residents are among the most vulnerable to global warming and don't want to become "climate terrorists".
The city is among more than 3,000 identified by the UN-Habitat's State of the World's Cities 2008/09 as facing the prospect of sea level rise and surge-induced flooding. The report warns policymakers, planners and the world at large that few coastal cities will be spared the effects of global warming.
Asia accounts for more than half the most vulnerable cities, followed by Latin America and the Caribbean (27 percent) and Africa (15 percent); two-thirds of the cities are in Europe, and almost one-fifth of all cities in North America are in Low Elevation Coastal Zones (LECZ).
During the 1900s, sea levels rose by an estimated 17cm; global mean projections for sea level rise between 1990 and 2080 range from 22cm to 34cm, according to the UN-Habitat researchers.
The report points out that by 2070, urban populations in river delta cities, such as Dhaka, Kolkata (India), Yangon (Myanmar), and Hai Phong (on the coast near Hanoi in Vietnam), which already experience a high risk of flooding, will join the group of populations most exposed to this danger. Port cities in Bangladesh, China, Thailand, Vietnam, and India will have joined the ranks of cities whose assets are most at risk.
African coastal cities that could be severely be affected by rising sea levels include Abidjan (Cote d'Ivoire), Accra (Ghana), Alexandria (Egypt), Algiers (Algeria), Cape Town (South Africa), Casablanca (Morocco), Dakar (Senegal), Dar es Salaam (Tanzania), Djibouti (Djibouti), Durban (South Africa), Freetown (Sierra Leone), Lagos (Nigeria), Libreville (Gabon), Lome (Togo), Luanda (Angola), Maputo (Mozambique), Mombasa (Kenya), Port Louis (Mauritius), and Tunis (Tunisia).
Dhaka is wedged between huge rivers like the Ganges and the Brahmaputra, with hundreds of tributaries swollen with increasing glacial melt from the Himalayan ranges as a result of soaring global temperatures.
"The elevation in Dhaka ranges between two and 13 metres above sea level, which means that even a slight rise in sea level is likely to engulf large parts of the city. Moreover, high urban growth rates and high urban densities have already made Dhaka more susceptible to human-induced environmental disasters," said the UN-Habitat report.
"With an urban growth rate of more than four percent annually, Dhaka, which already hosts more than 13 million people, is one of the fastest growing cities in Southern Asia, and is projected to accommodate more than 20 million by 2025.
"The sheer number of people living in the city means that the negative consequences of climate change are likely to be felt by a large number of people, especially the urban poor who live in flood-prone and water-logged areas."
A total 634 million people in the world live in LECZ that lie at or below 10 metres above sea level, according to a recent report, Planet Prepare, by World Vision, a Christian relief, development and advocacy organisation. Although LECZ constitute only two percent of the earth's landmass, they contain 10 percent of its population and have a higher rate of urbanisation than the rest of the world.
Ban Ki-moon, Secretary-General of the UN, notes his concern about the prospect of large-scale devastation in his foreword to the UN-Habitat report, saying: "Cities embody some of society's most pressing challenges, from pollution and disease to unemployment and lack of adequate shelter. But cities are also venues where rapid, dramatic change is not just possible but expected."
Dhaka is preparing for flood protection. The government, prompted by frequent flooding in the 1980s, has already completed embankments, reinforced concrete walls and pumping stations in the most densely populated part of the city.
The UN report cautioned that Dhaka's solutions should also take into consideration unresolved development problems, such as the growing slum population, which has doubled in the last decade and shows no signs of abating.
The World Vision report pointed out that other urban centres not physically challenged by global warming would also face tremendous challenges, with the possible influx of "environmental refugees" from affected cities.
The Intergovernmental Panel on Climate Change (IPCC) has urged global greenhouse gas emission reductions of 50 percent to 85 percent by 2050, based on 2000 emissions, to avoid a 2=B0Celsius increase in global mean temperature.
Such an increase is expected to destroy 30 percent to 40 percent of all known species, generate bigger, fiercer and more frequent heat waves and droughts, and more intense weather events like floods and cyclones.
The IPCC and activists have called on the global community to focus on preventing global warming from crossing the perilous 2=B0C threshold, which requires keeping atmospheric carbon dioxide (CO2) concentrations below 350ppm (parts per million).
"The problem is, they [concentrations] already stand at 385ppm (2008), rising by 2ppm annually," said the World Vision report. "Since there are no rewind buttons for running down emitted greenhouse gas stocks, implicational reasoning suggests immediate and stringent emissions cuts."
Eminent scientists, such as James E. Hansen, who heads NASA's Goddard Institute for Space Studies, are warning that even the 2-degree threshold may likely not be safe enough to avoid "global disaster".