Cities are now the center stage in the battle against climate change, contributing as they do about 75 percent of carbon dioxide (C02) emissions across the globe. This at a time when more than 50 percent of humanity lives in cities and towns, a figure that can only increase given the scale of urbanization in the developing world.

In the lead-up to the UN climate change conference in Copenhagen in December this provides us with plenty of food for thought on city-level strategies to deal with global warming. The cities have good reason to address the problem in order to improve the local environment for their residents.

What is happening sooner than expected is that the mega-cities of the developing world are already rivaling or even exceeding the CO2 footprint of major cities in the developed world, both in terms of total output and per capita.

The UN-backed Bangkok Assessment Report on Climate Change 2009 found that the Thai capital emitted 43 million tons of CO2 in 2005, lower than the figure for New York (58 million tons) but almost the same as London (44 million tons). In per capita terms, Bangkok residents were responsible for producing 7.1 tons of CO2 per year in 2007, the same level of emissions as New Yorkers and significantly higher than Londoners (5.9 tons per capita).

Transportation, electricity generation, solid waste and waste water account for about 90 per cent of the emissions in Bangkok.

The transport sector alone is responsible for 38 per cent of the yearly CO2 emission, reflecting a massive expansion in the use of passenger vehicles. The number of motor vehicles registered in Bangkok rose from 600,000 in 1980 to 4,163,000 in 1999, a sevenfold increase, and by the end of 2007 the figure had reached 5,614,294.

Let us not forget how vulnerable developing cities are to climate change. Bangkok gets its water supply from the Chao Phraya and Mae Klong rivers, both of which are fed by Tibetan glaciers, as are almost all the rivers of mainland Asia. So a rise in temperature, resulting in the further melting of the glaciers, would increase the likelihood of floods in Thailand.

The double-whammy for Bangkok is that it is also vulnerable to a rise in the sea level. Almost 55 percent of the city would be vulnerable to floods if the sea level rose by 50 cm, and 72 percent would be threatened by a rise of 100 cm.

So it is clear that Bangkok is primary example of a developing world city that needs to adapt to and mitigate climate change, not only as part of an international strategy to combat global warming, but also because of the immediate threat to its own residents.

The measures to be implemented by Asia's growing metropolises to cut their CO2 emissions and improve the quality of life for residents include investing in public transport in order to achieve a modal shift away from private vehicles, appropriate road pricing to deter vehicles from entering city centers, as has been adopted in Singapore and London, and better public information on travel options as well as education on the health costs of poor air quality because of increased use of private vehicles. Similar measures need to be implemented in the energy and waste management sectors.

In Copenhagen, alongside the formal procedures of the conference of the parties, which are predominately nation states, there will undoubtedly be a lot of focus on what cities can contribute to humanity's battle against climate change because the environmental impact of the world's major cities is much greater than that of many nation states.

Indeed, capital cities in the developed and developing worlds both often dominate their national economies, with Bangkok acting as the economic hub of Thailand's economy in a way that is not dissimilar to the role of London in the UK economy.

This does suggest that major cities should also be made into parties to the conference, legally bound to any future agreement and commitments. There could also be instances where cities and their regions may agree to many of the changes that their nation states' representatives reject. This is what happened in the US when the Bush administration refused to ratify the Kyoto Protocol, which many American cities and regions, such as San Francisco and the state of California, signed.

While opt-outs should be discouraged, this more flexible approach could be useful in any developing nation that refuses to sign an international agreement on the grounds that the developed world has failed to accept its responsibilities.

The author is Chair of UK's Environment Committee.