CNG switch a bonus for climate change

Subhra Priyadarshini

doi:10.1038/nindia.2008.238 Published online 7 July 2008

Conor Reynolds with an auto rickshaw driver in New Delhi and (inset) Milind Kandlikar.

The Indian capital switched over to compressed natural gas (CNG) from diesel and petrol for its public transport in 2003 to check the alarming level of air pollution. Fresh research now points out that New Delhi's thoughtful initiative might also have had a positive spin-off for its climate1.

Researchers from the University of British Columbia in Vancouver have found that since many of the vehicle emissions associated with air pollution were also significant contributors to global warming, it was only natural that curbing them would have obvious climate benefits.

Researchers Conor Reynolds and Milind Kandlikar from UBC’s Institute for Resources, Environment and Sustainability, examined the climate impacts of fuel-switching programmes in New Delhi, which has converted its public transportation fleet comprising almost 90,000 buses, cars, and auto-rickshaws from gasoline and diesel to natural gas.

The UBC team wanted to investigate whether Delhi's project to improve air quality also had an impact on emissions related to climate change. The team gathered data on the characteristics and activity patterns of the public transportation fleet in Delhi and calculated the change in global warming-related emission levels that resulted from the fuel conversion process. They found that fuel switching resulted in a 10% decrease in harmful greenhouse gases when a range of emissions (including carbon dioxide, methane, and aerosols) was considered.

The team, however, was not entirely happy with the fuel-switching programme and feels that it could do with some improvements. "Natural gas is composed mostly of methane, which is an important contributor to climate change. When the engines are converted to run on natural gas, they don't work as well as they were originally designed to," Kandlikar says.

Significant amounts of methane are lost to the environment and contribute to global warming. The research team is now investigating options to improve the process of converting engines. "If we can reduce the amount of methane emitted from these converted engines, the net climate benefit could increase from 10% to at least 20%," Reynolds says.

Policy incentives to target methane reduction could be found in the form of funding from the UN Framework Convention on Climate Change Clean Development Mechanism, they suggest. The researchers are now investigating the feasibility of aligning methane reduction efforts with this funding programme, which pairs developed and developing countries on joint projects to reduce global-warming emissions.


  1. Reynolds, C. C. O. et al. The climate impacts of air quality policy: Switching to a natural gas-fueled public transportation system in New Delhi. Environ. Sci. Technol. doi: 10.1021/es702863p (2008)