What does the ubiquitous auto-rickshaw and the plush aeroplanes have in common, other than getting us from one place to another? The auto-rickshaw, as India's largest manufacturer Rahul Bajaj will tell you, is the symbol of democratic mobility - it provides transport for large number of people at what he says is affordable costs. But it pollutes. How do you balance interests of equity and access with the interests of clean air and health?

One approach is to find fuel and technology options to reduce emissions. Delhi, for instance, now runs autos on compressed natural gas; Kathmandu has a fleet of battery-operated autos and Bangalore is experimenting with LPG. But if this emission-efficiency happens without controls on numbers of vehicles, then the "clean" atmospheric space created will be gobbled up and decimated by the hordes of private vehicles on the roads.

The other approach is to create ecological space for auto-rickshaws to emit. That is, atmospheric space would be allocated based on the number of people a vehicle transports.

Cars - which transport fewer numbers - would have to be reduced. This would also mean that we should reduce the numbers of auto-rickshaws and replace them with bus transport, which carry even larger number of people.

If the bus is emission-free, we get a double win - where mobility is possible without damaging our health and the health of our planet. Call it moving from autocratic pollution to democratic pollution control.

But what does this have to do with aircraft? We know that aircraft are responsible for greenhouse gas emissions: the average plane releases close to one tonne of carbon dioxide for each passenger it carries from London to New York.

Industry argues that its contribution to total human-made emissions is minuscule.

Scientists disagree saying high-altitude emissions are more damaging to the environment; nitrogen dioxide from airline engines leads to formation of ozone and they are worried about the impact of cirrus clouds formed because of airline travel.

But what is not disputed is the growth of industry and emissions. In Europe, it is estimated that emissions from air travel increased by 73 per cent between 1990 and 2003 and are spiralling upwards.

In fact, environmental NGOs estimate that this growth of airline emissions has just about cancelled out a quarter of the emission reductions made by European countries over the same period. Europe has just voted to cap airline emissions in the future with a European airline emissions trading scheme.

But here the similarity between autos and planes ends. The fact is that airline travel cannot be considered "survival" emissions but are "luxury" emissions. The fact also is that the rich in the world have overused their atmospheric space (or pollution quota) and that the poor need to be compensated for this overuse.

The sad and unfortunate fact also is that the poor are most vulnerable to adverse climate changes. Therefore, a tax on the airline industry is needed to pay for the unused carbon quota of the poor or indeed their adaptation costs.