Paul J Crutzen received the 1995 Chemistry Nobel prize for showing that nitrogen oxides react catalytically with ozone, thus accelerating the rate of reduction of the atmospheric ozone content. His findings have triggered off much research on biogeochemical cycles like the carbon and nitrogen cycle. But he tells Archita Bhatta that while the carbon cycle has been studied elaborately, dangers lie in the neglect of the nitrogen cycle

Where does the global research on biogeochemical cycles stand?
There's been much research on the carbon cycle. But the nitrogen cycle has been neglected.

What are the gaps here?
We do know how much nitrous oxide and other nitrogen oxides are emitted in total, but we don't know their hotspots. There is also a serious mismatch: the aggregate of individual emissions does not tally with the total emission figures for nitrous oxide and other nitrogen oxides. We are perhaps, not looking at the right places for oxides of nitrogen.

What are the greatest dangers?
Sources and sinks of nitrous oxide or laughing gas are not well known. The amount of nitrous oxide in the atmosphere is increasing by 0.2 to 0.8 per cent each year. So at some point, nitrous oxide could contribute significantly to global warming.

What possible sources of oxides of nitrogen could have eluded us?
We have looked at agriculture and fossil fuels. We should check on biofuels. They could be a major source, since we are looking at them as alternatives to fossil fuels. The nylon industry could also be a significant source.
There could be others too which we haven't looked into.

Why has the nitrogen cycle not been studied?
It seems that the emphasis on the carbon cycle has worked to the detriment of research on the nitrogen cycle.

What are the precautions that can be immediately adopted?
Only 30 per cent of the nitrogen fertilisers used in agriculture is consumed. The unused nitrogen enters the nitrogen cycle and disrupts it. We should use fertilisers more efficiently.

Your views on the ozone depletion and global warming.
The ozone hole problem has been solved. We have found replacements to ozone depleting substances like chloroflurocarbons. However it will take about 70 years to get rid of chloroflurocarbons from the atmosphere.
The global warming problem, however, is far from being solved. Everybody is talking about it, but nobody is doing anything about it.

What is the basis of the problem?
The financial intent of oil companies. But of late, they seem to be realising that the current state of affairs will not help them.

Why do you call this era the Anthropocene era?
Geologists call this era, the Holocene era. But in this era, influence of human activities on the earth's surface has been the maximum. So I would like to call it the Anthropocene era.

Is there enough political will to address human influence on earth?
It is poor but improving. What is positive is that industries have become aware of the enormity of the problem.

Have scientists been able to communicate the enormity of the problem?
I think we have done enough.

What do you think is the solution for the problem of global warming?
We have to cut down on the burning of fossil fuels. At the current pace of development, however, this does not seem very possible.
We have thought of a solution in case temperatures on Earth reach an unbearable level. This involves introducing sulphate aerosols in the stratosphere. If we can introduce a million tones of sulphate aerosols each year into the stratosphere, they will either reflect away or absorb the sun's rays and disallow them from reaching the Eath's surface. That will cool the Earth's surface.

But what about pollution problems of sulphate aerosols?
Let me be clear, I am not advocating this method. Aerosol introduction will be the last resort. There should be elaborate studies on this. It has been established that the method can cool the Earth's surface. There should be no restriction on studying the positive and negative impacts of aerosols.
The method does not require much aerosol. So we don't anticipate acid rains or depletion of ozone layer by aerosols. I also believe that photosynthetic activity will not be affected. But we do need to study the negative impacts on aerosol in greater detail.

Is there no alternative to sulphate aerosols?
I have also thought of carbon particles. But the case of aerosols is vindicated by a natural experiment: volcanoes.

What about the long term effects of air pollution?
We have to choose between the necessity of cleaning up the air and the necessity of solving global warming. It is a difficult dilemma. However, we have chose according to exigencies.