Climate Change

Geo-engineering to the rescue?

Paul Crutzen, Nobel Prize winner (1995) and renowned atmospheric chemistry expert at the Max Planck Institute in Germany, believes that the 2007 report by the IPCC risks “falling short of reality”. Last year the Dutchman broke a taboo when he declared that direct human intervention in the Earth’s atmosphere was an option that needed to be looked at – should the climate machine spin out of control.

Paul Crutzen Paul Crutzen – “The only criticism that could be made of the IPCC report is of it being too cautious.”
The gigantic eruption of the Indonesian volcano Pinatubo, in June 1991, served as a vast natural climatological laboratory for observing the impact of massive gas emissions into the atmosphere, and in particular the role of sulphur as a ‘moderator’ of the greenhouse effect. The gigantic eruption of the Indonesian volcano Pinatubo, in June 1991, served as a vast natural climatological laboratory for observing the impact of massive gas emissions into the atmosphere, and in particular the role of sulphur as a ‘moderator’ of the greenhouse effect.
© U.S. Geological Survey

What is your reaction to the conclusions of the latest IPCC report?

There are no major surprises for those who follow these issues. The figures are not really that different to those published in 2001 in the previous report. But this does not mean there has been no progress in climatology since then. The probabilities of the anticipated changes are now more precisely defined and better backed up by the facts.

For example, the discrepancy between temperatures recorded in the atmosphere and satellite data was a cause of concern. This has now been resolved as a result of errors identified in the interpretation of the satellite readings. What is more – and this is very important – it is now established that the rise in temperatures will reduce the oceanic and terrestrial carbon sinks, to the point where they could release their carbon stocks and thereby become a source of CO2. In 2001 this question was still open to debate.

The only criticism that could be made of the IPCC report is of it being too cautious and, I fear, falling somewhat short of reality. The situation may be more critical than it suggests. For example, the situation regarding the rise in sea level is no doubt underestimated, as a number of scientists have already pointed out.

The climate is perhaps less stable than we think and temperatures could rise more quickly than expected. Let me give you a comparison. The ozone layer is my specialist subject. Our initial evaluations of the ‘hole’ in the ozone layer proved to be grossly underestimated. This was because we had not taken into account what was happening over the Antarctic. We had not imagined that CFCs injected into the medium and high latitudes of the Northern Hemisphere had the principal (and disastrous) effect of changing the ozone situation at the opposite pole of the planet. Could we not be in for a similar ‘surprise’ with global warming? We must have a strategy ready that enables us to react in such an eventuality. The controlled emission of sulphurous aerosols is an option that could be envisaged. Released at the rate of a million tonnes a year this would slow the process significantly.

You sparked a controversial debate when you suggested looking at the possibilities of ‘cooling the climate’ by releasing sulphur into the Earth’s atmosphere. This suggestion has met with far from unanimous support.

If the climate warms too much and too quickly, with increasingly intolerable consequences for large sections of humanity, we could have to consider emergency solutions. We know that large quantities of sulphurous aerosols are released into the atmosphere naturally every time there is a major volcanic eruption. The result, which has been well observed, is a significant cooling of the atmosphere. This is due to a simple mechanism: the sulphur particles reflect the incoming sunlight, increasing what is known as the albedo (1) of the atmosphere.

Do you have any idea of the cost of such a strategy and of the technology that could be used?

When it comes to the technicalities I must be careful in what I say as I do not claim to be an expert on space matters. The National Academy of Sciences (NAS) in the United States has already looked at this. It seems that a possible action would be to use two rockets that would burn hydrocarbons while in the atmosphere and then switch to sulphuric acid on reaching the stratosphere. The aerosols must reach the stratosphere; otherwise they would be quickly washed away by rain.

What would be the side effects of these ‘provoked’ emissions?

Some of these aerosols would fall back to earth in the form of sulphuric acid, which would produce acid rain. But it is unlikely that the acidification would be more than a few per cent and ecosystems can probably absorb that. There were greater emissions of sulphur of human origin 20 years ago and emissions of this kind did not in any way have a catastrophic impact comparable to that of greenhouse gases. But clearly it is necessary to monitor any rise in sulphurous emissions by countries experiencing rapid industrialisation, such as China and India. So this must be taken into account.

One possible adverse side effect is increased damage to the stratospheric ozone. This needs to be verified. Finally, there is another possible and undesirable consequence on which we must be quite clear before we start: these aerosols may favour the creation of cirrus clouds. These are high-altitude clouds that would then reinforce the greenhouse effect. That is why research is needed.

Environmentalists react to your proposals by condemning a science that is seeking to play God. But what is the response among members of the scientific community?

Some are in favour and some are against. Of course some have attacked me very forcefully, but in the end… less so than I had expected. In the end, this has been a very moderate debate and I think we will find a consensus in favour of financing the acquisition of knowledge. Modelling work has already been done. The models were calibrated using the large volume of data collected during recent measurement campaigns carried out after the eruptions of Pinatubo (Indonesia) in 1991 and of El Chichon (Mexico) in 1982. Immediately after any further major eruptions in the coming years, we should be in a position to initiate in-depth observations.

Are there any other of these ‘geo-engineering’ solutions that you believe deserve attention?

Certainly. There is the geological storage of CO2, which is also a type of geo-engineering and one that has already been studied closely. We could also envisage distributing iron in the oceans to stimulate oceanic photosynthesis, which stores a lot of carbon. Another proposal made was to install pumps beneath the oceans so as to release dissolved salt particles that would increase the albedo. Finally, there is the idea of placing ‘mirrors’ in space to deflect the sun’s rays.

All these possibilities need to be explored scientifically. At least I am happy that, by publishing the article in 2005, I was able to contribute to this debate on geo-engineering.

Would it not simply be preferable to reduce our emissions?

Of course! I am not saying we should do all these things, but research should be carried out to explore the possibilities. However the existence of such research projects must not in any way be used as a pretext for continuing to pollute the environment. I hope that geo-engineering will never be necessary.

It is just that the past has made me pessimistic. The last IPCC report seems to have sparked a growing awareness not just among scientists but also among the general public and industry. It remains to be seen whether this will last. We have already seen these periods of euphoria after the Rio summit, following the Kyoto agreements and, even before that, in the 1970s. But nothing ever really came of them. So I hope that now we are going to see some genuine measures of sufficient magnitude to bring about a radical change of course.

  1. The albedo is the ratio between the solar energy reflected by a surface and incident light or radiation. It is measured on a scale of 0 (representing a black surface with no reflective property) to 1 (corresponding to a perfect mirror that reflects in all directions and with zero absorption of all the visible electromagnetic rays it receives).
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