PRINCETON – Many people who advocate draconian measures to counteract climate change base their argument on the so-called “precautionary principle,” which holds that when a possible future disaster would be unacceptably severe, action to prevent it is imperative. Cost-benefit analysis – balancing the cost of remedial action against the benefit of avoiding disaster – is no longer permissible. Action to counter the disaster must be taken, regardless of the cost.
This principle leads people to advocate enormously costly actions to prevent disasters that are even more enormous but whose likelihood highly uncertain. If a disaster is unacceptable, then, no matter how uncertain the likelihood of its occurrence, it must be prevented.
As a result of widespread reliance on the precautionary principle, doomsday scenarios have come to dominate discussion of climate change. It is easy to imagine disasters so severe that drastic action to prevent them would be reasonable, and advocates of drastic action can easily scare the public with imagined disasters. Nobody knows enough about the causes of climate change to prove that an imagined disaster is impossible.
What is wrong with the precautionary principle? It appears to be a statement of the obvious: unacceptable disasters require extraordinary counter-measures. The problem is that the principle cannot be applied consistently.
The world in which we live is a small garden of well-explored territory surrounded by a dim and dark forest of disasters. Disasters lurking in the distance are legion: asteroids and comets; world-wide pandemics and plagues; nuclear and non-nuclear wars; droughts, famines, and floods; volcanic eruptions, earthquakes, and tsunamis; human over-population and extinction of non-humans; rising temperatures and sea-levels; falling temperatures and spreading ice ages; exhaustion of clean air and water; disappearance of forests, farms, and fish.
All these disasters – and many others still to be imagined – are possible, and many of them are unacceptable. The precautionary principle prescribes action, regardless of cost, to prevent all of them. But this is impossible. There is no future free of risk.
No matter what we do or fail to do, the risk of unacceptable disasters will persist. Our resources are limited, and so are the costs we can pay for remedial actions. There is no escape from balancing costs and benefits. There is no way we can avoid making difficult choices. Some disasters are less likely than others, and some remedies are more costly than others. These are the facts of life that the precautionary principle tells us to ignore.
It sometimes happens that a drastic action designed to prevent an unacceptable disaster may make the disaster worse. Catastrophic disasters associated with climate change are easy to invent, but the effects of remedial actions may be difficult to predict.
For example, one of the most immediate and severe consequences of climate change could be a rapid rise in sea level. It is generally believed that the appropriate preventive measure is to stop burning fossil fuels and reduce the abundance of carbon dioxide in the atmosphere. But the preventive measure is extremely costly, and it might have an effect opposite to our intention.
We know that the sea level rose by roughly 100 meters during the last 12,000 years. This rise was clearly connected with the melting of the continental ice sheets at the end of the last ice age – that is, it had nothing to do with human activities.
During the last 200 years, a period when we have had accurate measurements from tide gauges, the sea level has continued to rise slowly. We do not know how much of the recent rise is caused by human activities. Some of the recent rise, associated with the shrinking of glaciers, is not caused by human activities, since the glaciers have been shrinking for hundreds of years while human activities became significant only in the last century.
The air surrounding Greenland and Antarctica has recently become warmer and more humid. Warm and humid air will increase melting of ice in low regions at the edges of the ice sheets while boosting snowfall over cold high regions in the interior. The melting causes the sea level to rise, whereas the snow causes it to fall. We do not know which of the two effects predominates.
If the Arctic Ocean becomes ice-free in summer, the melting and the snowfall will probably increase sharply. At that point, the precautionary principle might suggest that we take drastic action to stop burning fossil fuels. But we had better know for sure which way the response will go before we apply the remedy.
It would be unfortunate if China and India were to impoverish themselves by ceasing to burn coal, only to have the resulting decrease of snowfall over Greenland and Antarctica cause sea levels to rise faster. The precautionary principle is not a useful substitute for scientific understanding.