Caldeira Lab

Prudence on solar climate engineering

Ken Caldeira & Katharine Ricke

Caldeira, K., and K. L. Ricke, 2013: Prudence on solar climate engineering. Nature Clim. Change, 3, 941–941, doi:10.1038/nclimate2036


To the Editor — The call for prudence by Schäfer et al. (Nature Clim. Change 3, 766; 2013) in relation to field tests of solar climate engineering is welcome. We applaud their effort to help establish informal norms to stifle counterproductive experimentation. However, we should be careful to make sure that what is called ‘prudence’ does not hamper beneficial scientific and technical investigation. Furthermore, efforts to develop more formal governance mechanisms, specifically around solar climate engineering field experiments, may prove wrong-headed. It may be wiser to create mechanisms for governing the more general case of experiments conducted in international waters or airspace that have prima facie potential to produce more than trifling harm to an international commons or across international boundaries.

The phrase ‘field test of solar climate engineering’ cannot be unambiguously defined. If I paint a one metre square with white paint on my dark asphalt driveway and measure the reflected sunlight, is that a field test of solar climate engineering? It would seem that if my intent were to develop technologies that would ultimately modify climate at the global scale, then the answer would probably be ‘yes’. If the aim were simply to test which asphalt paints areeasiest on the eye, then the answer would probably be ‘no’.

So, whether this is a solar climate engineering field test or not depends not only on my actions, but also on my intent.

But what if someone else is funding this project, and they want to develop a solar climate engineering system but I just want driveway paints that are easier on the eye (or vice versa)? Whose objective counts, that of the experimental scientist or that of the funder?

It is problematic to require that issues of intent be resolved to determine which governance regime applies. In a workable regulatory system, a physical description of the action should determine whether the governance scheme applies. It seems for a governance regime to be triggered, the risks of damage from a project must derive from a physical effect that exceeds some specified minimal level: the intent of the various parties involved in a project should be taken into account when determining whether expected benefits exceed expected damage in any particular case.

Schäfer et al. are correct in suggesting that even such low-impact experiments could provoke a negative and ultimately counter-productive backlash, and therefore they are well justified in counsellingscientists and engineers to proceed cautiously and prudently. However, prudence does not always mean refraining from performing an experiment. Galileo’s peers may well have felt that he was imprudent in dropping the balls off the leaning tower of Pisa, but that doesn’t mean that he shouldn’t have dropped them.

The central point is that a governance regime can consider intent in weighing whether an activity can go forward, but determination of intent should not be a prerequisite for determining which scheme of governance applies. The trigger for a formal regime should be based on a physical description of the proposed activities and not its intent.

The governance regime should be responsible for determining intent. It would be impractical to have a ‘pregovernance’ process to first determine intent so that it can be decided whether a governance regime should apply. How would it be decided which activities are subject to this pregovernance process?