How should we approach uncertain threats of potentially very serious harm? For
example, how long should social distancing measures be enforced against the spread
of COVID-19? Should we research and develop climate engineering technologies
as a measure against climate change harms? Should glyphosate herbicides be
banned? Such and similar decisions have potentially far-reaching consequences
for the environment or human health; yet they often have to be made under
considerable uncertainty, for example, uncertainty about the extent of possible harm,
its likelihood, or cause-and-effect relations. Frequently, precautionary principles
(PPs) are proposed as an answer to such challenges, telling us that we have to
act to prevent harm even if it is uncertain. However, this idea also comes in for
criticism as being alarmist, anti-scientific, and in effect doing more harm than good
by causing high costs and stifling innovation. The question of how we should deal
with uncertain harms is clearly a controversial one. When we seek to address this
issue, we are not only faced with the question of whether precautionary principles
are justified. More fundamentally, the methodological question arises of how such
principles can be justified-what is an adequate method for the justification of a
precautionary principle?
