Summary :
Conventional wisdom has it that mankind’s knowledge doubles every ten years. Or is it every five years? When talking about knowledge, people are usually pondering problems of plenty nowadays. The general feeling is that there is an abundance of information out there, readily available through the Internet and other media, leaving experts and decision-makers with the challenging task of keeping up to date. Of course, gaps in our knowledge remain, but those will surely disappear with some more research. Against this background, deeper thoughts about the limits of our knowledge may appear obsolete, or even risky: when Donald Rumsfeld talked about the difference between “known unknowns” and “unknown unknowns” in a press conference, he earned himself an overwhelmingly cynical response, and the 2003 “Foot in Mouth Award” of the Plain English Campaign.1 After all, haven’t we known the response to the problem of ignorance ever since Francis Bacon noted that “knowledge is power”? The self-proclaimed knowledge society of the twenty-first century is having a hard time accepting ignorance as more than a temporary phenomenon, bound to shrink and disappear with the march of scientific progress. Environmentalists in particular have been hesitant to reflect more deeply about the social functions of ignorance. After all, they frequently insist that action, rather than knowledge, is the crucial challenge. The current debate over climate change is the most recent example: over the last decades, researchers have described and explained the ongoing changes with growing precision and certainty, and yet the political response is agonizingly slow. Ignorance seems to be a problem of politicians and lobbyists unwilling to take cognizance of the scientific state of the art—a situation that looks by all means typical for environmental debates. Time and again, environmental historians have described the identification of environmental problems through research as a mere prelude to the actual conflict. For example, the risks of DDT were known long before its ban, and actually before Rachel Carson’s famous rallying cry in Silent Spring.2 The health hazards of lead were also quite familiar when tetraethyl lead was introduced as a fuel additive in the 1920s, a fact that was already troubling to industrial hygienists back then.3 With that, the place of ignorance in environmental debates might seem clear: it is a notorious source of problems that we can control through careful, independent research.

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