When people say that ‘the science of climate change is settled’ they are often being problematically imprecise. Elements of the science are certainly settled beyond a doubt – for instance, the simple fact that adding carbon dioxide to the atmosphere raises global temperatures. Other elements are certain but less precise: overall warming of the planet will alter air and water currents, though we do not know exactly how. Still higher order questions have answers at lower levels of both precision and certainty.
This graphic sketches out a bit of what I mean:
Responding to climate change is perhaps the ultimate case of needing to make decisions under conditions of uncertainty. Simplistic conceptions of what it means for something to be ‘certain’ must give way to a more nuanced appreciation of the nature of knowledge and evidence.