Many public conversations we have about science-related issues involve communicating risks: describing them, comparing them and trying to inspire action to avoid or mitigate them.
Just think about the ongoing stream of news and commentary on health, alternative energy, food security and climate change.
Good risk communication points out where we are doing hazardous things. It helps us better navigate crises. It also allows us to pre-empt and avoid danger and destruction.
But poor risk communication does the opposite. It creates confusion, helplessness and, worst of all, pushes us to actively work against each other even when it's against our best interests to do so.
So what's happening when risk communications go wrong?
The more serious problem with California's law is one of effect size. Health, and cancer, aren't binary. Consumers can't just be concerned with whether a danger exists; they also need to be concerned about the magnitude of that risk. Even if there's a statistically significant risk between huge quantities of coffee and some cancer (and that's not proven), it's very, very small.
Cigarettes have a clear and easily measured negative impact on people's health. Acrylamide, especially the acrylamide in coffee, isn't even close.
Warning labels should be applied when a danger is clear, a danger is large and a danger is avoidable. It's not clear that, with respect to acrylamide, any of these criteria are met. It's certainly not the case regarding coffee. Whatever the intentions of Proposition 65, this latest development could do more harm than good.