Preferred method of conveying climate risk doesn’t work

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If I told you that something was "very likely," what would you consider the odds of it happening?

The answer isn't just academic. The Intergovernmental Panel on Climate Change (IPCC) reports on climate change use terms like "unlikely" and "virtually certain" to describe very specific degrees of certainty or probabilities of future events—information that informs government policy. And the challenges of conveying that information extend well beyond the climate. Pretty much any risk evaluation, from health to nuclear safety, involves some degree of conveying probability.

The IPCC's approach is to go for readability, using the phrases noted above instead of numerical values; it typically provides the translation between words and numbers in a table near the top of their reports. For example, crack open an IPCC report and you'll see that "very likely" means greater than 90 percent.