Public confused by risk language in IPCC reports

Savita Verma, Joshua Howgego and T.V. Padma in SciDev.net: The phrases used in UN Intergovernmental Panel on Climate Change (IPCC) reports to convey the probability of extreme events happening due to climate change are often misinterpreted by the general public in many countries, a study says.

As a result, it urges the panel to always give the percentage chance of an event occurring whenever it uses such risk phrases. The confusion arises with phrases such as ‘likely’, ‘very likely’, ‘about as likely as not’ or ‘virtually certain’, which the IPCC uses in its reports to denote the probability of extreme events such as floods arising. The numerical definition of the phrases typically appears in a separate appendix...

The IPCC uses these phrases to denote specific probabilities. But research shows that people worldwide often misunderstand the panel’s intended meaning. The study, published last month in Nature Climate Change (20 April), surveyed more than 10,000 people from 24 countries, asking them what they understood the IPCC’s phrases to mean.

Participants were randomly divided into two groups. One was given the IPCC’s risk phrases, translated into their language. The other saw the same phrases, but the numerical risk was also presented in brackets after the words.

...They found that 27 per cent of those in the first group correctly understood the IPCC’s meaning, but this rose to 40 per cent in the second group. Most people tended to underestimate what was meant by high probabilities of extreme events occurring and overestimate low probabilities....