The most comprehensive compilation of climate change research is using language that undersells how bad things are, a new paper argues. It's both skating over worst case scenarios and failing to express the strength of some evidence. The paper's authors argue that, along with the distinguished climate scientists writing IPCC reports, psychologists and professional communicators should have input to improve public understanding of the science they describe.

The 5th Intergovernmental Panel of Climate Change (IPCC) Assessment Report, published in 2014, brought together the best climate science in the world at the time. It shaped the thinking, not just of the governments that are its prime audience, but of businesses, journalists, and lobby groups. As part of this important role, the report, like those before it, attempted to explain the scientific uncertainty around aspects of climate science. Rather than expressing certainty, expectations are expressed in terms of confidence, for example that there is a 66-100 percent chance that something is happening or will happen.

However, Dr Salvador Herrando-Pérez of the University of Adelaide argues this cautious language can hinder public understanding. In BioScience, Herrando-Pérez and co-authors provide an analysis of the reports' language and describe it as “remarkably conservative”. Herrando-Pérez said in a statement: “We found that the main message from the reports – that our society is in climate emergency – is lost by overstatement of uncertainty and gets confused among the gigabytes of information.”

On questions where our knowledge is as certain as anything in science, Herrando-Pérez told IFLScience that the IPCC avoids expressing 100 percent certainty. Philosophers of science will note nothing in science is ever truly certain, but there are many things where the chances of being wrong are so small it makes sense to round to 100 percent. Herrando-Pérez claims that “greenhouse gasses as the primary cause of warming” falls into that category.

Moreover, Herrando-Pérez argues, the report softens the danger we are in. For example, while there is genuine uncertainty about how much sea levels will rise this century, the report gives a lower estimate that's 10 centimeters (4 inches) below the papers on which it is based.

When it comes to the summary for policy makers, which is edited by representatives of governments, Herrando-Pérez told IFLScience that direct pressure from inactivist politicians likely affects the wording. Elsewhere in the report, he thinks the caution reflects fears of another “glaciergate”, where a single error among the fourth report's thousands of pages was used by climate denialists to discredit the entire document.

In addition, Herrando-Pérez believes many IPCC authors may not be fully conscious of the way their use of uncertainty is exploited by those who wish to delay climate action. He would like to see specialists in communications assist scientists in future report writing.