We all like to go to the sources that we trust (Image: Win McNamee/Getty)

HOW do you get your point across over an issue as contentious as climate change? As a hearing in the US Congress last week showed, the evidence alone is not enough.

At issue was the authority of the Environmental Protection Agency to regulate greenhouse gas emissions. Republicans in the House and Senate are backing bills that would strip the EPA of that right, which is based on findings that rising carbon dioxide levels pose a threat to health and the environment.

At the hearing, House Democrats hoped to counter these moves by calling a cast of climatologists to explain the weight of scientific evidence for climate change. A meeting of minds it was not. The effort seemed only to harden Republican scepticism.


For Dan Kahan of the Cultural Cognition Project at Yale University, the result was predictable. He has previously shown that simply explaining the science behind contentious issues drives the two sides further apart. But Kahan’s work also suggests how warring parties can move towards consensus.

Kahan grades people on two scales of cultural belief: individualists versus communitarians, based on the different importance people attach to the public good when balanced against individual rights; and hierarchists versus egalitarians, based on their views on the stratification of society. Republicans are more likely to be hierarchical-individualist, while Democrats are more often egalitarian-communitarian.

People’s views on contentious scientific issues tend to reflect their position on these scales. For example, egalitarian-communitarians tend to accept the evidence that climate change is a threat, while hierarchical-individualists reject it.

Yet people’s views do change if the right person is offering the evidence. Kahan investigated attitudes for and against giving the human papillomavirus (HPV) vaccine to schoolgirls to prevent cervical cancer – another divisive issue. After he presented people with both sides of the argument, he found that 70 per cent of egalitarian-communitarians thought it was safe, compared with 56 per cent of hierarchical-individualists.

When the “pro” argument was presented as coming from an expert painted as being in the egalitarian-communitarian camp, and the “anti” view came from a hierarchical-individualist, the split widened to 71 versus 47 per cent. But strikingly, swapping the experts around caused a big shift: 61 per cent of hierarchical-individualists then rated the vaccine as safe, compared to 58 per cent of egalitarian-communitarians. In short, evidence from someone you identify with sways your view.

In practice, it is hard to find experts who will give “unexpected” testimony. But when the evidence was presented by experts with a variety of backgrounds, views were not so starkly polarised, with 65 per cent of egalitarian-communitarians and 54 per cent of hierarchical-individualists agreeing that the vaccine is safe.

So who might be best placed to change Republicans’ minds over the EPA bill? Maybe specialists from the insurance industry, which is factoring climate change into its calculations, the military, or religious environmentalists.

Kahan accepts that it would be naive to think that climate sceptics will suddenly abandon their position. But he says: “We want to create an environment in which people, regardless of their values, are giving considered attention to the information.”