Three distinct studies using four different methods have independently shown that the expert consensus on human-caused global warming is 97 ± 1%. The result is the same whether we ask the experts’ opinions, look at their public reports and statements, or examine their peer-reviewed science. Even studies that quibble about the precise percentage have accidentally reinforced the 97 ± 1% consensus.

The evidence is crystal clear that humans are the main cause of the current global warming, and the expert consensus reflects the strength of that body of evidence. It’s not easy to convince 97% of scientific experts about anything – that requires some powerful scientific evidence.

And yet public opinion is a very different story. Americans think experts are evenly split on the causes of global warming. The public is likewise split on the cause of global warming, with just over half understanding that humans are primarily responsible. As a result, Americans don’t see global warming as an urgent issue, putting climate policy low on the list of priorities.

The sources of this disparity and how it can be corrected are the subjects of an intense debate amongst social scientists. One school of thought says that we have a problem with ‘information deficit’ as well as what climate scientist Michael Mann calls ‘misinformation surplus.’

For example, experimental evidence shows that if people are presented with a basic explanation of how global warming works, they’re more likely to accept the reality of human-caused global warming. Other research has shown that if people are told about the expert consensus, they’re also more likely to accept the science. In both cases, presenting people with certain pieces of information trims the gap between what the scientific evidence and experts say, and what the public believes.

The other school of thought, led by Dan Kahan at Yale, argues that the problem boils down to cultural biases. In essence, liberals feel as though they’re on Team ‘global warming is a problem caused by humans’ while conservatives identify with Team ‘no it’s not.’ Kahan feels that people will take any new information and pass it through their cultural filter; if it conforms to their cultural identity, they’ll accept it, or otherwise they’ll just reject it. In fact, Kahan argues that giving people information that doesn’t conform to their cultural identity (like the 97% consensus) may just act to polarize them further.

In a recent editorial for The Guardian, Adam Corner made a similar argument, asking 'who cares about the climate change consensus?'. Corner suggested that climate information is ineffective if it’s not coming from “communicators whose cultural credentials are congruent with the audience they are speaking to.” Both Kahan and Corner have also argued that if consensus messaging could work, then it should have worked by now, whereas American public acceptance of human-caused global warming in 2014 is lower than in 2003.

Gallup poll results on the perceived causes of global warming. Photograph: Gallup

So if the ‘information deficit’ model is right, why hasn’t consensus messaging led to an increase in public acceptance of the science? Adam Corner identifies the problem in his Guardian piece.

In response, 'merchants of doubt' have tried to muddy the waters by exaggerating scientific uncertainty.

This is the ‘misinformation surplus’ that’s also been in play for several decades. For as long as the expert consensus on human-caused global warming has existed, there’s been a campaign to convince the public that the experts remain divided. This was articulated in a leaked 2002 memo from Republican political strategist Frank Luntz, which said,

“Voters believe that there is no consensus about global warming in the scientific community. Should the public come to believe that the scientific issues are settled, their views about global warming will change accordingly. Therefore, you need to continue to make the lack of scientific certainty a primary issue in the debate, and defer to scientists and other experts in the field.”

We don’t have a second America to use as a control group, but without the consensus messaging that’s happened over the past decade, my guess is that the public would be even more misinformed about global warming than it is now. The problem isn’t consensus messaging itself; the problem is that it’s fighting against a misinformation surplus.

Another key point is that while ‘expert consensus’ is vague, ‘97% expert consensus’ is concrete and memorable (a.k.a. ‘sticky’ messaging). While Naomi Oreskes first identified the consensus on human-caused global warming in the peer-reviewed literature in 2004, the first study to quantify it at 97% came in 2009, reinforced by 97% studies in 2010 and 2013. The above graph shows that the public became increasingly accepting of human-caused global warming during 2010–2014, so perhaps 97% consensus messaging is moving the dial after all.

Most social scientists believe that both information deficit/misinformation surplus and cultural biases contribute to the problem. Research by John Cook supports this idea. He asked a representative sample of Americans across the political spectrum what percentage of scientific experts agree on human-caused global warming.

Not surprisingly, the perceived consensus decreased from left to right across the political spectrum. However, even liberals believed the consensus is below 70%, in stark contrast to the actual 97%. Cook calls this the 'liberal consensus gap.' Cultural filters can't explain it, because liberals are supposed to be on Team ‘global warming is a problem caused by humans.’

These data come from research by John Cook, taken from a survey of a US representative sample (N=200). Photograph: John Cook

As the above figure indicates, the difference in perceived consensus between the left and right can be explained by Kahan's preferred cultural bias explanation, but the 'liberal consensus gap' can't. That's due to the information deficit/misinformation surplus. Both factors are partially responsible for public misconceptions about the causes of global warming.

Another team of social scientists from George Mason and Yale Universities explained why the global warming consensus is important in a recent paper,



"...knowledge of the scientific consensus on human-caused climate change can be considered a “gateway” cognition; as members of the general public come to understand the consensus, they more likely come to the conclusion that human-caused climate change is happening and harmful."

Frank Luntz came to the same conclusion 12 years ago. It's why fossil fuel interests have been trying to sow doubt about the expert consensus on global warming for over two decades.

So the 97% consensus message is important, and it's also important that this sort of information comes from sources that people trust within their own cultural groups. For example, President George W. Bush's Treasury Secretary Henry Paulson recently wrote,

"I’ve spent a considerable amount of time with climate scientists and economists who have devoted their careers to this issue. There is virtually no debate among them that the planet is warming and that the burning of fossil fuels is largely responsible ... The solution can be a fundamentally conservative one that will empower the marketplace to find the most efficient response. We can do this by putting a price on emissions of carbon dioxide — a carbon tax."

Four Republican former administrators of the Environmental Protection Agency gave a similar message in testimony before the US Senate last week. To break through our current climate roadblocks, we need more of these examples that address both the information deficit and cultural biases. This can be achieved with informed messages (especially "gateway" information like the 97% consensus) coming from sources that conservatives can trust.

