Note: This article was updated on October 30th at 5:30 pm to reflect a response from Exxon.
When ExxonMobil's public relations department plucks a complex chart from the authoritative report by the world panel on climate science and starts chanting an uncertainty mantra, put your thinking cap on.
Apparently, it's too easy to misunderstand—and just as easy to misrepresent—a rainbow-hued chart full of squiggly lines and obscure acronyms.
Exxon spokesman Ken Cohen either misunderstood or misrepresented his selected chart the other day as he pushed back against an InsideClimate News investigation into what Exxon's own scientists knew about the emerging risks of climate change, and when they knew it.
As it happens, a new peer-reviewed study shows that even well informed and highly educated people tend to misread this kind of chart. Like Cohen, test subjects got it wrong in a way that made the unknowns of climate science seem like insurmountable barriers to strong climate policies.
Cohen made it sound like the chart's wide range of climate outcomes was due to scientific uncertainty, when in fact much of the range is tied to social and economic unknowns. What path will the world choose to take? Will society decide on deep decarbonization, on half-measures, or on business as usual?
The charts in question are among the best known in the portfolio of the Intergovernmental Panel on Climate Change (IPCC), the established curators of the scientific consensus on global warming and the UN's chief scientific advisors to climate treaty negotiators.
The graphs show this century's rising global surface temperatures as simulated by climate models under different policy options.
Testing people's reaction to one such complicated graph, Rosemarie McMahon and two other Zurich experts found that the test-takers commonly missed the point. People didn't see that our choices, not the models, will determine how much warming we are in for.
The result, says an article they published in the journal Climatic Change, is "a misguided perception that climate science is too uncertain to play any significant role in policy decisions."
If the researchers found many of their test subjects utterly befuddled by the graph, Cohen did little to clarify things.
His point in highlighting that particular chart was to emphasize scientific uncertainty, an approach Exxon has pursued for decades.
The graph Cohen cited was an updated version from the latest IPCC scientific review. It was just as complicated as the version used in the Zurich research—maybe even more so. But its message was the same—within a range of uncertainty, models project that reductions in greenhouse gas emissions will lower global warming, and failure to act decisively will increase the warming.
The comments of the test subjects, when they were asked to describe the message, displayed "poor understanding of the graph," the Zurich researchers said.
"There is a lot of scientific uncertainty," said a government administrator. "Errors are huge," said a doctoral student in physics. "Impossible to model the climate with any level of accuracy," said a Swiss member of parliament.
And a lobbyist said: "I know you can make any model say anything about the same situation and the total opposite."
Here, by comparison, is how Cohen treated a similar, more recent IPCC graphic in a posting on his corporate blog on October 15:
"This should refute the claim, central to activists' conspiracy theories, that anyone had reached a firm conclusion about catastrophic impacts of climate change back in the 1970s and '80s.
"As you can see, the scientific community that contributes to the IPCC report is, even today, still projecting a broad range of potential outcomes."
But wait. Examine the chart (below) for yourself. Especially if you are versed in the underlying science, you'll see that it presents two kinds of uncertainties—those inherent in climate models, and those in the emission scenarios that are fed into the models.
Modeling uncertainty is only part of the story. Just as important are our future emissions pathways—and those are a matter of social choice.
"Novice readers were unable to identify the two different types of uncertainties in this graph without substantial guidance," the Zurich researchers wrote. "Instead they saw a great deal of uncertainty but falsely attributed it to the climate models."
A recurring theme in the InsideClimate News reporting on what Exxon knew is that its scientists understood early on what their computer models were saying about the risks of global warming. But even as the certainty of the models improved, Exxon focused instead on their uncertainty in its campaign to delay climate action.
In a response to this article, Exxon's Cohen said on Friday:
"At no point did I attribute the ranges in the chart solely to uncertainty in climate models. In fact, I clearly stated that the chart was an 'evaluation of the range of possible climate change scenarios.'
"Just to be clear, the ranges in the chart are due to uncertainty in a number of factors including uncertainty in the climate models but, more importantly, to uncertainty in future technology development as well as uncertainty about expected policy responses."
To really understand this graphic, you have to see what the various colors of the squiggly lines mean. Each color denotes a plausible scenario of how the world may choose to cut fossil fuel emissions. The red lines denote a pathway, in plain English, of business as usual. And the dark blue lines represent a pathway of making deep cuts quickly. The light blue and orange lines, in turn, represent middle-of-the-road policies.
Of course, many people looking at the chart's with cryptic code letters may be confused. They might not know that RCPs are so-called "representative concentration pathways," that they stand for how we might adopt new policies and technologies to control carbon pollution. They are, in short, scenarios and not predictions.
If you are interested in the details, the numbers for each pathway, such as 2.6 or 8.5, represents the radiative forcing that would ensue, measured in watts per square meter.
So this graph is meant to communicate with climate geeks. As the Swiss lawmaker in Zurich put it, this was not made for politicians or the general public, but for "scientists, because nobody else understands it and nobody else has the patience."
Still, if you put your mind to it, it's not impossible to understand the chart Cohen displayed, or the one the researchers presented to their test subjects.
Looking like the sash from Joseph's many-colored coat unraveling at one end, it simply depicts multiple modeling runs for each pathway scenario. Different models get different results for the red, business-as-usual choice. And different models get different results for the light blue, crisis-averting choice.
Why do the models differ at all?
Because models, like tennis players, have different strengths and weaknesses. Some pros play better on grass; some have more powerful serves, or nurse old injuries. Some have nerves of steel, others throw temper tantrums. Nobody wins every time.
Likewise, no one model is the best every time. So the IPCC uses multiple models, and feeds into them multiple scenarios, and presents the range of outcomes that we see here.
But you'll notice that the red lines tend to the top of the range, and the light blue lines toward the bottom, and the orange lines toward the middle.
What the model ensembles are saying is this: if society makes the right choices, warming is likely to slow, and if society makes the wrong choices, warming is likely to intensify.
If Cohen read his graph correctly, here's what he'd say: a lot of the uncertainty facing the world is due to our inability to predict what policies we'll choose to follow. And even though models are inherently imprecise, their combined evidence is strong that firm action to control pollution will head off the greatest risks of catastrophic climate change.
That, after all, is the advice coming with ever more clarity from mainstream climate scientists. And for decades, Exxon's management has had plenty of scientists to explain it to them.