Climate Science Glossary

Term Lookup

Enter a term in the search box to find its definition.


Use the controls in the far right panel to increase or decrease the number of terms automatically displayed (or to completely turn that feature off).

Term Lookup


All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

Home Arguments Software Resources Comments The Consensus Project Translations About Support

Bluesky Facebook LinkedIn Mastodon MeWe

Twitter YouTube RSS Posts RSS Comments Email Subscribe

Climate's changed before
It's the sun
It's not bad
There is no consensus
It's cooling
Models are unreliable
Temp record is unreliable
Animals and plants can adapt
It hasn't warmed since 1998
Antarctica is gaining ice
View All Arguments...

New? Register here
Forgot your password?

Latest Posts


How Exxon Overstates the Uncertainty in Climate Science

Posted on 26 February 2016 by Guest Author

This is a re-post from John Cushman Jr. at Inside Climate News

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?

Click here to read the rest

0 0

Printable Version  |  Link to this page


Comments 1 to 3:

  1. Up is still up.  All of the RCP are "up".  I think some of the problem has to do with a person's perception of the impact of a "couple degrees of temperature.  With respect to the climate in the dining room on the night your boss is coming over for dinner, a couple of degrees means nothing.  Climate scientists know that a, "couple of degrees of global averaged higher temperatures is a "big deal"".  So, let us not fret much about the Exxon folks or anyone else that doesn't get it.  Keep plugging away at the scientific efforts and the peer-reviewed results and more people will "sign on" to solutions, even if we "extinct-ify most of the human race before we "get there".  After all, the globe could use a drastic population reduction...think how much CO2 we wouldn't be pumping into the atmosphere?  (There, I've said it)  Sorry.

    0 0
  2. It seems to me that the main problem is that the graph (at least at the scale in the online postings) is illegible for *anyone* and so it invites misrepresentation. It would best be presented as a set of five graphs: four that show all the model results for a each of the four RCPs so as to give a good impression of the scatter of the models; then one graph that shows four *averages* of all the results for each of the RCPs. Such a presentation would be much harder to misinterpret and misrepresent.

    0 0
  3. Maybe these chart makers need to standardize their assumptions and only make charts based on current laws, or current pledges. Showing the difference between what has been pledged, and what has been implemented only.

    0 0

You need to be logged in to post a comment. Login via the left margin or if you're new, register here.

The Consensus Project Website


(free to republish)

© Copyright 2024 John Cook
Home | Translations | About Us | Privacy | Contact Us