As an economist studying climate change policy for several years, I often feel like I’m in the Twilight Zone. To listen to the constant drumbeat of catastrophic predictions based on the so-called scientific “consensus,” and to witness the scathing denunciation of the “deniers” who are supposedly selling out humanity for money, you would certainly think that the periodic reports issued by the UN’s Intergovernmental Panel on Climate Change (IPCC) would back up the alarmist rhetoric.

Yet I have found that the opposite is true. As I’ve documented over the years here at IER, all we have to do to defuse the alarmist position is quote from the UN’s own documents, or from the reports issued by the Obama Administration’s own teams. The baselessness of the catastrophic rhetoric is a secret hidden in plain sight, as it were. The people peddling paranoia are confident that not many Americans will actually read the compilations of the scientific literature, particularly the economic analyses comparing the costs and benefits of various proposed “solutions.”

An excellent illustration of this mismatch between the alarmist rhetoric and the actual research is a recent Vox article by David Roberts. Much as an Old Testament prophet, Roberts comes to his readers with a depressing message: “The obvious truth about global warming is this: barring miracles, humanity is in for some awful sh*t.”

Since I just got through writing a post on MIT professor Robert Pindyck—who admits that the only case for aggressive action at this point is to combat unlikely catastrophic scenarios that will probably not happen even if governments do nothing—I was curious to see how the Vox writer could possibly have come up with the opposite conclusion. In the rest of this post, I’ll show a few of the problems with his analysis. The whole episode shows the neutral outsider how to be careful when navigating the rhetoric in the climate change debate.

Problem #1: Confusion Over “Business as Usual”

The first major problem in Roberts’ Vox piece is his inaccurate description of the various climate scenarios contained in the latest IPCC report. Here’s the chart taken from the Fifth Assessment Report (AR5), followed by Roberts’ commentary on it:

2015.05.20 Murphy Figure 1


“The black line is carbon emissions to date. The red line is the status quo — a projection of where emissions will go if no new substantial policy is passed to restrain greenhouse gas emissions.” – David Roberts, commenting on the above chart.

This description of the Representative Concentration Pathways (RCPs) from the latest IPCC report is very misleading. However, I’m not really upset with Roberts, because when the AR5 report came out—with these RCPs instead of the previous Special Report on Emissions Scenarios (SRES)—I knew that people were going to assume that RCP8.5 represented “business as usual,” in other words as the default outcome if humanity continued on its present path. So we can’t really blame Roberts for telling Vox readers that that top line shows what will happen if governments do nothing; that’s exactly the (inaccurate) conclusion that any quick reader would take away from the diagram. It’s precisely for this reason that I was so disappointed when I saw the new IPCC AR5 report and how they had changed the way they classified future emission scenarios.

The specific problem is that the top line in the chart above is a very high end estimate of future emissions under a “business as usual” scenario. As Texas A&M Regents Professor of Atmospheric Sciences John Nielsen-Gammon explains in this detailed post, the RCP8.5 scenario from the latest IPCC report relies on extreme assumptions regarding population growth, the delay in technological development, and so on. He cites a 2011 paper from the literature which found that “RCP8.5 comes in around the 90th percentile of published business-as-usual (or equivalently, baseline) scenarios, so it is higher than most business-as-usual scenarios.”

In other words, if you study the literature of climate change and the various emission scenarios regarding “business as usual” where governments do not enact major policy changes, then some 90 percent involve lower emissions and hence lower global warming than the RCP8.5 scenario in the graph above. It is therefore misleading when the first plank in David Roberts’ Vox argument is to say matter-of-factly that humanity will experience the RCP8.5 outcome, absent aggressive government action.

The interested reader should consult Nielsen-Gammon’s post for all the nuances, but his overall conclusion is that a more accurate “business as usual” trajectory would fall in between the RCP6 and RCP8.5 pathways in the graph above, and his best guess is that with no government intervention, the globe will warm an additional 3 degrees Celsius by 2100 (meaning a total of 3.6°C warming since preindustrial times). I want to stress that Nielsen-Gammon isn’t challenging the IPCC report’s range of estimated “climate sensitivity” or other parameters. All Nielsen-Gammon is doing is trying to fit the scientific findings summarized in the latest report, in the context of the traditional estimates of future emission scenarios in the literature (and as outlined in the previous IPCC reports).

Problem #2: Quoting a Non-Expert for Hard and Fast Conclusions

In the previous section we showed that David Roberts got off to a shaky start by misrepresenting (probably innocently) what the “consensus” projections are for emissions and global warming if governments take no major actions going forward. But the next step in his argument—going from (exaggerated) warming to impacts on humanity—is also dubious. Here’s Roberts:

We recently passed 400 parts per million of CO2 in the atmosphere; the status quo will take us up to 1,000 ppm, raising global average temperature (from a pre-industrial baseline) between 3.2 and 5.4 degrees Celsius. That will mean, according to a 2012 World Bank report, “extreme heat-waves, declining global food stocks, loss of ecosystems and biodiversity, and life-threatening sea level rise,” the effects of which will be “tilted against many of the world’s poorest regions,” stalling or reversing decades of development work. “A 4°C warmer world can, and must be, avoided,” said the World Bank president.

But that’s where we’re headed. It will take enormous effort just to avoid that fate. Holding temperature down under 2°C — the widely agreed upon target — would require an utterly unprecedented level of global mobilization and coordination, sustained over decades. There’s no sign of that happening, or reason to think it’s plausible anytime soon. And so, awful sh*t it is.

To repeat, it is not accurate in the above quotation for Roberts to say “the status quo will take us up to 1,000 ppm,” because that assumes the RCP8.5 scenario is the status quo—which it is not. More reasonable, middle-of-the-road projections would put the concentration in the year 2100 below that level, so that even stipulating everything else in the latest IPCC report, we would not expect the level of warming that Roberts proposes in his piece.

However, let’s consider the next link in his argument. To show us just how unacceptable this stipulated status quo warming would be, Roberts doesn’t refer to the latest “consensus” science on estimated impacts from climate change in the AR5 Working Group II report—which came out in March 2014. Instead, Roberts refers to a 2012 report from the World Bank, and quotes from the president of the World Bank to get his money line on just how little hope remains for humanity.

Now don’t get me wrong, the president of the World Bank, Dr. Jim Yong Kim, is a really smart guy—he has an MD and a PhD in anthropology from Harvard. But it’s odd that the bulk of Roberts’ case comes from the summary provided by someone who is not trained in climate science, referring to a World Bank report from three years ago.

In contrast to the horrible picture painted by Roberts in his Vox piece, one of the three computer models selected by the Obama Administration for modeling future impacts of climate change concluded that there would be net benefits to humanity from global warming, up through about 3°C. And let’s reproduce a chart from the latest IPCC report to summarize the literature on global analyses of impacts from climate change:


SOURCE: Table 10.B.1, IPCC WGII AR5, p. 82.

As the above table indicates, there really haven’t been many comprehensive studies estimating the impacts on humanity from warming above 3°C. There is a study by Maddison and Rehdanz (in 2011) showing a very large impact, but it is clearly an outlier, well beyond the rest of the literature. Furthermore, the last item in the table—referring to a 2012 study by Roson and van der Mensbrugghe—projects that 4.9°C of global warming would merely reduce global GDP by 4.6 percent.

How should we think about that type of impact? Is that catastrophic? Is that worth mobilizing the entire globe to combat? Is such a threat one of the most important issues of our day?

Well, the very same AR5 report from the IPCC estimates that to keep global warming contained to 2°C, governments around the world would need to implement policies that would cause economic damage of 4.8 percent of global consumption in the year 2100. (I give full citations and an explanation in this post.)

To summarize, the latest IPCC report shows that in a middle-of-the-road outcome, the total damage to humanity from governments implementing a popular climate goal target (namely, limiting warming to 2°C) is greater than the total damage to humanity from unrestricted global warming.

This is why I say the climate change debate feels like the Twilight Zone to me: The advocates for aggressive government intervention go through this whole production of soliciting input from various scientists and economists around the world, and when all is said and done their own report shows that the most likely outcome is that “doing nothing” stacks up nicely against other possible strategies.

Roberts Admits Scientists Are Playing Politics

Now in fairness, I’m sure David Roberts or other proponents of massive government intervention could come back and say something like, “Sure, there aren’t comprehensive studies quantifying the exact global impacts from unrestricted emissions. But we have an idea of how bad things might be for particular groups of people or regions of the globe, and that’s what we’re talking about with our alarmist rhetoric.”

Well, nobody can prove that a catastrophe won’t happen, but readers should be on their guard when ostensible experts just start throwing out qualitative warnings without providing precise scientific reasons for their alarm bells. To back up my claim, all I have to do is quote from…David Roberts’ own Vox piece. Look at his incredibly candid discussion of how political and non-objective the supposed scientific experts have been, when telling the public the “truth” about climate change:

The latest contretemps was sparked by a comment in Nature by Oliver Geden….Politicians, he says, want good news. They want to hear that it is still possible to limit temperature to 2°C. Even more, they want to hear that they can do so while avoiding aggressive emission cuts in the near-term — say, until they’re out of office.

Climate scientists, Geden says, feel pressure to provide the good news. They’re worried that if they don’t, if they come off as “alarmist” or hectoring, they will simply be ignored, boxed out of the debate. And so they construct models showing that it is possible to hit the 2°C target. The message is always, “We’re running out of time; we’ve only got five or 10 years to turn things around, but we can do it if we put our minds to it.”

That was the message in 1990, in 2000, in 2010. How can we still have five or 10 years left? The answer, Geden says, is that scientists are baking increasingly unrealistic assumptions into their models. [David Roberts, bold added.]

Even though Roberts and I are (obviously) coming to this issue from completely different points, I respect his honesty in printing the above. (At least one leading alarmist climate scientist bit his head off for doing so.) Although Roberts, citing Oliver Geden, thinks the climate scientists are being pressured by politicians to paint a rosy picture that justifies aggressive government climate policy, the important point I want to emphasize is: Roberts in his Vox piece is claiming matter of factly that scientists keep tweaking their models to produce results that politicians want to hear. That’s part of the message we at IER have been telling Americans for years, and yet when we say it, we are called “deniers” who reject the “scientific consensus.”


Although it’s the opposite of what he intended, David Roberts’ Vox article on the climate debate underscores that the published literature on climate change does not justify the typical policy recommendations being pushed on the public and government officials. Roberts openly admits that the supposedly objective scientists are deliberately altering their assumptions time and again, to keep the output of their “models” on point and saying what the politicians want to hear. It’s refreshing when someone from “the other side” of this debate is so frank about the type of process producing the fodder which is then rushed to Capitol Hill as evidence for massive tax hikes and regulations on industry.

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