The piece, written by David Victor and Charles Kennel, both affiliated with the University of California, San Diego, was quickly challenged by Stefan Rahmstorf on the Realclimate blog and Joe Romm at the Center for American Progress.
Rahmstorf's detailed discussion of the history of the 2-degree limit and the science used to support it is well worth reading, but is cheapened by a preamble that includes not-so-subtle efforts to imply that Victor (a "political scientist") and Kennel (a "retired astrophysicist") are not legitimate voices on such an issue. Romm's argument is also worth examining, but echoes that unfortunate phrasing. [* This paragraph is corrected; see the asterisk below.]
That's odd given that Victor was a lead author of the most recent Intergovernmental Panel on Climate Change report on mitigation options for greenhouse gases and is the author of "Global Warming Gridlock," an influential book on climate change policy. Kennel is hardly a lightweight, either. As with the veteran climate scientist James E. Hansen, Kennel's focus on global warming grew out of a background in astrophysics, but he's been working at the interface of earth science and policy since he became the director of NASA's Mission to Earth program during the Clinton administration.
I sent links to the critiques to Kennel and Victor and Victor sent a detailed response yesterday. You can read it below (I recommend taking the weekend; it's long) with some links added and some of the unavoidable jargon unpacked a bit:
First, before digging into the substance, I think it is deeply disturbing that both these posts use the same tactics that are often decried of the far right—of slamming people personally with codewords like "political scientist" and "retired astrophysicist" to dismiss us as irrelevant to the commentary on a matter that is for climatologists. Other scientists, by contrast, are "internationally renowned" (quote by Joe) implying somehow that we are peripheral thinkers. People can say what they like about us, but we have not been irresponsible unqualified hacks weighing in on this matter. Getting serious about goals requires working across disciplines—especially between the natural sciences and the social sciences, which are about human behavior (which is what, ultimately, these goals are trying to change). The failure to do that effectively is one of the reasons why climate science hasn't been more directly linked to policy. And that is precisely why we are working as a team across disciplines and why I have devoted a whole career reading and working at the frontier of multiple disciplines. In late August there was a big "Charlie Fest" here at UCSD [link] to celebrate Charlie's life work—and that event, spread over two days, covered at least a dozen disciplines. So come on guys—don't slip into ad hominem slams and narrow views of what kind of science is really needed.
Part of the reason that elements of the climate change debate take on religious proportions—by the activists for and against policy—is that folks have so dug in around almost every aspect of the debate that it is hard to raise a question about some uncritically accepted element of the religious canon without folks first attacking you as an untrained heathen. The reality is that MOST of the debate about goals should centrally involve the social sciences—more on that below.
Now let's turn to the substance. The arguments in these two posts are far-ranging. I think I have boiled them down to all the main elements.
COMPLEXITY
Both of these posts seem to favor a single simple goal. According to Joe Romm, "…adding more vital signs just gives people more things to argue about. Indeed, the whole Victor and Kennel approach would be an excuse for more dawdling." And Stefan says "…but to be practical, there cannot be many … goals—one needs to agree on a single indicator that covers the multitude risks."
That's completely wrong and ignores our central argument. I would be surprised if anything as complex and multifaceted as the climate system could be boiled down to a single crisp goal. And being practical requires realizing that it is important to set goals that reflect the variety of long-term indicators as well as short-term milestones and indicators. This is where a little bit of political science is helpful. I can't think of any complex regulatory function that is performed according to single indicators. Central bankers don't behave this way when they set (unilaterally and in coordination) interest rates and make other interventions in the economy. Trade policy isn't organized this way. In our article we use the example of the Millennium Development Goals because that example is perhaps closest to what the UN-oriented policy communities know—again, multiple goals, many indicators. That's exactly what's needed on climate. Essentially all the evidence from the real world of policy coordination points to the need for goals that reflect the diversity of the phenomena that we are trying to manage as well as indicators that are rooted in what real firms and governments can actually deliver.
HOW 2 DEGREES GOT ADOPTED AND ITS SCIENTIFIC BASIS
Both posts seem to be upset that we have not given a more detailed tour of how the 2 degree goal got adopted and make the claim that this number came out of the science. In our essay, we were allowed 2 paragraphs to tour that horizon. So we made three brief points. First, the original formulation for Article 2 [the section of the 1992 U.N. Framework Convention on Climate Change (UNFCCC) stating the goal of avoiding "dangerous anthropogenic interference" with the climate; useful background here] carefully did not focus diplomats on a single number or metric. (Small world that it is, I was actually in the room in New York when most of that text was negotiated—visiting as an observer when I was a graduate student at M.I.T.)
That led to an explicit effort, launched by the UNFCCC and including a high profile meeting in Fortaleza, Brazil, to figure out what Article 2 actually meant. Those efforts led nowhere because scientists, wisely, could not agree on single indicators. To me it is astonishing that both of these posts seem to take us to task for not being aware of the "planetary boundaries" research (more on that below) when the central conclusion from that work is that real boundaries need to be set in multiple dimensions—exactly what we argue. Similarly, the famous "burning embers" figure from the Intergovernmental Panel on Climate Change (IPCC) says exactly the same thing—if it is some natural ecosystems that you care about then we are already way past the point of no return, if it is Greenland or parts of West Antarctica then the "guardrail" is different (but also, it seems, beyond us). And so on. The fact that different perspectives leads to different types of goals is intrinsic to the nature of the climate system and to the political system that must accommodate lots of different points of view.
Second, we make the point that what drove 2 degrees was a political movement. All this multidimensionality and complexity of the real science of climate impacts was really inconvenient for activists who, understandably, were trying to get governments to stop dawdling. And it is out of that pressure—the desire for simple, single numbers that could be used to drive climate policy that 2 degrees emerged. First in Europe because Europe was doing more on climate policy than any other region in the world. And then, mainly with European and nongovernmental organization pressure, the goal was spread via the G8 and eventually the UNFCCC into other parts of the world as well. We were allowed 10 citations for the whole article. We spent one of those citations (our reference 3) on a short essay that documents this political origin. We purposely did NOT cite the huge scientific literature that has, ex post, been used to justify 2 degrees because when you look back on that history it isn't the science that drove this and any serious look at the science points to the fact that there are multiple possible goals. The science was broadly consistent with goals like 2 degrees, but it was broadly consistent with lots of other goals as well. But what really drove the adoption of 2 degrees was the desire for a simple "tote board" number that could be used to drive policy. If I were an activist working in Europe pushing for climate policy at the time and pushing the G8 and others to stop dawdling I would have done the same thing. (Personally, I have been heavily influenced by an essay by Marc Levy that looked at how a similar process led to political focal points in the European debate over acid rain. [link] We cite that piece in the long version of our essay that we submitted to Nature—it got cut though, along with 36 other citations.) Third, we are not unaware of the avalanche of scientific literature that has been stitched together in favor of 2 degrees—such as the work in AR4, the "400 page book" [links added] and a multitude of other meetings and communiques. Mention of all this work is tossed around in these posts as if to imply that we are somehow morons for being unaware of all the science that has been shoehorned into the 2-degree debate. Our point is that the scientific community should not be lulled into thinking that it drove this number or that any single number would, in fact, be the right way to think about this problem. The reason it is important to get this story right is not so that the right community gets "credit" for focusing on 2 degrees but so that we can understand how the scientific community has allowed itself to get lulled into thinking that it is contributing to serious goal-setting when, in fact, we have actually not done our jobs properly.
It is very easy to mis-read this history and to mis-read the legal documents that are carefully designed to create the impression that these numbers come straight out of science. For example, Stefan quotes paragraph 4 of the official decision (1/CP.16) in Cancun [the 2010 round of treaty negotiations; link] that supposedly adopts the 2-degree goal. His full quote says: "…to hold the increase in global average temperature below 2 oC above pre-industrial levels." But if you go read the actual full decision—which is the ONLY way that carefully negotiated legal texts like this can be read accurately—you see that this statement comes from a pre-ambular paragraph that begins with the phrase "further recognizes." Statements that are "recognizing" are designed to set context for an agreement—and usually they are negotiated through a process by which some parties want a strong statement in this domain and others don't and so the agreement to disagree takes this artful form. Note that in the construction of the legal decision this paragraph comes BEFORE the text that states what the parties actually "agree" to.
I am not saying that some parties don't want 2 degrees as the goal. I am saying that other parties don't want that goal and that the zone of actual agreement is much narrower. But this has been the game all along—the people who want simple indicators get agreement in one friendly forum and then they move up the agenda, step by step, in other forums until other countries relent or forget or the text gets inserted into some paragraph where countries are less concerned about their disagreement (e.g., paragraph 4). In fact, in that very same paragraph from which Stefan plucks his quote there is careful language avoiding the statement that parties "must" immediately cut emissions but, instead, it says "…with a view to reducing global greenhouse gas emissions…" So that is what was actually adopted in Cancun. "With a view" isn't exactly language that sends the whole planet in lockstep to make 80% cuts in emissions. Incidentally, this kind of inflexibility in language is one reason why I (and many other people) have been more interested in agreements that aren't legally binding—not because we want to let governments off the hook but because binding law brings a lot of baggage with it.
GUARDRAILS AND BOUNDARIES
One of the big disconnects in this whole debate revolves around the word "guardrails" (which Stefan uses) or more generally on "boundaries" (which is widely used). For several decades, the natural science research related to goals has proceeded around the idea that we can identify particular limits in Nature and then work backwards to compute what humans are allowed to do. Research efforts on concepts like "tolerable windows" and "pathways" and "allowable carbon budgets" and the such are all rooted in this notion. In Stefan's words: "Once an overall long-term goal has been defined, it is a matter of science to determine what emissions trajectories are compatible…" By separating the decision on "long-term" goal from the "matter of science" to turn the crank and determine trajectories misunderstands how real goals function in nearly every area of complex and expensive policy coordination. Once again, this is an area where a little bit of insight from other disciplines can help explain how the real world works. If you take seriously the elegant argument made by Bill McKibben many years ago in his lovely "The End of Nature" then we are already past any limit. If you want to protect some of Nature in its pristine state then no globally mixed polluting gas can be allowed. I see Bill's original work and some related work in political philosophy, such as Peter Singer's work, as a debate about the value of nature and the willingness of humans to intervene and manage nature. (Similar questions come up in geoengineering, through which we become even more active managers of nature.) We have to have that debate, and nearly all formulations that start with nature end up with a different way of setting goals. But almost nobody, at least today, is willing to bear the cost of taking such goals seriously. That means that for nearly everyone, the question of goals is deeply intertwined with ultimate impacts, adaptability and costs. Very quickly we can see that matter of goal-setting isn't some abstract number that is a guardrail but it is bound up in our assessments of risk and of willingness to pay for abatement as well as bear risk. And those calculations aren't global—where we start with a single number and work backwards turning some single master science crank—but vary by political group because people see risks differently. That's one of the many reasons why international climate policy is so complex and why real world goal setting doesn't start with single numbers and work backwards.
This does not seem to be a central critique of Joe and Stefan against our piece, but I outline this issue here because there is a falseness in the way the whole climate science community has posed the goal-setting and crank-turning debate. And a lot of this falseness is rooted in a divide between the academic disciplines. Much of the natural science world has a view of politics that starts with experts setting goals and turning the science crank to compute what governments must do. Much of the social sciences, including political science in particular, sees the process basically in reverse order—with governments determining their interests (often with expert inputs) and then global "solutions" emerging from that decentralized process.
WHAT'S WRONG WITH THE PAUSE?
Both posts seem to be upset with our discussion of the "pause." Stefan says our discussion of the pause is disingenuous because we "pick 1998 as start year." By implication, if we had not been disingenuous then global mean temperature would be just fine as an indicator. And Joe says "global [surface] temperature is a perfectly reasonable indicator of planetary health." Joe's zinger also labels our work "beyond dubious." Michael Oppenheimer has sent a rebuttal to Nature making similar arguments in defense of global mean temperature. Our point was not to focus on 1998; in fact, in the longer version of our article that we sent to Nature we talk explicitly (and cite heavily) the work that has pinned the "pause" to shifts in El Nino/La Nina cycles and we also prominently mention the high latitude warming. Nature cut that stuff because this is a commentary piece focused on policy implications, not a dissertation on the underlying science.
It might be that a basket of vital indicators includes global mean surface temperature along with other indicators. But why focus on a global mean that is known to have only a sluggish relationship to real human stress–especially over the sub-decadal time periods that are relevant to most human decision-making—rather than other indicators that are more tightly coupled and better canaries? Joe Romm attacks us because we "perpetuate the myth" that there has been a pause. And then Joe goes on to point out that one possible explanation for the pause is measurement–there's been a ton of warming in the Arctic as if we are somehow hiding that fact when we talk about the pause. Yet we say exactly the same thing—in a whole paragraph we devote to the fact that high latitude temperatures are better indicators of stress than globally averaged temperatures. Joe cites to a very recent article that re-estimates global mean temperature in two ways that might offset some of the bias for under-sampling the arctic in one existing global data set. We cite to a different article that focuses on the rapidly building climate stress in the Arctic. So what's the beef here that leads us to be "beyond dubious"? Both of these lines of thinking point to a) the need for more attention to the real canaries as indicators; and b) the possible improvement in global indicators, including global mean temperature. Nobody disagrees with that. At the same time, all of us need to be very clear that each of these indicators and measurement strategies has flaws. Indeed, there's a world of difference between citing one paper that has done something that MIGHT rebalance the global mean temperature data—as Joe's post suggests—and then assuming that the problem is fixed and the indicator remains the first best only way to measure global goals despite the fact that natural variability in the global mean surface temperature will also make that a sluggish measure. Maybe as those adjustments are done that the global basket of vital indicators should include an improved measure of global mean temperature along with other indicators. Maybe it would be better just to focus on the more sensitive indicators—as we imply. Hashing out the merits and demerits of different indicators would be one purpose of the plan we outline.
OCEAN HEAT CONTENT AND EXTREME IMPACTS ARE JUNK GOALS
Stefan seems to be upset about our favoring ocean heat content (OHC) and extreme events. He plucks out of context a sentence about OHC while ignoring the central argument we are making about that indicator—which is that if most of the heat is going into the oceans and we now have substantially better ways to measure OHC then why not use that measure. So far, the data suggest it is a more responsive measure, but of course OHC alone is inadequate—not least because of coverage issues that are even worse than the GMT [global mean temperature] data sets. And he takes us to task for advocating a "volatility index" that would be based on extreme impacts because, he says, that index would be more volatile than global temperature. But that's not why we advocate looking at extremes. We advocate including extreme events in the global planetary health indicators because extreme events have a particularly large impact on human and natural ecosystems—and that's what, ultimately, people care about most. We are attracted to the work that Jim Hansen and colleagues have published (which we cite), but there are other approaches as well. There are huge problems with getting unbiased measures of extreme events—especially events linked to actual impacts on humans and nature. But with an incentive to improve those measures improvements will follow.
CONCENTRATION INDICATORS ARE BETTER
We suggest in our article that better goals would be more closely linked to what humans actually emit. We suggest that means setting some goals in terms of concentrations (or, even better perhaps, radiative forcing). Stefan and Michael Oppenheimer take us to task for favoring goals that are more remote from ultimate impacts. Oppenheimer's summary of the debate is the best: "[Global Mean Temperature, GMT] is indeed 'related only probabilistically to emissions' (quoting us) but CO2 concentration … is related only probabilistically to impacts and risks (excepting ocean acidification), which is a primary reason why GMT has been favored."
For now, I'll set aside why GMT has been favored politically—as I covered that above. But Oppenheimer has summarized the essence of the debate and the issue of how one designs goals. Stefan favors goals that have already baked into them the climate sensitivity (i.e., temperature goals). I assume that is because he is thinking about climate change as a climatologist. We favor a basket of vital signs that would likely include impact-oriented goals (perhaps GMT, although high latitude temperatures are probably better indicators) as well as goals that are more closely connected to what governments, firms, and humans actually do. That's because we are thinking about this question from the perspective of how goals actually affect the behavior of institutions (e.g., governments, firms) and people. This is a crucial debate to have—and one that must involve people who are real experts on how goals actually affect human behavior. We have used the example of the Millennium Development Goals [link] because our read of that literature is that abstract goals that may be well rooted in ultimate impacts are not what inspire actual changes in human behavior. One lesson from the MDG experience is that goals need to be linked to indicators that actually change in direct response to human intervention on a time scale of a few years. There are lots of other lessons from that experience and a host of other areas where society has set goals—some effective, others not. So let's have that debate, but it must be done in terms that are serious about how goals have real impacts—not by simply declaring that the climate science knows what goals are best for the climate and everyone should therefore fall into line. The diplomats have been doing that for decades and people haven't fallen into line. Strangely, neither of these posts deals in any detailed way with what is the centerpiece of this debate: how do goals actually work?
TWO DEGREES IS FEASIBLE AND AFFORDABLE
Both posts perpetuate this myth that the scientific literature says that 2 degrees is inexpensive and achievable. The real answer is that 2 degrees might be achievable, but only under heroic assumptions and efforts. Stefan says that our claim that the 2 degree limit is "effectively unachievable" is [solely supported] by self-reference to a study I wrote. That study was a book length, massively peer reviewed analysis of what's happened with emissions and was hardly the only thing written on this topic. [link] In fact, that book has 71 pages of references to supporting material. Moreover, two sentences after this supposedly gratuitous self-citation we cite the massive IPCC review of these studies (chapter 6 of the IPCC WG3 report) [link] and the sentence after that cites another IPCC chapter (1) that documents in some detail the assumptions that drive the model results that lead to the conclusion that 2 degrees is feasible and cheap.
Having taken us to task for somehow not properly handling the uncertainties in climate science—an error we did not commit, as I document above—he then proceeds to offer a horrifically misleading summary of what the IPCC actually found about the achievability and cost of meeting the 2 degree goal. He cites the Summary for Policy Makers (SPM) from IPCC Working Group 3 and plucks from that summary the statistic that the reduction in economic growth would be just 0.06%. This 0.06 number comes from column 4 of table SPM.2, which reports the median result from scenarios that stabilize concentrations at about 450 ppm [parts per million] CO2-equivalents. [link]
(Note that the economics community has been much more comfortable with concentration targets for the same reason we advocate them—they are more closely connected to what humans actually do. Climatologists like global temperature because it is linked closely to what they study. But people who study humans find that extra step toward global temperature to be a real problem because it explodes the error bars around the results. You can see the effect of that extra layer of propagating uncertainty in column 8 and the orange sections of table SPM.1.)
By focusing on this number, we get a totally misleading picture of what the science actually says. That's because Stefan ignores the heading on that column of table from which he plucks the 0.06% number. That heading says: "Consumption Losses in Cost-Effective Scenarios" along with a footnote that explains what cost-effective means. The key to understanding this result lies in the headline and the footnote. It turns out that I was centrally involved with writing the SPM, having devoted much of the last three years of my life as a volunteer for the IPCC and so I have a pretty good sense of what's "in" the SPM and crucially what's "out." And that's why Charlie and I cited the actual underlying scientific report (chapter 6) along with a detailed discussion of the assumptions that drive those results (chapter 1) rather than citing the SPM—because chapters 6 and 1 tell us a lot more about the actual state of the research.
The reality is that you get 0.06% drop in economic growth only under ideal circumstances—for example, all countries cooperate (pretty much instantly) and all technologies are deployed optimally and globally. That's a fun scenario to talk about, but it bears no relationship to the real world. That's why the SPM includes the orange columns in the middle of table SPM.2 and the blue columns on the right side of that same table—along with results by sector reported in SPM.7 that show the effect of sub-perfect assumptions about technology. And it is why chapters 1 and 6 talk a LOT more about this.
In the real world there will be imperfections and thus idealized cost-effective scenarios in these models don't really tell us much that is useful. One of the most important improvements in climate change economic system modeling in the last five years has been to understand how those imperfect "second best" worlds actually unfold. Some of those imperfections might lead to lower costs; most of them drive costs up—and as this work advances it points to MUCH higher potential costs. Chapter 6 unpacks this in detail.
While this work is just beginning, one thing is clear is that the models are very sensitive to assumptions about a few pivotal technologies. In particular, these models love a technology called "bioenergy carbon capture and sequestration (BECCS)" because it has negative emissions—you grow biomass, harvest it and burn it for electricity, and then store the pollution underground. Voila. The models love this—especially when the models are told to meet a very aggressive and difficult constraint like stopping warming at a concentration such as 450 ppm which has a decent change of stopping warming at 2 degrees. Facing that constraint, the models pour money into BECCS on the assumption that costs will go down and then, as costs come down, the technology is assumed to spread rapidly and ubiquitously. Indeed, the models that are responsible for essentially all of the 450 ppm scenarios rely massively on BECCS.
Yet, in the real world, there are zero BECCS plants in existence today and no sane firm is planning any serious investment in the technology because of the terrifying costs and regulatory risks. A few years ago the models loved a CCS technology fired with coal, but in the real world coal CCS has barely taken off as well. If you restrict CCS then the models love nuclear power, but in the real world there are limits on nuclear. Some models love renewables; others don't.
When you start telling the models about the real world the costs go up by a factor of up to 3—probably a lot more, but we don't know because the solution space with multiple real world constraints hasn't been fully explored in the scientific literature yet. (Look at the small N numbers in the orange section of table SPM.2). In fact, many of the models simply can't compute 450 ppm limits (i.e., they blow through 2 degrees) when you add real world constraints. Some of these insights are evident in the SPM that Stefan cites—for example, see the paragraph on p.14—but conveniently Stefan only quotes the idealized 0.06% number when he says that the "vast majority of scientific literature" says that 2 degrees is achievable with just a "minor delay in economic growth". When you look at real world scenarios, including studies that look at actual trajectories in emissions compared with the cuts needed for 2 degrees (see, for example, figure SPM.5, left panel or the very influential Peters et al 2012 article) a totally different picture emerges. We are not on track—even with the Copenhagen pledges—to come anywhere close to the near-term windows that are consistent with long-term limits of 2 degrees. In fact, the "vast majority" of the scientific literature doesn't even compute 450 ppm because it is so hard to reach. Look at the "N" numbers on table SPM.2. There are only 14 runs that are used to create the 0.06% number. (Technical point: this is not the "best" estimate, as Stefan quotes, but just a central estimate. There aren't enough model runs to do a serious "best" analysis.) When you look at the less aggressive scenarios, which are still hard for the models to generate, the number of feasible runs goes way up. For example, 550 ppm has become a benchmark scenario; it has 46 runs. If you want to know what the "vast majority" of the scientific literature actually says then look at 550.
So that is what the literature actually says. And the conclusion from that work is totally different from what Stefan says and completely in line with our characterization.
WE ARE SAYING NOTHING NEW
Some people seem to be upset about the article because, actually, we aren't saying anything new. There are various passing citations in Joe and Stefan's article to other research that has also made the point about the need for multiple indicators—including, notably, the planetary boundaries studies (Rockstrom et al, 2009). Our essay is a 2,000-word commentary on a pressing global problem, not a radically new piece of scientific research. We don't claim that we are the first to say all this—in fact, the original submission to Nature, which I attach [posted separately], had nearly 50 citations to other studies, including some that have looked at different strategies for setting vital signs.
But what's needed is a fresh look at where this literature stands and what it means for policy—that's why we wrote our article and why we think it is no longer possible to ignore the realities about the problems with the 2 degree goal. I apologize to all of you who were cited along the way (Nature capped us at 10 citations), and in the last 12 hours I have received at least a dozen emails from people saying "nice piece, but we already said all this already." One guy sent me links to nine articles and books. What's different about our piece is the effort to look beyond the simplistic 2-degree number to a process that could deliver better goals—and to explain why we must not dawdle further and how goals, in the real world, can work best.
We are mindful of the Rockstrom et al 2009 work, but we didn't dwell on it in this piece because our article is about the global climate problem. The planetary boundaries efforts are much broader and, frankly, run into bigger troubles with comparability across dimensions—something that has come out in the Nature published commentaries on those studies.
WE ARE TRYING TO SABOTAGE PARIS
Finally, I want to address the claim that we are saboteurs of real progress. Stefan makes that argument forcefully— implying that our attack on "finally agreed foundation" of 2 degrees is an ideal way to sabotage Paris [the 2015 round of climate treaty negotiations]. Joe repeats that attack and also adds the zinger: "Instead of trying to get the world's leading governments to agree on the commitments needed to avoid crossing the 2°C target, let's just ask them to agree on a 'path for designing' some new targets. So long Miami, New Orleans, and other coastal cities — it's been good to know you!"
I am quite familiar with these tactics as someone who said, very early in the debate, that the Kyoto style approach to negotiating binding targets and timetables would never work. Back then, the attack was that we didn't have time to focus on other options because that would be distracting to governments and we should double down on Kyoto. My argument, then and now, is don't double down on things that aren't working. Typically, such attacks then hang on your head the guilt for any climatic disasters that would follow if governments were to pause and take a breath and think rather than just doubling down. That why, I assume, Charlie and I are now responsible for the populations of sub-sea level cities. Stefan says "nobody in their right mind would aim to warm the climate by 2 degrees C.," which seems to imply that we are happy to see the planet blow through this goal. This is not only logically erroneous, it ignores the reality that building an effective system of management of the climate is a long-term process. If you make mistakes early on in building the right institutions it is important to fix them because institutions have path dependence. Witness the nearly two decades spent on the convention/protocol model that was, in my view, a lot of wasted time because it was obvious that better institutional models would be more effective.
Now, finally, we are moving to a more "bottom up" system—in part because of research that showed why the top-down, binding convention/protocol system wouldn't work. There are lots of reasonable disagreements to be had along the way, but pretending that those disagreements don't exist—even though the social science literature in this area shows that they do—is no way to create effective policy.
Charlie and I did NOT say that in Paris governments should "just" agree on a path for designing new vital signs. We said exactly the opposite of that. We said: "Getting serious about climate change requires wrangling about the cost of emissions goals, sharing the burdens and drawing up international funding mechanisms. But diplomats must move beyond the 2oC goal. Scientists must help them understand why, and what should replace it. New indicators will not be ready for the Paris meeting, but a path for designing them should be agreed there…."
We have said, starkly, that the core Paris agenda—emission cuts, burden-sharing, financing and the like—are critical. And we have said that Paris should ALSO launch a process to work seriously on goals, which is hardly a radical claim since the Cancun agreement quoted by Stefan above calls for the same thing. This time, though, we need to look at the very long term as well as the near term and come up with a better package.
There's a good National Geographic piece on the 2-degree debate by Michelle Nijhuis. I encourage you to consider Victor's defense in the context of "A Blueprint to End Paralysis Over Global Action on Climate," an invaluable policy-oriented essay by former senators Timothy E. Wirth and Thomas A. Daschle in Yale Environment 360.
I've written in the past about other issues related to setting a numerical limit for climate dangers given both the enduring uncertainty around the most important climate change questions and the big body of science pointing to a gradient of risks rising with temperature.
In haste, I failed to notice it was Stefan Rahmstorf's critique of the Victor-Kennel commentary that implied they lacked expertise; Romm's piece simply echoed Rahmstorf. Here's the original, faulty, language, which is now changed above:
