Responding to Vigdor and Londergan’s critique of Unsettled

Steven Koonin
12 min readOct 19, 2021

Earlier this month, Steven Vigdor and Tim Londergan, two nuclear physicists who co-author the blog “Debunking Denial,” published a critique of my book Unsettled on their blog. As I say in Unsettled, I encourage informed and good-faith criticisms of what I’ve written. To that end, here I offer responses to some of their points. I have also engaged with other critics here, on Medium, and here, at the Wall Street Journal.

I. General Comments

Vigdor and Londergan begin by taking issue with Unsettled’s cover design, claiming the question mark is “a ruse”. I find it ironic that two experienced scientists and educators would discourage a call for readers to inquire, educate, and decide for themselves.

Of greater substance, they mischaracterize my position as “skepticism.” Since virtually everything in the book is from the United Nations or United States assessment reports or the subsequent peer-reviewed literature, I’d hardly call it skepticism. It is better thought of as dissent from the alleged “consensus” as popularly portrayed in the media and political dialogs. And I am certainly concerned by the public portrayals of science. While some journalists do a very good job of accurately representing scientific findings, most journalists and many politicians overstate the claims of science in an effort to garner more attention or marshal support. For various reasons, scientists and scientific institutions have been reluctant to call them to task when they do so.

Vigdor and Londergan’s center much of their post on the relationship between climate science with its uncertainties and the consequences of action or inaction. Vigdor and Londergan characterize the policy-making process as “an assessment of worst-case scenarios.” This is too simplistic a description. Policy-making is complex and additional considerations are the probability and impact of the worst-case, the feasibility, efficacy, and downsides of proposed courses of action, what other problems might demand attention and resources that are more certain, more immediate, and more tractable.

II. Is Ongoing Global Warming Primarily Caused by Human Activities?

Vigdor and Londergan’s offer some points about the attribution of global warming. As they note, I acknowledge the importance of greenhouse gases (GHGs) retaining heat in the lower atmosphere and on the surface. I emphasize that the real uncertainty is the feedbacks that are thought to enhance the direct warming influence of CO­2 by a factor of two to three. These are emergent properties and cannot be determined from basic science.

But Vigdor and Londergan claim that I do not acknowledge an “extremely strong correlation” between measured surface temperatures and a scaled measure of the CO2 concentration. This is, at best, a cartoon of the actual science, as I told Richard Muller when he first created the graph that is their Figure 4:

For one, the correct driver should be radiative forcing, of which the [logarithm of] the CO2 concentration is only one component. Aerosols and other GHG gases are of comparable importance. Second, there is natural variability (internal modes, solar intensity) that needs to be taken into account to do a proper analysis. And finally, there is a few-decade time-lag between the forcing and the temperature response due to the ocean mixed layer.

If the correlation were so good, we should be able to extract the climate sensitivity from it. Unfortunately, those other factors make it difficult, and different assumptions by different researchers lead to very different results. See, for example, Section 4 of Sherwood et al and, earlier, Lewis and Curry. Both are cited in Chapter 5 of Unsettled.

Contrary to the claim of Vigdor and Londergan, I did not claim “that human-induced effects on global and local climate will be small and slowly varying.” I did say that human influences, namely radiative forcing, are physically small but I also emphasize in Chapter 2 of Unsettled that the climate is sensitive. Moreover, there is support for the notion that we have time to study the climate in more detail, including within mainstream economics literature, for example see Figure 5 of Nordhaus’ 2018 Nobel Lecture. Additionally, I do not disagree that there are high and rapidly rising levels of CO2 and methane in the atmosphere. I note on page 67 of Unsettled that it’s the recent rapid increase of these gases that is of greatest concern. And I also spend several paragraphs on pages 65 and 66 explaining why the recent rise in CO2 is anthropogenic, not natural. But I do not find close agreement of the curves in Vigdor and Londergan’s Figures 3 and 4 to be compelling. There is warming from 1910–1940 that is not reproduced by the solid curve which is as rapid as that in recent decades. Human influences were much smaller then, suggesting natural variability is significant, and might be enhancing the recent rate. Additionally, it is naïve to exclusively blame CO2 for the rise in temperature — this completely ignores aerosols, other GHGs, and natural variability. As I noted above, more rigorous analyses of the sensitivity suggested by Figure 4 give rather disparate values for the Equilibrium Climate Sensitivity, different enough that they would have very different policy implications.

III. Are We Feeling Impacts of Climate Change Yet?

One of the core tenets of the “consensus” view is that extreme weather events have grown more frequent or at least more severe in recent years. But the central truth is, that while the planet has indeed been warming, most extreme weather events don’t show an obvious trend, as documented in Intergovernmental Panel on Climate Change and U.S. Government reports, and in the peer-reviewed literature. Particularly, Vignor and Londergan accuse me of deliberately misreading the 2017 Climate Science Special Report’s (CSSR) claim:

“There have been marked changes in temperature extremes across the contiguous United States. The number of high temperature records set in the past two decades far exceed the number of low temperature records.”

I didn’t misread it, and I never said it was incorrect. It’s just very misleading. What is incorrect is the title of CSSR’s Figure ES.5 (“Record Warm Daily Temperatures Are Occurring More Often”), as I reproduce on page 101 of Unsettled, as well as in the CSSR’s text in Section 6, on page 192: “very generally, the number of record lows has been declining since the late-1970s while the number of record highs has been rising.” I give an extended treatment of the problems with this figure and the claim that record high temperatures are more frequent in Unsettled on page 100 and following. As discussed in Unsettled, a proper analysis of temperature extremes, one that does not have the structural decrease of the Meehl method, shows no change in the incidence of daily record highs over more than a century, while daily record lows have become rarer over the same period. This is entirely consistent with CSSR’s Figure 6.3, which shows the coldest temperatures rising over a century, but the warmest temperatures unchanged for the past 50 years, and essentially the same recently as they were in 1900. It’s also consistent with CSSR’s Figure 6.4, which shows US heat waves recently are no more common than they were in 1900.

Discussions of warming aside, climate models are severely limited. It is well-known among the modeling community, but not much publicized, that the models are practically useless for regional predictions. See, for example, Nissan et al.: “Climate models are unable to represent future conditions at the degree of spatial, temporal, and probabilistic precision with which projections are often provided, which gives a false impression of confidence to users of climate change information.” Vigdor and Londergan are dismissive of my claims based on the “technical data,” that being the actual observation records of weather events. Rather than responding to the claims, they quote Unsettled’s page 117 misleadingly: “there have been times before human influences became significant that were at least as active as today.” But they neglected to include the preceding sentence, which cites a 2012 paper in the Journal of Climate: “there have been periods before 1949 that were relatively active compared to the post-1995 era of heightened activity.” Indeed the World Meteorological Organization states that “… any single event, such as a severe tropical cyclone, cannot be attributed to human-induced climate change given the current status of scientific understanding.”

Vigdor and Londergan also argue from actuarial data that climate-related severe weather events have more than tripled since 1980 but this ignores the robust weather data that is directly collected. That data shows that there are no obvious global trends in most types of severe weather events. As I quote from IPCC’s Fifth Assessment Report (AR5) Working Group I on page 98 of Unsettled:

• “ . . . low confidence regarding the sign of trend in the magnitude and/or frequency of floods on a global scale.”

• “. . . low confidence in a global-scale observed trend in drought or dryness (lack of rainfall) since the middle of the 20th century . . .”

• “. . . low confidence in trends in small-scale severe weather phenomena such as hail and thunderstorms . . .”

• “. . . confidence in large scale changes in the intensity of extreme extratropical cyclones [storms] since 1900 is low.”

The Sixth Assessment Report (AR6) says very much the same things, although it does note that intense precipitation over land has become more common, albeit with regional variations.

Regarding Vigdor and Londergan’s criticism of the mock headlines or climate facts that I present in the Introduction of Unsettled,:

· Record high temperatures are becoming rarer

This is discussed at length in Unsettled chapter 5.

· Humans have had no detectable impact on hurricanes

I discuss this at length in chapter 6 and I discuss the source of Vigdor and Londergan’s Figure 7 on Unsettled’s pg 120 and note that the bottom line conclusion of that paper is hardly compelling:

Ultimately, there are many factors that contribute to the characteristics and observed changes in TC intensity, and this work makes no attempt to formally disentangle all of these factors. In particular, the significant trends identified in this empirical study do not constitute a traditional formal detection, and cannot precisely quantify the contribution from anthropogenic factors.

Further, a paper published in July (after AR6 literature closed) did a reconstruction of North Atlantic (NA) hurricanes over 150 years. They found a drop in major hurricane (MH) fraction from 1960, a minimum in 1980, and then a rebound to the 1960 value in the past few decades. They note:

“We hypothesize that these recent increases contain a substantial, even dominant, contribution from internal climate variability, and/or late-20th century aerosol increases and subsequent decreases, in addition to any contributions from recent greenhouse gas-induced warming.”

And they caution: “… care must be exercised in not overinterpreting the implications of, and causes behind, these recent NA MH increases.”

So it seems that the issue of whether the MH fraction is increasing is, if I may, “unsettled.”

· Greenland’s ice sheet isn’t shrinking more rapidly

Vigdor and Londergan acknowledge that this is accurate. But it is not misleading, as they claim, because the very high natural variability makes attribution more difficult.

· Global areas burned by fires are declining­­

The authors also acknowledge that this is accurate but again, contrary to their claims, this is not misleading. I explain, as Vigdor and Londergan note, that this is related to a decrease in intentional fires on Unsettled page 142. This is a great illustration of how direct human influences are much more relevant to wildfire damages than a changing climate as I elaborate on pages 143–144.

Regarding sea level rise, Vigdor and Londergan claim that I imply that it is not accelerating. This is not the case. In fact, the decadal-scale accelerations and decelerations of global sea level are the focus of Unsettled Chapter 8 (see for example, Figures 8.5 and 8.6 and the discussion around them).

Finally, Vigdor and Londergan claim that “the correlation of all the impacts discussed above during the past half-century provides a strong indication that we are already suffering impacts of human-caused climate change.” As I noted above, most extreme weather phenomena show long-term trends attributable to anthropogenic influences (at least according to the IPCC).

IV. What, If Any, Actions Should be Taken to Mitigate Climate Change?

In this section of their critique, Vigdor and Londergan take issue with the more cautionary responses to climate change that I advocate. This begins with their questioning of some of the most accurate reports on the economic impacts of climate change. The projections that they take issue with are not mine, but rather right out of the most recent IPCC and USG reports on the issue. One can find in citations of those reports exactly what is, and is not included in the calculation. But perhaps we have found a point of key agreement. I cover on page 178 of Unsettled all of the difficulties in making such projections. And I’m glad Vigdor & Londergan are skeptical of the results. They might then agree with me that the assessment reports deserve a much more rigorous “scrub.” Perhaps they’d even be interested in joining me and others to undertake such a task.

I would particularly draw attention to the Unsettled Figure 12.2. Contrary to Vigdor and Londergan’s claim, this is not my projection but is rather from the US Government’s Energy Information Agency (EIA), as cited. Their differences from other projections, such as ExxonMobil, reflect the degree to which the future is “unsettled” because of different, presumably plausible, assumptions which are determined by the EIA or respective modeling group. Needless to say, perhaps they, and others, would have criticized me for taking the projections of an oil company. So Unsettled deliberately uses only official or peer-reviewed sources.

Throughout their critique of my policy discussions, Vigdor and Londergan remain fixated on renewables. It’s true that wind and solar are the lowest cost generating technologies, but an acceptable grid is about much more than generation alone. After safety, reliability is the most important, and expensive, consideration. It requires some form of dispatchable generation to buffer the intermittency of wind and solar. Options at the moment are fission, gas with CCS, batteries, and chemical storage, with the latter three technologies not really ready for prime time.

The high reliability requirement (>99.9%) increases the cost of the grid by several times that for the renewables alone. That’s because one needs to buffer periods as long as a week when renewables don’t generate. The EU and UK have experienced that in recent weeks. And a study using real high-resolution weather data in the US doesn’t offer much cause for optimism.

Unfortunately, with regard to reducing emissions in the developing world, the analogy that Vigdor and Londergan make to chlorofluorocarbons (CFC) is flawed. Unlike carbon emitting energy sources, reasonable substitutes for CFCs (in both economic and performance metrics) were available. More importantly, CFCs were not woven throughout every aspect of society, as energy is. We do not have reasonable substitutes and even if we had substitutes available, the massive effort to transition entire economies to new sources of energy requires a tremendous amount of resources that countries are not prepared to commit.

These same challenges are present in both developing countries and in highly developed electric grids. The necessary modifications to handle the variability of renewable sources are extremely expensive and despite a decade of planning by national laboratories and others, remain a formidable logistical, technical, and political challenge.

I am glad that Vigdor and Londergan agree about the need for research into ways to adapt to a changing climate. As they note, atmospheric geoengineering in particular will rely on climate models for scalability and the models are, as they say, “unsettled.” This is true but the converse is even more significant. As I note on Unsettled page 96, a National Academies report on geoengineering said:

The uncertainties in modeling of both climate change and the consequences of albedo modification make it impossible today to provide reliable, quantitative statements about relative risks, consequences, and benefits of albedo modification to the Earth system as a whole, let alone benefits and risks to specific regions of the planet.

If this is true, why should we give any greater credence to climate model predictions of the response to GHG forcing?

Vigdor and Londergan acknowledge rightly, that we are witnessing “two massive social experiments.” One being the human endurance of a massive transformation in the worldwide economy and the second being the ability for humans and other species to adapt to the rapid growth in greenhouse gas concentrations and other changes in the climate. They argue that an analogy to the combustion engine or miniaturized electronics captures the response of people to an economic transformation but these are poor analogies. Each of these technologies provided a new capability that people were eager to acquire (mobility and computing/communications, respectively). We already have reliable and economic ways of providing energy, and any shift to emissions-free technologies will be invisible to the user.

Regarding the second experiment, Vigdor and Londergan are extremely pessimistic. They argue that there are no precedents for this challenge. That is not true. The globe warmed by 1.1 °C since 1900. During that time the population quadrupled. More importantly, there was the greatest improvement in the human condition in history on many fronts including health, nutrition, medicine, knowledge, and communication. There’s great reason for optimism that we’ll be able to handle another 1.5 °C warming in the next century. But, as I state explicitly in the book, I’ve written descriptively rather than normatively. I do believe that adaptation is what society will do. Having laid out accurately and fully the certainties and uncertainties in the science as expressed by the official science, as well as the technical, economic, and political challenges in reducing emissions, I’m content to let everyone else debate what we should do. That fully-informed debate is what we should be having.

As I say on Unsettled page 254, I respect those who’s conclusions differ from mine and am grateful for the opportunity to engage in dialogue with them. I hope my comments and citations to quality references improved Vigdor & Londergan’s perceptions of the science, the data, the technological challenges, and the uncertainties of climate science.