As described in Chapter 2, after Congress failed to pass climate change legislation in 2009, the Obama administration EPA moved very quickly to find that GHG emissions from autos and light trucks were reasonably likely to endanger human health or welfare. This – the Endangerment Finding – then provided the legal basis for a number of subsequent regulations promulgated under the Clean Air Act. Most directly, the EPA first imposed GHG emission limits for cars (using the same section of the CAA under which the Endangerment Finding had been made). In so doing, the EPA arrogated to itself the job of setting mileage standards for cars and light trucks, a job that Congress had explicitly given to a very different agency, the National Highway Transportation Safety administration, that had a very different historical mission. Moreover, the automobile mileage standards set under the Obama administration’s so-called tailpipe rule were essentially the standards that California and some northeastern states had imposed on themselves.

Long before the Obama administration EPA’s Endangerment Finding, early IPCC assessment reports were a call to action for American tort lawyers. After all, the IPCC ARs attributed all sorts of human and environmental harms to climate change, and confidently linked climate change to anthropogenic CO2 emissions. These reports thus established a causal connection between CO2 emissions and harm. Such a causal connection held out the prospect of holding CO2 emitters legally liable under American tort law for harm from climate change.

The EPA’s Endangerment Finding relied entirely upon IPCC Assessment Reports (and, to a lesser extent, USGCRP Assessments) as supplying more than enough evidence that rising atmospheric CO2 concentrations have caused changes in various measures of climate and that without steps to reduce anthropogenic CO2, climate changes will get event worse in the future. Having already explained how both the IPCC and USGCRP have developed into science advocacy organizations, rather than assessment institutions, in this chapter I begin my brief critical analysis of the output produced by the IPCC. I focus on the IPCC because its reports are the primary basis for not only the Endangerment Finding but for precautionary US climate policy more generally.

As known not only by lawyers, judges, and regulators but also businesspeople, scientists and pretty much anybody who has ever had to make a decision on the basis of technical assessments of the relevant world, in any tough decision of this sort, there is conflicting evidence and opinion. Some things are known with certainty. We know for certain, for example, that the sun will rise in the east. But most important decisions are taken under conditions of uncertainty. A farmer deciding when to plant his fields with corn should consider evidence about the likelihood of a late, crop-killing frost; in deciding how to design a new product for market, a prudent business will get evidence about likely consumer demand for alternative designs at varying prices; a court deciding whether or not the defendant committed a crime will hear not only the prosecution’s evidence but also the defendant’s. Even after hearing evidence on both sides, a decision maker will not be certain about the state of the world relevant to her decision.

In this part of the book, I take a critical look at the beliefs about the state of scientific knowledge about climate change and its economic impacts that are commonly taken to support the precautionary policies explicated in Part I. Such an inquiry is necessary because a balanced and rational climate change policy must be based on both what is actually known and what is unknown about climate change and its impacts.

A very typical story leading to domestic environmental legislation in countries such as the United States is one in which people in a number of localities within the country begin to experience harm from a particular kind of pollution and then legislators from those places take up the cause and ask scientists to identify which pollutant or pollutants are causing that harm so that legislation can be passed to curb the harmful pollution. As discussed earlier, precisely such a process led to the passage of the Clean Air Act of 1970. One might suppose that a similar pattern occurred on the international level with global warming: some countries might have been experiencing harmful warming, leading them to ask for international scientific cooperation to identify the cause of the warming. Such a pattern – a problem is identified, and scientists are asked to figure out what is causing it and what might be done to eliminate it – is what might be called the standard model of how science relates to policy.

As long as our species has been on planet Earth, humans have had to adapt to their external physical environment. During the cold upper Paleolithic era – which runs from about 40,000–10,000 years ago – Neanderthals died out, and most remaining homo sapiens were hunter-gatherers. They lived in widely dispersed bands that followed herds of animals such as reindeer. Such hunter-gatherer Paleolithic life was precarious, subject to cycles in the population of prey animals. Still, even during these cold and grim Paleolithic times, recent research has found evidence that in favorable locations, some human groups adopted agriculture and expanded rapidly after the Last Glacial Maximum (about 25,000 years ago) or perhaps even earlier, 60,000–80,000 years ago. Moreover, even during this, the stone age, humans colonized new territories, such as Australia and the Americas, and by the end of the Paleolithic had domesticated dogs.

As we have seen, the CPP represented a decision by the EPA that the EPA should assume the job of transforming the energy basis of the US electric power industry away from fossil fuels and toward renewables. Congress did not give the EPA this task. To the contrary, as we have seen, for half a century, since the creation of the EPA in 1970, the EPA’s role in regulating the electric power generation industry has been limited to imposing pollution reduction requirements. On several occasions, however, Congress has passed laws directly mandating the use of particular fuels, both by power plants, and by automobiles. The history of these laws displays two patterns: the EPA has never been given a primary role, and typically was given no role, in implementing them; more importantly, such laws have virtually always had perverse effects, causing environmental harm rather than averting it.

In the Summary for Policymakers to its AR5, the IPCC makes a number of unqualified statements attributing observed climate change to human GHG emissions.

In early 2008, then-presidential candidate Barack Obama described his climate change regulatory agenda by saying that “if somebody wants to build a coal-fired [electricity generating] plant they can. It’s just that it will bankrupt them.” After his election, President Obama made good on his promise.

In this concluding chapter, I set out what may called the bottom line conclusions that I believe follow from the explanation and analysis provided by previous chapters of this book. These conclusions consist of recommendations for institutional responses to three fundamental problems of climate change: how to facilitate efficient adaptation to changing climate; how to curb present-day CO2 emissions while minimizing the present-day environmental harms and the unfair, regressive costs imposed on today’s poor; and, finally, what to do about the climate science advocacy industry that has produced some very interesting science, but also succeeded in moralizing scientific disagreement in a counterproductive and indeed dangerous way. My proposals follow logically from the analysis in previous chapters. I make no claim that and frankly know of no method for determining whether any of my proposals are politically feasible.

In order to understand and evaluate any proposal, such as the Obama EPA’s Clean Power Plan, to shift American electricity generation to rely more heavily on renewable power, one must first understand the basics about how the US electricity system works. As we shall see in this chapter, moving to a higher share of renewable power while ensuring the reliability of electricity supply is far from trivial. The cost of a system with a high renewable power share is far greater than the cost of simply building and operating wind and solar farms. It includes not only the costs of building new transmission lines, and upgrading transmission stations and substations, but also the cost of electricity from rapidly dispatchable power sources such as natural gas turbines that can provide power when solar and wind power are unavailable. Together, these costs cause high electricity prices in systems with high renewable power penetration.

There are, generally speaking, two types of harm from climate change: harm to human health, economic prosperity and welfare, and harm to nonhuman species and ecosystems. In this chapter, I discuss how the human cost of climate change has been estimated for US regulatory purposes. This estimate is called the social cost of carbon (SCC). It is the most rigorous monetized measure of the harm to human economies from climate change. Harm to humans is not the only potential harm from changing climate, but as the quantification of such avoided harm was the primary benefit advanced to justify Obama-era climate change regulations, I focus here solely on the SCC.

IPCC projections about future climate are based primarily on the computer models of the earth’s coupled oceanic and atmospheric circulation system that I discussed earlier in Chapter 14. As we have seen, these models manage to reproduce industrial era temperature change only by tuning the way they parameterize – numerically approximate – certain crucial but poorly understood physical processes, in particular how clouds respond to a CO2-induced warming. The models’ one clear testable prediction about the present-day impact of rising CO2 – that tropical tropospheric temperatures should be rising more than surface temperatures – has not been consistently confirmed. And over the course of most of our present climate ear, the Holocene, work is conflicting on whether temperature has been rising along with CO2.