The closing chapter of the book illustrates the practical implications of Kant’s political and legal philosophy for climate change. Texts like the Doctrine of Right and Toward Perpetual Peace are used to rethink the complex political and collective challenges of the climate crisis. These, once again, confound the individualist and nonconsequentialist standard reading of Kant. First, I argue that Kant’s state of nature theorizing leads to prescriptions that are compatible with and justify coercive domestic and international policy to address the crisis. Second, I zoom out to consider whether Kant’s political philosophy as a whole remains too conservative or outdated to provide guidance regarding deep climate adaptation, mitigation, and radical institutional reform, answering in the negative. I close by discussing political obligations owed to peoples, interpreted in the face of the Hobbesian call for a global climate leviathan.

When you communicate climate change science, be sure to include information on solutions. Nobody wants to hear about hopelessness, and in the case of climate change, there are many reasons to be hopeful. Climate change poses difficult problems and challenges, but there are lots of solutions that are both creative and practical and that can help solve the problems and overcome the challenges of climate change. There is no silver bullet that solves all the challenges of climate change, but there is lots of silver buckshot, including increased energy efficiency and energy conservation and much more use of sun, wind, and water to provide the energy the world needs. These renewable resources are widely available now and already cost-competitive with fossil fuels. Help people realize that not acting is also making a choice, one that commits future generations to serious climate change impacts. Research suggests that messages that may invoke fear or dismay are better received if they also include hopeful messages. Everything depends on what people and their governments do.

How will the growth of atmospheric concentrations of greenhouse gases affect the climate? When we try to foresee the future global climate, we are not simply extrapolating past behavior. We are using our scientific understanding of how the climate system works. Keeping that distinction in mind, then, the typical benchmark figure by which climate scientists now predict the climate will warm in response to a doubling of CO2 is a range rather than a single number. A range often quoted is 1.5 to 4.5 degrees Celsius (which is 2.7 to 8.1 degrees Fahrenheit). Not long ago, a widely quoted consensus number was the midpoint of this range, 3 degrees Celsius (which is 5.4 degrees Fahrenheit). A similar range, also often quoted, is 2 to 5 degrees Celsius (or 3.6 to 9.0 degrees Fahrenheit). There is more than one way to arrive at such a range, both from observations and from models, and the details are important to scientists doing this research. For other people, it is more important to be familiar with the approximate range, because estimates of climate sensitivity will continue to vary as more research is done.

The physical science portion of the Summary for Policymakers of the latest assessment report of the Intergovernmental Panel on Climate Change states that the best estimate of climate sensitivity, defined as the warming expected at equilibrium from doubling the amount of carbon dioxide in the atmosphere, is 3 degrees Celsius (or 5.4 degrees Fahrenheit). It also states that the global average surface temperature will continue to increase until at least the middle of the current (twenty-first) century. Recalling that the Paris Agreement of 2015 specified a goal or target of limiting warming to 2 degrees Celsius (or 3.6 degrees Fahrenheit), with an even more ambitious aspirational goal of 1.5 degrees Celsius (or 2.7 degrees Fahrenheit), this Summary for Policymakers states that neither of these goals will be met during the twenty-first century unless deep reductions in emissions occur. The report also states that many of the climate changes caused by greenhouse gas emissions cannot be reversed and will persist for hundreds or thousands of years. It cites global sea level rise and the loss of ice sheets and glaciers as examples of changes that will be irreversible on human time scales.

Chapter 2 continues the thread from Chapter 1, moving from objections against Kant in animal ethics to broader concerns in environmental philosophy. I begin with problematic passages from Kant’s critical texts such as the Groundwork for the Metaphysics of Morals and the Critique of Pure Reason. While Kant does not discuss the environment, the standard interpretation of Kant suggests that nature has no intrinsic value and that environments are of mere instrumental worth. Environmental philosophers are warranted to suspect that Kant’s critical philosophy may be a nonstarter given its apparent dualism and anthropocentrism. Next, I examine three camps of Kant defenders who challenge these suspicions. Some commentators defend Kant’s system, others modernize him, and some synthesize Kant with other philosophers such as Aristotle. I assess the merits of their arguments, ultimately recommending a move beyond the standard reading to address the climate crisis.

Modern research has produced computer climate models that are based largely on weather-prediction models. Climate models, however, include simulations of the ocean and land surface and other components of the climate system, as well as the atmosphere. Climate models are also allowed to run for a longer simulated time, several months or even years, instead of the few days needed to produce a weather forecast. This variation in time scales is one of the fundamental differences between climate and weather. Climate modeling is computer simulation of a high order. We can change a number in the computer program and make the Earth spin faster or backwards, we can turn off the Sun, we can make the seasons disappear, or we can change atmospheric carbon dioxide. Of course, we are doing all this with a make-believe or virtual Earth. Climate modeling by computer simulation is an exciting area of research. It can provide valuable insights into how the climate system works. However, the results are approximate solutions of the climate problem, not exact depictions.

Kant’s Metaphysics of Morals, while useful for moving past the ecological limitations of the standard reading, is limited insofar as it focuses on individual actors—consumers, citizens, and politicians in particular. Kant’s ethical thought emphasizes individual humans rather than economic and political systems, and his teleological thought appears scientifically outdated. This chapter asks whether these aspects of Kant’s thought need revision. It begins by placing Kant in dialogue with Darwin and Marx, pursuing a critical discussion on the human species and political systems in the context of the Anthropocene. The Kantian reply, I suggest, encourages us to reconsider Kant’s philosophy of history and philosophical anthropology. Kant’s ideas are significant for the climate crisis insofar as they enjoin normative reflection on the human species globally and in the long term. I conclude with critical reflections on Kant’s racism and sexism as obstacles to reading Kant in the Anthropocene.

A feedback is something that happens in response to a prior cause, and which then itself makes a change in what caused it. It is the modification or control of a process or system by its results or effects. The challenge in making climate models realistic is largely that of understanding these feedback processes and incorporating them in models. As the air warms, does water vapor increase? To what extent? How much does that affect the warming? Do ice and snow melt? How rapidly? Does that change the reflectivity of the Earth’s surface and affect the warming? Does the ocean circulation change? In what ways? How does that affect climate? Do the clouds change? Are they more plentiful? Less plentiful? Higher? Lower? Darker? Lighter? How do they feed back to the climate? We need quantitative answers to all these questions. For example, we are not asking the qualitative question of whether clouds warm us or cool us. We know that they do both. Rather, we are asking the hard, quantitative question: Which of those two events is dominant, the cloud’s contribution to the greenhouse effect (warming) or the cloud’s contribution to reflecting away sunlight (cooling)?

This chapter first reproduces a fictional speech that I published in 2008, an election year for the Presidency of the United States. The candidates were Barack Obama and John McCain, both Senators at the time. In this imaginary speech, I expressed my thoughts on what the winner of the election might say about the steps he would take to give high priority to meeting the challenge of climate change. Climate change is not something the world can safely continue to procrastinate about. We cannot wait until coastal cities become abandoned before we start mitigating sea level rise. Waiting too long means doing too little and acting too late. There is a timescale built into the climate change issue by physics and chemistry, and the broad public has not yet fully realized the urgency of it. Climate change is fundamentally a moral and ethical problem, in my view. What do we who are alive today owe to the next generation, and to subsequent generations? We are literally creating the planet our children will live in. We must act energetically and wisely. Everything depends on what people and their governments do.

For many important aspects of weather forecasts, predictive skill has improved by about one day per decade in recent years. A seven-day forecast now, for example, is approximately as accurate as a three-day forecast was four decades ago. Thus, progress in improving forecasts during about four decades has resulted in extending the useful forecast range by about four days. This is a remarkable accomplishment. However, any error in specifying the initial conditions, and we know errors are inevitable, will make the forecast go wrong after a certain time. As for our current forecasting skill, we can predict weather for at least several days. For the largest-scale features – very large weather systems, highs and lows on continental scales – the limit is thought to be a few weeks. Recent progress in research has led to major advances in our understanding of climate. These advances have greatly increased the confidence of scientists in their ability to make skillful and useful forecasts of how the climate system will respond to increased amounts of greenhouse gases in the atmosphere.