A journalist asked me to comment on the efforts by Governor Cuomo to close down the Indian Point nuclear power plant, outside of New York City. An edited form of my reply follows (image from www.elp.com):

I am a climate scientist with no particular expertise on things nuclear and little knowledge specific to individual power plants and little knowledge about the details of New York’s power supply system, so I am a loathe to comment on Indian Point and other matters with great specificity.

I do know that nuclear power has been one of the safest and most reliable, if not the safest and most reliable, forms of electricity generation operating over the last half-century — and this is taking the tragic accidents at Chernobyl and Fukushima into account.

Coal kills something like 3000 people every day, largely due to health effects of particulate emissions. More people die from every week from coal-electricity production than have ever died as a result of nuclear power. The airplane crash gets the news; people dying on the highway every day is a bit ho-hum.

That said, if you were siting a nuclear power plant today, I don’t think you would site it near a giant population center. That is just sensible risk management. The risks are already small, but why not make them even smaller?

If Indian Point is closed down what will take its place? Will it be better or worse? What will be built additionally? Today, the cheapest electricity from new builds is typically natural gas. It is clear that natural gas is much worse for the environment than nuclear power.

I went to high school in Yorktown Heights, New York, less than 10 driving miles from Indian Point. Back then, I felt tangible disquietude, afraid that at some point the nuclear core might melt down and expose me to lethal radiation. Now, I understand intellectually that the likelihood of me dying in an automobile accident was many many thousands of times greater than ever dying as a result of a meltdown at Indian Point. But would I put many many thousands of times more effort into avoiding automobile accidents than I would put into trying to reduce risk from Indian Point? No. The desire to close Indian Point is mainly an emotional response to not-easily-quantified threats beyond our control, and not primarily based on a rational risk assessment.

A friend of mine did a study of a wide range of risks, and he decided that one of the main things we could do to reduce real risk in our lives is to wear motorcycle helmets while driving cars. His wife told him that if he did that, she wouldn’t ride in a car with him. So, he drives without wearing a motorcycle helmet.

It is a difficult question: How much should public policy cater to fears that are in large part irrational, but which nonetheless make people uncomfortable? A role of government is to help people feel better. To what extent is it appropriate for governments to undertake costly actions that cater to people’s largely irrational fears? (Isn’t that exactly what we did in Iraq?)

Tough questions. No simple answers.

How much of our political view is shaped by whether we come from an urban or rural environment?

If you come from a city, you understand that we all depend on each other. You interact with and come to appreciate people of all sorts of races and religions. You live and work and have become friends with people who have come from all over the world. You recognize that we need social institutions to do something about that psychotic homeless guy. You don’t want people walking around on your streets carrying guns. You are probably going to vote for Clinton.

If you come from the middle of no place, you probably feel like you made it as far as you did mostly because of your hard work. You probably interact with few people outside of your own ethnic group. You likely live and work mostly with people born near you live. You expect your neighbor’s family to deal with their crazy uncle. You want your gun so you can hunt and protect yourself, just in case. You are probably going to vote for Trump.

Democracy is supposed to be a system where government acts in the interests of the majority, while protecting the rights of the minority. But no major political party has, in living memory, worked to promote the interests of the majority of Americans.

One thing working people in both urban centers and the rural regions can agree on is that the major parties have concerned themselves primarily  with satisfying the short-term interests of their powerful and wealthy donors. The major political parties have been working in the interest of a narrow minority while trampling on the rights of the majority. We all have a right to share in prosperity.

No major political party has, in living memory, worked to broadly share the fruits of globalization, increased automation, or immigration. Broadly shared prosperity is in the long-term interest of nearly everyone, because stark inequality is not a foundation for sustained economic growth.

Our nation is in crisis. If we are to avoid fascism and tyranny, our political parties must become democratic parties and work to promote the interests of the majority.

We need to find a way to reach across that urban-rural divide. Maybe we can recognize that it might make sense for everyone to have a gun on a farm, but not on a city street. Maybe we can agree that our successes depend both on our own hard work and on being surrounded by functioning social institutions (schools, police, healthcare, etc). People working on farms and in cities can agree that when a job leaves for China, or a job is replaced by a machine, or taken by an immigrant, the displaced person still needs to share in the benefits of that globalization and automation and immigration. The benefits can’t all go to the wealthy few.

The crisis in American democracy is a consequence of an unnecessary conflict between the urban and the rural which is in turn a symptom of the widening gap between the rich minority and struggling majority. The primary problem for the average working person in America, whether they be urban or rural, is a lack of prosperity. The common foe is inequality. The common goal should be sharing the benefits of globalization, automation, and immigration.

The success of the American experiment depends on bridging the urban-rural divide.

Images from:
Population density and 2012 election results: http://davetroy.com/posts/the-real-republican-adversary-population-density
Average income between 1946 and 2008: http://www.cbpp.org/research/tax-data-show-richest-1-percent-took-a-hit-in-2008-but-income-remained-highly-concentrated

This little essay was prompted by a comment by Mike Pesca on The Gist: http://www.slate.com/articles/podcasts/gist.html

I was asked to be on a panel at the 2016 Fall American Geophysical Union Meeting on Planetary Intelligence: Managing Earth’s Future. This is what I wrote as an abstract before realizing I was limited to 2000 characters. (This is >2100 without spaces.)

We are global in our impacts, yet local in our thoughts and feelings. The daunting challenge facing Homo sapiens is learning to cooperate at global scale for the common good.

For millions of years, our ancestors, like most animals, consumed the fruits of their labors, and little capital or infrastructure accumulated over the ages. This radically changed over the past centuries. Following the inventions of the loom and the steam-engine, we have been developing ever more efficient ways of generating consumer products. Critically, some of the wealth generated by these more efficient technologies was reinvested into additional capital infrastructure, such as factories and machines, thus expanding the capacity to offer goods and services to insatiable consumers. Some of this reinvestment, and technological innovation, was in technologies that extracted and transformed natural resources into valuable goods and services and also into dangerous pollution. Improvements in medical technologies led to quasi-exponential population growth, mirroring and multiplying the quasi-exponential growth in per capita consumption.

We are reaching a stage where this quasi-exponential growth is starting to reach boundaries, but these boundaries are not sending signals to the market that would allow a laissez faire approach to work.

The central question is: How can we continue improving the well-being of living people (at least), while diminishing material flows associated with environmental pollution?

Globally speaking, if we don’t place constraints on ourselves, nature will impose constraints on us. We can impose constraints on ourselves to protect us from what nature would otherwise to do to us.

To have a sustainable future, we would need to level off population at the lowest feasible level. The difference between a future population of 6 billion and a future with 16 billion is a half-child per family less-or-more than the central projection of demographers. Empowering women with education and technology has proven to be a most effective strategy at reducing population growth.

To have a sustainable future, we would need strong disincentives on environmental damage, especially on the production of long-lived wastes such as carbon dioxide. It is of course a huge political challenge to get such disincentives in place. If we fail to get these global guardrails established, planetary management will be largely reactive, driven by competition among those with incentive and power.

In a resource- and pollution-constrained world, technological innovation is the surest path to economic growth and improved well being for all, especially the poorest on this planet.

With better policies in place, we can look forward to a future of continuous innovation and ever-improving well-being, with stable populations and diminishing environmental impact.

Some have criticized Bill Gates for saying that ‘we need an energy miracle’, suggesting this will be interpreted as Bill Gates saying that we should do nothing but sit around and wait for a miracle to occur.  I cannot speak for Bill Gates, but I can talk about what I understand him to be saying.

We live in a world of wonder, surrounded by technological miracles. We are surrounded by technological inventions which, if they were shown to our hunter-gatherer forebears, would have been attributed to magic or some divine power instead of to the laws of physics.

When I look out the window, I look through something that is hard as rock, yet almost invisible. Our ancestors would likely look at this strange artificial rock as some sort of miracle. Put a metallic film behind this rock and it turns into a mirror – surely an invention that Narcissus would have found miraculous.

We are so accustomed to technological miracles that we fail to appreciate the wonder of the technological world around us. We hurtle down highways in tin cans moving at 80 mph. We get in a cylinder and fly through the air at 500 mph. Our hunter-gatherer ancestors would have considered these technologies miraculous.

Electricity is magical. How do these wires cause my refrigerator to cool, my microwave to heat, and my audio system’s speakers to vibrate? Surely, the ancients would have found these technologies miraculous.

I can pull a little slab out of my pocket and instantaneously talk to someone on the other side of the planet. I turn on the television and see before me imagines from long ago and far away — miraculous.

Vaccines prevent disease and antibiotics cure disease — miraculous technologies.

With anesthetics, someone can slice me open and I wouldn’t even feel it — surely a miracle.

Technological miracles surround nearly our every waking moment. These come not from divine intervention but through the innovative work of brilliant people. Technology regularly creates miracles. We can expect further investment in clean energy research and development to generate more miracles.

Arthur C. Clarke once wrote “Any sufficiently advanced technology is indistinguishable from magic.” When I hear Bill Gates talk about the need for miracles, I hear him talking about the need for technologies that would, to our ancestors, be indistinguishable from something produced by divine intervention. These kinds of innovations happen all the time.

Recently, Bill Gates has written:

“Some people argue that deploying today’s technology and developing new ideas are competitors in a zero-sum game—that doing one means you can’t do the other. I disagree.  Successful industries that are built on innovation rely on both deploying the technology they have and developing the technology they need.”

This framing seems just about perfect to me: “Deploy what we have, and develop what we need.” We have enough to start down the path, even if we don’t yet have what we need to reach our destination. When real technologies confront real barriers out in the field, problem solvers innovate new solutions and create technological miracles.

The controversy over Bill Gates’s use of the word ‘miracle’ to describe what is needed to solve the climate problem comes from people’s perception of miracles being something that happens rarely as a result of divine intervention. However, we can also perceive miracles as something that commonly happens as a result of hard work.

When Bill Gates says ‘We need an energy miracle’, he means that we need to work hard to create the technologies needed to provide everybody with abundant and affordable clean energy. Technology miracles are something we can anticipate if we put in the effort to create those miracles.

Perhaps it would have been better for Bill Gates to use some other word, but we should try to understand what he is trying to communicate, rather than fret about how he might be misunderstood.

Bill Gates recognizes the deployment and innovation go hand-in-hand. Innovation doesn’t happen in a vacuum. Innovation will only create the needed miracles if we begin to address the climate problem with urgency using the technologies we already have.

Ordinary miracles are an expected outcome of hard work by creative people. These ordinary miracles will help us to reach our climate goals.

The Intergovernmental Oceanographic Commission, a branch of UNESCO, graciously awarded me their Roger Revelle Medal on World Oceans Day, Wednesday, 8 June 2016, and asked me to present the Roger Revelle Memorial lecture at the UNESCO facilities in Paris to the delegations from participating governments.  A lightly edited form of the abstract I sent them follows.

Ocean acidification and other stressors on marine systems: How can we help the oceans help us?

Ken Caldeira, Carnegie Institution for Science, Stanford CA 94305 USA, [email protected]

For all of human history, life in the oceans has greatly helped humans. Marine life not only provides humans with food, but also can build structures such as coral reefs that help protect coastlines. Living things in the ocean also play central roles in the global carbon cycle.

Life in the oceans is confronted with a wide array of direct human challenges: overfishing, farm runoff, coastal development, industrial pollution, and so on. In addition to these challenges, climate change is warming and further stratifying the upper ocean, reducing nutrient supply to the well-lit near-surface ocean. Further, when the ocean absorbs carbon dioxide from the atmosphere, the ocean becomes more acidic, and this increased acidity makes it more difficult for many marine organisms to build their shells or skeletons.

For most of human history, humanity has been a relatively small force on the planet. What we did didn’t matter very much for most natural systems. But since the industrial revolution, humanity has become a geologic force, affecting our planet with an intensity and scale that will be clearly visible to geologists in the distant future.

If we want to keep taking from the ocean, we will have to give something back. If the ocean is going to continue helping us, we will need to help the oceans.

After a brief survey of new challenges faced by the oceans, this talk will take a somewhat autobiographical walk through developing an understanding of ocean acidification. The story begins with a discussion of the extinction of the dinosaurs and what it tells us about the sensitivity of our coastal systems to changes in ocean chemistry. It then moves on to discuss how projected future changes in ocean chemistry compare with those of the ancient past – and the conclusion is that the changes we are inducing now are large even by geologic standards. I will close with a description of some field work we have been doing, studying coral growth in the Great Barrier Reef.

The central thing that we need to do to protect the ocean from ocean acidification and climate change is to convert our energy system into one that does not use the sea and sky as repository for our waste carbon dioxide – an energy system that does not depend on smokestacks or tailpipes.

But there is much we can do to help ocean ecosystems become more resilient to the changes that will occur. There are other things we can do to help the oceans help us.

We can get better at managing fishing, including establishing no-fish zones. We can work with farmers to control run-off, work with industry to identify and eliminate dangerous pollutants from the production system. We can develop our coasts sensibly, and recognize the value of building a sustainable relationship with the wild and untamed.

The organizers of the 4th  The Ocean in a High-CO2 World symposium asked me to write an OpEd piece for the Sydney Morning Herald.

The challenge was to write about ocean acidification in a scientifically accurate way but also in a way that would be understandable to the average reader of the newspaper. Also, I wanted to write something that the average person could relate to — to humanize the issue so it wouldn’t seem so abstract.

Furthermore, it being an editorial, I was encouraged to put forward my own political views in some sort of general way, but I wanted to be general enough that the conference organizers and attendees would feel comfortable with what I was saying.

Also, I wanted to avoid being overly depressing or disingenuously hopeful.

Further, I wanted it to have some structure and literary value — something I think I achieved in some parts but not in others. On top of all of this, I am trying to do too many things, so the piece had to be more-or-less written as a stream-of-consciousness, because I didn’t have time for wordsmithing.

The headline for the OpEd piece was from the editors at the Sydney Morning Herald, and was not my concoction.

Anyway, resisting the temptation to fine tune post-publication, here is what I came up with. (This is a first draft, except for correction of minor grammatical errors. There is a ‘the’ that should have been removed from the last paragraph. Both the word ‘real’ in the first paragraph and the ‘for it’ after ‘life and death’ should have probably been eliminated.)

http://www.smh.com.au/comment/ken-caldeira-on-the-reef-20160502-gokmoz.html

Oceans bearing the brunt of relentless carbon emission

by Ken Caldeira (published in the Sydney Morning Herald, 2 May 2016)

Most people live on land where the oceans are little more than a blue expanse of imagination. Does what I do right here on my spot of dry earth really matter to the far away vastness of the real ocean?

On a cold morning, when my home heater kicks on, natural gas burns and a plume of carbon dioxide streams out of my chimney and into the sky. When I make my morning toast, there is a power plant somewhere providing electricity to my toaster that is burning gas or coal and releasing giant plumes of carbon dioxide into the air. Much of this CO₂ will remain in the atmosphere for many thousands of years.

This pollution has physical consequences for our climate system, but it also has chemical consequences for our oceans.

In the atmosphere, too much CO₂ can make the world uncomfortably warm and melt the giant ice sheets and so on. Bad stuff.

This year has been just about the worst ever for coral bleaching. CO₂ in the atmosphere has been making Earth hotter and this is causing coral reefs to bleach, causing many colonies to die.

Most of the carbon dioxide we release to the atmosphere will eventually be absorbed by the oceans. They have already absorbed about one-quarter of the CO₂ produced by industrial civilisation over the past couple of centuries, and this process is making them more acidic.

When CO₂ reacts with seawater, it forms an acid. In high enough concentrations, this acid can corrode shells and skeletons of many marine organisms. In lower concentrations, it can make it harder for an organism to produce its shell or skeleton, and this could in some cases tip the balance between life and death for it.

There has been plenty of carbon dioxide in the atmosphere in the ancient past, and corals and clams and so on did just fine. There are natural processes involving rivers and sediments that buffer ocean chemistry over periods of thousands or tens of thousands of years. But right now, the ocean chemistry is changing way too fast to be buffered by Earth’s natural cycles.

The problem for marine organisms isn’t so much where we are going but how fast we are getting there. If we would spread out the emissions over tens of thousands of years instead of a few centuries, natural cycles would buffer the effects on ocean chemistry and there would be little to worry about. But if we do not dramatically reduce our rate of CO₂ emission, we will make the biggest and most rapid change in ocean chemistry the world has seen in many tens of millions of years – long before there were any humans on this planet.

We recently conducted experimental work in the Great Barrier Reef, providing evidence that ocean acidification is already slowing growth of the coral reef we examined. Increased stress from ocean acidification is probably making corals less able to stand up to heat stress and so contributing to coral bleaching. We have also made careful observations of tide pools along California’s coast, and the organisms there also seem to be affected by changes in ocean chemistry.

As a scientist, I work to better understand the relationships between our actions and what happens in the real world. On a chilly morning, I heat my home and make myself some toast and coffee, and sink into my easychair. I understand that in doing this I am contributing to killing off coral reefs and that I am affecting other marine ecosystems in unimagined ways. We know that protecting the oceans means we need, among other things, to stop using the atmosphere as a waste dump for our carbon dioxide pollution. We need to stop building things with smokestacks or tailpipes.

Scientific understanding is the cornerstone of good public policy. Science can never tell us what to do, but it can give us an idea of what might happen if we choose different courses of action. An intensified effort to develop the scientific knowledge can help us better understand the consequences of our choices. And we, as a society, can choose wisely.

Many years ago, I was protesting against nuclear power at the Shoreham Nuclear Plant on Long Island and I was arrested for protesting nuclear power. At that time, I thought, we had bioenergy and some wind and solar and that would be enough to solve the problem.

I’ve come to see now that the magnitude of the problem is so great that we can’t afford to leave technologies unused that can potentially help.

There’s really only one technology that I know of that can provide carbon free power [at the scale required by modern civilization] when the sun is not shining and the wind is not blowing at the scale modern civilization requires and that is nuclear power.* And whatever you think of nuclear power, we need to let it compete on its own merits given an appropriate regulatory environment and a sensible, cost-competitive market situation.

And we shouldn’t discriminate against individual technologies. It’s not about either/or, we’re not talking about whether we favor solar power, wind or nuclear power; I’m in favor of anything that can prevent climate change, protect the environment and allow poor people to get food and health care and education.**

The basic plea here is let’s focus on the climate agenda, and the climate agenda is about supplying energy [services] in a way that does not damage our environment.*** We need to allow technologies to compete on their own merits.

Transcription by: http://atomicinsights.com/

These were extemporaneous verbal comments made at a press conference at COP21 in Paris. Thus not every sentence contained every qualifier it needed, and not every important point was made.

*Qualifier about scale added here.

**This is not a complete list of filters. Key is that the technologies should be able to “compete on its own merits given an appropriate regulatory environment and a sensible, cost-competitive market”. This would include considerations of safety, etc.

***This should have read ‘energy services’ instead of ‘energy’. We need to work to provide more energy services with less energy consumption.

It is time for people to rethink their positions on nuclear power, and make arguments based on facts rather than prejudices.

Any good scientist and any good citizen should be constantly re-examining their positions, so the basic call for us to rethink our position on nuclear power is most welcome. I hope that the signers of this Civil Society Institute letter can bring themselves to re-examine the nuclear power issue with the same objectivity and lack-of-bias that they seek from us.

The letter confusedly suggests that I “embrace nuclear power”, and implies that I somehow discount the importance and potential of solar, wind, and efficiency. I cannot speak on behalf of my colleagues, but at least in my case, these claims are far from the truth.

We embrace things that we love. I don’t love nuclear power. Nuclear power has brought us Chernobyl and Fukushima. If the current industry were scaled up enough to solve the climate problem, there would be one such accident each year — and that is clearly unacceptable. Were I king of the world, I would decree that solar, wind, and efficiency would be the primary means we deploy to solve the climate problem.

But there is no energy storage system that works at the scale of the modern megalopolis. We need a way to power civilization when the sun is not shining and when the wind is not blowing. In a modern real economy, not ruled by benevolent kings, reliable power is required at competitive prices. There are very few technologies that can provide this reliable baseload power. Fossil fuels and nuclear power are the two leading candidates. I think an objective assessment of the facts shows that fossil fuels are far more dangerous than even today’s nuclear power.

But I do not defend today’s nuclear power industry. Even though most nuclear power plants have an excellent safety record, there are an important few that do not. There is no justification for the claim that this important type of electricity generation can never be made sufficiently safe and inexpensive.

To say that an entire category of technology can never be sufficiently improved is, I think, to adopt a position of technological myopia, where one lacks to the capacity to imagine that future technologies can differ substantially from today’s technologies.

I do not embrace nuclear power. There is no power source that one wants to embrace. They all have negative consequences. I do not want a solar PV factory, a massive wind turbine, or a nuclear power plant in my back yard. But I want the juice. The question is not about what power source I embrace, but about what power source I might think myself capable of not rejecting. Many people want to reject power sources, but want the juice that comes from those power sources.

In summary, I applaud the signers of the Civil Society Institute letter for their concern regarding climate change and for their support of solar, wind, and efficiency. Their call for us to rethink our positions on nuclear power is most welcome, and I ask only that they rethink their position with respect to nuclear power with the same degree of receptivity and objectivity that they ask of us.

This is from an email to John Upton on 10 Jan 2014. It, along with the ‘Civil Society Institute letter’ is included in his Grist piece: Enviros and climate scientists continue their fight over nuclear power

I wrote the following in response to this post:  http://news-oceanacidification-icc.org/2015/08/26/a-plea-to-ocean-acidification-scientists/

—

The Arctic is cold. It will remain cold even with global warming.

However, it makes sense to talk about the warming of the Arctic despite its being cold. It also makes sense to talk about the Arctic being warmer than it was a century ago even though it is still cold. One might also say that the Arctic is ‘warm’ relative to what it was a century ago.

It is not making a mistake to use the word ‘warm’ or ‘warmer’ in this context. In these contexts, ‘warm’, ‘warming’ and ‘warmer’ refer to signs of change and not absolute values.

—

Carbon dioxide in the ocean acts as a weak acid, in that it donates protons to solution.

The addition of a weak acid into the ocean is making the ocean more acidic, in that it is decreasing the pH of the ocean and bringing it closer to the acid end of the scale.

—

It is as if I were to declare that I am not going to call anything ‘warm’ unless the temperature is greater than 25 C, and then you claim that nobody can talk about the warming of the Arctic until the temperature reaches 25 C.

This is an absurd position.

It makes sense to use terms like ‘acid’, ‘acidic’ and ‘acidification’ in reference to directions of change and in comparative contexts (c.f., the Arctic is warmer than it was a century ago; the ocean is more acidic than it was a century ago.) These statements do not mean that the Arctic is warm or the oceans are acid in any absolute sense; they are relative statements.

In this context, ‘warmer’ means ‘higher temperatures’ and ‘more acidic’ means lower pH.

This has been standard usage in the discussion of ocean acidification for over a decade. It is not helpful to try to change this usage at this time.

The post referred to above ends:

“Some of us have made this mistake in the past but let us ban the future use of “acid” or “acidic” in the context of our work.”

Better would have been,

“With regard to ocean acidification, let us reserve the use of terms such as ‘acid’ and ‘acidic’ to contexts where comparisons are being made or reference is being made to a sign of change; in most oceanographic contexts, it is incorrect to use these terms to describe seawater in an absolute sense.”

Without carbon dioxide in the atmosphere, the Earth would be a frozen orb.

It is known with a very high degree of certainty that carbon dioxide keeps the Earth warm and more of it will make the Earth warmer.

It is also known with a very high degree of confidence that humans activities have increased atmospheric CO₂ content by about 40% since the dawn of the industrial revolution.

There is close to universal consensus among well-informed climate scientists that most of the global warming over the past 50 years was associated with our greenhouse gas emissions.

There is substantial uncertainty regarding how sensitive our climate system is to added CO₂, where something like 3 C per CO₂ doubling (about 5 F) might be somewhere near the central expectations but with semi-reasonable people arguing for half this or double this.

There is very little consensus regarding how adaptable humans will be to these changes. Humans already live from the equator to the Arctic circle. Houston used to be a malarial hell-hole and now it is a modern air-conditioned city.

At the one end of the spectrum there are people thinking climate change will be an existential threat to human existence. At the other end, there are people who think most people will barely notice the effects of climate change. Neither end of this spectrum represents a tenable position.

My own view is that climate change will impose a substantial cost on society but that climate change is unlikely to be the biggest problem that most people will face in their lives.  This is less true for sensitive ecosystems such as coral reef systems.

Humans are like weeds. We are the invasive generalists par excellence. We spread rapidly, grow quickly, and successfully inhabit almost any environment.

Climate change will impact the delicate flowers tuned to a narrow range of environmental conditions; climate change will benefit many weeds, which can take advantage of disruption.

Carbon dioxide also acts as a fertilizer for plants, so there is potential for crop yields to increase under a high-CO₂ atmosphere.

When the dinosaurs were around, the atmosphere was rich with CO₂ and life flourished. We are not followers of Leibniz and do not think we are living in the best of all possible worlds. There is nothing particularly special about the climate of the pre-industrial era, although it does seem to have been a particularly stable climatic period.

The problem is not that greenhouse gases are pushing us from a better climate to a worse climate so much as the problem is one of rates of change. Will climate change occur so rapidly that the transition imposes costs that were not anticipated, costs that are larger than we would like to deal with?

[Just in case it is not clear, my answer to the final question is ‘yes’. Not only that, even anticipated changes are sufficient to motivate eliminating fossil-fuel CO₂ emissions as soon as is practicable.]