Ken Caldeira: From an email to a friend, skeptical about the reality of human-induced climate change

Ken Caldeira explains what we know about climate change to a skeptical friend.  Originally published at the Ken Caldeira blog.

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.]

Posted on 21 August 2015 by Ken Caldeira, Carnegie Institution for Science, Department of Global Ecology at Stanford University

James Hansen on Big Green – it’s all about the money

The truth is that present energy and climate policies of the United States and the United Nations are dishonest and tragic.

In October 2014 Dr. Hansen wrote an essay covering some of his personal history. I would like to highlight just a few words that support my explanation:

Why do the big name “environmental” NGOs seem to support every policy except the ones that will actually work.

My thesis is they prefer to raise money over promoting sound policy. Their big contributors do not like nuclear power. But oh my, they do so love Amory Lovins’ soft power. So the NGO leaders have a stark choice – support policies that will impact emissions. Or raise more and more money. Dr. Hansen:

It is not always easy to speak truth to power, but all citizens have the opportunity if they choose. I have one minor, easy suggestion for you to consider, and another requiring more effort.

The first concerns “Big Green,” the large environmental organizations, which have become one of the biggest obstacles to solving the climate problem. After I joined other scientists in requesting the leaders of Big Green to reconsider their adamant opposition to nuclear power, and was rebuffed, I learned from discussions with them the major reason: They feared losing donor support. Money, it seems, is the language they understand. Thus my suggestion: The next time you receive a donation request, doubtless accompanied with a photo of a cuddly bear or the like, toss it in the waste bin and return a note saying that you will consider a donation in the future, if they objectively evaluate the best interests of young people and nature.

The other suggestion is to donate time to Citizens Climate Lobby. They need people to write letters to the editor and op-eds, and to visit members of Congress. The aim is to make the price of energy honest, in a way that spurs our economy, creates good jobs, and enhances the future of young people and nature. To be sure, our democracy has developed flaws, especially the inordinate role of money in Washington, but we still have the opportunity to make it work.

My view is the Big Greens have blood on their hands. Greenpeace in particular because they not only block nuclear around the world but they continue to block live saving advances like Golden Rice. Shame!

And kudos to James Hansen: Who speaks truth to power.

How did Climate Change become a US partisan fight?


I don’t have a solid answer to the captioned question. Survey data I’ve examined indicates the liberal/conservative split on climate is something new — since roughly the 1997 Kyoto Treaty.

My simplistic answer is:

  1. Kyoto was divisive because implementation fit very naturally with Democrat values emphasizing top-down control of the economy and international cooperation. Opposition fit naturally with Republican small-government values where Kyoto was seen as a path to larger, more intrusive government; and probably to slower growth.
  2. Kyoto was promoted by Al Gore. That was not a good choice for winning bipartisan support.
  3. Because Gore was pro-Kyoto, GW Bush had to be anti-Kyoto. Both those men affected the opposing party like fingernails on a chalkboard.
  4. The deflection around 2007 in above chart seems to support my last speculation: while both Obama and McCain proposed positive GHG action, the Kyoto concept was identified with Obama. That association was similar to the “Al Gore effect”.
  5. Gradually values-based disagreement over what-to-do-about-GHG was turned into a division over “The Science” and denialism was born. I don’t know why that happened.

For a more thoughtful analysis, there is the 2012 piece by Andrew Hoffman in Stanford Social Innovation Review Climate Science as Culture War. Andrew also examines ways to reach a negotiated social consensus. 

(…snip…)Climate change has become enmeshed in the so-called culture wars. Acceptance of the scientific consensus is now seen as an alignment with liberal views consistent with other “cultural” issues that divide the country (abortion, gun control, health care, and evolution). This partisan divide on climate change was not the case in the 1990s. It is a recent phenomenon, following in the wake of the 1997 Kyoto Treaty that threatened the material interests of powerful economic and political interests, particularly members of the fossil fuel industry.3 The great danger of a protracted partisan divide is that the debate will take the form of what I call a “logic schism,” a breakdown in debate in which opposing sides are talking about completely different cultural issues.4

This article seeks to delve into the climate change debate through the lens of the social sciences. I take this approach not because the physical sciences have become less relevant, but because we need to understand the social and psychological processes by which people receive and understand the science of global warming. I explain the cultural dimensions of the climate debate as it is currently configured, outline three possible paths by which the debate can progress, and describe specific techniques that can drive that debate toward broader consensus. This goal is imperative, for without a broader consensus on climate change in the United States, Americans and people around the globe will be unable to formulate effective social, political, and economic solutions to the changing circumstances of our planet.

One of the best qualified to comment on the partisan development is Roger Pielke Jr — for example, his 2007 blog post Why is Climate Change a Partisan Issue in the United States? I don’t wish to simplify Roger’s analysis, but will just note that he begins with the conflict between Al Gore and George W. Bush.

Appeals to the climate consensus can give the wrong impression

Credit John Cook 2014

Image credit John Cook, Closing the Consensus Gap on Climate Change

Dr. Will Howard, recently published an essay that will appeal to those of you interested in science communications, especially in the challenging and politically-charged context of climate change. Dr. Howard makes the extremely important point that “scientific consensus” on climate change reflects strong consilience of evidence. I confess that I had to look up “consilience” to learn that it is indeed the perfect term to capture how we have developed confidence in our understanding of the causal connections between human-generated greenhouse gases and climate change.

In public discourse, if we had chosen “consilience of evidence” to describe the accumulation of research, then perhaps people might have understood more readily that we are not talking about the results of an opinion poll or a negotiated statement (yes, the IPCC Summary for Policymakers [PDF] is a negotiated statement, though I don’t know how else such a summary could be produced).

I thought Will’s essay captured this science communications challenge succinctly, and especially how this strong consilience of evidence is separate from the politics of what to do about it:

“Consensus” is understood differently in science compared to politics or society.

Scientists use this word to refer to consilience of multiple lines of evidence that underlie widespread agreement or support a theory.

In the case of climate change, multiple lines of evidence underpin the prevailing view that the climate system is showing decade-on-decade warming over the past 50 years.

In particular, this warming bears temporal and spatial patterns, or “fingerprints”, that point to human causes.

For example, the stratosphere (that part of the atmosphere higher than about 11 km) has been cooling as the lower atmosphere and the ocean warm. This is the pattern we expect from the addition of greenhouse gases and not from, say, changes in the sun’s output.

But in public and especially political discourse, “consensus” tends to imply majority opinion or concurrence. As consensus in this public context is often arrived at by negotiation, saying there’s a scientific “consensus” may imply to the community that prevailing scientific views represent a negotiated outcome. This is the antithesis of science.

Consensus of the non-scientific kind does have a role to play in the climate debate. This includes negotiating whether warming is a “good” or “bad” thing and what, if anything, we should do about it.

These are not scientific questions. These are issues of values, politics, ethics and economics. As a nation and as a global society we need to reach consensus to resolve those questions and to make and implement appropriate public policy.

I’ve nothing to add to Will’s excellent essay, so I recommend that you go directly to The Conversation to read the original and the comments. Some effort is required to weed the growing number of comments so I will highlight a segment of the conversation which focuses upon the important question of effective science communication:

John Cook
Climate Communication Research Fellow at University of Queensland

This is an interesting article with many important points. I would be the first person to stress the importance of communicating the many “fingerprints” being observed in our climate (and in fact have created a human fingerprints infographic which I frequently use in public talks

However, the article is missing a crucial element to this discussion – what does the evidence tell us about the efficacy of consensus messaging? A number of studies have found that one of the strongest predictors of public support for climate mitigation policies is perception of consensus (i.e., the level of agreement among climate scientists about human-caused global warming). Also, consensus messaging significantly increases acceptance of climate change. A randomised experiment by Stephan Lewandowsky found that informing Australians of the 97% consensus increased their acceptance of human-caused global warming and intriguingly, the increase was greatest amongst conservatives. In this case, consensus neutralised ideology to some degree.

When people think there is still an ongoing debate about human-caused global warming amongst climate scientists, they’re less likely to accept climate change and support climate action. And given the Australian public on average think there is 58% agreement among climate scientists, rather than 97%, then this misconception has serious societal implications. Science communicators need to take into account that people use expert scientific opinion as a heuristic to inform their views on complex scientific issues.

To underscore this fact, I’ve actually tested the human fingerprints message (linked to above) and the consensus message in a randomised experiment. Consensus messaging significantly outperformed the fingerprints message. The lesson here is that we need to understand how laypeople think about complex scientific issues like climate change.

However, I don’t think there need be that much conflict between what social science is telling us and the views of the OP. A recent paper by Ed Maibach tested various forms of consensus messaging and they found the most effective was a message that emphasised both consensus and the evidence-based nature of the scientific method:

“Based on the evidence, 97% of climate scientists have concluded that human-caused climate change is happening”

John Cook
Climate Communication Research Fellow at University of Queensland
In reply to Anna Young

Anna, the problem you raise is exactly why communication like the John Oliver YouTube video embedded in the OP are so powerful. Not only does Oliver communicate the 97% consensus, he also does something equally important – he communicates how people cast doubt on the consensus (in this case, by perpetuating false balance in the media). What Oliver is doing is equipping people with the knowledge and the critical thinking skills so that when they see the mainstream media show a debate between a climate scientist and a tinfoil guy, they can see it for what it is. It’s not only a funny video, it’s brilliant communication. The fact that it’s been viewed millions of times means millions of people have now been “inoculated” against the misinformation of false debate in the mainstream media.

So kudos to Will Howard for embedding the video.

Will Howard
Research scientist at University of Melbourne
In reply to John Cook

Thanks John, for contributing that perspective. The points you raise, I would suggest, may be applicable to many areas of “contested” science, in health, resources (e.g. coal seam gas) and others. 

Whatever is said about the consensus, I do think we need to do a better job of communicating what underpins it. As your co-author Peter Jacobs notes

“to those suggesting that the consensus message is an appeal to authority that ignores evidence- the consensus exists *because of* the overwhelming physical evidence, which is detailed at length in the scientific literature.”

But I wonder about this: both the consensus and the consilience of evidence (my preferred term) seem to be strengthening, yet public support for policies aimed at mitigating climate change seem not to be.

I note polls suggesting climate change and environmental issues have moved down peoples’ priorities. Here in Australia, our current government was elected with a major plank in its platform being the removal of the carbon tax. (Whether we agree or disagree with their policy they ran on that issue and were elected).

Is this because people are skeptical of the science? Is it just that other issues take on more urgency: jobs, the economy, international conflicts, etc.?

John Cook
Climate Communication Research Fellow at University of Queensland
In reply to Will Howard

I like the term “consilience of evidence” also but when I test-drive it in public talks, it tends to inspire blank looks from the audience. It’s a term that scientists love. Laypeople, not so much. Which is why, again, it’s important that we understand our audience when we do science communication.

Why is public support not changing that much? Public concern about climate change does correlate with economic performance hence the drop in climate concern after the GFC. Another predictor of public concern about climate change is cues from our political leaders so you can see why Australia has a problem in that department at the moment. There’s certainly a number of factors that influence people’s attitudes to climate.

But as I said above, several recent studies have found perception of scientific agreement on climate change is one of the biggest factors. And given public perception of consensus is very low (I measured it at 58% on a representative Australian sample), this misconception is definitely a significant problem. It’s not the only factor delaying public support for climate action but it’s a big one.

Also, communicating the 97% consensus is a lot easier to understand than explanations of why greenhouse gases in the upper atmosphere are more efficient at radiating longwave radiation to space, hence contributing to the cooling stratosphere. From a communication point of view, consensus is a low lying fruit. This is why consensus messaging outperformed fingerprint messaging in my data.

So communicating the 97% consensus can help with removing one roadblock delaying climate action. It won’t fix everything – it’s not a magic bullet. But ignoring the “consensus gap” only serves to give extra life to that stumbling block.

I wrote a post a while back How to break the climate change gridlock including a conversation with  Andrew Dressler, Professor of Atmospheric Sciences at Texas A&M, about how we might more explicitly get each party’s values and economic interests on the negotiating table.

Will Howard has received funding from the Australian Research Council, the Australian Government Department of Climate Change, the Cooperative Research Centres Program, and the Australian Antarctic Science Program.

This article was originally published on The Conversation. Read the original article.

Roger Pielke Jr. on FiveThirtyEight and his Climate Critics


Keith Kloor published an interview with Roger to discuss the Twitter-storm and blog-o-gale that blew up when Roger offended the climate-hawks by publishing on FiveThirtyEight a summary of his academic publications on disaster losses.

The attacks on prof. Pielke came from the usual suspects, but this time elites such as Paul Krugman and Obama advisor John Holdren piled on. The fragments that crossed my desk were examples of “non-contact criticism”. By that I mean they ignored Roger’s published work (including Congressional testimony, blog posts and public appearances). Instead the attacker applied the demon-label of “climate denier” and then proceeded to shred various straw man positions that Roger has never argued.

My view is that there’s nothing newly provocative in Roger’s FiveThirtyEight article. It expresses the science behind what we know about connections between global climate change and severe weather events like Katrina. What is new is that Roger was published by a hot new website illuminated by Nate Silver’s fame. The hawks evidently thought “this is too dangerous, to have a scientist explaining to Joe Six Pack why we can’t attribute every tornado to Global Warming”.

I’ve been reading Roger Pielke Jr. for at least a decade – motivated by his research and writing on science policy advice. I learned most of what I know about science policy from his numerous policy blog posts and from his 2007 book The Honest Broker.

Roger’s science policy background prepared him well to contribute to the group of thinkers that produced The Hartwell Paper, which I first encountered in Kyoto Wrong Trousers: Radically Rethinking Climate Policy. There you will find climate policy ideas appropriate for the real world where politicians and economics operate. Then came Roger’s book The Climate Fix: What Scientists And Politicians Won’t Tell You About Global Warming. That’s the book I recommend to associates for training on how to advocate for effective policies. Hint: Kyoto isn’t one of those policies. 

In 2008 Roger joined The Breakthrough Institute, which is populated by other serious people who are focused on changing the world (really). BTI has adopted much of the thinking behind The Hartwell Paper – so not surprisingly several of Roger’s Hartwell colleagues are now working with the institute. E.g., Steve Rayner. And Nature Conservancy Chief Scientist Peter Kareiva.

Through all this reading I have observed Roger “calling it the way he sees it”. Consistently I have found Roger’s writings to align with what I think is the objective truth cast into pragmatic policy options. 

Kerry Emanuel: An Obligation to Take on ‘Tail Risk’ vs. Alarmism

On the 24 March Econtalk Russ Roberts interviewed John Christy and Kerry Emanuel. Prof. Roberts is very effective at moderating an informal debate like this – he keeps each party focused on reply and rebuttal to the key points. This is far more effective than the usual “debate” where each side essentially repeats prepared talking points, with very little contact with the arguments made by the opposition.

I have been following the writings of MIT prof. Kerry Emanuel for a long time. Besides his climate science expertise, he has been an effective voice for pragmatic carbon policy that includes nuclear power. E.g., on 3 November Dr. Emanuel and three other top climate scientists joined together in an open letter directed to the Baptists in the “Bootleggers and Baptists” coalition that have made it impossible to make any real progress decarbonizing the global economy.

Related posts on Kerry Emanuel’s work are Enviros and climate scientists continue their fight over nuclear power, and Kerry Emanuel: Reddit AMA on climate change and severe weather.

Though I’ve not reviewed the book here, I highly recommend Emanuel’s compact primer What we know about climate change. It is a remarkably short, apolitical and information-dense survey of a complex subject.

In the above-captioned short essay by Emanuel, he takes a similar theme to the Econtalk interview — that to develop effective climate/energy policy we need to focus on the risk management. It won’t be a surprise that I support Kerry Emanuel’s risk framing — because that is how I look at climate policies. I think we need to keep our attention on both mitigation and adaption policy options. Generating more policy options is how we get better results (exactly the opposite of what activists want – which is to limit our options to the activists’ preferred technology/approach).

This is all about risk – and risk appraisal and management are skills that we humans do not manage well at all. 

Three climate scientists examine recent slowdown (or ‘pause’) and online science communication

The recent slowdown (or ‘pause’) in global surface temperature rise is a hot topic for climate scientists and the wider public. We discuss how climate scientists have tried to communicate the pause and suggest that ‘many-to-many’ communication offers a key opportunity to directly engage with the public.

I recommend “Pause for thought” in Nature Climate Change. This very short essay by Ed Hawkins, Tamsin Edwards and Doug McNeall is ungated, after free registration. You can get a preview of the technical overview by studying the two following charts carefully. You’ll need to pay attention to the chart key underneath – there is a lot of information compressed into the two panels.


Observed global mean surface air temperatures (HadCRUT433, solid black line) and recent 1998–2012 trend (dashed black line), compared with ten simulations of the CSIRO Mk3.6 global climate model, which all use the RCP6.0 forcing pathway (grey lines). The grey shading represents the 16–84% ensemble spread (quantiles smoothed with a 7-year running mean for clarity); the ensemble mean trend is around 0.20 °C per decade. Two different realizations are highlighted (blue), and linear trends for specific interesting periods are shown (red, green, purple lines). a, The highlighted realization shows a strong warming in the 1998–2012 period, but a 15-year period of no warming around the 2030s. b, The highlighted realization is more similar to the observations for 1998–2012, but undergoes a more rapid warming around the 2020s. Note also that this realization appears outside the ensemble spread for 9 out of 10 consecutive years from 2003–2012.

The charts and discussion illustrate a central truth of climate science – the results are often only understood in a framework of statistics. The pretty, clean projected temperature curves that we see in the media are heavily smoothed over many runs of multiple models. That presentation conceals the natural variability that is part of the challenge of understanding, then testing hypotheses against observations. It is similar to the agonizing process at the Large Hadron Collidor (LHC) as the teams tried to develop enough data to tease out a sufficiently confident identification of an anomaly corresponding to the Higgs.

If you have a specific question about the authors’ presentation, you can ask the scientists directly on twitter. It is uncommon for authors to reveal their twitter handles in a paper, so please don’t make them regret the open door!

I recommend two other articles in this Nature Climate Change series:

1. Heat hide and seek [PDF] Natural variability can explain fluctuations in surface temperatures but can it account for the current slowdown in warming? The authors offer an excellent summary of the more promising current research, including particularly the variability in heat distribution such as

  • El Niño/Southern Oscillation
  • Pacific Decadal Oscillation
  • Atlantic Multi-decadal Oscillation

2. Media discourse on the climate slowdown where I learned among other things that the biggest recent media spike seems to be in Oceania – where we are presently (cruising). Australia has been suffering from a severe drought – that no doubt generates increased interest in climate.

Kerry Emanuel: Reddit AMA on climate change and severe weather

I’m Kerry Emanuel, a Professor of Atmospheric Science at the Massachusetts Institute of Technology in Cambridge, Massachusetts. I do research on hurricanes and other types of severe weather, on climate change, and how climate change might affect severe weather. My research is mostly theoretical, but I also build computer models and occasionally participate in field experiments and build and use laboratory experiments. I have flown research aircraft into hurricanes, and wrote a book called “Divine Wind: The History and Science of Hurricanes”, aimed at a general reader and covering both the science of hurricane and how they have influenced history, art, and literature.

We discovered this conversation after it was concluded. Kerry Emanuel is one of the four leading scientists who wrote this open letter: ‘To Those Influencing Environmental Policy But Opposed to Nuclear Power’. He also wrote a short book for the informed layman called “What We Know about Climate Change” (recommended as an efficient and readable overview of the science)

Here I have cherry-picked a few of Dr. Emanuel’s answers. The questions are my paraphrasing, as the information is largely in his replies:

Q: …claims civilization as we know it will end with that 4°C

A: In my view, the only really good way to look at this is to view it as a problem of risk. By its very definition, risk is probabilistic. The consensus view of global temperature increase over the next century is a curve with a peak in the 2-4 C range, but a non-trivial tail at higher temperatures. The most probable outcome (at least on the 100 year time scale) has risks that are probably manageable, but as Marty Weitzman at Harvard has pointed out, we need to pay attention to the tail of the risk distribution, because the economic and societal risks can be very large there. Scientists by nature are conservative and do not like to talk about what might happen in the tail, but we do need to think carefully about tail risk as part of our overall assessment of the risk.

Q: …increasing hurricane risks…

A: In my view, at the moment, we in the U.S. deal so poorly with existing hurricane risk that climate change considerations take a back seat. We actively subsidize folks to live and build in hurricane prone regions, and we bail them out massively when disaster strikes. The subsidies come in the form of state-mandated caps on insurance premiums, cheap federal flood insurance, and federal disaster relief. We need to solve these problems regardless of whether climate change results in more frequent and/or intense storms. But there are two climate-related issues that we need to consider now: rising sea level (which is already affecting the magnitude of storm surges, which in practice do much of the damage in hurricanes and other coastal storms), and projections that the incidence of very intense hurricanes should increase in the 100-year time scale. These considerations may, for example, enter into calculations of how high and how strongly we need to build sea walls in certain places.

Q: …are weather forecasts improving? 

A: Weather forecasts have demonstrably improved over the past half-century or so, but as Lorenz demonstrated, there is a fundamental limit to how far out one can make a forecast. (We think this fundamental limit is at about 2 weeks.) But faster computers have allowed us to do something we could not do just 20 years ago or so, that is quantify the uncertainty in each individual forecast. This is done by running ensembles of computer models, or ensembles within just one model but starting from slightly different, but equally plausible, initial states. These slight differences in models or initial conditions typically amplify with time, but do so at different rates at different times and places. The divergence yields a measure of uncertainty.

Q: …aren’t there more hurricanes due to global warming?

A: We do see some signals in open-ocean hurricane statistics, but since only about 1 and 3 Atlantic hurricanes make landfall in the U.S., and these do damage over a tiny fraction of their lifetimes, the record of landfalling storms is too short to see any climate signals, save perhaps for El Nino-related signals. We do not expect to see a global warming signal in U.S. hurricane damage for some decades. [highlighted because this agrees with Roger Pielke Jr. analysis of US damage data. Ed.]

Second, there is some indication that hurricanes (and cloud clusters in general) dry out the atmosphere, and this could have climate impacts. But this is very early, tentative work.

It is very hard to attribute individual events, or even groups of events, to climate change. This is simply a matter of statistics. We usually need long records to detect climate signals. There are also natural, long-period fluctuations of the North Atlantic climate that modulate rainfall in places like England.

Q: How drastic do you predict climate change to affect the United States in the next 20, 50 and 100 years?

A: I think we have to avoid the idea of a prediction. We know enough about climate risk to assert that the level of risk is enough to be a serious issue, more so as time goes by.

Almost all studies that I am aware of show differences in hurricane response to climate change, among the various ocean basins where hurricanes occur. But there is almost no agreement in the magnitude or even the sign of these differences.

Q: What are the chances that Earth will enter a new Ice Age in the coming decades?

A: Nill. But the chances in 30,000 years are excellent!

Q: My question is, what is the most interesting cause and effect relationship you learned about in the course of your research, where it turned out that seemingly disparate things were actually closely related?

A: For me, the most exciting and robust finding of climate research to date is the determination of the ultimate cause of the great glacial cycles of the last 3 million years or so. There is now very strong evidence that the root cause of these cycles lies in periodic variations in the earth’s rotation axis and orbit around the sun. Such cycles obey very precise mathematical relations, and we can see these signals in ice core and deep sea sediment records.

Q: …you’ve surely run into people who think climate change is a “hoax” or people who are just misinformed … What essays or books would you recommend?

A: All I can say to this is that I try to get people to look at this as a problem of risk. But most risk problems we are used to dealing with (e.g. the risk that our house might burn down) confront problems that may develop in our own lifetimes. We are less used to thinking about risk to future generations. We have to intelligently weigh climate risks (and possible benefits) against the risks (and possible benefits) of any actions we might contemplate to deal with climate change. We have to get away from binary thinking… climate change will be either an apocalypse or nothing to worry about; solutions will either be a complete panacea or not work at all. I do think this is actually the way most people think about the problem of climate change. As usual, the extreme elements are the noisiest, though….

Q: where would you say you have seen the most change in YOUR views on climate change as more evidence has stacked up?

A: Back in the 1980s, I did not feel there was enough evidence to warrant much concern about climate change. But great advances in paleoclimate, analysis of in-situ and satellite observations, my own acquisition of some basic understanding of climate physics and, yes, climate models have all added up to very compelling evidence that we are changing climate and engendering serious risks in doing so.

Q: Does the data you are seeing suggest that everything..

A: It is a great human temptation to attribute just about everything to the cause-du-jour. I remember when, in the 1980s. everything under the sun was blamed on El Nino. But we have to stand back, fight that temptation, and look at the data. This says that precipitation extremes are likely to increase (and there is some evidence that they have, in some places), and that heat waves will become more common and cold waves less so. We think hurricanes might become more intense, but we do not know much about how many other phenomena — such as tornadoes and hailstorms — might be affected by climate change.

Q: To what extent was the severity of Hurricane Katrina affected by AGW? 

A: It is virtually impossible to attribute any one event in a chaotic system to any particular cause. We can say that had that exact same storm followed that exact same track, with exactly the same environmental winds but through the thermodynamic environment of the 1980s, its winds would have been perhaps 20 MPH less. But that is a very restricted statement.

Unfortunately, like energy policy, climate policy depends upon the ability to understand long term risk – to evaluate and choose amongst imperfect options. That’s just the way it is.

A Factual Look at the Relationship between Climate and Weather

…I, along with many colleagues, have argued that instead of focusing primarily on making dirty energy expensive, we should focus to a greater degree on making clean energy cheap.

I recommend to you the January 24, 2014 responses to hearing questions of Roger Pielke, Jr. It is refreshing to see the concepts of The Hartwell Paper presented so crisply. I wonder how much the honorable congress-persons understood?

Enviros and climate scientists continue their fight over nuclear power

It didn’t take long for the Bootleggers to organize a roomful of Baptists to respond to the open letter from four climate scientists Caldeira, Emanuel, Hansen and Wigley. The response was signed by 300 of the usual crowd including Greenpeace USA and the Environmental Working Group. John Upton at Grist asked the climate scientists for a response. Ken Caldeira replied with this very civil email:

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.

I would like to add one point: There is no perfect energy source. What motivated Caldeira, Emanuel, Hansen and Wigley to propose that the environmental community reevaluate their position is because opposition to nuclear is support for coal. Nuclear power is the only scalable, dispatchable, low-carbon energy source that is economically acceptable to China, India and the rest of the fast-developing world. And per terrawatt-hour of delivered energy, nuclear electricity has proven to be one of the safest sources: slightly better or slightly worse than onshore wind, depending on which study you read. There is no perfect energy source.