Category Archives: Climate Science

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.

James Hansen et al “the accepted 2 degrees target is dangerously too warm”

“Although there is merit in simply chronicling what is happening, there is still opportunity for humanity to exercise free will.

I have finally found the time to read the entire Hansen et al paper Assessing “Dangerous Climate Change”. The complete paper was released December 3rd on the open access journal PlosOne as Assessing “Dangerous Climate Change”: Required Reduction of Carbon Emissions to Protect Young People, Future Generations and Nature.

I think this is one of the most important climate papers of 2013. James Hansen and 17 coauthors succeed to boil down the current state of climate research to 26 pages (including the five pages of references). The authors make a strong case that the two-degree-consensus is dangerous.  Unlike other high profile climate scientists, actions are proposed that will actually work, included the “N word” advanced 4th generation nuclear power.

To announce the paper Hansen and coauthor Pushker Kharecha published a letter outlining the case that two degrees is dangerous, then go straight into solutions: cooperative technology development and deployment, and especially, rapid deployment of gen 3+ and gen 4 nuclear power. 

(…snip…) Governments should also support technology research, development and demonstration of carbon-free energy including advanced generation nuclear power as well as renewable energy, especially in view of the urgency with which emissions from coal and unconventional fossil fuels must be eliminated. (Unconventional fossil fuels include tar sands, shale-derived oil and gas, and methane hydrates.)


A preferable approach, for the sake of both global climate and local pollution reduction, would be a combination of renewable energy and advanced (3rd and 4th) generation nuclear power plants2. Abundant affordable clean energy is essential to provide the energy needed to raise billions of people out of poverty, which empirical evidence indicates is a requirement for reducing fertility rates, thus lowering human population, and giving hope that we can provide the opportunity of a good life to all humanity while allowing other life on the planet to flourish.

When the world’s leading nations recognize the urgency of phasing out fossil fuel emissions, and realize that we are all in the same boat, it should be possible to agree on cooperative technology development and deployment. History, including World War II and the Apollo program, reveal how rapidly technology can be developed and deployed. Phase-out of most coal emissions and a substantial reduction of oil and gas use could be achieved rapidly. This would require agreement among leading nations not only to have common internal rising carbon fees, but also an agreement to cooperate in rapid technology development.

Surely rapid phase-down of coal emissions requires a major role for advanced-generation safer nuclear power. Nuclear technology has advanced significantly over the past few decades such that there is now the potential to produce modular 3rd generation light-water reactors that are passively safe, i.e., reactors that would shut down automatically in case of an anomaly such as an earthquake and have the ability to keep the nuclear fuel cool without an external power source. The same concept, modular3 simplified reactor design with factory production and shipping to the utility site, is appropriate for 4th generation reactors, and these should also be pursued to deal with nuclear waste, utilizing the waste as fuel.

Fortunately, the place where deployment of advanced nuclear technology is most urgently needed, China, is also the place that has the potential to rapidly build and grow the manufacturing capability. What is needed is cooperation with nations that have developed relevant technical abilities, especially the United States. Such cooperation has potential for enormous mutual and global benefits via development of scalable affordable carbon-free energy. Contrary to assertions of dedicated anti-nuke activists, such technology can be made more resistant than existing technology to exploitation by terrorists who may seek weapons material. Dangers from rogue states or terrorists will always exist, and the best way to minimize such danger is to cooperate in developing the safest technology, not to pretend that anti-nuclear activism will cause nuclear technology to disappear from the planet.

The principal policy allowing renewable energies to grow to almost 2% of global energy use has been laws imposing specified “renewable energy portfolio standards” (RPS) on utilities or other mandates for renewable energy use. These policies have aided growth of renewables, and by spreading costs among all utility customers of feed-in tariffs, added transmission lines, and the backup power needed for intermittent renewables (usually fossil fuel based), the electricity cost has been bearable as long as the portion of renewables is small. Now for the sake of moving rapidly to carbon-free power while minimizing electricity costs, the need is for “clean energy portfolio standards” (CPS), thus allowing nuclear energy to compete with renewable energies.

The previously discussed 3 November open letter ‘To Those Influencing Environmental Policy But Opposed to Nuclear Power’ has provoked much needed debate. Let us hope that this new paper and the PlOS ONE call for solutions papers builds on that interest to get something done.

there is still opportunity for humanity to exercise free will.

and free will means “be effective” not more failed “Kyoto commitments”.

Jeffrey Sachs: On climate, more ‘now’ and ‘how’ is needed

John Rennie interviews Jeff Sachs for The Gleaming Retort:

Sachs … is also a coauthor, with climatologist James Hansen and a multidisciplinary team of other specialists, of a recent report in the journal PLOS ONE that made a plea for 1 degree Celsius, not 2 degrees, as the appropriate ceiling for permissible warming in the future.

To get his impressions of the report’s content and of its policy implications, I spoke with Sachs a few days before the paper’s publication. What follows is a summary of that conversation.

2 °C is too much

Asked to describe the PLOS ONE report, Sachs calls it “one of the best, concise, up-to-date summaries” of current scientific understanding about the state of the warming problem, drawing on paleoclimate data, climate models, and empirical tracking of global temperatures. (He is also quick to credit it primarily to Hansen, who led the work.)

All those indications, Sachs says, lead to the same conclusions: that the impacts of climate change are already being felt, that they will multiply tremendously in the future, and that feedbacks in the climate system could greatly amplify both the future warming and the consequences associated with it.

No matter whether one favors the limit for future warming to be 1 °C or 2, Sachs says, “we’re off course for either,” with current mainstream projections suggesting that future warming could be headed toward 3-4 °C. But the PLOS ONE paper argues that even the 2 °C target accepted in past global discussions is potentially far more dangerous than was realized. “That two degree figure, which is taken as optimistic by most mainstream observers, is itself wildly complacent,” Sachs says.


Oxford Physics: The Trillionth Tonne

This is the most concise presentation of the math of climate change – by the physics department at Oxford University. I’m surprised I don’t see more references to this site. Click on the “Find out more…” button for the background. At the bottom you’ll find the scientific references behind the numbers.

David Montgomery – Testimony for Hearing on EPA’s Greenhouse Gas Regulations

Prof. Montgomery’s prepared testimony is here [PDF]. It’s really excellent, science-based guidance to the politicians — it is worth reading the whole text. Fortunately Judith Curry also took an interest in Montgomery’s testimony so Judith and her commenters offer lots of useful insights. Altogether this is a very long post (26,000 words) but very worthwhile. Included are attempted rebuttals by Georgia Tech colleague Paul Baer.

I am not a fan of the EPA endangerment finding on CO2 – if any GHG policy is to be effective and affordable, regulation is not that tool.

Personally I found the most useful comments were those by Judith Curry , Richard Tol, and “Max Manacker” (you can search for (“curryja”, “richard tol” and “manacker”). I will quote Max Manacker’s summary comment as I agree with Montgomery and Max. For brevity I have excised Max’s comments on the Baer, Heinz rebuttals:

Here is my take on all this, for what it’s worth.

Dr. David Montgomery makes four important points at the start of his written testimony:

First, if the U.S. were to act without solid assurance of comparable efforts by China, India, and other industrialized countries, its efforts would make almost no difference to global temperature, especially if industrial production and associated emissions are simply exported to other countries.

Second, even global action is unlikely to yield U.S. benefits commensurate with the costs it would incur in making steep GHG emission cuts.

Third, globally, even with moderate emission reductions, benefits would not be much greater than costs and,

Fourth, conflicting economic interests will make international agreements on mandatory limits unstable.

Montgomery discounts the idea that regulations will cause companies to take actions to save money, which they would otherwise not do:

Any claim that a regulation or standard will on balance save money should be regarded with a high degree of skepticism unless accompanied by a well researched and peer reviewed demonstration that the specific action will cure a market failure, and do so without administrative costs great enough to wipe out the gains.

He points out why climate policy will not promote a new clean energy export industry in the U.S., citing the experience of the past 10 years. This experience shows that they rather cause the loss of U.S. jobs with the possible addition of a few new jobs located outside the U.S.

Montgomery then addresses the great uncertainties plus the “winners and losers” argument mentioned by Dr. Curry in her testimony before U.S. Congress:

Even if the goal of industrial policy were accepted, mandatory reductions on greenhouse gas emissions are the wrong way to go about it.

The most fundamental error is failing to admit how little is known about the direct causes of damage to human and economic systems that have been attributed to climate change.

Some changes may be beneficial, such as increased growing seasons and carbon dioxide fertilization in high latitudes, and some are negative, such as drought or storms in tropical areas. But the range of possibilities and whether it adds up to a positive or a negative in any particular region is impossible to predict with confidence. Therefore, any economic evaluation of damages is equally uncertain.

He points out how cost/benefit analyses for specific actionable proposals are hardly ever made. Instead the whole palette of possible worst-case scenarios is presented as justification for action.

In analyzing any particular policy the costs of that policy must be compared to the damage it avoids. It is shocking how rarely this fundamental economic principle is violated.

Montgomery makes a good case for his conclusion that attempts to change our planet’s climate will neither change the climate perceptibly nor show cost effective economic benefits, such as creating jobs.

He also points out that they would be totally meaningless without world-wide cooperation, and this is highly unlikely to occur.

{snip Baer, Heinz criticisms}

I’d say the testimony of Montgomery is much more convincing than the rebuttals of either Baer or Heinz.

But then, Montgomery had a lot of time to prepare his testimony, while Baer and Heinz were just “shooting from the hip” in response.


Rob Dunbar: Discovering ancient climates in oceans and ice

We recommend Rob Dunbar’s recent TED Talk. In this post we are collecting a few of the links we have found researching the drillship JOIDES Resolution and the IODP Wilkes Land Expedition. The photo above is from Rob’s mid-expedition dispatch “Iceberg City “.

Rob Dunbar-Home Page-Stanford University

Robert Dunbar | Center for Ocean Solutions

Rob Dunbar | Ice Stories: Dispatches From Polar Scientists