Climate of Risk and Uncertainty contacted me asking what I thought about Bret Stephens’ first column in the New York Times. Here, is a slightly edited version of my response.

Bret Stephens’ opinion piece, titled “Climate of Complete Certainty”, is attacking a straw man. No working scientist claims 100% certainty about anything.

Science is the process of falsification. Hypotheses that have withstood a large number of attempts at falsification, and that are consistent with a large body of established theory that has also resisted falsification, are widely regarded as true (e.g., the Earth is approximately spherical). Many hypotheses of modern climate science fall into this category.

It is also true that some ‘environmentalists’ go far beyond the science in making claims, but that is not cause to denigrate the science.

Bret Stephens writes of ‘sophisticated but fallible models’ as if ‘sophisticated but fallible’ gives one license to ignore their predictions. A wide array of models of different types and levels of complexity predict substantial warming to be a consequence of continued dependence on using the sky as a waste dump for our CO2 pollution. It doesn’t take much scientific knowledge to understand that the end consequence of this process involves approximately 200 feet of sea-level rise. We already see the coral reefs disappearinga predicted consequence of our CO2 emissions. How much more do we need to lose before recognizing that our ‘sophisticated but fallible models’ are the best basis for policy that we have?

Yes, we should take uncertainty into account when developing policy, but we should recognize that those ‘sophisticated but fallible models’ are as likely to underpredict as overpredict the potential consequences of our greenhouse gas emissions.

Stephens would have been on more solid ground if he would have confined his comments to uncertainty in the ability of human systems to adapt to the relatively more certain projections of changes in the physical climate system. Will we be able to give up low-lying countries and the major coastal cities of the world (New York, London, Tokyo) without much of a transition cost? Will people in India and the Sahel be able to migrate or air-condition their way out of the harsh conditions projected for those areas? These are open questions about which well-informed people can disagree.

It is dangerous to act as if uncertainty in climate model projects justifies inaction. Uncertainty equals risk. One way to reduce uncertainty is to increase the amount and quality of climate science being conducted. Another and more important way of reducing uncertainty is to reduce human influence on the climate system. This requires a major transformation of our energy system to one that does not rely on the atmosphere as a waste dump for our CO2 pollution.

Climate science does not offer complete certainty about the future. Instead, it points to substantial risks and ways to avoid that risk.

Straw-man attacks on climate scientists do not productively advance the discussion.

For reference: My first reaction to the announcement of the The New York Times decision to hire Bret Stephens.


Scientific reproducibility, communication of uncertainty, and the US House of Representatives

Bobby Magill of Climate Central sent me an email asking me to comment on several bills recently passed by the US House of Representatives. Specifically, he asked me to comment on bills rescentely
– H.Res.229. … would require EPA actions to be based on science that is “transparent” and “reproducible.”
– HR 1431, …would prevent the EPA Science Advisory Board from communicating uncertainties.
My email comments to Bobby are below: His story is here:

All of the climate science, and related environmental science, that I read in the peer-reviewed literature is in-principle reproducible. The reason it is not in fact reproducible is that the Federal funding agencies rarely provide resources to redo work that someone else has already done.

If our Congressional and Senate representatives really want to see us do science that is reproducible in a practical sense, they should double or triple research budgets so that scientists can afford to do the same thing two or three times.

In practice, once someone has done something to the satisfaction of thee peer-review system and the broader scientific community, people move on to try to make new discoveries.

You can be sure that scientists love nothing more than showing that our colleagues are wrong. If something gets published that smells fishy, that’s when scientists are motivated to redo the study and show that they are wrong. This, for example, famously happened with the cold fusion studies that were published some years ago.

Why would a working scientist with limited funds want to allocate scarce resources to testing something the scientific community already thinks it knows rather than exploring something new? To have enough resources to want to spend it treading over old ground would require a substantial increase in science funding.

Science is all about communicating uncertainty. Science doesn’t prove things. Science works by trying to disprove things. The harder people work to disprove a statement, and the more they fail at disproving it, the more people come to believe the statement is true. Science is about expanding the range of what we know to be false. Truth lies in the range of what we don’t know to be false — that is the uncertainty range.

People who don’t want scientists to communicate the uncertainty range are people who don’t understand what science is all about.

Image from Climate Central story: Credit: C.L.Baker/flickr

Dark ages: Do you know what to do?

A friend and colleague wrote me saying “The US is clearly entering the dark ages in terms of climate, environment, etc. This requires action. … I’m not sure what to do. Do you?”

My response (lightly edited) is below:

A few thoughts:

— It is important to focus on the Congressional and Senate Republicans. It is they who are enabled by and who are enabling Trump. They can get rid of Trump if he becomes too much of a liability. We should not focus on a single man, but on the whole corrupt apparatus behind him.

— We all need to get more politically engaged, and in particular get more people out to vote and vote the right way. If more people had just gone out to vote, Trump would not be President today.

— The Democrats needs to have real plans. In the next 10 to 15 years, 3.5 million Americans who work as drivers may lose jobs to automation. What do the Democrats believe someone in their 50’s should do if they have been a driver all their lives and now lose their job to automation? The Democrats need to come out for guaranteed basic health care, a guaranteed basic job or income, access to free or low-cost high-quality education, etc, etc. They need to stand for things that are meaningful to the average person who is not a policy wonk.

— We need to get better at telling stories with happy endings. People respond to narratives. People have be able to envision a better future. Trying to sell the double negative of the bad that will happen if we don’t do something just isn’t going to work.

We go through our days acting as if we are in normal times, when the times are clearly not normal. The level of corruption and destruction and malevolence and incompetence is mind-boggling.

— We need to be vigilant and aware, and help others be vigilant and aware. Already, things that would have seemed crazy in the past are being considered normal behavior. We cannot act like doing terrible things is normal.

I am shocked at how unprincipled the Republican Party is. I thought they stood for things like free trade, containment of Russian expansionism, etc. It turns out all they stand for is power and wealth. I thought they were children of Adam Smith, when they are really just children of Machiavelli.

Part of the problem the Republicans are having now is that they were all about negativism, about being against things. So, now when they are in power, they cannot get consensus on what positive actions to take.

It will ultimately take responding to the negativism of the Republicans with a positive vision. Focusing on being anti-Trump and anti-Republican is ultimately not a winning strategy. It needs to be there, but we need the yin along with the yang.

IMG_1936-IMG_1940_arty2_1920x1080 (1)Colorized photo I took of the Michelson Building at the Potsdam Institute of Climate Impact Assessment, where I am visiting now.

Where do the winds come from?


Eva Ahbe and I wanted to know where the energy came from to make winds.

This is infeasible to directly observe in the global atmosphere. Therefore, we used a model of the atmosphere to study where the energy comes from to drive winds.

The potential energy available to generate winds is created most strongly high above the tropical western Pacific Ocean where the condensation of water in convective systems heats up already warm air, and also in the high polar night where heat radiates to space, cooling already cold air.

These heat fluxes create density contrasts that tend to make the tropical air rise and the polar air sink, and this is a primary driver of global winds.


2016 is Earth’s hottest year on record: A glimpse behind the Washington Post story

Jason Samenow of the Washington Post wrote to me asking for some comments for a story he was doing on the announcement of year 2016 as the hottest year on record.

Here is what he used:


Reaction: 2016 ‘should tip the balance’ for those unconvinced about human-caused warming

If there are still any people out there who remain unpersuaded by past science and data of climate change, the record high temperatures of 2016 should tip the balance.

With the high temperatures of 2016, the evidence for human-induced global warming is now so strong that no sensible person can deny a human role in these temperature increases.

We can argue about what we should or should not do with this knowledge, but the argument is over: Greenhouse gas emissions cause our climate to get hotter.

Ken Caldeira, climate scientist, Carnegie Institution for Science

Here is the full text of what I provided him:


I don’t have time to say anything long and thoughtful but here it is …


Weather naturally varies over time periods ranging from minutes and hours to days and centuries and longer.  Climate is the statistical properties of this weather. As the saying goes: “Climate is what you expect, weather is what you get.”

Because weather is naturally variable, it is not easy to know whether weird weather is just a product of natural variability, or whether it is a consequence of human interference in the climate system.

Scientists try to estimate the amount of ‘weather noise’ to see whether a climate signal remains in temperature data. I remember when I was a graduate student in the late 1980’s, discussing that the human imprint on the climate system would become statistically significant sometime in the 1990’s. Indeed, in 1995, the Intergovernmental Panel on Climate Change suggested there was a ‘discernible influence human influence on global climate’ and by 2001 they stated that most of the warming of the past 50 years was likely due to the increase in greenhouse gas concentrations.

Then, in the early 2000’s, global warming seemed to pause in its increase. To most climate scientists, this was an indicator that decade-scale trends could be strongly influenced by natural variability. To others (pseudo-scientists and so-called ‘climate skeptics’), this hottest (at that time) decade on record was interpreted as evidence that human-induced climate change was a fiction.

If there are still any people out there who remain unpersuaded by past science and data of climate change, the record high temperatures of 2016 should tip the balance.

With the high temperatures of 2016, the evidence for human-induced global warming is now so strong that no sensible person can deny a human role in these temperature increases.

We can argue about what we should or should not do with this knowledge, but the argument is over: greenhouse gas emissions cause our climate to get hotter.

Happy for you to edit or copy-edit etc. If you think you may be changing meaning, please ask.


I thought he did a good job of editing for the pithy parts.

Full story is here:


Time, books, and nice words from Mr. Gates

I was pleasantly surprised to read  Bill Gates calling me ‘my amazing teacher’ on his GatesNotes blog and calling me ‘brilliant’ in a tweet:


It is very nice to be called ‘my amazing teacher’ or ‘my brilliant teacher’ by anyone. It is especially nice to have those words said about you by Bill Gates.

The curious thing is that I don’t feel like I have taught Bill Gates much of anything. For the last decade or so, a few other people and I have been running a series of learning sessions for Bill, bringing in experts on different topics related to climate and energy. All I have done is help expose Bill Gates to some information. He is a self-learner, and generous enough to attribute his self-learning to the people around him.

The thing that I have learned the most from interacting with Bill is to value my time and use it thoughtfully.

I have never seen Bill Gates try to multi-task. I have never seen him check his text messages or email in the middle of a meeting. He does one thing at a time and gives that one thing his full attention.

Bill is limited by resources in many of the big things he wants to accomplish: eradicate diseases, bring prosperity to the poor, solve the climate / energy problem, etc. However, in terms of personal consumption, Bill is not limited by money. He is limited by the amount of time he is willing to allocate to an activity. For Bill, time his is his most precious resource. And he thinks very carefully about how to allocate his limited time.

If time is Bill Gates’s most precious resource,  maybe it is my most precious resource as well.

One of the things that is great about Bill is that he takes time to read. He usually reads at least one non-fiction book each week. Here is the richest man in the world, who can allocate his finite time to any activity he wants, and the best thing he can think to do with his time is sit in a chair and read.

When people think about the lifestyles of the rich and famous, maybe they think of wild beach parties in Bali. However, sitting in a chair and reading a good book is also part of the lifestyle of the more intelligent of the rich and famous. And I can partake of the lifestyle of the rich and famous simply by buying a book and sitting in an easy chair and reading.

Why don’t I read more? Is it because of the cost of books? No. The amount of time I spend reading is limited primarily by my willingness to allocate time to that activity.

My mom lives in a retirement community. She brings a kindle with her when she has to stand on line in the cafeteria so she can read while she waits to reach the steam tables. She asked another person on line why he was just waiting without doing anything else. The man replied, “What does it matter? I’m retired. I have all the time in the world.”

My mom responded, “What do you mean? You’re in your 80’s. You don’t have much time at all.”

My interactions with Bill have taught me that money can relieve constraints, but even with those constraints relieved, we need to ask ourselves the question: “How do I want to allocate my time? What do I want to spend my time doing?”

Yes, we are more constrained than Bill Gates, but we all have time that we can allocate more wisely. Money opens up possibilities, but we can all be choosing better among the possibilities that are already open to us.

I remember, as a kid, spending whole summers playing Monopoly with my friends, and these summers seemed to last forever. Perhaps the last time that time seemed infinite was playing bridge with my friends in college. Time then wasn’t zero sum. There would be time enough for everything. I look back fondly on that feeling of time abundant.

As one progresses through life, it becomes clear that time is very finite. Time is in short supply and there will not be time enough for everything.

Time is our most precious resource, and we must learn to use our time wisely.

This is what I have learned from Bill Gates.


Coffee and Climate: A Common Problem


There is a shared departmental coffee pot for my office – and my office is filled with people claiming that they are willing to sacrifice a little bit of their short-term self-interest to help solve the climate problem.

The person taking the last cup of coffee is supposed to make a new pot for the next coffee drinker. This involves throwing out the old grinds and filter, putting in a new filter and some ground coffee, and filling the water reservoir. It takes a little bit of work – a couple of minutes at most.

What happens as the coffee gets low is that people start taking smaller and smaller cups of coffee, leaving enough in the pot to represent a plausible cup of coffee. Of course, this little bit of coffee evaporates down to some burnt-tasting brew and sometimes ends up as a pasty semi-solid on the bottom of the pot. Even though we are an office full of people claiming to be willing to sacrifice a little bit for the greater good, we can’t get people to cooperate enough to maintain a steady flow of drinkable coffee. (And don’t get me started on the tea kettle situation!)

The problem is that, as perhaps too simply described by Carl Sagan in The Dragons of Eden, deep beneath our modern and rational neo-cortex lies an emotional structure derived from an ancient reptilian brain. We might know cognitively that we should make that next pot of coffee for the greater good of the community but our reptilian brains are narrowly focused on the short-term benefits. This is related to Malcom Gladwell’s Blink or Daniel Kahneman’s Thinking Fast and Slow. We make snap, almost automatic, decisions that do not accord with what our slower, more thoughtful, selves would decide.

We evolved as hunter gatherers, where rapid response could mean the difference between life and death, where thinking about long time scales meant thinking about saving enough food to last through the winter, where thinking about big spatial scales meant worrying about attacks from the village in the next valley. Now, we have created a technological world to which we are no longer adapted. Problems like climate change mean we must think about problems extending out over decades to millennia and even millions of years, and that we must think on spatial scales that encompass the whole globe. Our ancient lizard brains can’t do this. We need to solve modern problems with our neo-cortex.

To oversimplify once again, we might imagine that Hillary Clinton asked us to vote with our neo-cortex. She asked us to think about what policies government could institute to help solve some of our problems. Donald Trump asked us to vote with our lizard brains. He asked us to vote our emotions. He asked us to ignore that what he was saying didn’t make cognitive sense, but to follow our emotions and him into the voting booth.

Imagine how our coffee situation might change if there was a public list where each person wrote their name when they took a cup of coffee, and maybe put a star next to it when they made a pot of coffee. Then you would know who left this last bit of black goo (and think a bit less of them) or who made that gleaming new potful (and think a bit better of them). The solution lies in aligning self-interest a little more closely with the community interest.

How do we solve the climate problem? Is it by getting everybody to agree to sacrifice in the here-and-now to help people far away and in the distant future? Do we expect people to deny themselves something in the sensory field of their lizard brains to help people that exist only in the abstract thinking of their neo-cortex? Seems unlikely to me.

We will not solve the climate problem by teaching people to be less selfish. If we have to wait until people learn to make self-sacrificing snap judgments before we can solve the climate problem, we will be waiting until it is too late.

The challenge then is to create incentives that more closely align narrow short-term self-interest with the broader long-term collective interest. What can do this is policy. A carbon tax. Standards regulating greenhouse gas emissions per mile driven or kilowatt-hour used.

Even if we act in the here and now with our emotional lizard brains, we can hope that we produce a government of people with fully functioning neo-cortexes that make decisions based on rational considerations. In this context, the election of Donald Trump to the US Presidency is particularly disturbing. We are emotional beings so we need a government that acts rationally. We need a government that will help us to align self-interest with community-interests. Instead, I fear we are getting a government that steers narrow self-interest down avenues that advance only narrow self-interest.

We need to move beyond the emotional lizard brain to solve the coffee and climate problems. We need rational, thoughtful policies that will better align individual interests with community interests. It is difficult to get such policies enacted at the level of my department, even harder to get such policies enacted at the level of a country, and even harder at the level of the entire world.

We have little choice but to try.

This is a slightly shorter version of an essay I wrote in an effort to think about what I might say in an opening statement for a panel I will be on at the Fall 2016 American Geophysical Union in a session titled Planetary Intelligence: Managing Earth’s Future. It was easier for me to cut paragraphs in a new version than to cut the previous