Continuing Education... Martin Weitzman on Climate Change

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by Amy Willis
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Is climate change the ultimate Black Swan? Harvard's Martin Weitzman joined Russ this week to talk about the potential risks of rising CO2 levels and what policies might be appropriate as a response.

Here are questions for thinking about this week's episode. We feel to respond in the comments making EconTalk more useful to our audience.

Climate Shock.jpg

1. What are your top three takeaways from this week's episode?

2. What does Russ mean when he refers to rising temperatures as "an infra-marginal problem?" What does this suggest about the sorts of solutions that might be best suited to mitigate the externalities of climate change?

3. Weitzman mentions a $40/ton tax on carbon emissions. Try to find out where this estimate comes from. What key assumptions underlie that number?

4. Russ says of Weitzman and Wagner's book, " Your book is a breath of fresh air in the sense that you don't overclaim. You are extremely modest; and yet despite that modesty you still want some dramatic solutions. Which I'm slightly more interested in being in favor of, after reading your book." To what extent has this episode changed your thinking on climate change. Explain.

5. Most people have very strong views on climate change and whether policies should be put in place to affect carbon dioxide emissions. If you have a strong view on the matter, can you imagine empirical evidence that might change your view or get you to reconsider your position?

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COMMENTS (17 to date)
Walter Clark writes:

I really appreciate Russ doing this interview. I'm still skeptical though and it is because of the bathtub analogy. He left out THE most important parameter of that model. The higher the water level, the higher the pressure at the outlet. He made no mention of how increasing CO2 levels increases the rate of its consumption; that green things are greener. All natural systems are like that. If there were any natural systems where the undoing of something didn't increase with the more of that something, it would have destroyed itself long ago. Yes there are example of runaway, such as a super nova, but they are rare.
It may be that the math includes the drain rate but his not mentioning it, leaves out the most controversial part of the science.

Gernot Wagner writes:

Dear Walter Clark, increasing CO2 levels does increase the rate of its consumption, but that's FAR from the most important parameter -- and certainly not in human timescales.

In short, the bathtub analogy holds here, too. Yes, increased water levels increase the outflow, but the increase in the latter isn't enough to prevent the tub from overflowing. It's clearly not enough at current levels of 400 ppm CO2 in the atmosphere, with us still adding 2 ppm per year.(Take a look at the book for the full answer.)

arde writes:

Question 5. It is not scientific, but I am most influenced by what I see around. Many people are like this. If you are working in a company and you had to fire people because of the increase of minimum wage, it would be difficult to convince you that minimum wage has no impact on employment even if people waved around sophisticated studies. Or, if your boss asked one day to accept a decrease of salary or leave because there are immigrants who would be happy to work for half the wage, then it would behard to believe the hundred studies that say that immigration has no impact on wages.

I believe that there is climate change because I see it around. I live in Northern Europe. When I was a child, there was snow from November to March. Nowadays, there is snow some 2-3weeks per year, and most of time it's just rain. When I was a child I never saw a snake (snakes generally prefer warmer places), but now there are much more snakes, people have to figure out ways how to prevent them from entering in the garden. Often I read in newspapert that biologists report new species of insects and birds have appeared in my country, previously it was too cold for them. When I was a child, it was chilly in August, I had to wear a jacket, but nowadays people go to beach and swim till late August.

Which empirical evidence could make me reconsider my position? Several years of white Christmas, just like the ones I used to know.

Jim H. writes:

Top Three Takeaways:

1. Despite my respect for Dr. Weitzman and his sense of urgency, we have time to let the climate science develop further. I recall as a child in elementary school back in 1975 or so reading in the Weekly Reader about the coming ice age. The article was vivid and alarming (and likely overconfident in its conclusions), like much global warming advocacy today. As Dr. Weitzman concedes, there is a lot of uncertainty about what will actually happen, and Russ Roberts’ analogy with macroeconomics is apt.

2. Dr. Weitzman is reasonable, and unlike global warming fear-mongers, he seems to be willing to give up something substantive in order to achieve a carbon tax. Even if I disagree with him on the likelihood of a future catastrophe, as a matter of political expediency I might go along with a carbon tax (in order to give him the insurance he desires) if in return we get to kill off some counterproductive taxes and regulations.

3. Even if we high-minded “First world” nations manage to agree on and implement a carbon reduction scheme, is the rest of the world going to get on board? As Russ said, it ain’t gonna happen (or words to that effect).

To what extent has this episode changed your thinking on climate change. Explain.

• I’m more willing to listen to somebody who is deeply concerned about the problem, and I’m willing to concede it might – might – be a problem – some day. And I’m willing to at least entertain a carbon tax (offset by reforming or removing other taxes and regulations) if it would result in a more productive and competitive economic system.

If you have a strong view on the matter, can you imagine empirical evidence that might change your view or get you to reconsider your position?

• I’m not sure what specific evidence would convince me to leave the skeptic/agnostic camp, but what might be enlightening would be substantive interactions between people like Dr. Weitzman and reputable scientists such as Richard Lindzen who disagree with him about the possible effects of increased CO2 in the atmosphere.

Earl Rodd writes:

Mr. Weitzman seems to have made two large errors in analysis.
First is that he needed to hear the prior econ-talk episode on "mega projects." In this case, I think he vastly over-estimates our ability to actually affect the climate by possible changes in human activity (CO2 emission). Next, he vastly under-estimates the cost of a dramatic cut in CO2 in human lives and social and political upheavel. His next error is to look at only one side of the probability distribution. Since, as he notes, we really do not know the probabilities, especially at the extremes, we need to think about the tail on the other end. This is the probability we are entering another mini-ice age cold period. With current world population, such a shift to cold carries great risks in food production. And there is even some possibility that lowering man-made CO2 would contribute to such a shift to cold!

Andrew Bruce-Sach writes:

Russ is making a fundamental error when it comes to interpreting the uncertainty of global climate change. He talks as if all of climate science was based on models. However, the science of CO2 and heat absorption are very determinate and easy to demonstrate in the lab. CO2 absorbs heat. More CO2 absorbs more heat. This is not a disputable fact and can even be seen by heat sensing satellites pointed towards earth.

Information in science comes in many different forms. Some of it is deterministic: "If you press the button, the light comes on." Some of it is probabilistic: "If you press the button, there is a 50:50 chance that the light comes on." Some of it is chaotic: "If you push the button even a little bit, nothing could happen or the light might turn on to its maximum brightness. If you push the button a little more, then something different might happen. It is completely impossible to predict precisely what will happen, but we know what the range of possibilities are."

It can be confusing because one subject can involve multiple types of information and can even switch between them based on frame of reference, new information, or even time period.

The cause of climate change is deterministic: "If you input more CO2, you will get more heat storage." However, the consequences are chaotic: "If there is more heat storage in the atmosphere, then any number of changes could happen. They range from mild to catastrophic. But it is completely impossible to know precisely when and where the effects will appear with any certainty."

Just because there is uncertainty as to the precise nature of the effects, does not mean that there is uncertainty as to if global climate change is happening. The cause is deterministic, even if the effects are chaotic.

The question is do we want to push our system to the limit and risk run away problems, or do we want to take out cheap insurance.

Urstoff writes:

A very complex model says that there is probability X that the temperature will rise by Y degrees in Z years.

Let's assume that for the sake of argument (as Andrew points out, that may not be how some of the probabilistic predictions get made). How do we evaluate as individuals the probability that the model is getting its probabilities right? My subjective confidence in complex macroeconomic models, for example, is pretty low. I don't much about climate modeling, so what is the relatively informed person's confidence in the accuracy of the models?

Note this isn't an argument against climate change. Just personal curiosity. The state of macro seems to be that no one knows much, but we don't have anything better; thus, we have a very weak base on which to make any policy decisions. Is climate change like this?

MattK writes:

Did anyone else get the feeling listening to Martin that he thought the potential effects of climate change so bad that it justifies scaring people and exaggerating the effects in order to spur people to action? I wonder how wide spread this attitude is in the climate change community?

I don't disagree with any of the basic facts (CO2 reflects more in the IR spectrum than Nitrogen/Oxygen, leading to more trapping of heat. But then the conssequences of that, and how it shows up in local temperature changes are really up in the air at the moment. That comment about twiddling the models really floored me!

Andrew writes:
The state of macro seems to be that no one knows much, but we don't have anything better; thus, we have a very weak base on which to make any policy decisions. Is climate change like this?

Climate change is not like macro overall because it is based on easily observable physical factors.

It is true that there is a high level of uncertainty as to what will happen on either small time scales or small space scales. It is hard to say what will happen to the weather at a particular location at a particular time, for example. However, some large scale statements can be made with certainty. Statements such as "Global climate change will increase extreme weather events" and "Polar ice will melt and seas will rise" can be made with confidence because the large scale of the statements means that all of the noise from local conditions averages out and fundamental physical processes return to play.


It might be tempting to say some adaptive mechanism will limit the change to 0 degrees. An example some people use is increased cloud cover. Increased cloud cover can mean that more sunlight is reflected away from earth back into space, which can lead to lower temperatures. This may be true to some extent. An example that has been very well supported is the absorption of CO2 by the oceans to slow down the increase of CO2 in the atmosphere. However, any adaptive system has its limits and the very complexity of the system means we don't know exactly where those limits are. When people say that the system is complex and we don't fully understand it, that is a good reason to NOT mess with it. Would you pull on cords and push buttons on your life support system if you didn't understand how it worked?

Hana writes:

#5 I don`t believe most people have strong views relative to climate. I do believe that a limited number of people on both sides of the disagreement have strong views, and those views are closely correlated with their political viewpoint.

It is my understanding that increased CO2 allows plants to grow faster with less water. Living in California, and recalling Dr. Henderson`s recent post about farm water usage in the state, increasing the CO2 levels of the atmosphere may have positive effects for the farmers and the water situation.

The earth`s climate is a very complicated system. Temperatures and CO2 levels in the past have been much higher than current levels and the earth survived. It is really folly to think there is a perfect temperature, which is?, and modifying one input will keep it in perfection.

In order to change my mind, I would need evidence that the costs to insure now exceed the costs to mitigate later. I don`t believe they do. Additionally I view all government tax efforts described as `revenue neutral` or `defined uses` as lies told to the gullible. Again citing California, the gas tax was raised to improve the roads, of course it was dumped into the general fund, and if you have driven in California you know the state of the roads.

I really appreciate Russ`s interviews and style.

Fred Feirtag writes:

"I recall as a child in elementary school back in 1975 or so reading in the Weekly Reader about the coming ice age."

That might be, but be sure also to read, "The Myth of the 1970s Global Cooling Scientific Consensus," as well.

If the vast majority of the world's scientists being published in refereed, peer reviewed journals, told me global warming wasn't a grave concern, after all, that would change my mind.

I'd say I'm a "pro-environment" kind of guy, and I've also been pro-nuclear power, too. I've recently become less pro-nuclear, only because of the amazing advances in photovoltaic & battery technologies, which I think even without subsidies may win out in cost -- just my hopeful hunch, based on the avalanche of energy technological advances I keep reading of....

Recently I read that if you took all the coal, petroleum, and natural gas in the earth and burned it all in a mythical bonfire, the total energy released from this remnant of sunlight-past would only equal three days of the energy of sunlight now continuously hitting the earth. I tried my best to check the math, and that actually seems about right.

I certainly agreed with the points regarding energy storage. Even today's wind & solar price points start to challenge other energy sources, but the key is storage.

Vangel writes:

I am sorry but Dr. Weitzman seems to lack knowledge that he should have. First of all, we are now in an icehouse period that is significantly colder than most of the history of this planet. Most of the time the planet has been much warmer on average and the temperature has been a positive for the biosphere. It may have escaped Dr. Weitzman's attention but exposure to excess cold is not good for plants, animals, or humans, not to mention civilizations. There is no evidence that the 0.8 C increase from the end of the Little Ice Age has anything to do with CO2 or that it has been harmful. In fact, the IPCC has admitted that it has been good for us and that further increases will be net positive until temperatures get much higher than the current average. Even if the IPCC is correct, which is looking less and less likely given the empirical evidence that Dr. Weitzman has conveniently chosen to ignore. While it may have escaped his notice that AR5 failed to provide a most likely sensitivity estimate others have not. And they my have also noticed that the AR5 attribution statement took a step back. We note that AR4 stated that, "Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations." But AR5, changed that to,"more than half of the observed increase in global average surface temperature from 1951 to 2010 was caused by the anthropogenic increase in greenhouse gas concentrations and OTHER OTHER ANTHROPOGENIC FORCES TOGETHER."

While Weitzman may have been able to ignore the pause that was not possible for the Lead Authors who worked on the IPCC report. That is why they brought up other anthropogenic forces, which I assume bring into play the previously neglected Urban Heat Island effect and other change in land use factors. It is also not possible to ignore the fact that the IPCC models are running at least twice as hot as the official observations and much more than that for the unadjusted measurements.

The simple fact is that the models have failed and the theory has failed. The data shows that other factors are far more important and that warming is not doing harm. Data included in Congressional testimony shows no trends in severe weather, per capita economic losses as a percentage of GDP, weather related deaths, etc. In fact, the data is showing the opposite. The mild warming that we have enjoyed since the end of the Little Ice Age has lengthened growing seasons, reduced frost kills for vulnerable crops, and reduced mortality rates.

Note that I have not even began to bring up questions such as what is the meaning of average annual global temperature even if we did have the equipment to gather accurate data or to bring up the point that the upward adjustments to the real measurements are greater than the warming signal shown after those adjustments.

The way I see this is simple. The AGW story is just as fraudulent as the ozone hole story. After spending billions to get rid of CFCs and switching to more toxic, more expensive, and less effective refrigerants we are finally told that the laboratory data does not support the assumption for the decomposition rate of dichloride peroxide that is required to make the ozone destruction narrative work. And after more than a decade of watching we have found that the ozone hole changes according to the 11 year solar cycle as would be expected in a process that has UV radiation involved in ozone formation. The latest research shows that the decomposition rate is an order of magnitude lower than the model assumptions. That research falsifies the arguments used to justify the Montreal Protocol.

Now we are asked to buy the same type of arguments yet again even though the empirical evidence shows that they do not stand up to scrutiny. I am sure that the good Dr. Weitzman gets well rewarded to sell to consumers and voters another tall tale that is only supported by models that can be made to do anything by a skillful fiddler. But there is no reason for rational consumers or voters to fall for that approach yet again.

It is time that Russ bring back Dr. Curry again. I am sure that she could dispense with most of Dr. Weitzman's positions in a very short period of time. Or it may be time for another episode on reproducibility and P-hacking.

Sunil writes:

I have one important takeaway from this discussion. The debate on climate change has turned the corner. At least for me.

- Martin Weitzman made a halting, tentative case for climate change. I thought he was one of the least forceful speaker for action on climate change. And still he was effective in obtaining a general agreement for the reality of climate change and that action needs to be taken.

- Russ articulated the case for stepping back from wall of resistance that he defended so hard for all these years. He gave a nod to the possibility of harmful effects of climate change. This probability (3%, 10%, doesn't matter) is gradually increasing. It is now significant enough to commend action. Further, the case for climate change action is sealed by the recognition (fear?) of the harmful impact of carbon-burning on that which is most precious to us, our future: our children and grandchildren.

I see a situation where climate activists have no cause to be strident (and obnoxious), because now they will be heard. I see a situation where climate change deniers (I hate this characterization.) are less recalcitrant, more willing to both accept the possibility of and take reasonable action against climate change.

The arc of trajectory of our acknowledgement of (the possibility of) climate change turned with Katrina (2007) and Sandy (2012). It took us a while to realize that we have changed.

Prepare for the next fight - what actions are reasonable? what increments acceptable?

On a side note, first lights of a confirmation. The energy battles in 2015+ USA no longer black vs. green but Oil vs. coal. Let the patricidal wars begin. See this http://nationalobserver.com/2015/05/28/news/big-oil-takes-king-coal-climate-fight-shifts-gears.

Fred Feirtag writes:

"the models have failed and the theory has failed"

I thought Dr. Weitzman was very thorough in his discussion of the great uncertainty of the models and theories.

"...this is simple. The AGW story is ... fraudulent."

Strong words. I simply cannot evaluate the often lengthy arguments of the deniers, as I am not by training, or avocation, a climate scientist.

But more fundamentally, I always have the same problem with deniers, who reject the mainline, published, peer reviewed professional climate scientists:

Once trust is lost in the body of scientific reporting, how can one even know what the facts are? CO2 is going up? Maybe CO2 is going down? Sea level is going up? Is it? I've never been to the Indian Ocean. For all I know, it's all evaporated and dried up...or never existed at all. I have no firsthand knowledge of ice cores, dying coral reefs, methane gas escaping from under the tundra, or any such things.

I pretty much have to conclude that if the vast majority of experts tell me there is such a thing as "CO2" and that it's going up, and that this is a problem, I can't reject only their conclusions, while retaining trust in the intermediate observations, or even preliminary so-called facts or data, with which contradictory conclusions might be created.

Gregory McIsaac writes:

This episode did not change my mind about climate change or what to do about it because I did not hear very much new information. I am largely in agreement with Dr. Weitzman. His views about the causes of climate change and likely need to act seem to represent the scientific mainstream, which has been endorsed by practically every relevant scientific society in the US and other developed countries. I am aware of the criticisms raised by a handful of scientists, such as Judith Curry, John Christy, Roy Spencer and Richard Lindzen. Their contributions underscore the uncertainties about the likely rate of climate change and the consequences.

I have been following this topic to some extent since I took a graduate level course in meteorology in the early 1980s, when this subject was not controversial. I have since done research and teaching on aspects of hydrology and ecology that are related to climate change. My main source of information has been reputable scientific journals and the National Research Council, not Al Gore. I find it somewhat amusing and annoying that otherwise intelligent people consider Al Gore to be an expert on this topic. I don’t think he is any more an expert than is Jim Inhofe, who has expressed considerable certainty that human caused climate change is a hoax. Gore, Inhofe and similar advocates can be legitimately criticized for excessive certainty and “bad marketing.”

The National Research Council and National Academies Press has provided a large number of sober and accessible assessments of the state of the science and recommendations on for additional research. One of their most recent publications is on geoengineering and calls for more research on that subject (in contrast to Russ Robert’s snarky comment that “we can’t talk about it”).
http://www.nap.edu/catalog/18988/climate-intervention-reflecting-sunlight-to-cool-earth

I would change my mind on this subject if a significant number of scientists with relevant expertise began to report data that undermined the existing consensus. The “pause” is not yet sufficiently long to do that, but if it lasts another ten years, then it might, unless some other factors (like ocean temperature cycles) provide compelling explanations for the “pause” that leaves the consensus largely intact.

I know many climate change skeptics argue that there is a conspiracy among climate scientists that will not allow anything to be published that contradicts the consensus. But there are papers published that contradict the consensus. So far, they have not been very compelling papers. It is possible that thousands of climate scientists are engaged in “group think”, but I think this is unlikely, given the large numbers of people involved who come from different disciplinary and cultural perspectives, and the presence of skeptical voices in the mix. And given the projected costs of responding to climate change, there is a significant incentive for scientists to provide evidence that the costs can be safely avoided.

It is interesting that just a few years ago, many skeptics were claiming that the global temperature data were fabricated. But now that they’ve recognized that there has been a “pause” in the reported global temperature rise, I’ve seen very little commentary from skeptics that questions the accuracy of the global temperature record. A good scientist would be concerned about accuracy whether or not the data were increasing, decreasing or remaining the same.

I think the discussion of global climate change has been unfortunately polarized, and I think Al Gore and his supporters contributed to that, but there have also seem to have been some significant contributions from Jim Inhofe and the skeptic community.

Greg McIsaac

Stephen Williams writes:

Dr. Weitzman often refers to the increasing amount of CO2 however he seems unaware that the relationship between CO2 levels and heat trapped is logarithmic. Here are a couple of references. I haven't made a search of science papers but many scientists have endorsed the relationship. If the relationship isn't linear then what we see is what would be expected with rising levels and flat temps. I know that the AGW crowd say that the theory predicts that a small rise in temp will lead to a large increase in water vapour (very potent greenhouse gas) and increasing temps. We don't see it. The theory isn't a theory just a rotten hypothesis.
http://clivebest.com/blog/?p=1169
http://wattsupwiththat.com/2010/03/08/the-logarithmic-effect-of-carbon-dioxide/

jw writes:

Just listened to the podcast, sorry I am late...

Weitzman took a one sided view of climate change, extrapolated out a CENTURY, then came to the conclusion that there was an exactly 3% chance of it being catastrophic.

If Weitzman did the same calculations a century ago, he would conclude that there was a 6.876% chance that by now we would all be up to our ears in horse dung (just to be clear, from carriages, wagons, etc).

When you do modeling properly, you look at the timescales involved, take representative in sample (IS) data, construct your model, then test it against out of sample (OOS) data.

The IPCC did that in 2000. It failed miserably.

Since then, they have "tweaked" their models (in modeling-speak, they curve fitted and increased their degrees of freedom, both extremely flawed techniques), and worst of all, "adjusted" older data to help make their case.

On a geological climate timeline, the last 150 years is a drop in the bucket. There is no way to determine if any warming that might be taking place is natural or AGW. In a century (or two), we MIGHT be able to say with some certainty that it is AGW.

In the meantime, to claim that a 3% chance of the worst case scenario happening is, sorry Dr. Weitzman, statistically insane. Considering the failure of the models so far, it may be 3 millionths of a percent, it may be zero, no one knows. I don't need to pay for insurance now for a 3 millionth (or less) probability now, especially via a tax.

A couple of short notes: The Arctic ice has been growing back to its normal size for the last few years, not shrinking.

And if seeding the atmosphere with SO2 is the answer, then why is Obama's EPA putting all of the coal companies out of business by onerous SO2 regulations? Their justification is that SO2 is THE major component of acid rain. Of course, the coal companies have already significantly reduced SO2 emissions, but the EPA wants zero.

They haven't gotten the message from Weitzman on SO2 or nuclear.

It is always good to hear opposing views and Russ asked some great questions (and received VERY poor answers), but I was concerned when he said that his needle was moved by the book. It shouldn't be, the evidence so far is that AGW is a (very, very expensive) hoax.

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