Monday, April 08, 2013

Global Warming: Implications of the Current Data

There has been a good deal of talk lately, much of it set off by a recent article in the Economist, about the fact that global temperatures have now been nearly constant for over a decade despite large increases in atmospheric CO2. Looking at the situation as a non-expert observer, it seems to me there are three possible explanations both for the recent pause and for the earlier pause from about 1940 to 1970. 

1. The theory is wrong. Warming over the past century+ is due to something other than the greenhouse effect of CO2 produced by human action.

This is possible but does not strike me as very likely.

2. The theory and models are right. Anthropogenic CO2 produces warming at about the rate implied by the IPCC models. There are, however, other factors that also affect global temperature. Recent periods of stable or falling temperature occurred because those other factors were pushing temperature down about as fast as the greenhouse effect was pushing it up.

3. The theory is right but the models are wrong—they substantially overestimate the sensitivity of temperature to CO2.

This is, I think, a more plausible variant of the previous explanation because of two of the latter's implications. The first is that the other factors are about as important, at least in the short run, as CO2, since otherwise they could not have cancelled its effect. The second is that the other factors were not adequately included in the IPCC models, since if they had been those models would not have seriously over predicted global temperatures, and they did.

As best I understand the relevant theory, sensitivity is an open question—we do not have climate models good enough to calculate it with confidence, so rely instead on deducing it from statistical data. But if global temperature depends on both CO2 and other things and the models left out or underestimated those other things, then calculations when the non-CO2 effect was pushing temperature up instead of down would tend to overestimate the CO2 effect. That seems to me consistent with the fact that temperature change over the past century is significantly positive, but at a rate much lower than what the IPCC models imply for the rest of this century. And, of course, it would explain why global temperatures for the past decade are lower than would be expected from the IPCC models and the increase in atmospheric CO2.


Robbo said...

Three more possibilities:

1. We do not have an exhaustive and correct cause-and-effect model of the climate. Therefore our models cannot map the behaviour of the actual climate because the cause-and -effect in the models is not the same as the cause-and -effect in the climate

2. Climate is weather writ large. Weather has the characteristics of a chaos system; it is intrinsically unpredictable in that the differences between prediction and subsequent measurement grow exponentially over time. No model can accurately predictnits behaviour over an extended period of time.

3. There is a warming effect from CO2 but there is at least one part of the climate system which has put an upper bound on temperatures fqor at least tens of millions of years.

David Friedman said...

With regard to 3, I am guessing that your point is that we have just hit that upper bound, and warming has then stopped.

If that is your point, it doesn't explain the period of over two decades in the 20th century when temperatures were not rising. My explanations 2 and 3 do.

Tibor said...

Uhm, David, you seem to study the topic (at least from the economist's perspective) quite extensively. What would you suggest are the other major factors that might have an effect on the temperature? I know it is a question from climatology and not economics, but I don't know any climatologists I could ask...also this is a question for anyone else with suggestions and reasonable arguments to back them up. I personally have very little idea about how the climate works, so I cannot even make an educated guess on this one.

Other than that your 2 and 3 seem to be quite reasonable. I would rather go with 2 actually, because I think those statistics cover a century or so now and it might be so that all the factors that were uncontrolled in the observation average out over such a long period leaving us with quite a good estimate on the CO2 effect without knowing all the others. Of course this requires quite strong assumptions on the other uknown effects (basically no trends, fast mixing and zero mean value of their sum ), so 3 is also quite possible. It is hard to judge merits of assumptions on something unknown.

Joey said...


I'm sure some other commenters may be able to elaborate, but one of the most significant unknowns is the effect on cloud formation. Different types of clouds reflect, absorb, and are transparent to different light wavelengths in different proportions, so the net result on surface temperatures is hard to predict.

David (not Friedman) said...

For one possible mechanism, read The Chilling Stars by Svensmark and Calder. The key suggestion is that cloud formation is affected by cosmic rays. When the solar cycle is active, magnetic activity shields us from some of these cosmic rays, so we have fewer clouds, more sunshine, and warmer weather. When the solar cycle is quiescent, more cosmic rays get through, so more clouds, so less sun, so cooler.

It sounds pretty science-fictiony, but the book is cleanly and calmly argued, and I found it quite persuasive. As I recall (it having been a while since I read it) the authors suffer slightly from the "everything looks like a nail" syndrome, but even if CO2 is relevant this effect could modulate it. And I notice that the last solar cycle (starting in 1996) was comparatively quiet.

David Friedman said...

One obvious candidate is insolation--I gather the sun varies somewhat in how much light it puts out.

I think Joseph is describing one of the reasons why climate sensitivity is uncertain, but I don't see how the effect of increased temperature, or increased CO2, on cloud formation would explain why global temperatures were rising and then stopped.

I suppose it's possible that you get negative feedback only above some level of global temperature--but again, there's the puzzle of the earlier pause.

Anonymous said...

I am not an expert, but it is my understanding that the models predict the long-run impacts of increased carbon on temps, not the short run. There is no reason for temps and carbon to move in lock step. Temps can follow carbon with a lag, just as rising prices can follow increases in the money supply with a lag. The current pause is such a lag.

One possible explanation for the lag is the distribution of melted polar ice, particularly from the arctic cap and the Greenland glaciers, which has been dramatic in the past ten years. This has kept ocean temps from rising which has moderated the world average temp.

Joey said...

I was answering what I might have misunderstood to be a general question about the major unknowns.

But to speculate wildly about the temperature plateaus:
There could be multiple different cloud-related negative feedbacks that kick in at different temperatures. Brief periods during which the system seems to have a lot of inertia as cloud composition shifts to a different set point. Of course, there's no reason why it may not be due to things other than clouds. Solar cycles seem like a good possibility.

I just hope this temperature plateau lasts for a few more years so the alarmism can fizzle out. Long-term, I think we'd benefit from a little more GW.

VangelV said...

The theory is wrong David. The primary driver of temperature trends over the periods we are looking at is solar activity. The data shows that CO2 concentration follows changes in the temperature trend, not the other way around.

Eric Rasmusen said...

I could be wrong, but I thought nobody was claiming that the pre-1940 warming was due to carbon dioxide because the quantities emitted were too small by comparison with emissions later. Am I?

A specific math problem with the models, I think, is that they assume positive feedback effects of CO2 emissions instead of zero or negative. That's similar to a commentor's suggestion that there's an upper limit to the CO2 effect. Changes in cloud cover could be the negative-feedback mechanism.

Anonymous said...

I believe the sensitivity estimates come mainly from model output, not historical statistics: the direct effect of CO2 (which is very well understood) is plugged into the models as an increase in radiative forcing, and then the model dynamics try to simulate the various feedbacks to give us an estimate of the total sensitivity. Whether they're good enough to let us have confidence in the answer is pretty much the main point at issue.

David Friedman said...

Eric and Paul:

I think the sensitivity estimates come from models fitted to data. That was part of my point. If the data was from a time when some other factor was pushing up temperatures, that would tend to bias the sensitivity estimates upwards.

I had thought the claim was that all of the temperature increase of the past century+ reflected increased CO2 concentration--at least, all of the "hockey-stick" talk uses graphs showing the increase starting well before 1940. The fact that CO2 concentration was rising more slowly in the early part of the period presumably would explain why projected temperature increase for the next century is substantially larger than observed increase for the past century.

VangelV said...

I think the sensitivity estimates come from models fitted to data. That was part of my point. If the data was from a time when some other factor was pushing up temperatures, that would tend to bias the sensitivity estimates upwards.

We already know of other factors David. It is very clear that we can link temperatures to solar activity (and CRF) over decadal, century, and millennial time frames. The IPCC ignored the published literature because the explanation destroyed its narrative and made human emissions of CO2 irrelevant.

Anonymous said...

Though I know of at least one attempt to estimate CO2 sensitivity from paleoclimate data (it came back with rather a "denialist" value, as I recall), most of the temperature reconstructions that bear on the climate-change question appear to be addressing the mostly separate issue of looking for a human fingerprint in the past century or so-- for which you need a good estimate of natural variability. What made the "hockey stick" famous was not really anything it told us about the recent warming, but its suppression of the Medieval Warm Period. Proving a significant anthropogenic role is easier if you have a lowball estimate of natural variability to work from.

Tibor said...

VangelV: Any links to data, models, research papers...?

VangelV said...

VangelV: Any links to data, models, research papers...?

There are hundreds of papers on this issue. A good place to start is a short book The Chilling Stars: A Cosmic View of Climate Change, by Calder and Svensmark. It does a wonderful explanation of explaining how changes in cosmic ray flux in the lower atmosphere affect cloud cover and how that impacts temperature trends. The idea is simple. If you have more clouds in the lower atmosphere you will have more of the sun's energy reflected out to space and have colder temperatures. During periods of lower solar activity more clouds are formed because cosmic rays in the lower atmosphere create cloud condensation nuclei. (The level of solar activity impacts the cosmic ray flux and that in turn regulates cloud cover and drives the temperature trends.)

Celestial driver of Phanerozoic climate?

Variation of cosmic ray flux and global cloud coverage-a missing link in solar-climate relationships

Cosmic ray decreases affect atmospheric aerosols and clouds

The spiral structure of the Milky Way, cosmic rays, and ice age epochs on Earth

Influence of Cosmic Rays on Earth's Climate

Cosmic Ray Diffusion from the Galactic Spiral Arms, Iron Meteorites, and a Possible Climatic Connection

Towards a Solution to the Early Faint Sun Paradox: A Lower Cosmic Ray Flux from a Stronger Solar Wind

The bottom line is that there has been plenty of very good work that uses radioactive isotopes to show that there is a very strong correlation between CRF and temperatures. Periods of low solar activity have given us periods like the Little Ice Age and other cooling cycles while periods of high solar activity have led to periods of higher temperatures. The theory even predicted equatorial glaciation during a period that was thought to have been very warm. When scientists looked harder they found ice rafting evidence that the theory had predicted but was previously unknown. The CERN experiments have shown that it is possible to significantly increase the number of cloud condensation nuclei as cosmic ray flux increases. The ongoing experiments should yield more empirical data some time in the next few years.

I hope that I used the HTML codes properly and the links work. If not I will try to repost them again. But please note that there is a great deal more information about the issue and quite a few papers written in a number of languages. The interesting part for me is the work of the Russians. They are predicting that the next few solar cycles will be very weak and that we will slip into another period similar to the Little Ice Age as the current cycles weakens. Solar activity was the greatest it had been for nearly 1000 years during the latter part of the 1900s. It looks like that will all change in the next few decades and that cooling will be our worry before long. All we need are a few early frosts and we could see a massive increase in food prices as yields fall as cooler and dryer weather hits the Midwest and the Canadian Prairies.

Tibor said...

VangelV: Thanks, that's much better than just stating conclusions. Well, I think in the 1970s the mainstream was "global cooling is coming" too, was it not?

Also what causes the differences in solar activity? Of course nothing on earth could, but it would be interesting to know. The naive model of the sun in my head is a perfect ball of burning gas, that is homogenous in each layer...and in that case I don't see why the solar activity can be volatile like that. But my "model" is almost certainly wrong.

Daublin said...

While I don't think the core theory is the biggest issue, note that your observation mean the theory as summarized by the IPCC is missing something important. None of those theories, to my knowledge, had a reason to predict 10-year flat periods except at very low probability.

You can't pin this on the "models" alone. There is a causal factor in the core theory that is missing.

Keep in mind that there is a previous question about why warming did not ramp up already, if CO2 feedback is positive and large. The previous answer was aerosols.

David Friedman said...


My impression that at one point some people were predicting cooling, but I don't think it was ever a generally accepted view in the sense in which warming currently is.

VangelV said...

Also what causes the differences in solar activity? Of course nothing on earth could, but it would be interesting to know. The naive model of the sun in my head is a perfect ball of burning gas, that is homogenous in each layer...and in that case I don't see why the solar activity can be volatile like that. But my "model" is almost certainly wrong.

I do not think that my model will be any better but let me give you a brief overview of what I think is important.

First of all, you have to keep in mind that the cosmic ray flux is not constant. As the solar system moves around the galactic core it sometimes passes through the galactic arms, which are denser and have a higher concentration of cosmic rays. In the past whenever the earth has gone through the arms it experienced glaciation that had ice sheets intrude into equatorial regions. These are the or Snowball Earth periods that you hear of now and then. In the past we had such cooling and glaciation even when CO2 levels were ten time higher the current level. No matter how active the sun if we go through a region that has high cosmic ray density (that can happen from a supernova as well) we could experience cooling.

The other factor is the solar system itself. As you know the sun rotates around the centre of mass (barycenter) of the solar system, and that centre moves around depending on the positions of the planets. I would imagine that the position of the barycenter would have some impact on the reactions that take place within the sun and that would show up as a number of cycles that are superimposed on one another. I really recommend that you look at the book, The Chilling Stars. Even if you are not a science type the writing is very clear and the way that the theory can link all kinds of disciplines is fascinating. It is science the way it used to be; find a theory to unify what is observed in several fields and have a way to devise empirical tests to see if it makes sense. I could not sleep until I went through the entire book and have used some of the insights to sift through much of the information deluge that has appeared in the field.

VangelV said...


You can't pin this on the "models" alone. There is a causal factor in the core theory that is missing.

The theory is wrong.

First, the ice core data shows that the concentration of CO2 follows changes in the temperature trend. That makes CO2 concentration the effect, not the cause.

Second, the temperature trend slope is not at all unusual. Even Phil Jones admitted that the two trends prior to CO2 emissions becoming material 1860-1880 and 1910-1940 were not very different from the current trend, which began in the late 1975 and ended in 1998. The IPCC claimed that the first two trends had nothing to do with human CO2 emissions. Since they were around the same as the trend that ended in 1998 there is nothing to suggest that the same factors that created the previous trends are not in play now. Then there are the Holocene Optimum, the Roman Warming, and the Medieval Warm Period. All were as warm or warmer than today.

But it gets worse for the alarmists. The previous warm periods were times of prosperity for most of the world as agricultural yields and lifespans increased and civilizations flourished. The world was much greener and much healthier. Most of the problems were caused by cooling, not warming. And they still are.

VangelV said...

My impression that at one point some people were predicting cooling, but I don't think it was ever a generally accepted view in the sense in which warming currently is.

Sorry David but that is not true. There were books on the subject of the next ice age coming and the media was writing stories advising governments to do something to stop the cooling. People like John Holdren and Paul Ehrlich were warning of a coming ice age. In a book that they edited they wrote:

...This is the reduced transparency of the atmosphere to incoming light as a result of urban air pollution (smoke, aerosols), agricultural air pollution (dust), and volcanic ash. This screening phenomenon is said to be responsible for the present world cooling trend—a total of about .2°C in the world mean surface temperature over the past quarter century. This number seems small until it is realized that a decrease of only 4°C would probably be sufficient to start another ice age. Moreover, other effects besides simple screening by air pollution threaten to move us in the same direction. In particular, a mere one percent increase in low cloud cover would decrease the surface temperature by .8°C. We may be in the process of providing just such a cloud increase, and more, by adding man-made condensation nuclei to the atmosphere in the form of jet exhausts and other suitable pollutants. A final push in the cooling direction comes from man-made changes in the direct reflectivity of the earth’s surface (albedo) through urbanization, deforestation, and the enlargement of deserts.

The effects of a new ice age on agriculture and the supportability of large human populations scarcely need elaboration here. Even more dramatic results are possible, however; for instance, a sudden outward slumping in the Antarctic ice cap, induced by added weight, could generate a tidal wave of proportions unprecedented in recorded history.

These are not exactly nobodies. One of them is working for Obama as a scientist activist and pushing the global warming story at this time. The other is doing what he always did well; make money from scaring people by telling them a bunch of nonsense.

VangelV said...


My impression that at one point some people were predicting cooling, but I don't think it was ever a generally accepted view in the sense in which warming currently is.

And these guys were not alone. Even the CIA got into the act and wrote papers about the danger of third world governments collapsing because of cooling related crop failures. And let us not forget Newsweek and its article on the subject. In the article the writer brings up reports from the NOAA and NAS and quotes a number of known scientists. He writes:

To scientists, these seemingly disparate incidents represent the advance signs of fundamental changes in the world’s weather. The central fact is that after three quarters of a century of extraordinarily mild conditions, the earth’s climate seems to be cooling down. Meteorologists disagree about the cause and extent of the cooling trend, as well as over its specific impact on local weather conditions. But they are almost unanimous in the view that the trend will reduce agricultural productivity for the rest of the century. If the climatic change is as profound as some of the pessimists fear, the resulting famines could be catastrophic. “A major climatic change would force economic and social adjustments on a worldwide scale,” warns a recent report by the National Academy of Sciences, “because the global patterns of food production and population that have evolved are implicitly dependent on the climate of the present century.”

A survey completed last year by Dr. Murray Mitchell of the National Oceanic and Atmospheric Administration reveals a drop of half a degree in average ground temperatures in the Northern Hemisphere between 1945 and 1968. According to George Kukla of Columbia University, satellite photos indicated a sudden, large increase in Northern Hemisphere snow cover in the winter of 1971-72. And a study released last month by two NOAA scientists notes that the amount of sunshine reaching the ground in the continental U.S. diminished by 1.3% between 1964 and 1972.

To the layman, the relatively small changes in temperature and sunshine can be highly misleading. Reid Bryson of the University of Wisconsin points out that the Earth’s average temperature during the great Ice Ages was only about seven degrees lower than during its warmest eras – and that the present decline has taken the planet about a sixth of the way toward the Ice Age average. Others regard the cooling as a reversion to the “little ice age” conditions that brought bitter winters to much of Europe and northern America between 1600 and 1900 – years when the Thames used to freeze so solidly that Londoners roasted oxen on the ice and when iceboats sailed the Hudson River almost as far south as New York City.

Just what causes the onset of major and minor ice ages remains a mystery. “Our knowledge of the mechanisms of climatic change is at least as fragmentary as our data,” concedes the National Academy of Sciences report. “Not only are the basic scientific questions largely unanswered, but in many cases we do not yet know enough to pose the key questions.”

I have provided other links below that show that there were many people pushing cooling just as there are many pushing warming. You are confused by the deniers who want to rewrite history because it spoils their current story.,9171,944914,00.html

Anonymous said...

Lichanos said...

From a scientific point of view, using the word 'theory' in the context of discussing anthropogenic global warming (AGW) is not quite right. People use the word 'theory' too loosely.

We can speak of the hypothesis of AGW - there is no theory to speak of. Too many loose ends, too much modeling, too little data, too much controversy.

So, as for your three possibilities, I would simply say:

4 - There is no theory of AGW. There is an hypothesis that has some supporting data, i.e. data that is consistent with the hypothesis, but that's all.

VangelV said...

The data falsifies the hypothesis. That is the problem for the AGW crowd, which is why we have gotten a lot of hand waving, false claims of consensus, and personal attacks instead of rational debate.