Scientific Method and Anthropogenic Global Warming

Suppose we have ten sick people. Dr. Quack persuades them to take his Patent Medicine. Five of them die and five of them recover. Dr. Quack says, "My medicine saved five lives!" But Dr. Nay says, "Nonsense, your medicine killed five people." Both claims are 100% consistent with the facts, and yet they are contradictory. Consistency with the facts is a necessary quality for a scientific theory, but it is not sufficient. If we allow consistency with observation to be sufficient proof of a theory, we are practicing pseudoscience. The Food and Drug Administration (FDA) rejects both Dr. Quack and Dr. Nay's claims, saying the Patent Medicine has absolutely no effect upon the recovery of the patients until experiment has proved otherwise.

The FDA has adopted the null hypothesis. The null hypothesis is the foundation of scientific reasoning. We determine the null hypothesis with Occam's Razor, by which we cut off any unnecessary parts of our hypothesis until we arrive at the simplest possible explanation of our observations. And the simplest possible theory about the relationship between one thing and another is that there is no relationship at all. The only way to disprove the null hypothesis, according to scientific method, is with observations. Compelling arguments and sensible speculation are insufficient, nor is consensus among scientists, nor the authority of experts.

When it comes to the climate, our initial null hypothesis is that the climate does not vary at all from one year to the next, nor does its carbon dioxide concentration. We will have to disprove this with observations before we can begin to discuss how humans might cause climate change. So let us look at what observations are available to disprove this hypothesis. We observe valleys carved by glaciers in warm climates. We find fossils of tropical plants in cold places. We pull out ice cores and they suggest the Earth's temperature has varied dramatically in the past few hundred thousand years, along with its atmospheric carbon dioxide concentration (6-16°C and 200-300 ppm when measured with a 1000-year running average). These observations and many others disprove our null hypothesis. The climate does vary. It varies dramatically and naturally, whithout any human influence. This is our new null hypothesis. We call it the theory of natural variation.

We can use the infra-red absorption spectrum of carbon dioxide to argue that doubling the carbon dioxide in the atmosphere will warm the planet (by roughly 1.5°C if we ignore clouds, and 0.9°C if we account for clouds, according to our own simulations). Before we can hope to show that human carbon dioxide is affecting the climate, however, we must show that human carbon dioxide emissions affect the atmospheric carbon dioxide concentration, and on this subject our theory of natural variation states that human emissions have no effect. So we must disprove the theory of natural variation. Natural emission and absorption of carbon dioxide were already in equilibrium before man started burning fossil fuels. Our annual emissions are only 4% of the natural emissions (8 Pg/yr from burning fossil fules compared to 200 Pg/yr of natural emission). In the simplest chemical equilibriums, absorption is proportional to concentration, so our 4% increase in emission will, to the first approximation, cause atmospheric CO2 to increase by 4%, or 10 ppm. Such an increase is so slight that it's not clear how we could distinguish it from the larger natural variations.

Even if we could prove that the recent increase from 330-400 ppm atmospheric carbon dioxide was due to our burning of fossil fuels, we would still have to prove that increasing carbon dioxide concentration causes the world to warm up. We may have a compelling reason to suspect that is has this effect, but we cannot abandon the theory of natural variation until it has been disproved, and we need observations that contradict the theory to disprove it. We cannot disprove the theory with compelling arguments alone. Even if we accept that increasing carbon dioxide traps heat somewhere in the atmosphere, this does not neccessarily mean that the climate will, as a whole, warm up. It may seem obvious that lighting a fire in my fireplace will warm my house, but the reality is that my children's bedrooms get cold when I light a fire. That's because the thermostat is near the fireplace, so when I light the fire the radiators turn off. The climate is a complex system. It could be that it contains similar surprises, where we observe the opposite effect to the one we expected. In fact, looking at the ice cores, it appears that atmospheric carbon dioxide increases occurr one thousand years after increases in temperature, which could mean that carbon dioxide somehow stops the world from getting any warmer at the end of an ice age, by a process that we don't understand.

So far as we can tell, scientific method, when applied to our observations of the Earth's climate, arrives at the assumption that the climate varies dramatically and naturally, and that human carbon dioxide emissions have no effect upon it. We look forward to seeing this assumption disproved by observations of nature, but so far we have been disappointed.

Conclusion

The anthropogenic global warming (AGW) hypothesis presented by the majority of today's climatologists has two parts. First it claims that the world is getting exceptionally warm, and second it claims that human carbon dioxide (CO2) emissions are the cause of this warming. Seven years ago, we began our personal investigation of this hypothesis, and we did so by considering whether or not the world was indeed getting exceptionally warm.

The first thing we did was estimate the uncertainty inherent in the measurements of global surface temperature. We concluded that natural variations in local climate introduce an error of roughly 0.14°C in the measurement of the change in temperature between any two points in time. The fact that the error is constant with the time over which we measure the change is a consequence of the particular characteristics of local climate fluctuations.

We downloaded the weather station data from NCDC and calculated the global surface anomaly using a method we called integrated derivatives, but which others have called first differences. The graph we obtained was almost identical to the one obtained by CRU using their complex reference grid method. It remains a mystery to us why institutions like CRU, NASA, and NCDC use such a complex method when a far simpler one will do. All graphs show roughly a 0.6°C rise in global surface temperature from 1950 to 2000. This rise is significant compared to our expected resolution of 0.14°C.

We made this plot superimposing the number of weather stations and the global surface anomaly versus time. The number of weather stations drops dramatically from 1960 and 1990. Only one in four remain active at the end of this thirty-year period. During the same period, the global surface anomaly shows a 0.6°C rise. By selecting subsets of the weather stations, we found that the apparent warming from 1950 to 1990 varied from 0.3°C to 1.0°C depending upon whether we used stations that disappeared in that period, persisted through that period, or existed shorter or longer intervals in the same century. Thus is seemed to us that some significant amount of work would have to be done to eliminate the change in the number of weather stations as a source of error in the data. But we saw no mention whatsoever of this source of error in published papers in which the global surface anomaly is presented, such as Jones et al..

We plotted a global map of the available weather stations, color-coded to show the date they first started reporting. The map shows that almost all stations in the tropics began operating after 1930, while most of those in the temperate regions were operating by 1880. This seems to us to be another source of systematic error in our measurement of the global surface anomaly.

Weather stations might also be affected by the appearance of buildings, tarmac, and road traffic. We found examples of weather stations in which such urban heating caused an apparent warming of several degrees centigrade over a few decades. It seemed to us that this effect would have to be examined in depth by any paper presenting a global surface trend. But papers such as Jones et al. do not address the urban heating issue directly. Instead, they claim that the effect is negligible and refer to other papers as proof. But when we looked up those other papers, we did not find any such proof.

In order to argue that modern temperatures were exceptionally warm, climatologists produced the hockey stick graph, in which a collection of potential long-term measurements of global surface temperature were combined together under the assumption that they could be trusted only to the extent that they showed a temperatures increase from 1950 to 2000. Indeed, if a measurement showed a temperature decline in that period, the hockey stick method would flip the trend over and add it to the combination so that it now contributed to a rise in the same period.

The hockey-stick graph shows no sign of the Medieval Warm Period, in which Greenland was inhabited by farmers, nor the Little Ice Age, when the Thames was known to freeze over, and nor should we expect it to. Given a random set of measurements, the hockey-stick combination method will almost always produce a graph that shows a sharp rise from 1950 to 2000 and a gentle descent during the thousand years before-hand. When applied to the existing measurements of temperature by tree rings, ice cores, and other such indirect methods, it is no surprise that the method produced that same shape.

We presented our doubts about the surface temperature measurements and the hockey stick graph to believers in the AGW hypothesis. We were received with disdain and given no satisfactory answers. Furthermore, the Climategate affair revealed several significant breaches of scientific method by the climate science community. For example, in this graph produced by climatologists for the World Health Organization, the authors removed the tree ring temperature data from 1960 onwards because it showed a decline in temperature, and substituted temperature station measurements in their place. They plotted the combination as a single line. When I asked a prominent climatologists what exactly had been done, he said, "The smooth was calculated using instrumental data past 1960." He declared that a better way to handle the divergence of the tree-ring data from the station measurements would be to cut short the graph of tree-ring data at 1960, so as to hide the decline in temperatures measured by the tree rings.

What we see here is the assumption by climatologists that the world has been warming up and that the global temperature measured by weather stations is correct. This assumption leads them to delete conflicting data on the grounds that it must be bad data. Thus it becomes impossible for them to discover that their assumption is incorrect. By this time, we were skeptical of the global surface anomaly we obtained from the station data. We were no longer certain that the data itself had not been modified by NCDC. We had little reason to trust any other measurement produced by climatologists, we were unimpressed with the hockey-stick method of combining measurements, and we were quite certain that recent temperatures were not exceptional for the past ten thousand years.

We turned our attention to the second part of the AGW hypothesis: the one that says doubling the atmosphere's CO2 concentration will increase the surface temperature by roughly 3°C. It took us a long time to come to a conclusion on this one. The climate models upon which such predictions are based are private property of various climatologists. In any event, we do not trust models produced by a community that is willing to delete data that conflict with its assumptions. If they are willing to delete data, we must assume that they are willing to adjust their models until the models give predictions consistent with their AGW hypothesis.

We began with some laboratory experiments on radiation. We stated the principle of the greenhouse effect. After a great deal of searching around, we eventually obtained the absorption spectrum of various layers of the Earth's atmosphere. This allowed us to confirm that, if the skies remained clear, a doubling of CO2 concentration would cause the world to warm up by about 1.5°C.

But of course the skies don't remain clear. The formation of clouds is a strong function of surface temperature. If the world warms up, there will be more clouds. They will reflect more of the Sun's light, while at the same time, slowing down the radiation of heat into space by the Earth. To determine how these two effects would interact, we built our own climate model, which we called Circulating Cells.

When it comes to determining the effect of increased cloud cover, the most critical parameter to decide upon is the reflection of sunlight by clouds per millimeter of water depth in the cloud. It seemed to us that there should be a large body of literature written recently upon this subject because it is so important to climate modeling. The best paper we found upon the subject was written in 1948, Reflection, Absorption, and Transmission of Insolation by Stratus Cloud. We found a couple of more recent papers about reflection, such as this one, but they do not attempt to provide an empirical formula for the reflection of clouds with increasing cloud depth. We concluded that climatologists are not examining this issue in detail.

In a long sequence of small steps, we built up our climate model until it implemented surface convection, surface heat capacity, evaporation, cloud formation, precipitation, and radiation by clouds. We tested every aspect of the simulation in detail, and based its operating parameters upon our own estimates and upon whatever measurements we could find in climate science journals. We did not choose our model parameters to suit any hypothesis of our own, nor could we have done, because we did not have a model capable of testing the AGW hypothesis until the final stage, and we did not change the parameters in that final stage.

The latest version of our climate model shows that cloud cover increases rapidly as the surface warms above the freezing point of water. The evaporation rate of water from the surface increases approximately as the square of the temperature above freezing, and the only way for water to return to the surface is to form a cloud first. If we ignore the increased reflection of sunlight due to increasing cloud cover, and consider only the slowing-down of radiation into space by the same increase in cloud cover, our model shows roughly 3°C of warming due to a doubling in CO2 concentration. But when we take account of the increased reflection of sunlight by the increasing cloud cover, the warming drops to 0.9°C.

It seems to us that the climate models used by climatologists ignore the reflection of sunlight due to clouds. They may allow for some fixed fraction of sunlight to be reflected by clouds, but they do not allow this fraction to increase with increasing surface temperature. Thus they conclude that the warming due to CO2 doubling will be 3°C. If they took account of the increased reflection, the effect would be far smaller and less dramatic: roughly 1°C.

Doubling the CO2 concentration of the atmosphere will indeed encourage the world to warm up, but not by enough that we should worry. Right now CO2 concentration has increased from roughly 300 ppm to 400 ppm in the past century. If it gets to 600 ppm then we can say that the rise in CO2 concentration will tend to warm the Earth by 1°C. But we are unlikely to be able to check our calculations, because the natural variation in the Earth's climate is itself of order ±1°C from one century to the next.

And so we find ourselves at the end of our journey. Modern warming is not exceptional, and doubling the CO2 concentration will cause the world to warm up by roughly 1°C, not 3°C. The only part of the AGW theory we have not investigated is its assertion that human CO2 emissions are responsible for the increase in atmospheric CO2 concentration over the past century.

My thanks to those of you who took part in the effort, both by private e-mails and in the comments. I would not have continued the effort without your participation. I hope it is clear that my use of "we" instead of "I" is in recognition of the fact that this has been a group effort. I will continue to answer comments on this site, and I will consider any suggestions of further work. To the first approximation, however: we're done.

This Time It's Different

In The Right and the Climate, an opinion piece for the New York Times, Ross Douthat discusses the abandonment of cap-and-trade legislation by the US senate. He argues that Democrats must share the blame for the failure of cap-and-trade because they have exhausted the population's patience for doomsday stories. "The Seventies were a great decade for apocalyptic enthusiasms, and none was more potent than the fear that human population growth had outstripped the earth’s carrying capacity," he says. "The catastrophes never materialized, and global living standards soared." But the global warming doomsday story is different, Douthat says, because, "History, however, rarely repeats itself exactly — and conservatives who treat global warming as just another scare story are almost certainly mistaken."

People like Paul Ehrlich, who predicted global famine, and Rachel Carson, who claimed that DDT was killing humans, both believed in what they were saying. It turns out that they were wrong in their most famous claims, but they were doing their best to understand the dangers presented by lower infant mortality and widespread use of new chemicals. They believed in their cause and they believed in what they told us.

When Douthat says, "the evidence that carbon emissions are altering the planet’s ecology is too convincing to ignore," he seems to think that the evidence for global famine and chemical poisoning were unconvincing at the time that Ehrlich and Carson made their claims. But that's not the case. The evidence was convincing. A lot of people were convinced, including the US government under John Kennedy. But "convincing" is not the same as "correct". It turns out that their arguments were convincing but not correct.

Douthat is an example of the many well-educated people who have chosen to believe in anthropogenic global warming despite the history of environmental scare-mongering. The internet bubble was caused by people saying "this time it's different: revenue counts, not profit." The housing bubble was caused by people saying, "this time it's different: prices will never go down." The anthropomorphic global warming bubble has been caused by people saying, "this time it's different: the evidence is too compelling."

Here's my prediction: this time it's not different.

Intelligent Design and AGW

Intelligent Design and Creationism both propose the existence of a super-natural power, and so cannot be considered scientific theories. This was the finding of Federal Judge John E. Jones, and requires no assumption about the truth or falsehood of either theory. You can read his ruling here. He says, intelligent design "is a religious view, a mere re-labeling of creationism, and not a scientific theory".

Anthropogenic Global Warming makes no claim about super-natural power. Nevertheless, the theory has no empirical basis. Nobody has performed experiments upon the climate to show that increasing C02 concentration causes a rise in temperature and decreasing CO2 causes a drop in temperature. All we have are climate histories of dubious accuracy.

The fact that we have not tested the AGW theory with repeated experiments on the climate means the theory has no empirical basis. It does not matter whether AGW is true or not. It does not matter how many climatologists believe in AGW.

Climatologists protest that they cannot perform experiments upon the climate. They are quite right. They say that they will be unable to make predictions if they are required to perform such experiments. Yes, that is indeed the case. So they say they are entitled to make predictions without experiments. Well, they can do what they like.

For every ten convincing and superb theories I come up with in my lab, only one turns out to be true. That's because I subject my ideas to the test of experiments. Maybe I'm incompetent too, but at least my incompetence is held in check by experimental tests. Climatologists don't have to bother with experiments. They can believe whatever they like. Consensus and Peer-Review are their basis for their theories.

UPDATE: I posted the above statement, or close to it, at The Lippard Blog.