More than anything, Science relies on data. The most elegant theory is empty, if the data contradict it. The old saying is true: The Scientist proposes and Nature disposes.
This post outlines serious problems in the data behind the theory of Anthropogenic Global Warming (AGW). But before we start, let's take a short look at the climate history of the last millennium.
Has the climate changed over the last 1000 years?
Yes, and in a big way, several times. The following figure is a reconstruction of the global temperature over the last 1000 years:
The planet started warming around 800AD, and reached a maximum called the "Medieval Warm Period" (MWP) a couple centuries later. The MWP is understood to be as warm - or probably warmer - than it is today. Around 1300AD the temperature began to fall dramatically; in the space of just a couple generations all of the warming from the MWP was erased. This period is called the "Little Ice Age" (LIA), and it was absolutely catastrophic for the populations of the time. As examples, a population weakened by repeated crop failures was decimated by the Black Plague, and the Norse colony of Greenland starved to death.
The Little Ice Age continued into historical times. Not only do we have written records describing what are clearly much colder conditions, but we have thermometer readings from around 1650AD and later that confirm that temperatures have been increasing - at least up to 1940 or so. We'll come back to that later - there are disturbing questions about the thermometer record.
Reason #1 to be (scientifically) skeptical about AGW: The climate has changed several times over the last 1000 years, and things have been getting warmer for at least the last 150 years, probably longer.
If we've only had thermometers for 350 years, how do we know the temperature 1000 years ago?
Scientists use "proxies" - things that react to temperature, and which are measurable. Trees will tend to grow faster when it's warmer, and slower when it's colder, so examining the tree ring width will tell you that some years were probably warmer, and some were probably colder.
There are other proxies, notably ice cores drilled from glaciers, which also provide visible annual layers. Colder years will typically have more snow and less melting, and so the layer will be thicker; warmer years have less snow and more melting, and layers will tend to be thinner.
You have to be careful using proxy temperatures, though. People tend to forget that one of these things is not like the others:
Proxies are not thermometers. There are other things that effect tree ring width than temperature: drought, shade from older trees that are nearby, etc. There is a maximum biological limit to how much a tree can grow in any year, no matter how hot it is.
This means that joining ("splicing") historical temperature data from two or more different data sets - say, tree rings for 1000AD to 1750AD, and thermometer readings from 1750AD to the present - is tricky and error prone. Certainly the annual temperature variation will be different; other things like rate of change may very well be off as well.
Reason #2 to be (scientifically) skeptical about AGW: Any time you see a long-term climate record chart (like the one I used earlier), you should ask to yourself: "How many different data types did they use, and how accurately were the data sets spliced together?" We'll come back to this in a bit.
What About Al Gore's "Hockey Stick"? chart? It showed that warming was historically unusual, sudden, and very pronounced.
You don't hear much about the "Hockey Stick" in the press anymore, although it was all over the news back in 1999. The Intergovernmental Panel on Climate Change (IPCC) relied heavily on it, and the Kyoto Accords were based on its analysis. Countries signing the treaty agreed to cut their Carbon Dioxide output levels (unsurprisingly, none have). George W. Bush took a lot of heat (so to speak) from progressives when he (like Bill Clinton before him) refused to submit the treaty to the US Senate for ratification.
The Hockey Stick appeared prominently in Gore's film, An Inconvenient Truth in 2006, even though the Hockey Stick itself was the subject of a considerable scientific controversy, and was soon shown to be not just incorrect, but likely knowingly falsified. Two amateur researchers, Steve McIntyre and Ross McKitrick demonstrated conclusively that one of the data sets used by the stick's creator, Michael Mann, was inappropriate for showing temperature. Further, one of the data sets was labeled "Censored" (suggesting that Mann knew or should have known not to use them), and his computer model contained a bug that caused even random data input to produce a Hockey Stick shaped curve. The best introduction to this controversy is "Caspar and the Jesus Paper", although Orson Scott Card has an excellent - if pungent - introduction, too. You can find both of them here.
Reason #3 to be (scientifically) skeptical about AGW: The "Hockey Stick" is a big, big problem for people advocating for AGW, with its documented history of exaggeration. This is why you don't hear about it anymore.
OK, no Hockey Stick. What have temperatures really been doing? Is it getting warmer?
There's no doubt that it is warmer than it was in 1750. Direct temperature measurements show this, and the historical record provides supporting evidence. For example, the Continental Army dragged captured British cannons from Ft. Ticonderoga down the frozen Hudson River during the American War of Independence. Ice simply doesn't get thick enough today. Likewise, the story of Hans Brinker skating on the frozen canals of Holland suggests that it was a lot colder several hundred years ago.
But no Hockey Stick. Let's look at this, from a skeptical-but-scientific perspective. First, a Hockey Stick graph of historical temperature, from the IPCC:
Looks like a Hockey Stick, right? To analyze it scientifically, first look at the time scales - 1000 years or more. Obviously, this is not a representation of thermometer readings, so what data were used? In this case, it is a combination of tree rings and thermometers (the black line after around 1850 is the thermometer data). Remember the rule of different data sets:
How well did they splice the data together?
We don't know, but we should be (scientifically) skeptical:
I made the point that this offended my scientific training: When one gets an inflection point right at the place where two data sources are spliced, as is the case here, one should be suspicious that maybe the inflection is an artifact of mismatches in the data sources, and not representative of a natural phenomenon. And, in fact, when one removes the black line from measured temperatures and looks at only proxies, the hockey stick shape goes away:Stop and look at that for a minute. You can clearly see the Medieval Warm Period around 1000AD, you can see the Little Ice Age bottom out around 1700AD, and you can see that we're a little less warm now than we were in the MWP.
The data here are purely tree rings, so we're comparing the same thing. The moral is that sometimes when you try to turn an apple into an orange, you get a lemon. Notice that this does not say that things are not warming - in fact, it confirms the warming trend. What it suggests is that historically this is not unusual. Neither is it sudden, or a Hockey Stick. Remember, this data is all from the IPCC's own report.
Reason #4 to be (scientifically) skeptical about AGW: The data do not show sudden warming, except at the point where you join two different types of data together.
What about Carbon Dioxide?
We now need to shift from history to Chemistry. We've heard of the "Greenhouse Effect", where sunlight passes through the atmosphere to the ground, the energy is absorbed and re-emitted as heat, and the heat is trapped by the atmosphere. In more precise scientific terms, certain gases are transparent to visible light, but obaque (blocking) to heat (infrared) radiation.
Carbon Dioxide (CO2) is one of a set of greenhouse gases, including methane and water vapor. One justification for the Hockey Stick that proponents of AGW theory used was that the Industrial Revolution began to produce large amounts of CO2 around 1850, which is when we saw the spike in temperature. There are a couple problems with this:
1. Correlation does not imply causation. Just because something happens at the same time as something else, doesn't mean that it's caused by it. If we see a big increase in, say, the number of lemons imported from Mexico, and simultaneously see a big reduction in the number of traffic fatalities, we shouldn't jump to the conclusion that Mexican lemons reduce traffic deaths. This seems obvious, but is really at the heart of the proposed policy mitigations like Kyoto, Cap and Trade, and Copenhagen.
2. More importantly, CO2 is a very - even surprisingly - weak greenhouse gas.
What this means is that as you put more CO2 into the atmosphere, it has less and less of a greenhouse effect. This isn't really surprising, because this sort of "exponential decay curve" is the norm in nature - things tend to rapidly achieve equilibrium because this "negative feedback" keeps things from running away out of control. Chemistry (actually spectroscopy) tells us that CO2 is not really opaque to infrared except at a very narrow frequency band, and therefore "leaks" heat back into outer space at the edges of the bands.
Reason #5 to be (scientifically) skeptical about AGW: CO2 is a surprisingly poor greenhouse gas.
So why all the talk about CO2?
Proponents of AWG know this, and have proposed a theory of "Positive feedback", where CO2's greenhouse power is multiplied, or "forced", sort of like Popeye after he opens a can of spinach. This forcing is reached after a particular CO2 concentration, and causes a "runaway greenhouse effect". There is a fatal problem with this: we simply don't ever see this in nature.
The universe is stable because of negative feedback. The best (not to mention shortest) description of this is:
Name three positive feedback systems in nature. Get back to me on that when you're done.There is, of course, a theoretical justification for positive feedback from the AGW proponents - the details are complex, and I don't want to get into them. Instead, is there a way that we can test the theory? There is indeed. We have measurements of both temperature levels as well as CO2 concentrations for at least the 20th Century. How do they match?
Rather than lots of science and math and stuff, he looks at what the proponents of AGW say. And find a lot to be desired:Reason #6 to be (scientifically) skeptical about AGW: While positive feedback is theoretically possible, it does not seem to be happening, based on the evidence.5. The claimed “proof” of positive feedback is a model prediction of a hot spot in the tropics at mid troposphere levels. However all the experimental evidence from many, many measurements has failed to find any evidence of such a hot spot. In science, a clear prediction that is falsified experimentally means the underlying hypothesis on which the prediction is based is wrong....8. If I adopt this 10:1 ratio by looking at the last 100 years worth of data I find 1910-1940 temperatures rising while CO2 was not. 1940 to 1975 temperatures falling while CO2 rising, 1975 to 1998 temperatures rising while CO2 rising and 1998 to 2009 temperatures falling while CO2 rising. Three quarters of the period shows no correlation or negative correlation with CO2 and only one quarter shows positive correlation. I do not understand how one can claim a hypothesis proven when ¾ of the data set disagrees with it. To me it is the clearest proof that the hypothesis is wrong.
I thought there was a consensus that Global Warming is occurring? The "science is settled", isn't it?
Actually, there's never been a consensus. We'll come back to this later, but the most interesting thing about this argument is that it's not a scientific argument. Science simply doesn't care about consensus, it cares about data and reproduceability of results. If your data is solid, and other people can get the same results, it simply doesn't matter if you run with the crowd or not.
And if you've read this far, you know that the science very much is not settled, and where, and why. However, it's worse: the historical thermometer records appear to have been modified in a way that introduces significant warming where the original data shows none:
The Fed.Gov says that the lower 48 states have warmed on average by 0.6° between 1940 and 1999. Of that, 0.5° is from adjustments, not from raw data. In other words, 83% of the warming is from adjustments.Keep your eye on this, because there are a lot of people looking at the difference between "raw" temperature data and "adjusted" temperature, all over the world. We're seeing more places - for example, Norway - that have this divergence between recorded and reported temperature, with all the recent warming due to ill-defined "adjustments". The implication is immense:
A week ago, a group called the Climate Science Coalition of New Zealand made a bombshell announcement: all of New Zealand's reported 1°C warming between 1850 and 2000 was due to adjustments.
Like I said recently, almost every climate scientist uses data from one of a very small number of data sets. If the people who control the data sets can inject a warming signal, then you will indeed reach a consensus that the climate has been warming. All scientists using those data sets will find the warming signal. The science will, in a sense, be "settled".Reason #7 to be (scientifically) skeptical about AGW: The temperature readings in the major climate data sets have been modified in a way that guarantees a global warming output. Why and how has not yet been well explained.
It will be wrong, but it will be settled.
Well, shouldn't the Deniers explain what's going on, if they don't like AGW?
Actually, no. It's not their job - scientifically speaking - to explain what's causing the warming. It's the job of the AGW proponents to provide a coherent theory that is backed by observational results. So far, they have not.
At this point we've seen that the theory of AGW does not map well to the historical record, and that the scientific justifications for CO2 forcings are highly problematic. That's the state of the science. Everything else is something other than science.
But since we've left the realm of science, and entered the realm of politics, there is a lot to see that should give anyone a healthy case of skepticism:
There is evidence that the most important climate scientists have tried to subvert the peer-review process, used to vet papers submitted for publication in scientific journals. This includes getting "friendly" reviewers assigned for papers that support their theories, and hostile reviews for papers opposing them. There are credible charges that they worked to get the editor of at least one scientific journal fired because he published papers with opposing views.
There is evidence that these same climate scientists conspired to subvert lawful Freedom Of Information Act requests for the data and computer code used to produce their results. One of these scientists has been suspended from his job as head of a climate research organization, another is being investigated by his university. Add in the overheated rhetoric by scientists saying that people who "deny" AGW should be jailed, and you have something very unscientific, and very unsavory.
A (non-) scientific reason to be skeptical about AGW: Something stinks. It's going to get worse before it gets better, as people investigate just what's been going on. As more and more rocks get turned over, we'll see what else crawls out.
Skepticism? Science demands it in general. The science of AGW in particular demands a whole heapin' helping of it. Yes, you should be an AGW skeptic, if you want to be at all scientific.
UPDATE 2 December 2009 16:29: Welcome visitors from The Gormogons. I must say that the Czar of Muscovy is - as any good Autocrat should be - a mixture of absolutely gratifying combined with absolutely terrifying.
UPDATE 18 December 2009 18:23: I've updated this post and turned it into a slideshow.