Guest post by Hans Custers. Nederlandse versie hier.
A very, ehhrmm… interesting piece on
Variable Variability, Victor Venema’s blog: Interesting what the interesting Judith Curry finds interesting. And I don’t mean interesting in a rhetoric, suggestive way; I mean it is a well-written and well-reasoned article, worth reading.
Victor writes about the meme regularly used by the anti climate science campaign, often supported by some straw man arguments, that the science of human impacts on climate would not be falsifiable. He shows it’s nonsense, by giving some examples of how it could be falsified. Or, more likely, already would have been falsified, if the science would be wrong. Victor’s post inspired me to think of more options to falsify generally accepted viewpoints in climate science. If there are any ‘climate change skeptics’ who want to contribute to real science, they might see this as a challenge. Maybe they can come up with a research proposal, based on one of the options for falsification. Like proper scientists would do.
First, a few more things about falsifiability in general. Bart wrote a concise post about the subject four years ago, explaining that a bird in the sky does not disprove gravity. What looks like a refutation at first, might on second thoughts be based on partial or total misunderstanding of the hypothesis. Natural climate forcings and variations do not exclude human impacts. Therefore, the existence of these natural factors in itself, cannot falsify anthropogenic climate change. A real skeptic is cautious about both scientific evidence and refutations. ‘Climate change skeptics’ like to mention the single black swan, that disproves the hypothesis that all swans are white. Of course that is true, unless that single black swan appears to be found near some oil spill.
Some of the falsifications that I mention later on might be somewhat cheap, or far-fetched. It is not very easy to find options to falsify the science of human impacts on climate. Not because climate scientists don’t respect philosophical principles of science, but simply because there’s such a huge amount of evidence. There are not a lot of findings that would disprove all the evidence at once. A scientific revolution of this magnitude only happens very rarely. Whoever thinks differently, doesn’t understand how science works.
Even more, the claim ‘The AGW hypothesis is unfalsifiable’ demonstrates a lack of understanding of Popper’s ideas, in which falsifiability is so important. I don’t think Popper’s philosophy implies that some three word hypothesis – Anthropogenic Global Warming – can be rejected by nothing but a few simple claims. Popper would expect a more serious intellectual effort from a scientist. First, he will have to find an accurate wording for his hypothesis. The next step is some thorough thinking about the consequences. This will help him to design tests that can either support or falsify his idea. If, in the end, the result of the test appears to be worthwhile, the scientist will write a paper on this whole enterprise.
As a matter of fact, the ‘AGW-hypothesis’ is not a hypothesis in the Popperian sense. The human impact on climate is a theory, supported by many hypotheses, each of them tested according to widely accepted scientific standards. Just as Popper and his successors in the philosophy of science would have wanted.
One more thing. The philosophical principle of falsifiability and the feasibility of tests for it are two different subjects. Scientists are still busy testing some of the implications of Einsteins ideas, because the technology did not exist in Einstein’s days. And it is highly unlikely that the scientists that proposed the Higgs boson ever even dreamed of the Large Hadron Collider, because it was beyond anyone’s imagination at the time. Philosophy of science does not set a time frame for hypotheses testing. The issues involved in the testing of hypotheses are the story of almost every scientist’s life. They’re not sitting back, thinking of new and brilliant ideas, most of the time. Instead, they are busy digging for data, messing with measuring equipment, or evaluating errors in experiments. For climate scientists, one of the major issues is the pace at which they can get new information: one year of data every year. And one year of data is not a lot for climate research. There are no test tube planets for climate experiments. They will have to do with what is left: observations of (changes in) the climate in the present and the past and simulations of the relevant processes in the climate system in computer models. Most self-proclaimed skeptics seem to have objections to the latter as well. Wouldn’t it be nice if they, just for a change, would say how it should be done?
That’s it for falsifiability in general. Here are the 10 way to disprove the human impact on climate.
1. A drop in global temperatures for some period of time to the level of 50 years ago or longer, without a clear cause
The average global temperature is almost 1 °C higher now than it was in the early 20th century. The widget by Skeptical Science (which unfortunately does not work very well in a WordPress blog) adds some perspective to the amount of energy accumulating in the climate system. These huge amounts of energy do not simply stay in the climate system without a cause. It is what we expect to happen, based on the greenhouse theory. And there’s no other explanation that is supported by a reasonable amount of evidence. It would be very clear that science overlooked something important, if all the energy would suddenly escape without something extraordinary happening (like a huge volcanic eruption), or hide in some unknown place.
2. A drop in global sea level for some period of time
There are two major causes for sea level rise: thermal expansion of seawater and the melting of land ice. Water extraction from and (temporal) accumulation on land play a minor role. At this moment, thermal expansion is the main factor. This is evidence for warming of the oceans, which is important because the oceans can store much more heat than the atmosphere. Thus, the ocean level falling, would not only be evidence for cooling of the oceans; it would be strong evidence that the climate system as a whole would be losing energy. (Note: pure water has a strange property: the density decreases with an increase in temperature between 0 and 4 °C. This effect disappears with increasing salinity. For almost all sea water, the maximum density is at freezing point).
Changes in sea level on a short term are not caused by thermal expansion or contraction, so they do not falsify anthropogenic climate change. The figure below, from the University of Colorado’s Sea Level Research Group, for instance, shows a substantial seasonal variation. This variation can be filtered out of that data, and that’s the graph that is usually shown.
Since the late 50′s, the Keeling Curve shows an ongoing rise in the amount of CO2 in the atmosphere. If there would be a sudden huge change in the CO2 level, without a clear, demonstrable cause, that would be proof that our knowledge of the carbon cycle falls short.
Climate change skeptics sometimes refer to a graph by Ernst-Georg Beck, in which thousands of megatons of CO2 mysteriously seem to appear in atmosphere within a few years, and then disappear again, causing wild fluctuations in CO2 levels. The fluctuations miraculously stop in 1958, exactly when Keeling started his measurements on Mauna Loa. Maybe we are being fooled for more than half a century by all CO2 molecules in the world. But it’s more likely that the graph below, from Cripps, father and son Keeling’s home base, displays the more accurate data.
4. The discovery that climate forcings in the past were much larger, or temperature changes much smaller, than science thinks
One of the ways to estimate climate sensitivity, is by looking at temperature changes in the past and the knowledge of their causes. It is very likely that the magnitude of a temperature change mostly depends on the magnitude of a change in the radiation balance at the top of the atmosphere, rather than the exact cause of this change. In other words: a Watt per square meter is a Watt per square meter, no matter if it comes from the sun, from an increased greenhouse effect, or something else. So, smaller temperature changes in the past, of larger forcings causing them, would be evidence for a low climate sensitivity.
5. Warming of the stratosphere
Many changes that are happening in the climate system are caused by warming itself. Observations of these changes cannot be used as evidence for the cause of warming. But there are some changes – fingerprints – that are specific for the increased greenhouse effect. Cooling of the stratosphere is one of these fingerprints. This cooling is confirmed by measurements, as is shown in the figure below, from ‘State of the Climate 2012‘ by the Bulletin of the American Meteorological Society.
Stratospheric warming is not the only human fingerprint that can be found. More detailed information on fingerprints can be found in last year’s paper: ‘Human and natural influences on the changing thermal structure of the atmosphere‘ by Santer et al.
6. Major errors in equipment in satellites, measuring outgoing longwave radiation
We can see the absorption of heat by greenhouse gases in satellite measurements of longwave radiation that leaves the earth’s atmosphere. The absorption bands of CO2, methane, ozone and water vapor are clearly visible in these measurements, as shown in the figure below. Whoever can demonstrate the measurements to be wrong, will make it into the history books. It would not only disprove the human impact on climate, it would wipe quite a lot of established physical science off the table.
7. Evidence of a substantial fall of relative humidity with rising temperature
If specific humidity would not follow temperature, the relative humidity would be lower in a warmer world. Then, there would not be a positive water vapor feedback, or it would be very small. It is highly likely that this would make matters rather worse than better. Our greenhouse gas emissions would lead to a smaller rise in temperatures than expected, but the downside would probably be disastrous: world-wide drought. Unless Clausius and Clapeyron were wrong.
8. A source of heat in the climate system that we do not know yet
All the evidence shows the heat in the climate system has been increasing for decades, and still is. Assuming even climate change skeptics do not dispute the law of conversation of energy, there has to be a source of heat somewhere. Who knows, one day, we might find some kind of mini-sun, hidden deep in the oceans. It would be a game changer for climate science.
9. A fundamental flaw in the scientific understanding of radiation physics or thermodynamics
This one is especially for the ‘slayers’, who deny that there is a greenhouse effect at all. Their ideas are either utter nonsense, or they are about to discover the very biggest mistake in the history of science. It would mean that we’d have to reevaluate fundamental physical science, that has been undisputed for decades to centuries, like the Stefan-Boltzman law or even the laws of thermodynamics. We would probably end up rewriting every single physics book in the world.
10. CO2 molecules appear to behave differently in the wild, than they do in a laboratory
I added this last one as a ‘tribute’ to one of the veterans of the war on climate science in The Netherlands. He, whose name I will not mention, does not dispute the greenhouse effect, but thinks it is relevant to mention that absorption of longwave radiation by CO2 has only been measured ‘in laboratory conditions’. He’s wrong, of course, because there are satellite measurements as well. But let’s forget about that. I think the idea of molecules behaving differently in the lab, compared to their behavior in the wild, is so creative that it deserves attention. I won’t go into the consequences of this revolutionary hypothesis. I will leave that, dear reader, to your imagination.