I am really just amazed by these remarks by NCAR's Dr. Ken Trenberth to be given, apparently planned for the American Meteorological Society gathering this month. The pdf is here and Anthony Watt has reprinted it on his blog.
It is hard to know where to start, but the following excerpt is an outstanding example of climate science process where 1. Conclusions are assumed; 2. Conclusions are deemed unequivocal by reference to authority; 3. Debate rules are proposed wherin it is impossible to refute the conclusion; 4. All weather events that make the news are assumed to be caused or made worse by man-made warming, and thereby, in circular fashion, further prove the theory.
Normally, when I cite the above as the process, I get grief from folks who say I am mis-interpreting things, as usually I am boiling a complex argument down to this summary. The great thing about alarmist Trenberth's piece is that no interpretation is necessary. He outlines this process right in a single paragraph. I will label the four steps above
Given that global warming is “unequivocal” , to quote the 2007 IPCC report , the null hypothesis should now be reversed, thereby placing the burden of proof on showing that there is no human influence . Such a null hypothesis is trickier because one has to hypothesize something specific, such as “precipitation has increased by 5%” and then prove that it hasn’t. Because of large natural variability, the first approach results in an outcome suggesting that it is appropriate to conclude that there is no increase in precipitation by human influences, although the correct interpretation is that there is simply not enough evidence (not a long enough time series). However, the second approach also concludes that one cannot say there is not a 5% increase in precipitation. Given that global warming is happening and is pervasive, the first approach should no longer be used. As a whole the community is making too many type II errors .
Are you kidding me -- if already every damn event in the tails of the normal distribution is taken by the core climate community as a proof of their hypothesis, how is there even room for type II errors? Next up -- "Our beautiful, seasonal weather -- proof of global warming?"
Remember that the IPCC's conclusion of human-caused warming was based mainly on computer modelling. The IPCC defenders will not admit this immediately, but press them hard enough on side arguments and it comes down to the models.
The summary of their argument is this: for the period after 1950, they claim their computer models cannot explain warming patterns without including a large effect from anthropogenic CO2. Since almost all the warming in the latter half of the century really occurred between 1978 and 1998, the IPCC core argument boils down to "we are unable to attribute the global temperature increase in these 20 years to natural factors, so it must have been caused by man-made CO2." See my video here for a deeper discussion.
This seems to be a fairly thin reed. After all, it may just be that after only a decade or two of serious study, we still do not understand climate variability very well, natural or not. It is a particularly odd conclusion when one discovers that the models ignore a number of factors (like the PDO, ENSO, etc) that affect temperatures on a decadal scale.
We therefore have a hypothesis that is not based on observational data, and where those who hold the hypothesis claim that observational data should no longer be used to test their hypothesis. He is hilarious when he says that reversing the null hypothesis would make it trickier for his critics. It would make it freaking impossible, as he very well knows. This is an unbelievingly disingenuous suggestion. There are invisible aliens in my closet Dr. Trenberth -- prove me wrong. It is always hard to prove a negative, and impossible in the complex climate system. There are simply too many variables in flux to nail down cause and effect in any kind of definitive way, at least at our level of understanding (we have studied economics much longer and we still have wild disagreements about cause and effect in macroeconomics).
So we frequently hear that “while this event is consistent with what we expect from climate change, no single event can be attributed to human induced global warming”. Such murky statements should be abolished. On the contrary, the odds have changed to make certain kinds of events more likely. For precipitation, the pervasive increase in water vapor changes precipitation events with no doubt whatsoever. Yes, all events! Even if temperatures or sea surface temperatures are below normal, they are still higher than they would have been, and so too is the atmospheric water vapor amount and thus the moisture available for storms. Granted, the climate deals with averages. However, those averages are made up of specific events of all shapes and sizes now operating in a different environment. It is not a well posed question to ask “Is it caused by global warming?” Or “Is it caused by natural variability?” Because it is always both.
At some level, this is useless. The climate system is horrendously complex. I am sure everything affects everything. So to say that it affects the probability is a true but unhelpful statement. The concern is that warming will affect the rate of these events, or the severity of these events, in a substantial and noticeable way.
It is worth considering whether the odds of the particular event have changed sufficiently that one can make the alternative statement “It is unlikely that this event would have occurred without global warming.” For instance, this probably applies to the extremes that occurred in the summer of 2010: the floods in Pakistan, India, and China and the drought, heat waves and wild fires in Russia.
Now he has gone totally off the scientific reservation into astrology or the occult or something. He is saying that there is a high probability that if CO2 levels were 120ppm lower that, for example, the floods in Pakistan would not have occurred. This is pure conjecture, absolutely without facts, and probably bad conjecture at that. After all, similar events of similar magnitude have occurred through all of recorded history in exactly these locations.
1. For those unfamiliar with the issues, few skeptics deny that man's CO2 has no effect on warming, but believe the effect is being enormously exaggerated. There is a bait and switch here, where the alarmist claims that "man is causing some warming" is the key conclusion, and once accepted, they can head off and start controlling the world's economy (and population, as seems to be desired by Trenberth). But the fact that CO2 causes some greenhouse warming is a trivial conclusion. The hard part is, in the complex climate system, how much does it cause. There is a an argument to be made, as I have, that this warming is less than 1C over the next century. This number actually has observational data on its side, as actual warming over the last century, given past CO2 increases, is much more consistent with my lower number than various alarmist forecasts of doom. Again, this is discussed in much more depth here.
2. One interesting fact is that alarmists have to deal with the lack of warming or increase in ocean heat content over the last 12 years or so. They will argue that this is just a temporary aberration, and a much shorter time frame than they are working on. But in effect, the core IPCC conclusions were really based on the warming over the 20 years from 1978-1998. So while 12 years is admittedly short compared to many natural cycles in climate, and might be considered a dangerously short period to draw conclusions from, it is fairly large compared to the 20 year period that drove the IPCC conclusions.
Update: More thoughts from the Reference Frame.