John A thought that it would be worthwhile to draw attention to some articles on scientific reaction to Al Gore’s film "An Inconvenient Truth". and started this post. I have kept his links and quotations, but otherwise re-written this post.
I haven’t seen Al Gore’s film and may comment on it myself later. I suspect that the film uses the most lurid and sophomoric images available and invites equally sophomoric responses. I think that there are some valid issues, but these debates tend to get reduced to sound-bites.
John A cited the following articles and provided some quotes from them, which I discuss below:
Here’s one kind of issue that I think that it’s pointless to discuss:
Gore repeatedly labels carbon dioxide as "global warming pollution" when, in reality, it is no more pollution than is oxygen. CO2 is plant food, an ingredient essential for photosynthesis without which Earth would be a lifeless, frozen ice ball.
Both sides are trivializing the issue. It’s not obvious to me that any effects of higher CO2 so far have been adverse to humans, but I also think that the impact of 2xCO2 is a large and important issue, worth studying and understanding. I’m assuming that most readers of this site are interested in more nuanced analysis.
A next quotation from a Gore critic:
The hypothesis that human release of CO2 is a major contributor to global warming is just that — an unproven hypothesis, against which evidence is increasingly mounting.
In fact, the correlation between CO2 and temperature that Gore speaks about so confidently is simply non-existent over all meaningful time scales. U of O climate researcher Professor Jan Veizer demonstrated that, over geologic time, the two are not linked at all. Over the intermediate time scales Gore focuses on, the ice cores show that CO2 increases don’t precede, and therefore don’t cause, warming. Rather, they follow temperature rise — by as much as 800 years.
Personally, I have only carried out detailed analysis of arguments which purport to show that the 1990s were the "warmest decade" of the millennium. When I try to venture into other arguments and issues, I have far less knowledge. Extrapolating from the lack of due diligence in the hockey-stick arguments, I am concerned about the level of verification and due diligence in these other areas, but perhaps it’s different. On the argument of CO2 leading or lagging ice age changes, I don’t see that it gives much comfort to either side. My understanding of the evidence is that changes in dO18 levels lead changes in CO2 levels in ice cores; however modelers argue that changes in CO2 level are an important feedback which intensify the changes.
Even in the past century, the correlation is poor; the planet actually cooled between 1940 and 1980, when human emissions of CO2 were rising at the fastest rate in our history.
It would be worthwhlie pasing through the history of this issue. If you look back at material written in the late 1980s or 1990 – for example, the interesting text by Crowley and North – they attribute the seeming lack of response to natural variability. With the subsequent warming in the 1990s, everybody in this particular debate seems to have switched sides on natural variability. Sulphur dioxide emissions and aerosols have been invoked as an explanation. Here there don’t seem to be valid estimates of the forcing other than by difference, so it’s hard to see that anything very much is settled. The lack of a more monotonic response to CO2 increases does raise question marks for me, but no more than that.
Similarly, the fact that water vapour constitutes 95% of greenhouse gases by volume is conveniently ignored by Gore.
I don’t get this point at all. So what? I think that there are important and interesting issues about negative feedbacks associated with water vapor, as well as the more publicized positive feedbacks. I don’t see the purpose of exchanging soundbites of this type.
While humanity’s three billion tonnes (gigatonnes, or GT) per year net contribution to the atmosphere’s CO2 load appears large on a human scale, it is actually less than half of 1% of the atmosphere’s total CO2 content (750-830 GT). The CO2 emissions of our civilization are also dwarfed by the 210 GT/year emissions of the gas from Earth’s oceans and land. Perhaps even more significant is the fact that the uncertainty in the measurement of atmospheric CO2 content is 80 GT — making three GT seem hardly worth mentioning.
This seems like a frivolous point expressed this way. Yes, human CO2 emissions are a small fraction of annual flux, but I don’t see that that has any relevance to the issue of the impact of CO2 build-up. The measurement issue also is a total red herring. I have no doubt that CO2 measurements are more than accurate enough for the purposes of this particular debate.
Scientists who actually work in these fields [of atmospheric physics] flatly contradict Gore. Take his allegations that extreme weather (EW) events will increase in frequency and severity as the world warms and that this is already happening. Former professor of climatology at the University of Winnipeg Dr. Tim Ball notes, "The theories that Gore supports indicate the greatest warming will be in polar regions. Therefore, the temperature contrast with warmer regions — the driver of extreme weather — will lessen and, with it, storm potential will lessen."
If you have warmer oceans, it seems plausible to me that there will be more hurricanes, even if there is a somewhat lessened temperature contrast. I suspect that the temperature contrast would be sufficient. However, I think that there are real attribution issues. There seems to be evidence of very high solar activity in the 20th century and especially in the late 20th century. The attribution studies that I’ve sen, which attempt to allocate between solar and CO2, are very weak. In fact, Mann’s attribution arguments in MBH98, discussed about one month ago here, included outright falsehoods in his statistical claims – first identified in blogworld by Chefen, Jean S and myself.
In an emotional debate, I think that there’s an important role for analyzing individual arguments being relied upon. I’ve focused on the multiproxy studies and have come to the conclusion that all the hockey-stick studies are flawed and biased. De-constructing each individual study is very time-consuming. I view this exercise as not dissimilar to that of a pre-war analyst studying proxy evidence for WMD such as aluminum tubes. At the end of the day, an analyst is sometimes obliged to say that maybe an aluminum tube is just an aluminum tube. That does not mean that some other piece of evidence may not be valid – only that the aluminum tube wasn’t.
In response to the criticisms of the hockey stick, the main defence or excuse has been that the hockey stick doesn’t "matter". The concern about 2xCO2 arises from basic physics and the HS could be wrong but still leave us with an important problem. In one sense, I agree. If the HS were wrong, 2xCO2 is still an issue. Then why did IPCC and governments feature the HS so much? I presume that it was for promotional purposes. I would be shocked if Al Gore didn’t rely on arguments of this type for promotional purposes and this is the type of thing that I will be looking for when I see the film rather than silly issues like measuring the amount of CO2 in the atmosphere.