Climate change

October 17, 2008

Two denialist talking points quashed

Filed under: Climate Change — Barry Brook @ 10:48 pm

Two things that Professor Ian Plimer confidently touted during his presentation at the SA Skeptics annual conference was (1) the relevance of David Evan’s so-called missing tropical hotspot (as supposed proof against greenhouse theory) and (2) that sub-sea volcanoes along the Gakkel Ridge is likely to be the cause of accelerated melting of the Arctic summer sea ice. So what is the latest scientific opinion on these?

Well, regarding (1), as RealClimate reports, Dr Ben Santer (who recently gave a talk at my Institute at the University of Adelaide), Dr Tom Wigley (now retired to Adelaide and an Adjunct Professor at the University of Adelaide) and 15 other colleages, have published a new paper in the International Journal of Climatology on this very issue. It thoroughly quashes the Evan’s claim, and also hammers the related critiques of climate science, by Dr David Douglass, Dr John Christy, Dr Benjamin Pearson and Dr S. Fred Singer, which claimed a significant discrepancy between theory and observations in terms of the warming of the lower atmosphere. What’s particularly good news for the large non-scientific community who has interest in science behind these issues, is that the paper’s authors have also put together a FAQ. In it, they explain, using non-technical language, all the key sceptical arguments on this issue, and the latest evidence. The figure above is from the fact sheet. I’ll just quote a couple of key  points from it:

Using state-of-the-art observational datasets and results from a large archive of computer mode simulations, a consortium of scientists from 12 different institutions has resolved a long-standing conundrum in climate science – the apparent discrepancy between simulated and observed temperature trends in the tropics. Research published by this group indicates that there is no fundamental discrepancy between modeled and observed tropical temperature trends when one accounts for: 1) the (currently large) uncertainties in observations; 2) the statistical uncertainties in estimating trends from observations. These results refute a recent claim that model and observed tropical temperature trends “disagree to a statistically significant extent”. This claim was based on the application of a flawed statistical test and the use of older observational datasets.


The bottom line is that we obtained results strikingly different from those of Douglass et al. The “robust statistical test” that they used to compare models and observations had at least one serious flaw – its failure to account for any uncertainty in the “signal component” of observed temperature trends (see QUESTION 7). This flaw led them to reach incorrect conclusions. We showed this by applying their test to randomly generated data with the same statistical properties as the observed temperature data, but without any underlying “signal trend”. In this “synthetic data” case, we knew that significant differences in temperature trends could occur by chance only, and thus would happen infrequently. When we applied the Douglass et al. test, however, we found that even randomly generated data showed statistically significant trend differences much more frequently than we would expect on the basis of chance alone. A test that fails to behave properly when used with random data – when one knows in advance what rresults to expect – cannot be expected to perform reliably when applied to real observational and model data.

Go read the whole thing (there are 10 frequently-asked-questions answered in all).

Then there is question of the influence of those sub-sea Arctic volcanoes. Could they possibly be the cause of the melting surface ice, due to a slow diffusion of heat from the ocean floor, many kilometres deep, to the surface waters? (and, one presumes, a recent increase in volcanic activity). NY Times investigative journalist Andy Revkin handballed this question to his extensive scientific contact list, to get a decent spread of informed answers. The response on this issue, by 7 different scientists who work in this area, is an unequivocal NO! I’ll quote a couple below, but I suggest you read the two posts by Revkin on this issue, here and here, for the full story and links.

Jamie Morison, University of Washington (I went with Dr. Morison and the rest of the North Pole Environmental Observatory team to the North Pole sea ice in 2003):

It occurs to me that we have primary evidence that heat from the bottom is not reaching the ice. Temperature profiles from virtually everywhere in the Arctic Ocean display a maximum temperature at a depth from 200-400 [meters]. This is associated with the Atlantic Water entering the basin from the Norwegian Sea. Fundamental laws of physics require that below the depth of this maximum, the heat flux is downward. Very near the bottom temperatures have been found to increase with depth indicating a small upward heat flux from geothermal sources, which help to heat only the very deepest water.

The heat flux above the Atlantic temperature maximum is upward. The rate of this flux of Atlantic Water heat flux is variable depending on depth of the maximum and overlying stratification (stratification is controlled by salinity in the Arctic Ocean). Treshnikov estimated it from Atlantic Water heat content to be a couple of Watt/m2 in much of the Euarasian Basin. It is smaller farther from Fram Strait and greater near Fram Strait. How this flux changes is potentially very important to the ice cover. Changes in geothermal heat flux are not.


Dr. Schlindwein sees almost no chance of surface disruption from the eruptions:

I am currently working on a reconstruction of the Gakkel volcanic episode from 1999-2007 integrating seismicity data and water column observations and I have started to look at sea ice images as well. We know pretty well when the 1999 eruption took place; it will be easy to check for effects on the sea ice. I doubt there will be such effects:

In 2001, the volcano at 85E was still erupting explosively, although in a less vigorous mode (Schlindwein et al., GRL, 2005). The associated event plume in the water column is well surveyed and described in Edmonds et al. (Nature 2003). That plume of relatively “warm” water – temperature anomaly less than 1/10 degree – reaches a minimum water depth of about 1700 m, its center being around 2500 m water depth. These data make it very evident that the sea ice is not influenced by the heat released from the ongoing eruption.

So, two more sceptical questions bite the dust. But I wonder if Ian Plimer, David Evans, Fred Singer and others who have put store in these theories, will pay any attention?


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