I have a day off today and have been surfing a number of websites looking at elements of the skeptic criticism of AGW theory.
Chylek’s letter got me thinking about these pillars he sees as being undermined by the CRU emails and why I have been so little moved by all the evidence skeptics have put forward. It’s likely because, in the end, no real pillars were toppled.
If you go into a house and build a pillar or three in the interior and then topple them, the house remains standing — because it was not premised on those pillars in the first place.
I have found repeated in various locations on the skeptosphere reference to the “pillars” of man-made or anthropogenic global warming and efforts to topple them. However, when I ponder what I read, I have come to the conclusion that the pillars the skeptics are toppling are “their” pillars — pillars they have created in order to topple. Strawmen, in other words.
In my opinion, the real AGW pillars are:
- Measured increase in the atmospheric concentration of CO2 and other GHGs to levels not seen in hundreds of thousands of years
- Theory of the greenhouse effect
- Measures of climate sensitivity
- Globally averaged temperature record over the past 150 years and other temperature records via ground based, satellite, sea surface temps.
- Evidence of environmental impacts of warming — sea level increases, arctic ice extent, antarctic melting and ice extent, glacier retreat, impact on animals and plants, droughts, etc.
I don’t include the model predictions or hockey stick and issue of paleoclimate because logically, the models are tools used to explore the above pillars and as to the hockey stick and paleoclimate, it is entirely possible for it to have been warmer a thousand years ago due to natural influences and GHGs could still pose a threat to our climate, leading to unprecedented warming.
This decision of mine can be argued, and yes, the TAR includes sections on paleoclimate and models.
Keep in mind that skeptics and deniers hold the hockey stick and paleoclimate reconstructions as one of the pillars of the man-made global warming theory. They view toppling it as a major accomplishment that undermines the theory as a whole.
So, what does the TAR say about paleoclimate? The section on paleoclimate asks and answers the question — is current warming unprecedented? However, they were truly quite circumspect in the assessment report.
Here is a bit of the report, to refresh our recollection:
From the TAR, Summary for Policymakers:
- New analyses of proxy data for the Northern Hemisphere indicate that the increase in temperature in the 20th century is likely7 to have been the largest of any century during the past 1,000 years. It is also likely7 that, in the Northern Hemisphere, the 1990s was the warmest decade and 1998 the warmest year (Figure 1b). Because less data are available, less is known about annual averages prior to 1,000 years before present and for conditions prevailing in most of the Southern Hemisphere prior to 1861.[my emphasis]
(Note: in IPCC terms, “likely” means between 66-90%)
Keep in mind that they made it very clear that they were talking only about the Northern Hemisphere as data for the Southern Hemisphere is very sparse.
Here’s a section from the TAR Assessment Report, Paleoclimate:
Several important caveats must be borne in mind when using tree-ring data for palaeoclimate reconstructions. Not least is the intrinsic sampling bias. Tree-ring information is available only in terrestrial regions, so is not available over substantial regions of the globe, and the climate signals contained in tree-ring density or width data reflect a complex biological response to climate forcing. Non-climatic growth trends must be removed from the tree-ring chronology, making it difficult to resolve time-scales longer than the lengths of the constituent chronologies (Briffa, 2000). Furthermore, the biological response to climate forcing may change over time. There is evidence, for example, that high latitude tree-ring density variations have changed in their response to temperature in recent decades, associated with possible non-climatic factors (Briffa et al., 1998a). By contrast, Vaganov et al. (1999) have presented evidence that such changes may actually be climatic and result from the effects of increasing winter precipitation on the starting date of the growing season (see Section 22.214.171.124). Carbon dioxide fertilization may also have an influence, particularly on high-elevation drought-sensitive tree species, although attempts have been made to correct for this effect where appropriate (Mann et al., 1999). Thus climate reconstructions based entirely on tree-ring data are susceptible to several sources of contamination or non-stationarity of response. For these reasons, investigators have increasingly found tree-ring data most useful when supplemented by other types of proxy information in “multi-proxy” estimates of past temperature change (Overpeck et al., 1997; Jones et al., 1998; Mann et al., 1998; 1999; 2000a; 2000b; Crowley and Lowery, 2000).
You can see that this section is quite chaste in its description of the use of tree ring chronologies for temperature reconstructions. It even mentions the dread “Briffa divergence” issue.
Right there for all the world to see.
This is why the whole attack on paleoclimate by skeptics and denialists is so suspect in my opinion. The scientists were very forthright discussing the problems with the use of tree rings, even mentioning divergence and bias, etc. The paleoclimate data is seen as being quite uncertain such that they felt empowered to only use “likely” in the summary for policymakers.
While I acknowledge that paleoclimate recons have been used to bolster the case for policy action by many AGW advocates such as Gore and others, the science itself is not premised on paleoclimate, reconstructions or the hockey stick.
In an effort to undermine the IPCC, skeptics and denialists have attacked the science and scientists, looking for errors and mistakes and blowing them up into evidence of fraud and hoax, where IMO, none exists. What they should have been attacking is those who misrepresented the science as being more certain than it really was. The IPCC report is what it is — all of us can go and check it out. What I have posted shows the uncertainties.
What is done with that by the politicians, special interests and journalists is a whole other issue.
Personally, I think that this misplaced attack on the science and the scientists involved in paleoclimate (and other areas — more on that later) is a very sad, sad episode in our history at a time when science is all the more important to understanding what we may face from global warming.
While not every skeptic is part of a larger concerted strategy to discredit the science and scientists, their work is nonetheless used in order to diminish public support for the concept of global warming, its links to burning of fossil fuels and the need for policy action. The way Latif’s comments were taken out of context and trupeted around the world by denialists shows how this occurs.
I’ll look at models at another time.