Responding to the CO2 Coalition's "Facts #17 and #26" on Whether Current Warming is Unprecedented

CO2 Coalition's "Fact #17" and "Fact #26" are parts 2 and 3 of an apparent rebuttal of the fact that "current warming" is unusual and "unprecedented" since the beginning of the Holocene. Part 1 (Fact 16) was an attempt to deal with Holocene temperatures. Parts 2 and 3 attempt do deal with temperatures over the last 2000 years, whether using Moberg 2005 (Fact 17)[1] or Loehle 2008 (Fact 26)[2]. I'm including both together here because both of these "facts" have the same fatal flaw - both eliminated "current warming" from their graphs. It should seem pretty obvious to most that you can't show that current warming is neither unusual nor unprecedented over the last 2000 years if you first cut out current warming from consideration. Here's how CO2 Coalition "hides the incline" in their plot of Moberg 2005.

CO2 Coalition says from this that "this chart by Moberg et al is a multi-proxy paleo temperature reconstruction of the last 2,000 years using both high and low resolution data. The Medieval Warm Period was the most recent warming period and likely had similar or warmer temperatures than modern ones." Note that the last data in their graph is from 1979 (Moberg 2005 included instrumental data following 1979), so this graph eliminates all warming from 1980 to 2023, or a significant chunk of current warming. And Moberg disagrees with the CO2 Coalition's evaluation of the paper. Right in the paper, Moberg et al state, "The peaks in medieval times are at the same level as much of the twentieth century, although the post-1990 warmth seen in the instrumental data ... appears to be unprecedented." Moberg's paper directly contradicts what CO2 Coalition said about it; NH temperatures post 1990 are "unprecedented" in the last 2000 years. If we include HadCRUT5 with Moberg 2005, this is what the graph looks like. Sure enough, Moberg was right - after 1990, warming is "unprecedented."

And here is CO2 Coalition "hiding the incline" with their plot of Loehle 2008.

Astute observers will again note that the most recent data here is stated to be from 1949, so this graph eliminates 1950-2023, or the last 74 years of "current warming." However, this actually overstates things. Loehle 2008 is actually a correction to Loehle 2007, published in Energy and Environment, that eliminated all tree ring proxies from their reconstruction. This omission left them with only 18 proxies. The number of proxies dropped from 11 to 8 in 1935, which is the actual last year of the reconstruction. CO Coaliton fudged this a bit because Loehle's reconstruction couldn't get annual resolution for the proxy; it only manages a 29-year running mean. The actual last date in Loehle 2008 is 1935, which is the mid-point of a 29 year mean. CO2 Coalition claims 1949 for this because 1935 was that was the last year in the last 29-year running mean. In point of fact, Loehle 2008 eliminates almost 90 years of "current warming." I go into more detail about Loehle 07/08 here. If you include data through 2023, though, it turns out that even in Loehle 2008, current warming is unprecedented. Below I plotted both Loehle 2008 and Moberg 2005 and HadCRUT5, and both of the latter were set to 29-year running means to match the resolution of Loehle 2008.
To date I know of no hemispheric or global proxy reconstructions that show current warming (post-1990) is anything other than "unprecedented" over the last 2000 years. It's objectively dishonest to say that "current warming" isn't unusual by means of eliminating current warming from consideration. Now I've read some object to combining proxy data with instrumental data, but this is not a rational objection, provided you keep the same resolution in both (which I did above). But even here, Pages 2K contains annually-resolved proxy data through the year 2000, and this also shows "unprecedented" warming in the latter half of the 20th century. Below I plotted Pages 2K with HadCRUT5 faded sufficiently for you to see clearly how global temperatures within the proxy database have changed.
As best I can tell, there's no possible world in which CO2 Coalition is both truthful/competent while at the same time claiming "the current warming trend is neither unusual nor unprecedented" over the last 2000 years.


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