Since I’ve discussed hockey sticks before, I thought I would briefly mention a new paper by Wilson et al. called Last millenium northern hemisphere summer temperatures from tree rings: Part 1: the long-term context. The key message seems to be that the result is
relatively insensitive to the compositing method and spatial weighting used and validation metrics indicate that the new record portrays reasonable coherence with large scale summer temperatures and is robust at all time-scales from 918 to 2004
Good to see that we can now describe at least some hockey sticks as robust 🙂
The main figure is below and, bearing in mind that this is northern hemisphere summer, it doesn’t appear to really present anything that is particularly different to our current understanding; a warmer period during medieval times, a general cooling trend towards what is often called the little ice age, and then a general warming trend over the last century or so. In fact, to the untrained eye, it’s hard to see how this differs from what was presented in the Mann, Bradley & Hughes papers published more than 15 years ago. My understanding of the significance of this newer work, is that it increases the spatial and temporal resolution and allows one to probe details like variability and, potentially, climate sensitivity.
Maybe one of the interesting results of this new paper is that
1161-1170 is the 3rd warmest decade in the reconstruction followed by 1946-1955 (2nd) and 1994-2003 (1st – see Table 2). It should be noted that these three decades cannot be statistically distinguished when uncertainty estimates are taken into account.
It may be true that they’re not statistically distinguishable in this data, but I think we can distinguish decades in the 20th century using the instrumental temperature record. The three most recent decades have all been warmer than any previous decade in the instrumental temperature record, and – given this result – it seems that the last two decades were probably warmer than any other decade in the last 1000 years.
The result in the paper also still seems broadly consistent with what was presented in the recent IPCC documents which says (in Chapter 5)
the mean NH temperature of the last 30 or 50 years very likely exceeded any previous 30- or 50-year mean during the past 800years (Table 5.4)…….NH reconstructions covering part or all of the first millennium suggest that some earlier 50-year periods might have been as warm as the 1963–2012 mean instrumental temperature, but the higher temperature of the last 30 years appear to be at least likely the warmest 30-year period in all reconstructions (Table 5.4).
However, it does say that
the confidence in this finding is lower prior to 1200, because the evidence is less reliable and there are fewer independent lines of evidence.
It would, therefore, be interesting to know if this recent paper allows for stronger statements about the period prior to 1200.
That’s really all I have time to say, but if anyone has anything to add, feel free to do so through the comments. I think it looks like an interesting paper that hasn’t really changed our overall broad understanding, but may allow for more detailed analysis of variability on scales that earlier reconstructions were unable to consider. As you can probably imagine, those on Bishop Hill think there are issues, and apparently Steve McIntrye is going to be looking at it. I can hardly wait.