A new paper by Wilson et al. combines data from paleoclimate reconstructions over the last 1000+ years, by a number of different researchers, to create a sort of “consensus” reconstruction. Hence the name: Northern hemisphere TREe-Ring Network Development, or N-TREND. As pointed out by And Then There’s Physics, it’s not groundbreaking or earth-shattering, it pretty much tells the story we already knew.
What’s different about this effort is that it’s limited to tree-ring data. I agree there’s merit in focusing on that specific proxy, but it highlights some weaknesses of the approach. If you want a global or even hemispheric temperature history, and if you want it to cover each full year, tree rings are far from ideal. They tend to reflect seasonal temperature most strongly, and they’re most useful for a limited latitude range. That’s why the paper makes it clear that the new combined reconstruction only covers latitudes from 40N to 75N (which only covers 16% of the globe), and only reflects temperature during the four months from May through August.
One advantage of tree rings is that they do give annual resolution, which makes them good for identifying changes on a time scale of a few years, such as the impact of volcanic eruptions. Nonetheless, it seems to me (and to many in the research community) that the advantages of multi-proxy reconstructions (greater geographic and year-round coverage, to name a few) outweigh the disadvantages.
Their reconstruction gives this:
They smooth it using a 20-year spline, which gives results nearly identical to other methods on the same time scale, for instance a lowess smooth:
Even with this relatively brief smoothing time scale, it emphasizes the “hockey stick” nature of climate change.
I prefer a 30-year time scale, more in line with the traditional time to define climate. It doesn’t look much different; here are 30-year moving averages together with a 30-year time scale lowess smooth:
What I find most interesting is to smooth on a more centennial time scale, or even longer. This can have the drawback of failing to capture some of the more recent, faster changes. But I’ve been playing around with various smoothing ideas, and one I’m toying with is what I’m calling an “optimal spline” smooth (someone has probably already invented it, but I’m having fun with it). Here’s a centennial-scale lowess smooth, compared to 30-year running means:
Here’s a new approach:
That’s a hockey stick for you.
As far as the global warming discussion is concerned, the salient point is this: that all the foregoing make it abundantly clear just how utterly stupid is the too-often repeated idiocy (a favorite of Ted Cruz and other deniers) that “climate is always changing.” Of course it is. But not like it is now. The medieval warm period is there (no surprise, especially since this reconstruction only covers northern-hemisphere mid-latitudes). The little ice age is there. So too is modern, man-made global warming, starting around 1850 — and it rather dwarfs those other events.
I suppose I could point out that of course politicians have always been idiots. But not like they are now.
If you like what you see, feel free to donate at Peaseblossom’s Closet.