mike blackadder #4 — You can’t trust any of the data going all the way back to the 1400s because Briffa’s ‘world average temperature proxy’ is obviously garbage.
Yes, you _can_ trust proxy data. For one thing, this is how we know about (e.g.) the MWP, Roman Optimum, Ice ages, and the LIA (and others.) Modern era (last 2500 years) data are corroborated by written records of various sorts. We know Leif Erikson settled in Greenland. And so on. Earlier than that, there’s a lot of other evidence (e.g. geology.) Proxy data is almost like evolution in that there’s a massive pile of diverse circumstantial evidence that says one thing, and it’s really tough to claim it’s all a plot when said evidence comes in from mutiple diverse sources and unrelated scientific fields of endeavour. Geological evidence agrees with ice cores which agree with coral fossils which agree with… and so on. This is how we know that CO2 rise comes avg 800 years *after* warming among other fun things.
What you _can’t_ trust is *cherrypicked* proxy data, which is how the hockeystick was created. As in all things, it wasn’t the blade that was significant, but the shaft (insert inappropriate joke here.) The flat shaft did away with the pesky MWP thus exaggerating the blade. Look at Craig Loehle’s data (I’m sure Charlie Martin can provide you a pointer) where the MWP is clearly displayed. For much of the 90′s and the early 00′s the MWP was pooh-pooh’d as a “local phenomenon” and the flat shaft remained prominent due merely to the lack of enough published data to flatten Mann and his work. Skeptics pointed to CO2science.org and others with increasing volumes of data on the MWP and The Team simply ignored it. I always found this amusing in that CO2science founder Idso was co-author with Graybill on the use of bristlecone pines as proxies… but I, umm… diverge. (In any other venue, I’d simply digress…)
It’s the cherrypicking that’s ultimately at issue here and why McIntyre was repeatedly rebuffed by The Team with FOIA requests. Science isn’t done with secret data, hidden methods, one time only computer algorithms, and newly conjured inapproriate statistical tricks (e.g. see Wegman on Mann’s incorrectly applied version of PCA.) This refusal to supply data/methods is what climategate is all about.
And finally, the decline is in fact of paramount importance because it speaks to the basic problem of opacity in climate “science” as it was being done by The Team. In science, one doesn’t throw away data that isn’t convenient. So yeah, count me on the side that thinks the divergence hiding is important.
