A timely reminder that tree rings, ice cores, and speleotherms, which are all used to reconstruct climate in the past by geologists as much as climate scientists, are not as reliable as sometimes projected – see http://phys.org/print279271653.html
The paper is in Nature Climate Change and is written by Swiss and German researchers from the Oeschger Centre at the University of Bern, and the University of Mainz, and they say that most temperature and precipitation variations and extremes are over estimated, putting into question many of the proxy climate models and reconstructions used in climate science. Mike Baillie made this point a couple of years ago during the dispute between Queens University (and the release of tree ring data) and researcher Douglas Keenan. Proxies such as tree rings and lake sediments, even corals and stalagmites are not thermometers. They are a general but incomplete record of climate variation. The annual width or density of tree rings are influenced by a number of factors (as Barry Curnock keeps on telling us) but I don't suppose the doomsayers will take any notice. Indeed, they haven't – witness the latest dollop of misinformation, a new hockey stick. This time it is supposed to encompass the whole of the Holocene – but for some reason they are loathe to avoid the Younger Dryas period. After all, it could be taken all the way back to the end of the Ice Age – but isn't. The reason is that ice cores show a remarkably fast spike in temperature at the boundary of the Younger Dryas with the Holocene. In addition, it involves a new kind of proxy. If the authors had hoped to stump sceptics they are due to be disappointed as Steve McIntyre has been looking at these proxies for a long time and knows all about the limitations that will be inherent in this very long attempt to engineer paleo-climate into a flat handle, over 11,000 years.
Apparently, the new proxy is based on alkenones, transfats produced by algae. Alkenones are used to construct sea surface temperatures from ocean sediments – see the sceptic response to the new hockey stick at http://climateaudit.org/2013/03/13/marcott-mystery-1/ and http://climateaudit.org/2013/03/14/no-uptick-in-marcott-thesis/ and at http://wattsupwiththat.com/2013/03/13/marcotts-proxies/ and http://wattsupwiththat.com/2013/03/14/another-hockey-stick/