Heads of the Hydra - The Hockey Stick and the Climate Wars - page 130

“20th century values.” Had the paper somehow identified key new sources of information or a more
appropriate methodology to overrule the findings of all other recent studies?
The paper, in fact, suffered from serious problems that would presumably have been identified
had it been submitted to a peer reviewed scientific journal and reviewed by individuals with the
relevant paleoclimatological expertise. 40 Loehle was evidently unaware of the dating convention in
paleoclimatology that in “BP” (nominally, “before present”), “present” actually refers to the standard
reference year of A.D. 1950. By assuming that “BP” instead meant “relative to A.D. 2000,” Loehle
erroneously shifted many of his records forward by fifty years, in essence portraying the warmth of
the records in the mid-twentieth century as if it pertained to the end of the twentieth century. This
error thus had the effect of erasing all of late-twentieth-century warming. Most paleoclimate
reconstructions, including the original hockey stick, show peak medieval warmth to be comparable to
that of the early and mid-twentieth century. It is only the late twentieth century that stands out as
anomalous.
Among other problems, many of the sediment records Loehle used in his analysis had
chronologies that were determined by just a few radiocarbon dates distributed over the past two
thousand years. The dating in these records is consequently uncertain by as much as four hundred
years or so, precluding their use in reconstructing centennial timescale temperature variations. 41
There were several records that Loehle wrongly assumed to reflect temperature but instead reflected
some other quantity, 42 and he inappropriately averaged records that had different temporal
resolutions. Loehle did issue a correction that appears to have dealt with some of the most glaring
problems, 43 but the fundamental problem remained that his estimates were insufficient to allow for a
meaningful comparison of past and present global temperatures. 44 Yet even so, had he performed the
critical step of statistical validation emphasized in all serious paleoclimate reconstruction studies,
and had he published the work in an actual scientific peer reviewed journal, the paleoclimate
community might not have so readily dismissed it.
Loehle's approach was laudable by comparison with that of many of the contrarians. He did
attempt to make a positive contribution, putting his own reconstruction out there to be scrutinized and
criticized. While the reconstruction didn't stand up to the scrutiny (and the venue for its publication
was dubious), he made an attempt to contribute to the scientific discourse in a meaningful and
constructive manner. This can be contrasted with many others who are more than happy to take
potshots at peer reviewed studies from their blogs but are unwilling to produce a reconstruction
themselves, or even to provide evidence that genuinely contradicts the current scientific consensus
that recent warmth is anomalous.
When the Loehle paper came out in late 2007, we were in the process of finalizing our own
revised set of surface temperature reconstructions. I had presented the preliminary results of that
work more than a year earlier at the December 2006 AGU meeting in San Francisco. A decade after
we'd begun the original hockey stick work, we had now amassed a much expanded set of more than a
thousand proxy records, thanks to the laborious work of numerous paleoclimatologists who had
developed many new and different kinds of proxy records in the intervening years. If there were
numerous important new tree ring records, there were also many new coral and ice core records, and
new proxy records such as “speleothems” (stalagmite/stalactite layers containing calcite, whose
oxygen isotopes can be analyzed for climate information) as well as very-high-resolution lake and
ocean sediment records. We had compiled more than twelve hundred proxy records worldwide, more