Signals in the Noise - The Hockey Stick and the Climate Wars - page 25

supplanted by an increasing number of more robust and quantitative studies suggesting otherwise.
But what was the “present” in the context of the Lamb curve anyway? The record Lamb
compiled captured temperature averages only over fifty-year blocks, and the end of the record
roughly corresponded to the mid-twentieth century. It did not reflect most of the recent warming,
which has taken place during the past half-century. In a recent reassessment of Lamb's original work,
Phil Jones—the current director of CRU—and a large group of other paleoclimate researchers
(including me) tried to answer the question of whether Lamb's reconstruction actually indicated
greater than present-day warmth. 11 They overlaid Lamb's original estimate (as depicted in the 1990
IPCC report) with an up-to-date record of central England temperatures. This comparison made it
clear that Lamb's original estimate (if it is indeed reliable; Jones and others have argued otherwise)
implies medieval warmth in central England that may have indeed rivaled mid-twentieth-century
warmth. The warmth did not, however, reach current levels.
As more widespread climate proxy records were developed through the early 1990s and
researchers were able to begin to piece together a picture of the larger-scale patterns of climate
during medieval times, a more nuanced view of this period emerged. While various regions of the
globe—including parts of Europe, China, western North America, and Australia—appear to have
been relatively warm by modern standards during some part of the medieval era, the warmth did not
appear synchronous among the various regions. Other regions, including, for example, the
southeastern United States and the Mediterranean, showed no evidence of warmth that rivals modern
levels. 12 Moreover, many of the more profound changes in regional climate that paleoclimate
researchers were discovering were tied to shifts in atmospheric circulation and rainfall patterns,
rather than to changes in temperature. For these reasons, paleoclimate researchers have increasingly
favored the use of the term “medieval climate anomaly” (MCA) over the potentially misleading
“medieval warm period” moniker. 13
Figure 3.1: The Medieval Warm Period
The graph shows two slightly different versions of Lamb's early qualitative reconstruction of temperatures in central England over the