The Wall Street Journal vs. The Scientific Consensus

The actual prevailing view of the paleoclimate research community that emerged during the early 1990s, when long-term proxy data became more widely available and it was possible to synthesize them into estimates of large-scale temperature changes in past centuries, was that the average temperature over the Northern Hemisphere varied by significantly less than 1 degree C in previous centuries (i.e., the variations in past centuries were small compared to the observed 20th century warming). This conclusion was common to numerous studies from the early and mid 1990s that preceeded Mann et al (1998). The Mann et al (1998) estimates of Northern Hemisphere average temperature change were, in fact, quite similar to those from these previous studies (e.g. Bradley and Jones, 1993; Overpeck et al, 1997), but simply extended the estimates a bit further back (from AD 1500 to AD 1400). In reality, the primary contribution of Mann et al (1998) was that it reconstructed the actual spatial patterns of past temperature variations, allowing insights into the complex patterns of cooling and warming in past centuries. In fact, regional temperatures changes (e.g. in Europe) appear to have been significantly larger, and quite different, from those for the Northern Hemisphere on the whole. Neglecting the significance of the large regional differences in past temperature changes is another classic pitfall in the arguments put forward by many climate change contrarians (see Myth #2 here).

The WSJ editorial continues,

This included a Medieval warm period when the Vikings farmed Greenland and a “little ice age” more recently when the Thames River often froze solid.

The sentence, first of all, perpetuates two well-known fallacies regarding the so-called “Medieval Warm Period” and “Little Ice Age”. See the RealClimate discussions of the Little Ice Age and Medieval Warm Period for explanations of why both the Viking colonization of Greenland and the freezing of the River Thames actually tells us relatively little about past climate change.

The actual large-scale climate changes during these intervals were complicated, and not easily summarized by simple labels and cherry-picked anecdotes. Climate changes in past centuries were significant in some parts of the world, but they were often opposite (e.g. warm vs. cold) in different regions at any given time, in sharp contrast with the global synchrony of 20th century warming.

The WSJ then continue with a statement that is problematic on several levels,

Seen in that perspective, the slight warming believed to have occurred in the past century could well be no more than a natural rebound, especially since most of that warming occurred before 1940.

Firstly, the overall warming of the globe of nearly 1 degree C since 1900 is hardly “slight”. That warming is about 1/5 of the total warming of the globe from the depths of the last Major Ice Age (about 20,000 years ago) to present.

Secondly, the argument that the climate should have naturally “rebounded” with warming during the 20th century defies the actual peer-reviewed scientific studies which, as discussed earlier, suggest that the climate should have actually cooled during the 20th century, not warmed, if natural factors were primarily at play. Anthropogenic greenhouse gases are required to explain the observed warming. Also, it is incorrect that most of the warming occurred before 1940; in contrast, the warming since 1970 is larger than that up to 1940.

The WSJ proceeds with the claim that key scientific findings that are common to numerous independent studies (specifically that late 20th century hemispheric warmth is anomalous in the context of past centuries) can somehow be pinned on one particular research group or even individual (see Hockey Stick Myth #1 here):

Enter Mr. Mann, who suggested that both the history books and other historical temperature data were wrong. His temperature graph for the past millennium was essentially flat until the 20th century, when a sharp upward spike occurs — i.e., it looks like a hockey stick. The graph was embraced by the global warming lobby as proof that we are in a crisis, and that radical solutions are called for.

This is patently incorrect.

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