How do we recognize climate change in the cacophony of proxy signals in the paleoenvironmental record? A prime criterion has long been recognition of the same or similar change over regional or larger spatial scales. The idea is that only climatic forcing can elicit parallel and nearly synchronous response over significant distances. Is this criterion sound, and is it adequate? The history of the concept of the European “elm decline” is the story of efforts to explain a phenomenon that has exercised the ingenuity of scientists for over fifty years, yet its environmental significance remains unclear at best.

Early in the development of the northwestern European pollen studies, investigators noticed a sharp mid-Holocene decline in the abundance of elm pollen, a loss of 50% or so in a century. Peat-bog stratigraphy indicated that the decline occurred very close to the transition between the Atlantic and Sub-Boreal phases of the Blytt–Sernander scheme (Fig. 8.2). That transition had been earlier interpreted as the result of climatic change from a wetter “Atlantic” to a drier “Sub-Boreal” phase, both falling within the postglacial peak of warmth. Efforts to interpret the elm decline in causal terms emphasized (1) the wide geographic extent of the decline throughout northwestern Europe, (2) its apparent synchrony, and (3) its coincidence with the Atlantic/Sub-Boreal transition.