Academic journal article The Geographical Review

The A.D. 1300 Event in the Pacific Basin

Academic journal article The Geographical Review

The A.D. 1300 Event in the Pacific Basin

Article excerpt

It has been clear for a long time to scientists studying recent climate changes that two periods of climate distinct from that of the last 200 years or so occurred within the preceding millennium (for example, Lamb 1977; Broecker 2001). The earlier of these periods, known as the "Medieval Climate Anomaly," or "Little Climatic Optimum," lasted from circa A.D. 750 to circa A.D. 1250. The later of these periods, known worldwide as the "Little Ice Age," and took place circa A.D. 1350-1800. Scholars have focused on the contrasts between these periods and the problems caused to living things by the cooler temperatures, apparently increased climatic variability, and more marked extremes during the latter (Mayewski and others 2004). Comparatively little attention has focused on the transition between the Medieval Climate Anomaly and Little Ice Age, even though in most parts of the world it was perhaps the most rapid period of climate change to have occurred within the past several millennia.

In the Pacific Basin, comprising the Pacific (continental) Rim, the Pacific Islands, and the Pacific Ocean, evidence shows that the transition between the Medieval Climate Anomaly and the Little Ice Age lasted at least 100 years, causing rapid environmental changes and enduring societal disruption throughout this vast region. The earliest attempt at drawing together the evidence of changes in the Pacific Basin during this transition, named the "A.D. 1300 Event," was mine (Nunn 1999). Later I targeted the evidence for sea-level change, added details of the associated environmental catastrophe in the Pacific Islands, and then placed this in the context of last-millennium environmental and cultural evolution in the region (Nunn 2000a, 2000b, 2003a; Nunn and Britton 2001). Recent work has added to the physical and human evidence for the A.D. 1300 Event at key sites in Fiji and Palau (Kumar and others 2006; Masse and others 2006).

The idea that climate and sea-level change, both directly and through indirect environmental changes, had major and enduring effects on human societies in the Pacific Basin has parallels elsewhere (Fagan 1999; Jones and others 1999; de Menocal 2001; Berglund 2003; Catto and Catto 2004; Yasuda and others 2004). Implicit in such studies is the concept of environmental determinism, long regarded as a philosophical pariah by most scientists (and still so regarded by many), yet worthy of resurrection in the face of overwhelming evidence in favor of the role of environmental change in cultural transformation. The present study explicitly involves influences of societal evolution by externally driven environmental change.

LAST-MILLENNIUM CLIMATE AND SEA-LEVEL CHANGES IN THE PACIFIC

Almost all paleoclimate records for the Pacific Basin show a period of warmer-than-present climate known as the "Holocene Climatic Optimum," approximately 6000-3000 B.P. in the central tropical Pacific (Nunn 1999). This period marked a time of maximum opportunity for biota, warm temperatures, and higher sea level, which produced a greater range of habitat diversity than today. In most parts of the Pacific Basin, mean annual precipitation also appears to have been greater than today. Since the Holocene Climatic Optimum ended, this region has generally experienced cooling, sea-level fall and, in places, a fall in precipitation and loss of biodiversity attributable to climate change.

Owing to the imprecision of methods for calculating paleotemperature over short time periods, few such records for the Pacific span the past 1,200 years or so (Figure 1A). Of those that have been compiled, most show that temperatures reached close to modern levels around 750 and then rose slowly throughout the Medieval Climate Anomaly until around 1300. Around or shortly after this time, temperatures fell rapidly, reaching levels below their modern levels early in the Little Ice Age, or about 1450. Sea-level change has proved to be a useful proxy for temperature change during the past 1,200 years along tropical Pacific coasts. …

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