Friday, December 7, 2007

Polynesian voyaging curbed by climate change?

Is there a role for climate science in archaeology.

Increasingly, the answer seems to be yes.

One of the mysteries of Hawaiian history has been why voyaging between the Hawaiian Islands and the South Pacific stopped several hundred years before the arrival of Europeans in the Islands.

Climate researchers say that the decline in long-distance Pacific voyaging may have coincided with a significant change in climate, which would have changed weather patterns throughout the region.

For traditional navigator Bruce Blankenfeld, the link between climate and voyaging success is perfectly reasonable.

“You take a lot of your cues from the weather. If the weather changes, that changes everything,” he said.

Blankenfeld is one of five Hawai'i non-instrument navigators who recently was inducted into a traditional Micronesian navigation society. He is one of the veteran navigators of the Polynesian Voyaging Society's canoe, Hōkūle'a.

Around the year 1300 the global climate began a switch from a warm period, often referred to as the Medieval Warm Period, to a cooler pattern known as the Little Ice Age.

There were changes in weather patterns and climate patterns, and there were more storm events in the Little Ice Age. This would have made traveling much harder, less predictable and less successful,” said Oliver Timm, a paleoclimatologist with the University of Hawai'i's International Pacific Research Center.

What caused the climate to cool? There are a couple of suspects, Timm told RaisingIslands.

One is that solar radiation dropped at the end of the warm period, although the drop was so small, about a tenth of a percent, that Timm believes it was unlikely to be the sole cause of cooling.

The other possible cause is volcanic activity, which can throw a great deal of material into the atmosphere that can block solar radiation.

If you have several major volcanic events, that can significantly change incoming solar radiation,” Timm said.

The change in global average temperatures caused other changes, including a significant drop in sea level.

The Medieval Warm Period sea level was a half meter to one meter higher than during the Little Ice Age. There was a significant drop in the sea level. That was a major stress for the societies of the Pacific islands. Suddenly, with a drop in sea levels, it changes the biology and food supply,” he said.

University of the South Pacific researcher Patrick Nunn addressed the impact of climate change on Polynesian societies in November 2007 at a conference of the International Pacific Research Center.

Nunn, a professor of oceanic geoscience, said that the change from the warm to the cool was the most rapid climate change in several thousand years.

Timm said significant change may have taken anywhere from a few generations to as long as couple of hundred years, but it was significant against a backdrop of a long period of relative climate stability.

The problem is for societies that have adapted to one climate for hundreds of years, and then you have a change that occurs over a few generations,”
Timm said.

One of the impacts of Little Ice Age lower sea levels in Hawai'i were that some salty marshes became fresh. Kawainui Marsh on O'ahu was among these. The plain inland of Bellows also went from salty to fresh. On Kaua'i, the low coastal plain at Mānā was populated during the 1300s, perhaps associated with a reduced salinity of its marshlands.

Nunn cites similar changes around the Pacific. At Tikiopia in the Solomon Islands, an inlet was cut off from the sea by dropping sea levels and became a lake.

Also during the Little Ice Age, there were increased numbers of disruptive El Nino climate events.

There was ecosystem stress and associated societal stress. As rich reefs were suddenly above sea level, coastal habitations were abandoned. Polynesians were moving, sometimes taking up residence on now-dry former swamplands, moving out to newly formed islands on the reefs, or moving to inland villages.

Climate change, both directly and through environmental filters, caused profound societal changes in the tropical Pacific Islands during the last millennium,” Dunn said.

Associated with these changes was the dropping off of long-distance voyaging across much of Polynesia. Hawai'i and New Zealand, in particular, became isolated from the rest of Polynesia during this period. Other islands also suffered.

Trade routes were abandoned. In the Kiribati islands, the trade in stone tools from the Marquesas stopped, Nunn said.

It may be that the changes in society alone were enough to inhibit voyaging, or perhaps the mental maps that traditional navigators used were no longer accurate in a time of changing winds, changing temperatures, perhaps altered currents, and even possible changes in the movement patterns of fish and birds.

© 2007 Jan W. TenBruggencate

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