SYDNEY, April 13, 2012 (AFP) - Sea levels in the southwest Pacific started rising drastically in the 1880s, with a notable peak in the 1990s thought to be linked to human-induced climate change, according to a new study.
The research, which examined sediment core samples taken from salt marshes in southern Australia's Tasmania island, used geochemistry to establish a chronology of sea level changes over the past 200 years. Patrick Moss, from the University of Queensland, said major environmental events which impacted the ocean such as the introduction of unleaded petrol and nuclear tests, showed up in the samples and were used for dating. The chronology revealed a major jump in sea levels around 1880 after 6,000 years of relative stability, Moss said, with peaks in the 1910s and 1990s -- the latter of which appeared to be linked to human activity. "Overall, over the past 200 years or so, sea levels have increased by about 20 centimetres (eight inches)," Moss told AFP on Thursday. The first peak coincided with an end to what was known as the Little Ice Age, "a 500 or so year period of slightly cooler conditions that ended roughly around 1850" and saw glaciers around the world retreat. Sea levels in the southwest Pacific rose at four times the average 20th-century rate between 1900 and 1950, according to the study. That was followed by a period of "relative quiet" broken by a second spike in 1990 which saw sea levels rise at a rate that defied projections. "The natural climatic factors seem to be not as apparent and anthropogenic climate change seems to be the key possible culprit," said Moss.
The study, which also involved researchers from Britain and New Zealand and was published in the journal "Earth and Planetary Science Letters", found that sea levels had risen much more in the southwest Pacific than elsewhere. Moss said a large ice melt was like a "fingerprint" which could be tracked across the Earth's surface, and the study had determined that the water which had caused the rising Pacific sea levels had come from the northern hemisphere. The Arctic's Greenland ice sheet looked to be the primary source, along with "mountain glaciers in Alaska, western North America and the Canadian Arctic," he said. Most scientists have until now said the sea level rise in recent decades is due to thermal expansion, the expansion of water due to heating, and from glacier melt and there is much debate as to how much Greenland is melting.
Some pro-melt research indicates the run-off is quite recent and probably contributes only about half of the current sea level rise, but Moss suggests the melt began long ago and began to affect sea levels as much as two decades ago.