By Carl Smith
Sea levels remained steady for thousands of years before recent rapid rises, a study led by the Australian National University shows.
The researchers have described the study as the most comprehensive paper of its kind looking at the period.
ANU's Professor Kurt Lambeck said sea levels were oscillating by no more than 20 centimetres over several millennia.
"In the last 6,000 years before the modern onset of sea level rise, the sea level has been quite stable," he said.
"We see no evidence for oscillations in sea level greater than say plus or minus 25 or 30 centimetres, on timescales of 100 years or longer - there's just no evidence for that."
But he said there has been a rapid upward trend accompanying global industrialisation.
"For the last 150 years we've been seeing this increase, this rising sea level, at a rate of a few milimetres per year and in our older records we do not see similar behaviour," he said.
He said comparing the historical data with recent data from tidal gauges shows an increasing rate of sea level rise in recent times.
"We really have established the background signal from say 150 years ago to 6,000 years ago, and we can compare that with the tide gauge record," Professor Lambeck said.
"What we see in the tide gauges we don't see in the past record, so there's something going on today that wasn't going on before.
"I think that is clearly the impact of rising temperatures."
He said increasing temperatures have been documented to have clear effects on sea levels.
"Both because the thermal expansion of the oceans, the oceans are warming up, that's reasonably well documented, and it's the melting primarily up until now of the mountain glacier systems, so those two contributions are probably the most important part to what's happened in the last 100 years," Professor Lambeck said.
The study will create a comprehensive historical background for sea levels so researchers can better monitor current trends.