Friday, June 20, 2008

Sea levels rising faster than thought

In Hawai'i, we know sea levels are rising.

New science is suggesting they're rising faster than most scientists have predicted up to now.

In the Islands, ocean levels lapping the beaches are up more than half a foot since the overthrow of the Hawaiian monarchy.

In some areas, notably on the Big Island, they appear to be up more than that. That's because the Big Island is sinking slowly due to its vast weight, at the same time ocean surfaces are rising.

Because our lifetimes are short on a geological scale, we don't think much about the massive variability in ocean levels. But it's clear that oceans were once so low that Maui, Moloka'i, Lāna'i and Kaho'olawe were one island. There were no humans here then to name it, but today we call that Maui Nui, Big Maui.

The USGS says that just 20,000 years ago, when glaciers were at their peak, oceans were nearly 400 feet lower than they are now. (See

At times between glacier eras, sea levels were 10 to 60 feet higher than now.

The agency reports that if every glacier in the world melted—an unlikely occurrence—oceans would rise 80 feet.

Ocean scientists have been reporting for some time that the average rise in sea levels for the past century or more has been 1 to 2 millimeters per year. Over a century, that's 10 to 20 centimeters or roughly 4 to 8 inches.

Now, scientists reporting in the journal Nature say it's been going considerably faster than that in recent decades.

“Following the review of millions of ocean measurements, predominantly from expendable instruments probing the upper 700 metres of the ocean, we were able to more accurately estimate upper-ocean warming, and the related thermal expansion and sea-level rise. We show that the rate of ocean warming from 1961 to 2003 is about 50 per cent larger than previously reported,” said weather and climate researcher Dr. Catia Domingues, of Australia's Commonwealth Scientific and Industrial Research Organisation (CSIRO). She is the organization's Wealth from Oceans National Research Flagship scientist, and works with the Centre for Australian Weather and Climate Research.

She worked with co-authors John Church, Neil White, Peter Gleckler; Susan Wijffels, Paul Barker and Jeff Dunn, who are variously from the Centre for Australian Weather and Climate Research, the Antarctic Climate and Ecosystem Cooperative Research Centre and California's Lawrence Livermore National Laboratory.

So, what's going on?

The short version is this: The climate is warming. The oceans soak up 90 percent of the additional heat. Water expands as it heats. Therefore sea levels rise.

And it all appears to be happening faster now than previously guessed—and faster than the estimates of the Intergovernmental Panel on Climate Change.

At the very least, this information is valuable to people making decisions about the uses of coastal lands. As an example, in Hawai'i, that would include planning for coastal highways, sewer and water lines, utility corridors and the like.

“Our results are important for the climate modelling community because they boost confidence in the climate models used for projections of global sea-level rise resulting from the accumulation of heat in the oceans. These projections will, in turn, assist in planning to minimise the impacts and in developing adaptation strategies,” Domingues said in a CSIRO news release. (

© 2008 Jan W. TenBruggencate