Friday, September 24, 2010

Royal Society of New Zealand paper highlights new research around sea level rise

From: The Royal Society of New Zealand

Download the full paper: Emerging Issues – Sea Level Rise (PDF, 645 kB)

Listen to the Science Media Centre briefing: Scientists on implications of sea level rise

Emerging Issues – Sea Level Rise

New research on the melting of ice sheets is helping coastal managers understand how to plan for future sea level rise, says a paper released by the Royal Society of New Zealand.

In its paper the Royal Society says warmer climates have always resulted in rising oceans, but how much rise and how rapid that rise will be are critical questions for an island nation like New Zealand.

Professor Keith Hunter, the Society’s Vice President of Physical Sciences who contributed to the paper, says researchers are starting to be able to estimate the amount of rise that we should expect to see over this century and beyond. But he says these projections of future sea level rise depend upon the future melting of ice sheets, which is poorly known.

“The uncertain knowledge about ice sheet behaviour is the key reason why IPCC projections in 2007 did not state upper bounds for sea level rise. Similarly, Ministry for the Environment guidance in 2008 wisely left open the question of any upper limit on sea level rise.”

The paper states that some early scientific work into the effect of a warming climate on ice sheets in Greenland and Antarctica suggested that many metres of sea level rise could occur within a century. However, it says few scientists now consider that such rates are possible.

In contrast, recent estimates of sea level rise are greater than those given by the IPCC in their last report. Between those two bounds, researchers are not yet able to make precise estimates of the probability of a given ocean rise within a given timescale.

Professor Hunter says the majority of New Zealand’s large towns and cities are on our coasts.

“Sea level rise will compound the hazards from erosion, flooding, storms, and waves to a degree that is currently hard to quantify.”

The paper, called ‘Sea Level Rise’, has been produced by the Royal Society of New Zealand as one of a series that seeks to inform the public on emerging and sometimes contentious issues around science and technology.

Wednesday, September 22, 2010

Study finds marsh being drowned as sea off S.C. rises

By Bo Petersen

The (Charleston) Post and Courier/The Sun News

The salt marsh might be the defining feature of the Lowcountry coast, miles after miles of sweeping grasses. It's the nursery of countless marine creatures including shrimp. It's a filter that helps keep the waters clean.

And it's drowning, right in front of our eyes, being flooded faster than it can move inland as the sea rises. A Boston University study of tidal creeks in Cape Romain National Wildlife Refuge offers some of the first, see-it-for-yourself evidence.

The loss of marsh compounds the damage from the overwash of barrier islands, jeopardizing the future of the 64,000-acre island seascape refuge northeast of Charleston that is singular habitat for a host of species. For example, the refuge is maybe the best nesting area in the Southeast for sea turtles.

What the marsh loss suggests for the rest of the coast is even more disturbing. The study is the latest in a series of alarming research that shows the coastal grasses being literally eaten away.

There's an estimated 400,000 acres of coastal marshes in South Carolina. A federal Environmental Protection Agency study in 1998 indicated sea level is rising about a foot per century on the East Coast. Conservationists warn the climate warming is exacerbating that.

The study focuses on a stretch of Horsehead Creek behind remote Cape Island east of McClellanville. On the south bank of Horsehead, smaller tidal creeks work their way back into the marsh in the classic, winding pattern. But on the north bank, creeks are forming that plunge straight into the marsh, to pits where crabs have devoured the grasses.

It's called rapid headward erosion, and it's trouble. The sediment is disappearing, the grasses aren't replenishing, and the bare spots are filling in with creek, not marsh.

"There's no doubt it's happening there," said Dennis Allen, lab director at Baruch Marine Institute in North Inlet, just outside Cape Romain, who has spent 30 years studying tidal creeks in the Lowcountry. In North Inlet, researchers have found low-lying marshes flooding more frequently, the marsh grasses thinning and dying off.

"There are signs for sure the marsh is having a hard time keeping up with sea level rise in this day and age," Allen said. Research by Baruch director Jim Morris suggests 20-50 percent of what we see today as salt marsh will become sand flats and open water lagoon systems in the next 20-30 years, he said.

For Sarah Dawsey, U.S. Fish and Wildlife Service biologist at Cape Romain, the study is documentation of what she has been seeing. Cape Island alone holds 1,041 of a total 3,129 sea turtle nests in South Carolina this year. Nearly 25 percent of the island has been overwashed since 1954. There is, as Dawsey says, "not much we can do about it."

On Bull Island, south of Cape Island, 20-25 feet of shoreline is disappearing per year. A levee has been rebuilt twice back in the dunes for a brackish water impoundment on the island's edge, because the impoundment is habitat for hundreds of wading birds, waterfowl and alligators. There's no longer any dune shoulder left to attach the levee. One big storm will likely destroy the impoundment, said Raye Nilius, refuge project leader.