Eco-engineering on a giant scale

The disagreement underscores a debate that has been raging over marsh restoration for decades. Even before the spill, the marshes were disappearing at an alarming rate - the consequence of the dams, levees and canals built to provide shipping channels and protect New Orleans from flooding. Without intervention Louisiana's bayous could become open water within 50 years.

As a result, support has been growing for a suite of projects to resurrect the marshes (see map). At one end of the spectrum are those who advocate minimal intervention and letting nature take its course. At the other, the call is for yet more engineering: new, hardier breeds of grasses, seeding from the air and artificial reefs to shore up the sinking sediment.

Ultimately, the marshes are vanishing because sediment is in short supply. Wind and waves constantly erode the shoreline, and dams and levees hold back sediment flowing down the Mississippi. What's more, a network of canals dredged by the oil and gas industry carry saltwater inland, killing freshwater marshes. Add to all this rising sea levels and the largest oil spill in US history and the situation is desperate. Without its marshes, Louisiana's thriving seafood industry would crumble and the state's coast would lose its natural defences against the powerful storms that blow in from the Gulf of Mexico.

Turner advocates small-scale intervention: filling in thousands of kilometres of abandoned canals with the dredged sediment that is still piled up alongside them. He also favours helping sediment flow to the marshes. Historically, when the Mississippi's waters ran high, "crevasses" appeared in the river banks and carried sediment into the deltas. Dams and levees now prevent this, so Turner suggests punching holes in the river's embankment to spur the process. "So many marsh restoration ideas assume we can do better than nature," says Turner. "I think that's pretty arrogant."

Others say we need to think big. "Over the years, we've done all kinds of patchwork projects," says Harry Roberts, a retired sedimentary geologist at LSU. "They're not long-term solutions." Roberts has calculated that 18 to 24 billion tonnes of sediment will be needed to maintain the delta as the sea level rises in the next century (Nature Geoscience, DOI: 10.1038/NGEO553). Small crevasses can never meet that demand, he says.

For researchers like Roberts the question has become not how to restore Louisiana's lost Eden but how to create a new, improved one. As part of that, in April, a $23 million project kicked off to pipe mud more than 6 kilometres from Cote Blanche Bay to Vermilion Bay's Marsh Island Wildlife Refuge. The aim is to recreate 160 hectares of marsh.

Sun's activity flies in face of climate expectations

IF NEW satellite data can be trusted, changes in solar activity warmed the Earth when they should have cooled it.

Joanna Haigh of Imperial College London studied satellite measurements of solar radiation between 2004 and 2007, when overall solar activity was in decline. The sun puts out less energy when its activity is low, but different types of radiation vary to different degrees. Until now, this had been poorly studied.

Haigh's measurements showed that visible radiation increased between 2004 and 2007, when it was expected to decrease, and ultraviolet radiation dropped four times as much as predicted.

Haigh then plugged her data into an atmospheric model to calculate how the patterns affected energy filtering through the atmosphere. Previous studies have shown that Earth is normally cooler during solar minima.Yet the model suggested that more solar energy reached the planet's surface during the period, warming it by about 0.05 °C (Nature, DOI: 10.1038/nature09426).

The effect is slight, but it could call into question our understanding of the sun's subtle effects on climate. Or could it? Stefan Brönnimann of the University of Bern in Switzerland says Haigh's study shows the importance of looking at radiation changes in detail but cautions that the results could be a one-off. He points out that the sun's most recent cycle is known to have been atypical

Grey wolf hunt creates bitter row in US

THE iconic grey wolf of the wild, wild west is the subject of a bitter row in the US. Idaho and Montana both established hunting seasons in 2009, after the US Fish and Wildlife Service decided the states' wolf populations were no longer endangered. But in August a federal judge ruled the decision illegal, halting the 2010 hunts.

Both states are now appealing that ruling. Officials argue that hunting has little effect on populations because many wolves die anyway of starvation or disease, and females can compensate by producing more young. These assumptions are wrong, says Scott Creel of Montana State University in Bozeman.

He analysed the findings of previous studies of 21 North American wolf populations, and found that hunting increased overall death rates and also reduced population growth rates (PLoS ONE, DOI: 10.1371/journal.pone.0012918).

A combination of sport hunting and state-sponsored culls killed 63 per cent of the Montana population last year. Creel calculates that humans should only take 22 per cent for the population to remain stable.

Vague carbon emission checks put deal in balance

CHINA is this week playing host to the last stage of preparatory climate talks before delegates gather at the annual United Nations climate change summit, in Cancún, Mexico, in December. They will attempt once again to reach a deal on limiting emissions of carbon dioxide and other greenhouse gases.

But any deal may fail because those emissions cannot yet be measured with sufficient accuracy. This has been a significant sticking point in talks. The world badly needs an independent carbon police to check the figures and catch the carbon frauds. Can science deliver?

Even the easiest emission to assess - CO2 from burning fossil fuels in developed nations - may only be known to within 10 per cent, according to Gregg Marland of the Oak Ridge National Laboratory in Tennessee. And a report by energy consultant Irving Mintzer for WWF, published in June, found that China does not record CO2 emissions from its small coal-burning factories and long-standing fires in mines, which may result in under-reporting by as much as 20 per cent.

The uncertainties for other greenhouse gases are even greater. Globally, declared nitrogen dioxide emissions are less than half those known to reach the atmosphere.

Verifying national emissions requires both "bottom-up" independent oversight of the inventories, and better "top-down" monitoring of the atmosphere, says Matthias Jonas of the International Institute for Applied Systems Analysis in Laxenberg, Austria.

The first step will be to add to the global network of some 150 stations measuring CO2 and other gases in the atmosphere, run by the World Meteorological Organization. This logs gas levels at places distant from major pollution sources, but what is now needed is the exact opposite - stations sniffing the air close to major sources. Such a network is being discussed by the WMO.

As well as this, there should be more research aircraft doing spot checks. This summer, the US National Oceanic and Atmospheric Administration flew aircraft downwind of refineries and power stations in California. Their preliminary results suggest that methane emissions from Los Angeles are a third higher than expected.

Also needed are more flights to remote regions. Last year, a research flight by the US National Center for Atmospheric Research discovered methane leaking out of the Arctic Ocean. The race is on to find out if the source is new gas fields off Alaska or melting permafrost.

A new climate treaty will also need carbon sniffers in tropical forests, especially in countries that sign up to a part of the deal called REDD (Reduced Emissions from Deforestation and Forest Degradation). REDD would offer cash to countries that conserve their forests so they can soak up atmospheric CO2. This means knowing how much carbon is actually being absorbed by the forests. In August, a study of Peruvian forests by Greg Asner of Stanford University, California, found existing estimates of carbon stored and released could be out by as much as 50 per cent.