Global warming is accelerating carbon leakage from peat to the oceans. An analysis of UK rivers indicates that rising temperatures could leach billions of tonnes of carbon from peatlands worldwide, which may one day degrade to greenhouse gases itself1.

Levels of organic carbon derived from decomposing plants dissolved in some UK rivers have risen dramatically. Chris Freeman of the University of Wales in Bangor, UK, and his colleagues, have reported that water draining from peaty sites over the past 12 years show increases of up to 65% in 'dissolved organic carbon' (DOC).

The 0.66 ºC temperature hike over the past decade best explains the rise, the team think; peat breakdown and DOC-release increases with higher temperatures. When multiplied by the world's peatland areas, the potential for carbon release is huge, says Freeman: "There's a vast amount that can potentially be leached."

Washed into the oceans, at least some peat-derived carbon is likely to end up as the greenhouse gas CO₂, says oceanographer John Hedges of the University of Washington in Seattle. Although the timescales may be long - tens to a hundred years - and the size of the effect unknown, the risk is real, he thinks. "We're talking a positive feedback mechanism," he says. "It might be a warning shot."

Rivers carry large amounts of carbon from land, but plant-based DOC is sparse in the oceans, explains Hedges. This implies it is rapidly recycled into CO₂ in the atmosphere, a process thought to happen in coastal areas either as microbes respire or light breaks it down.

The global carbon imbalance is worsened by peat leachingPeter Raymond, Woods Hole Marine Biological Laboratory

Peatlands have been accumulating since the last ice age from part-decomposed plants, and are an immense carbon source compared to the amounts stored in plants or fossil fuels.

"It's sort of ignored," says wetland researcher Robert Wetzel of the University of Alabama in Tuscaloosa. Yet if converted to CO₂, the carbon locked in high latitudes such as Canada, Siberia and Scandinavia would double the amount currently in the atmosphere.

Although the complex structure of such organic carbons make them difficult to decompose in peat bogs, once in the ocean, conditions make breakdown more likely, adds Wetzel.

By potentially mobilizing carbon otherwise locked away, the global carbon imbalance is worsened by peat leaching, agrees Peter Raymond who studies carbon flux at Woods Hole Marine Biological Laboratory in Massachusetts - even if only some becomes CO₂. As temperatures rise, "[carbon] is potentially being released at an accelerated rate," he warns.

Long-term research projects such as Freeman's "raise a red flag," says Raymond. More are now needed to explore the fate of the carbon.