Groundwater use is unsustainable in many of the world's major agricultural zones.

Now you see it, now you don't. According to news reports the plume of oil in the depths of the Gulf of Mexico is no more. But just days earlier, the subsurface plume had been proclaimed a long-lived menace.

It started with a story in the Press-Register of Mobile, Alabama. On 16 July, the paper reported that beleaguered oil giant BP was hurriedly signing up scientists to gather data for the company, to aid its defence in cases arising from the Deepwater Horizon spill. The catch was that these lucrative contracts also restricted the scientists

A study suggests that trees can act like chimneys, moving methane gas produced by soil microbes up through roots, stems and leaves before releasing it into the atmosphere. This effect could account for as much as 10% of methane emissions globally2. It could also help to explain why methane fluxes are higher than expected in wet tropical regions.