http://news.bbc.co.uk/2/hi/science/nature/8489985.stm

Governments around the world have reaffirmed their plans to cut greenhouse gas emissions in support of last month's Copenhagen climate summit.

Nations signing up to the summit accord were urged to outline pledges by Sunday. States producing at least two-thirds of emissions have done so.
Correspondents say the accord is widely seen as a disappointment.
However, the level of support for it is seen as an indicator of prospects for a legally binding deal later in the year.
Many developing countries who face the worst impacts from climate change seem willing to sign up to the agreement, as it includes firm commitments on funding in both the short and the medium terms.
But others are unhappy with the idea that the accord could become a new basis of negotiations towards a legally binding treaty, and it is feared that some may refuse to associate with it.
Lacking teeth
The UN's Climate Change Secretariat says it will publish a list of signatories on Monday.
Leading emitters such as the US, India, China and the EU have already written in.
Some smaller emitters have also sent pledges or asked to be associated with the deal.
December's Copenhagen climate conference reached an accord including a recognition to limit temperature rises to less than 2C (3.6F).
It also promises to deliver $30bn (£18.5bn) of aid for developing nations over the next three years, to cope with the impact of climate change, and further funds to help them reduce emissions.
But analysts say the accord looks unlikely to contain temperature rises to within 2C, the threshold that UN scientists say is needed to avert serious climate change.
Environmentalists and aid agencies have branded it a failure, but UN Secretary General Ban Ki-moon described the deal as an "essential beginning".
BBC environment reporter Matt McGrath says the accord lacks teeth and does not include any clear targets on cutting emissions.
But if most countries at least signal what they intend to do to cut their emissions, it will mark the first time that the UN has a comprehensive written collection of promised actions, he says.
The next round of negotiations is due to be held in December in Cancun, Mexico.
It is unclear whether a legally binding deal can be reached at Cancun, amid uncertainties such as about whether the US Congress can pass a bill which includes emissions reductions.