The US is not interested in more legally binding targets (Image: Thinkstock/Getty)

The “gigatonne gap” looms large as UN climate talks in Cancún, Mexico, enter their final days without new commitments from big polluters to cut their carbon dioxide emissions. A five to nine-gigatonne gap, to be precise. That is the gap between what has been pledged and what is needed to avoid dangerous global warming.

To keep the world on track to cap global warming at under 2 °C by mid-century, rising CO 2 emissions should be kept below 44 gigatonnes a year in 2020, more than a third higher than today. But the UN Environment Programme warned here today that current national pledges would leave 2020 emissions anywhere between 5 and 9 gigatonnes too high.

The 9-gigatonne gap will arise “if countries follow their lowest ambitions and [carbon] accounting rules are lax,” according to the UNEP Emissions Gap report.


In either case, “the best science we have suggests that all chances of staying below 2 °C of warming would be gone,” said UNEP director Achim Steiner. Two degrees is widely seen as a threshold for dangerous climate change.

Tallied pledges

The report analyses current pledges, as made by major nations in the Copenhagen Accord, agreed at abortive UN talks last year. They include a 20 per cent cut from the European Union by 2020, 17 per cent from the US and a 45 per cent improvement in the “carbon efficiency” of the Chinese economy.

In nine days of talks here, no nations have raised their offers, increasing fears that talks could collapse in acrimony either this year or – more likely – at next year’s meeting in Durban, South Africa.

How might the gap be bridged? Developing countries are demanding higher emissions cuts by industrialised countries – they cite 40 to 50 per cent by 2020. The EU says it would go to 30 per cent if other nations made similar promises.That would go a long way to bridging the gigatonne gap, according to the EU climate commissioner Connie Hedegaard.

Entrenched

But the omens are not good. Japan has joined in the US in saying that it is not interested in joining a second era of legally binding targets after the current Kyoto Protocol “compliance period” expires at the end of 2012. British environment secretary Chris Huhne is leading side-negotiations to agree ways of extending the Kyoto Protocol, but many see that outcome as increasingly unlikely.

Elliot Diringer the Pew Center for Global Climate Change, a US-based think tank, echoed a widely held view among US observers that governments are not going to raise their numbers beyond the promises made in Copenhagen – whatever the science says. “The numbers are not under negotiation,” he said on Monday. He added that he did not expect a deal on any legally binding targets in Durban. “The politicians are not ready. If they try and set a new deadline, it will be Copenhagen all over again.”

Methane

If governments will not sign up to greater cuts than they have already, could other measures bridge the emissions gap? The smart money is on new initiatives to curb emissions of greenhouse gases other than CO 2 . They include methane, tropospheric ozone (a byproduct of vehicle emissions) and black carbon (from open fires). Plans to cut methane emissions are now being put together by the Methane Blue Ribbon Panel, a group of experts headed by the former chairman of the Intergovernmental Panel on Climate Change, Bob Watson.

The US is keen to pursue non-CO 2 options. In this, at least, they are joined by poorer states: in side events here, Micronesia, a nation of low-lying Pacific atolls threatened by sea level rise, argued that “addressing short-lived pollutants can reduce warming significantly and better protect the most vulnerable human populations”.

Methane is a potent greenhouse gas, so emissions cuts could provide a “quick hit” against global warming. But the gas only stays in the atmosphere for around a decade before it degrades. They do not accumulate in the way that CO 2 does and so the benefits of curbing them are transitory. It would only delay the need for even tougher action on CO 2 .

British climate ambassador John Ashton argued this week against being diverted by plan Bs. At the end of the day “there is no alternative to a global, legally binding agreement” on the main greenhouse gas, carbon dioxide.