The gap between what is being pledged to tackle carbon emissions by 2020 and what is needed remains as wide as ever, perhaps wider, the UN said on Wednesday. Reporting ahead of world climate talks, the UN Environment Programme (UNEP) said annual carbon emissions would have to fall by around 8.5 percent compared with 2010 to bring Earth on track for reaching a commonly-accepted goal for warming. In 2010, the last UN climate conference in Cancun, Mexico, decided to limit the increase in global average temperature to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels. The UNEP report sketched scenarios giving a \"likely\" chance -- more than 66 percent -- of meeting this target. Annual emissions that in 2010 were 48 billion tonnes of carbon dioxide equivalent (CO2e), a standard benchmark of greenhouse gases, would have to peak before 2020 and then fall to 44 billion tonnes of CO2e in that year, it said. Yet the report also pointed to a possible widening in the \"emissions gap,\" a term describing the difference between carbon-curbing pledges and what is needed to reach the 2 C (3.6 F) objective. Last year, UNEP estimated that this \"emissions gap\" was set to be between five and nine billion tonnes in 2020. Its new estimates are higher, at six to 11 billion tonnes, \"but are still within the range of uncertainty of estimates,\" the updated report said. The size of the gap depends on how rigorously pledges are implemented and monitored, it explained. Assuming that the 2020 global carbon curb is reached, emissions would still have to be followed by a steep decline, of an average of 2.6 percent per year, UNEP cautioned. \"To have a likely chance of complying with the 2 C target, total greenhouse-gas emissions in 2050 must be about 46 percent lower than their 1990 level, or about 53 percent lower than their 2005 level,\" the report said. But it also highlighted a range of strong options for reducing the gap. Potential reductions of around 16 billion tonnes of CO2e in 2020 lie in efficiency gains in electricity production, industry, transport, construction and agriculture; in switching to renewable energy sources and installing carbon capture at power stations; and in cutting emissions from deforestation and agriculture. Gains could also be made if countries toughened the conditions of pledges that so far are voluntary and minimised use of \"forest sinks\" and surplus credits on the carbon market to offset their own emissions. The estimates are made in an update of a report, \"Bridging the Gap,\" issued ahead of the November 28-December 9 talks in Durban, South Africa, of the UN Framework Convention on Climate Change (UNFCCC). Set up nearly 20 years ago, the forum has been dogged by bickering over how to share out the burden of reducing carbon emissions, especially from coal, oil and gas, which are the backbone of the energy supply today. Concentrations of CO2, the principal greenhouse gas, have surged as China and other emerging countries have burned fossil fuels to power their economies. Reacting to the report, the green group WWF said the figures showed \"the world is heading for very dangerous levels of climate change if we don\'t take decisive action right now... the gap is not technical or economic -- it is a gap in political will and leadership.\" Britain\'s Nicholas Stern, chair of the Grantham Research Institute on Climate Change in London, said the onus in Durban fell on rich countries to show the way with low-carbon growth. \"Many developing and emerging countries, such as China, are making real progress towards the transition to low-carbon economic growth, but their absolute emissions are still likely to rise significantly over the coming 10 to 15 years,\" he said. \"There is also a serious risk that countries, particularly the rich ones, will lock in high-carbon infrastructure now which will make it more difficult and expensive to reduce emissions over the next few decades.\"