LIMA (Reuters) - Government pledges due in 2015 to cut rising world greenhouse gases will be too weak to avert the worst of global warming and merely be part of a long haul to agree far tougher curbs, the United Nations said on Wednesday.

Christiana Figueres, head of the U.N. Climate Change Secretariat, told Reuters TV at 190-nation talks in Lima on limiting warming that it was unrealistic to expect a miracle solution at a U.N. summit in Paris in a year’s time.

Governments agreed in 2010 to a long-term goal of limiting global warming to 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial times to avert the worst of heatwaves, floods, desertificiation and rising sea levels.

“We already know, because we have a pretty good sense of what countries will be able to do in the short run, that the sum total of efforts (in Paris) will not be able to put us on the path for two degrees,” she said.

“We are not going to get there with the Paris agreement ... We will get there over time,” she said during the Dec. 1-12 climate negotiations in Lima to prepare the Paris deal.

The mood at the Lima U.N. talks is far from the run-up to the Copenhagen summit in 2009, when governments tried and failed to agree a U.N. climate deal. At that time, many nations hoped for a sweeping new treaty.

Figueres said hopes this time are lower. “It is not about knocking people over the head and saying ‘now we have to miraculously solve climate change’,” she said.

This time, she predicted a deal was achievable, partly because the top emitters - China, the United States and the European Union - have already set goals to limit emissions beyond 2020.

In Paris, the focus would be on finding ways to toughen the initial pledges with regular reviews in future years. “The sense of urgency is there,” she said.

Tthe long-term goal is to reduce greenhouse gases to zero by 2100, a target she says will require leaving three-quarters of fossil fuels in the ground. “We just can’t afford to burn them,” she said.

In what Figueres called bad news, the U.N. weather agency said on Wednesday that 2014 is on track to be the warmest year on record, or among the very warmest.