COP20: Cautious optimism as delegates descend on Lima ahead of UN climate talks

It is more than 20 years since the Earth Summit in Rio put climate change on the international agenda, 17 years since the Kyoto protocol was hammered out and five years since the Copenhagen talks ended in bitter recriminations.

This week delegates from more than 190 nations are descending on Lima, Peru, for COP20, the 20th climate change conference and the last ministerial meeting before a new global deal is due to be inked in Paris in a year's time.

So is the world any closer to a new deal? Here are five things you need to know:

1. There's a note of cautious optimism

Many analysts are upbeat about what might be achieved in Lima. They say there is real momentum thanks to the US-China emissions deal, the recent UN climate summit in New York and the long-promised injection of funds to help poor nations deal with climate change.

But the optimism is tempered by past experience. Securing coordinated and enforceable global action in the face of competing national priorities, economic constraints and domestic political opposition has so far proved a herculean task for the international community.

2. The hangover from Copenhagen has been long and painful

Those hoping for a binding deal in Copenhagen were sorely disappointed, with marathon talks ending in disarray and Danish organisers slammed for the "chaotic" nature of negotiations. Big polluters Beijing and New Delhi joined forces to ensure binding targets were defeated, and US president Barack Obama - hampered by Senate negotiations over his ultimately-doomed cap-and-trade scheme - was criticised for failing to offer deeper US cuts. An eleventh-hour face-saving "accord" brokered by Mr Obama and the major emerging economies was big on rhetoric and light on commitment. Since then, expectations for global action have been far more modest.

3. There's little desire to make it legal

It has long been a key sticking point - should emissions cuts be legally binding? In reality, there is little appetite from the big polluters for binding cuts. China and India have long argued that binding targets would undermine their efforts to lift millions out of poverty; while the US would have little hope of seeing a binding pact pass through Congress. In the spirit of post-Copenhagen realism, countries are now being asked to submit voluntary emissions targets for after 2020 by early next year. These pledges will be aggregated to create a "bottom up" global target rather than a "top down" imposition on each nation. Climate activists warn this risks falling far short of the emission reductions needed to keep warming to no more than two degrees Celsius, but supporters say it will provide a springboard for deeper cuts further down the track.

4. Money is on the table

The long impasse between rich and poor nations over responsibility for climate change may be close to some resolution now that funds have been committed. The Global Climate Fund - designed to help poor countries cope with global warming through mitigation and adaptation projects - has raised $US9.7 billion ($A11.4 billion) from 22 nations, turbo-charged by a $A3.5 billion pledge from the United States and $A1.76 billion from Japan. But it remains to be seen how and the when funds will materialise to reach the more ambitious goal, set down in the Copenhagen accord, of ensuring multilateral climate finance is available to the tune of $100 billion a year by 2020. The Lima meeting is meant to start laying the groundwork for which nations will pay up.

5. The clock is ticking

"There is still time, but very little time" to tackle global warming at a manageable cost, according to Rajendra Pachauri, chair of the Intergovernmental Panel on Climate Change (IPCC). He says keeping warming to below two degrees Celsius - thus avoiding dangerous climate change - will need a cut in emissions of 40 to 70 per cent globally between 2010 and 2050, falling to zero or below by 2100. The deal agreed by China and the United States - which together produce 40 per cent of the world's emissions - falls far short of this goal, he says. India, meanwhile, as the world's third largest polluter, remains silent on its own emissions targets. Meanwhile, the United Nations Environment Program warns that the gap between what countries say they will so and what scientists say needs to be done is growing ever wider.