Politically sidelined since a 2009 UN summit almost ended in a bustup, climate change has resurfaced as a priority but faces a brutal test at talks opening in Lima on Monday.

The 12-day haggle will show what happens when high-minded global vows enter an arena where national interest rules the roost.

"Things are still fragile, but there's been good news," said French climate negotiator Laurence Tubiana -- pointing to recent political noises, and pledges of money, to protect Earth's climate system.

The meeting in the Peruvian capital is tasked with steering 196 parties toward the most ambitious climate pact in history -- "the matrix for managing climate issues for the next 30 years," according to Tubiana.

Due to be signed in Paris in December 2015 and take effect from 2020, the accord would roll back carbon emissions and ease the threat of misery, ecosystem damage and species loss for future generations.

Given the UN's shaky record on climate change, the challenge is vast.

The last climate treaty was the Kyoto Protocol, inked in 1997. A bid to follow it up in Copenhagen in 2009 was a near fiasco.

But in recent months, the political tone has changed, strengthening hopes that the creaking negotiations may finally yield a result.

"The broad outlines of a deal have begun to emerge and the three largest emitters have stepped forward early and encouraged others to follow suit," said Elliot Diringer of the Center for Climate and Energy Solutions (C2ES), a US thinktank.

"We're in about as good a shape in these negotiations as I think we've been for some time."

Science has been a big driver of the shift.

In a new overview, the UN's Intergovernmental Panel on Climate Change (IPCC) painted a tableau of a carbon-ravaged world just a few generations from now if emissions continue their present trajectory.

By 2100, hunger, drought, floods and rising seas would stalk humanity and spur the risk of bloodshed as nations fight for resources.

Against this grim backdrop, UN Secretary General Ban Ki-moon staged a summit in New York in September where leaders renewed oaths to fight the scourge. Hundreds of thousands of protestors rallied in cities around the world.

Ahead of schedule, China, the United States and Europe have unveiled emissions pledges.

Key details are fuzzy, but the announcement should raise the stakes next year when all countries are meant to put pledges on the table.

Money, too, has added a dose of goodwill.

Rich countries have promised funds to the Green Climate Fund (GCF), the main vehicle for channelling help promised to poor nations in Copenhagen -- a total of $100 billion (80 billion euros) annually by 2020.

An inaugural pledging session of the GCF in Berlin last week yielded $9.3 billion, just shy of an informal $10 billion benchmark set ahead of Lima.

- Pitfalls -

In spite of a sunnier mood, the talks face many tripwires -- defence of narrow national interests, foot-dragging, finger-pointing and nit-picking that have bedevilled the climate process for years.

Problem No. 1 is agreeing on the information countries will be required to provide when they make their emissions pledges next year: things like which gases to cut, by how much and over which period.

Without transparency -- the means to compare one country's effort to that of another -- trust in an already troubled process could easily break down.

Another question is whether existing and future pledges meet the UN's target of curbing warming to two degrees Celsius (3.6 degrees Fahrenheit) over pre-industrial levels.

Right now, the answer is clearly no, said Sam Smith of WWF.

"When you look at all these pledges together, they're still keeping us very far away from where we need to be in order to avoid dangerous climate change," she said.

"We are going to have to have a review of these pledges, and maybe more than one review, in the year that we have remaining before the negotiations in Paris."

Developing countries are worried that too much effort is being lavished on emission mitigation, said Mohamed Adow of Christian Aid, rather than helping vulnerable states adapt to a changing climate.

"There's a danger that some countries, and particularly developed countries, could decide their contributions could be focussed on emissions reductions targets only and not on climate finance," he said.

"Many developing countries are concerned," Adow said. "A lot of procedural wrangling can be expected in Lima."

Climate deal: What the scientists say
Paris (AFP) Nov 28, 2014 - A snapshot of what scientists are saying about climate change ahead of the next round of UN talks opening in Lima on Monday.

WHERE ARE WE NOW?

Atmospheric levels of three greenhouse gases from burning coal, oil and gas are the highest in 800,000 years.

Global temperatures for the 10-month period from January to October were the hottest on average in 2014 since record-keeping began in 1880.

Since the start of the Industrial Revolution in 1750, about 2,000 billion tonnes of the most plentiful greenhouse gas, carbon dioxide (CO2), have been emitted.

From 1880 to 2012, the global average surface temperature rose by 0.85 degrees Celsius (1.5 degrees Fahrenheit).

The global mean sea level rose by 19 centimetres (7.6 inches) from 1901 to 2010.

WHERE ARE WE HEADING?

Depending on how much carbon is spewed into the atmosphere, the global mean temperature could rise by 0.3 C to 4.8 C this century, and sea levels by 26-82 cm.

Wet countries will become more prone to heavy rain and flooding and dry countries more exposed to drought. Poor tropical countries and small island states will see their coastlines carved away by rising seas.

The impacts could translate into species loss, hunger, homelessness, the spread of disease and wars for natural resources.

WHAT CAN WE DO?

Nations have agreed to limit warming to 2 C over pre-Industrial Revolution levels. A tighter target of 1.5 C comes under review next year.

Meeting these goals carries a cost, as countries have to switch from cheap, plentiful and polluting fossil fuels to cleaner renewable sources.

The UN's Intergovernmental Panel on Climate Change (IPCC) says a 2 C pathway requires annual greenhouse-gas cuts of 40-70 percent by 2050, compared to levels in 2010 -- and to zero or below by 2100.

For a "likely", 66-percent, chance of meeting the target, carbon concentrations in the atmosphere should not exceed 450 parts per million of CO2 equivalent (CO2eq) by 2100.

The level was 430 ppm CO2eq in 2011 and heading, on current trends, for 750-1,300 ppm CO2eq by 2100. This leaves a "budget" of about 1,000 billion tonnes of CO2 to emit in total.

SOURCES: The IPCC's 2014 Fifth Assessment Report; October 2014 report by US National Oceanic and Atmospheric Administration (NOAA).