Just four months ahead of a UN conference in the French capital tasked with producing a historic climate pact, US scientists this week said 2014 was a record year for sea level rise, land temperatures, and the greenhouse gases that drive dangerous global warming.
But overwhelming consensus on the urgency of the problem has not translated into significant progress on united action to prevent the planet from overheating.
"The negotiations have not, strictly speaking, begun yet," Laurence Tubiana, France's chief climate negotiator, told journalists this week.
The political discussions will be followed in Bonn at the end of August with technical negotiations on the content of a draft agreement, with another ministers' gathering slated for September.
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The 32 foreign and environment ministers and 13 senior negotiators in Paris, working under the guidance of France's chief diplomat Laurent Fabius, have their work cut out for them.
A draft agreement emerging from earlier rounds is little more than an exhaustive laundry list of problems and options, and is too unwieldy, Tubiana said.
Scientists say disastrous climate change can be avoided at this threshold, but warn the planet is on target for double that, or more.
Small island nations and poor countries in Africa and Asia, which will be hardest hit by climate-change effects, say 2C is not ambitious enough, and favour a 1.5 C target.
"As a people and a nation, our very survival is absolutely threatened by the effects of climate change," Tony De Brum, foreign minister of the Marshall Islands, told AFP ahead of the meeting.
The Paris agreement will be supported by a roster of national emissions-curbing pledges. Many parties -- including China, the United States and the European Union -- have already submitted their plans.
An internal briefing document identifies seven major sticking points, and urges diplomats to focus on two in particular, "ambition" and "differentiation".
Poor nations say the West, which has polluted more for longer, should carry more of the burden for emissions cuts, but the US and other rich countries insist on equal treatment and point the finger to emerging economies like China and India now among the top emitters.