European Union leaders will push Thursday "to advance work" towards setting a target of net zero greenhouse gas emissions by 2050, according to a draft resolution.
The language in the draft summit conclusion appears to be an attempt to include reference to the 2050 target adopted by some members, without offending the others.
The finely-nuanced text obtained by AFP reflects growing public and political pressure for the 28-nation EU to become "climate neutral" by at least mid-century, but also exposes the lack of unanimity.
The leaders will urge the EU "to advance work on the conditions, the incentives and the enabling framework to be put in place, in order to determine how to ensure a transition to a climate-neutral EU by 2050."
The aim must also "preserve European competitiveness, be just and socially balanced, take account of member states' national circumstances and respect their right to decide on their own energy mix."
Countries in central and eastern Europe that depend heavily on coal-fired plants have expressed concerns how they will be able to finance the shift to green energy, EU sources said.
The draft appeal is directed at both the members and the European Commission, the EU's executive arm, which is due to be reconstituted following elections in May and begin a new term in November.
"Strategically it is the most important issue for the next five-year commission," an EU diplomat told journalists before a summit to debate appointments for the new commission chief and other top jobs.
The growing stress on climate action comes after Green parties made substantial gains in May's European Parliament elections.
Spurred by a wave of student strikes, voters in many countries highlighted climate concerns and the parliament's main political blocs for the first time adopted climate action as a rallying cry.
Maintaining the pressure, Greenpeace said it projected onto the Commission's headquarters on Wednesday night a large animation of the Earth as a bomb with a lit fuse.
"Climate emergency. Time's running out. EU act now," the projection said, according to photos and video provided by Greenpeace.
Many scientists and activists say 2050 is too late to become "climate neutral," where countries emit no more greenhouse gases than they absorb. They want the date set at 2040.
Warnings have multiplied since 2015 when 195 countries meeting in Paris sealed a landmark agreement to keep temperature rises well below two degrees Celsius (36 Fahrenheit) above pre-industrial levels.
The UN Intergovernmental Panel for Climate Change (IPCC) warned in October that warming is on track towards a catastrophic 3C or 4C rise, and avoiding global chaos will require a major transformation.