Officials from almost 200 nations haven't managed to finalize the rules for international carbon markets that economists say could help drive down emissions.

Another contentious issue is poor countries' demand for aid to help them cope with the damage and destruction wrought by natural disasters blamed on climate change.

Unlike at many past climate summits, few heads of government will join the talks. Most are sending environment ministers or other senior officials instead , worrying some observers.

"It shows that there has not yet been an internalization of the emergency situation that we are in, that so few heads of state are coming to Madrid and ready to roll up their sleeves and do what it takes to actually respond to the science," said Jennifer Morgan, executive director of Greenpeace International.

She also accused some governments, such as Brazil and Saudi Arabia, of trying to weaken the agreements, and called on the European Union to work with vulnerable nations to counter those efforts.

Environmental campaigners are hoping the EU will present an ambitious plan this week for cutting emissions in the medium- and long-term that would send a message of hope to weary negotiators in Madrid.

The new head of the bloc's executive Commission, Ursula von der Leyen, has backed a call for the EU to stop all net emissions of greenhouse gases by 2050.

Scientists say emissions worldwide need to start falling sharply from next year onward if there is to be any hope of achieving the Paris climate accord's goal of capping global warming at 1.5 degrees Celsius (2.7 Fahrenheit)

A senior official said negotiators in Madrid had worked till 3 a.m. to prepare the ground for ministers.

"Let's hope to see that we can sort of really sort of give shape and meaning to the call 'Time for action,'" said Sigrid Kaag, the Netherlands' minister for foreign trade and development cooperation, referring to the motto of the U.N. talks.

"It's now or never," she told The Associated Press.