U.N. climate talks in Madrid are kicking into high gear Tuesday, with ministers arriving to tackle some of the tough issues that negotiators have been unable to resolve over the past week.

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.

U.N. High Commissioner for Human Rights Michelle Bachelet speaks at the COP25 Climate summit in Madrid, Spain, Monday, Dec. 9, 2019. A global U.N.sponsored climate change conference is taking place in Madrid. (AP PhotoAndrea Comas)

U.N. High Commissioner for Human Rights Michelle Bachelet speaks at the COP25 Climate summit in Madrid, Spain, Monday, Dec. 9, 2019. A global U.N.sponsored climate change conference is taking place in Madrid. (AP PhotoAndrea Comas)

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