Given the threatening climatic changes, U.N. chief Antonio Guterres on Monday said to convene a "no-nonsense" climate ambition summit in September next year.

He urged leaders from government, business, civil society and finance to step up with "new, tangible and credible" action.

Guterres also said he "will not relent in persuading peace in Ukraine in line with international law and the United Nations Charter." A key principle of the founding U.N. Charter is respect for sovereignty and territorial integrity.

Speaking at his year-end news conference, Guterres said he is "not optimistic" about the possibility of effective Ukraine peace talks in the immediate future and believes the military confrontation will go on, but added that he "strongly hopes" peace can be reached in Ukraine in 2023.

He also said he will keep pushing for a climate solidarity pact that would require big emitters to reduce emissions this decade and ensure support for those who need it.

Countries are under pressure to ensure emissions are cut in half by 2030 and down to net zero by 2050 – the only path to hold global warming to within 1.5 degrees Celsius.

"I will convene a climate ambition summit in September 2023. I call on every leader to step up," he said.

"The invitation is open. But the price of entry is non-negotiable U.N. chief calls 'no-nonsense' climate summit in 2023 U.N. chief calls 'no-nonsense' climate summit in 2023 – credible, serious and new climate action and nature-based solutions that will move the needle forward and respond to the urgency of the climate crisis. It will be a no-nonsense summit," Guterres said.