Guterres issued the statement as the COP25 concluded its marathon meeting voicing "the urgent need" for new carbon cutting commitments but falling well short of what was required.

"I am disappointed with the results of COP25," Guterres said. "The international community lost an important opportunity to show increased ambition on mitigation, adaptation and finance to tackle the climate crisis."

COP25 brought together representatives of nearly 200 countries to finalize implementation of the 2015 Paris Agreement to limit the rise in global temperatures to less than two degrees Celsius (3.6 Fahrenheit).

But competing national interests proved insurmountable despite global calls for action in the face of extreme weather phenomena and increasingly dire warnings from climate scientists.

"We must not give up and I will not give up," Guterres said.

"I'm more determined than ever to work for 2020 to be the year in which all countries commit to do what science tells us is necessary to reach carbon neutrality in 2050 and a no more than 1.5-degree temperature rise."