Governments have begun work on implementing the 2015 Paris Agreement to limit global warming.
The planning comes after NASA reported last month was the warmest April in statistics dating back to the 19th century, the seventh month in a row to break temperature records.
The meeting of government experts on Monday is the first since 195 nations reached a deal in Paris in December to limit climate change by shifting from fossil fuels to green energies by 2100.
It will begin to work out the detail of the plan.
"The Paris Agreement represents the foundations. Now we have to raise the walls, the roof of a common home," French Environment Minister Segolene Royal told a news conference.
The agreement sets targets for shifting the world to green energies by 2100 but is vague, for instance, about how governments will report and monitor plans to curb greenhouse gas emissions.
Many government delegates at the start of the week long UN talks in Germany expressed concern about rising temperatures and extremes events such as damage to tropical coral reefs, wildfires in Canada or drought in India.
"We have no other option but to accelerate" action to limit warming, Christiana Figueres, the UN climate chief, told a news conference, asked about the NASA data.
She said record temperatures were partly caused by a natural warming effect of an El Nino weather event in the Pacific Ocean, magnified by the build-up of man-made greenhouse gas emissions.
She said national promises for curbing greenhouse gases put the world on track for a rise in temperatures of between 2.5C and 3C, well above an agreed ceiling in the Paris text of "well below" 2C with a target of 1.5C.
"Certainly we are not yet on the path" for the Paris temperature targets, she said.
The agreement will enter into force once 55 nations representing 55 percent of world emissions have formally ratified.