The annual emissions gap report shows that even if all current promises are met, the world will warm by more than double that amount by 2100.
Richer countries have failed to cut emissions quickly enough, the authors say.
Fifteen of the 20 wealthiest nations have no timeline for a net zero target.
Hot on the heels of the World Meteorological Organization's report on greenhouse gas concentrations, the UN Environment Programme (Unep) has published its regular snapshot of how the world is doing in cutting levels of these pollutants.
The emissions gap report looks at the difference between how much carbon needs to be cut to avoid dangerous warming - and where we are likely to end up with the promises that countries have currently committed to, in the Paris climate agreement.
The UN assessment is fairly blunt. "The summary findings are bleak," it says. "Countries collectively failed to stop the growth in global greenhouse gas emissions, meaning that deeper and faster cuts are now required."
The report says that emissions have gone up by 1.5% per year in the last decade. In 2018, the total reached 55 gigatonnes of CO2 equivalent. This is putting the Earth on course to experience a temperature rise of 3.2C by the end of this century.
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