The UN weather agency said on Monday (October 25) that greenhouse gas concentrations hit a new record in 2020.
It warns that the world was "way off track" for capping rising temperature.
A World Meteorological Organization report showed that carbon dioxide levels in 2020 has risen more than the average rate over the last decade.
Secretary-General Petteri Taalas said this could result in a 2.5 to 3 degree Celsius temperature rise. That's around 37 degrees Fahrenheit, rather than 1.5 to 2 degrees - a target that was made in the 2015 Paris Agreement.
"And last time that we saw such high concentrations of carbon dioxide, it was around 3 to 5 million years from now and there was an estimate that the temperatures were 2 to 4 degrees higher than today, and the sea level was 10 to 20 meters higher than today. So, this is demonstrating that already, this current level of carbon dioxide is too high."
Carbon dioxide can remain in the atmosphere for centuries.
So even though emission rate dipped during lockdowns in 2020, the report confirmed it "did not have any discernible impact on the atmospheric levels of greenhouse gases and their growth rates."
The report also flagged concerns about the ability of the ocean and land to absorb roughly half of CO2 emissions.
These so-called "carbon sinks" should act as a natural buffer for dramatic temperature increases.
But the data collected by WMO over ten years showed that some of these carbon "sinks" have turned to carbon "source" for the first time, including the Amazon rainforest.
Taalas urged leaders who are heading to the COP26 conference to make a quote "dramatic increase" in commitments in tackling global warming.