Carbon dioxide levels in the atmosphere grew more in past 12 months than at any time in the past 56 years.
Measurements at the Mauna Loa Observatory in Hawaii went up by more than three parts per million(ppm) in 2015.
Scientists say the spike is due to a combination of human activities and the El Niño weather pattern.
They argue that the data increases the pressure on global leaders to sign and ratify the Paris Climate Agreement.
Mauna Loa is the world’s oldest continuous atmospheric measurement station, with records dating back to the later 1950s.
It is regarded as the most important site in the global monitoring network, recording the see-saw, rise and fall of carbon in the atmosphere over a year.
Plants and trees tend to absorb more CO2 during the spring and lose it as autumn approaches and leaves die off.
For the past decade the average increase in carbon dioxide at the station has been 2ppm. But in 2015 the level grew by 3.05ppm – In the year to February 2016, the level went up by 3.76ppm.
The global climate phenomenon, El Niño, is believed to have played a role in the rise.
Scientists at the World Meteorological Organisation (WMO) say that the previous biggest increase was in 1998, also an El Niño year.
The weather event drives drought in many parts of the tropics and in 2015 this led to forest fires in Indonesia and other locations which pumped large amounts of stored carbon into the atmosphere.
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