Greenhouse gases in the atmosphere hit a new record in 2018, rising faster than the average increase in the last decade and cementing increasingly damaging weather patterns, the World Meteorological Organization (WMO) said on Monday.
The UN agency's Greenhouse Gas Bulletin is one of a series of studies to be published ahead of a UN climate change summit being held in Madrid next week and is expected to guide discussions there.
It measures the atmospheric concentration of the gases responsible for global warming, rather than emissions.
"There is no sign of a slowdown, let alone a decline, in greenhouse gases' concentration in the atmosphere - despite all the commitments under the Paris Agreement on Climate Change," WMO Secretary-General Petteri Taalas said.
"This continuing long-term trend means that future generations will be confronted with increasingly severe impacts of climate change, including rising temperatures, more extreme weather, water stress, sea-level rise and disruption to marine and land ecosystems."
The concentration of carbon dioxide, a product of burning fossil fuels that is the biggest contributor to global warming, surged from 405.5 parts per million in 2017 to 407.8 ppm in 2018, exceeding the average rate of increase of 2.06 ppm in 2005-2015, the WMO report said.
Irrespective of future policy, carbon dioxide stays in the atmosphere for centuries, locking in warming trends.
"It is worth recalling that the last time the Earth experienced a comparable concentration of CO2 was 3-5 million years ago," Taalas said.
Levels of methane –– a much more potent greenhouse gas than CO2 –– and nitrous oxide also hit new records, the report said.
The UN Environment Programme's annual "emissions gap" report, due on Tuesday, assesses whether countries’ emissions reduction policies are enough.