The concentration of heat-trapping Greenhouse gases in the atmosphere reached another record high last year.
The World Meteorological Organization has reported that average global concentrations of carbon dioxide rose to 407.8 parts per million in 2018 up from 405.5 parts per million in 2017.
General Secretary of the WMO Petteri Taalas said last time the earth experienced comparable concentrations of carbon dioxide was three to five million years ago.
He said that back then the temperature was two to three degrees Celsius warmer, and sea levels were 10 to 20 metres higher than now.
The WMO 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.
Global levels of greenhouse gas crossed the symbolic and significant 400 parts per million in 2015 and are now 47% higher than pre-industrial levels.
Carbon dioxide remains in the atmosphere for centuries and in the oceans for even longer.
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Since 1990 there has been a 43% increase in the warming effect on climate caused by long-lived greenhouse gases with carbon dioxide accounting for about 80 per cent of this effect according to the US National Oceanic and Atmospheric Administration.
Mr Taalas said there is no sign of a slowdown, let alone a decline, in greenhouse gas concentrations in the atmosphere despite all the commitments under the Paris Agreement on Climate Change.