The atmospheric concentrations of the three gases most responsible for climate change reached record highs in 2017, the most recent annual Greenhouse Gas Bulletin released Thursday from the UN's World Meteorological Organization (WMO) found.

The concentration of carbon dioxide in the atmosphere is now at 405.5 parts per million (ppm), or 146 percent of pre-1750 levels. The concentration of methane is now at around 1,859 parts per billion (ppb), around 257 percent of pre-industrial levels, and the concentration of nitrous oxide reached about 329.9 ppb, or 122 percent of pre-industrial levels.

"The last time the Earth experienced a comparable concentration of CO2 was three to five million years ago, when the temperature was two to three degrees Celsius warmer and sea level was 10-20 meters (approximately 32.8 to 65.6 feet) higher than now," WMO Secretary General Petteri Taalas said, as The Guardian reported. "The science is clear. Without rapid cuts in CO2 and other greenhouse gases, climate change will have increasingly destructive and irreversible impacts on life on Earth. The window of opportunity for action is almost closed."



The new findings add to the growing number of reports supporting urgent action to curb climate change. A little over a month ago, the UN's Intergovernmental Panel on Climate Change (IPCC) found that policy makers must reduce greenhouse gas emissions by 45 percent of 2010 levels within 12 years to limit warming to 1.5 degrees Celsius above pre-industrial levels.

"The new IPCC Special Report on Global Warming of 1.5 [degrees Celsius] shows that deep and rapid reductions of emissions of carbon dioxide and other greenhouse gases will be needed in all sectors of society and the economy," IPCC Chair Hoesung Lee told BBC News. "The WMO greenhouse gas bulletin, showing a continuing rising trend in concentrations of greenhouse gases, underlines just how urgent these emissions reductions are."

This month's Greenhouse Gas Bulletin did find that carbon dioxide and methane levels had increased less between 2016 and 2017 than between 2015 and 2016, but were roughly equal to the average increase over the past decade. Further, the reduction in the increase of carbon dioxide last year wasn't because of any change in energy policy. Instead, it was because the El Niño event that peaked in 2015 and 2016 caused drought in some regions, which meant vegetation in those areas absorbed less carbon dioxide from the atmosphere, BBC News explained. That effect was reduced during the 2016 to 2017 period.

"I am very concerned that the three greenhouse gases most responsible for climate change (CO2, methane, and nitrous oxide) are all rising upwards unabated," professor Corinne Le Quéré from the University of East Anglia told BBC News. "CO2 concentrations are now well above 400ppm—levels were 321ppm when I was born, that is a big rise in a human lifetime!"



When it comes to nitrous oxide, a greenhouse gas that also weakens the ozone layer, its levels actually increased from 2016 to 2017 compared with 2015 to 2016. About 40 percent of it enters the atmosphere through human activities like fertilizer use, soil degradation and industry. The report also marked the surprise decline in the decrease of CFC-11, a greenhouse gas that also weakens the ozone layer. It was supposed to be banned by the 1987 Montreal Protocol, but reports have sourced new emissions of the gas to some factories in China.

World leaders will have a chance to act on the findings of this bulletin, as well as the most recent IPCC report, when they meet in a little over a week to discuss ramping up their commitments under the Paris agreement at the 24th Conference of the Parties to the United Nations Framework Convention on Climate Change (COP24) in Katowice, Poland.

UN framework convention on climate change (UNFCCC) head Patricia Espinosa explained to The Guardian that the world was at a crossroads:



"On one hand, greenhouse gas emissions have yet to peak and countries struggle to maintain the concentrated attention and effort needed for a successful response to climate change. On the other hand, climate action is occurring, it is increasing and there is a will to do more. I highlight this because falling into despair and hopelessness is a danger equal to complacency, none of which we can afford."

A UNFCCC report published Wednesday looked at climate action pledges by the numbers in 2018 and found that commitments had been made by:

