The concentration of greenhouse gases in the atmosphere has reached a new record, according to the United Nations, which warned that the world is running out of time to curb warming.
The warning came as UN officials stepped up pressure ahead of the COP24 climate summit in Poland, urging governments to honour the 2015 Paris accord pledge of keeping global warming well below 2 degrees Celsius.
World Meteorological Organization chief Petteri Taalas said the science leaves little room for doubt. “Without rapid cuts in CO2 and other greenhouse gases, climate change will have increasingly destructive and irreversible impacts on life on Earth,” he said in a statement. “The window of opportunity for action is almost closed.”
UN rights chief Michelle Bachelet also issued an open letter to states before COP24, warning that failure to change course could bring severe consequences. “Entire nations, ecosystems, peoples and ways of life could simply cease to exist,” she said, pointing to evidence that countries are not on track to meet the commitments made in Paris.
US President Donald Trump, who withdrew his government from the Paris agreement, again questioned climate science on Thursday. In a tweet, he wrote: “Brutal and Extended Cold Blast could shatter ALL RECORDS - Whatever happened to Global Warming?”
Asked about Trump’s remarks, WMO deputy chief Elena Manaenkova said the science behind global warming was “unequivocal,” without directly taking on the US leader.
Record readings in the 2017 data ¶
The WMO’s Greenhouse Gas Bulletin, its annual flagship report, tracks atmospheric concentrations of dangerous gases back to 1750. This year’s report covers 2017 data and puts carbon dioxide at 405.5 parts per million, up from 403.3 ppm in 2016 and 400.1 ppm in 2015.
Taalas said the last time Earth saw a comparable CO2 concentration was 3-5 million years ago, when temperatures were 2-3°C warmer. Researchers have reliable estimates of CO2 levels going back 800,000 years from air bubbles trapped in ice in Greenland and Antarctica, while fossilised material has allowed rough estimates to be pushed back as far as five million years.
The UN agency also said methane, nitrous oxide and CFC-11 were rising.
Scientists say there is no quick fix ¶
Emissions remain the main driver of greenhouse gas levels, but the concentration in the atmosphere reflects a complex exchange between the atmosphere, biosphere, lithosphere, cryosphere and oceans. About 25 percent of emissions are currently absorbed by the oceans and biosphere.
The Intergovernmental Panel on Climate Change has said that keeping warming below 1.5 degrees Celsius requires net CO2 emissions to fall to net zero, meaning the amount released must be matched by the amount removed through natural absorption or technology.
Manaenkova said CO2 stays in the atmosphere and oceans for hundreds of years. “There is currently no magic wand to remove all the excess CO2 from the atmosphere,” she said. “Every fraction of a degree of global warming matters, and so does every part per million of greenhouse gases.”
The UN said 17 of the 18 hottest years on record have occurred since 2001, and that climate-related disasters cost more than $500 billion in 2017.
