With atmospheric carbon dioxide concentrations having reached a "symbolic and significant milestone" in 2015—and with no signs of them abating this year—the World Meteorological Organization (WMO) said Monday that "a new era of climate change reality" is upon us.

Boosted by the year's exceptionally strong El Niño, that milestone was reaching worldwide average concentrations of carbon dioxide of 400 parts per million (ppm) for the first time ever. "The last time CO2 was regularly above 400ppm was three to five million years ago, say experts," the BBC writes.

New era of climate reality. For 1st time, CO2 in atmosphere averaged 400 ppm for whole world and whole year in 2015. #climatechange. pic.twitter.com/67ESDODoyc — WMO | OMM (@WMO) October 24, 2016

The data in for this year offers little hope for a better emissions scenario. "I think we're essentially over for good," Ralph Keeling, director of the greenhouse gas monitoring station at Mauna Loa, Hawaii at the Scripps Institution of Oceanography, said in May. With data from September (typically the low point of the year) showing levels above 400 parts per million, Keeling warned last month, "it already seems safe to conclude that we won't be seeing a monthly value below 400 ppm this year —or ever again for the indefinite future."

With that in mind, the WMO in its Greenhouse Gas Bulletin states that it is likely that "2016 will be the first year in which CO2 at the Mauna Loa Observatory remains above 400 ppm all year, and hence for many generations."

One bright spot that occurred last year in the fight to avert climate crisis, said WMO Secretary-General Petteri Taalas in a press statement, was the Paris climate agreement, which will enter into force next month.

SCROLL TO CONTINUE WITH CONTENT Never Miss a Beat. Get our best delivered to your inbox.







Still, Taalas said, 2015 "will also make history as marking a new era of climate change reality with record high greenhouse gas concentrations." He added, "The El Niño event has disappeared. Climate change has not."

Though he offered praised for the international commitment made last month to limit hydrofluorocarbons, Taalas said "the real elephant in the room is carbon dioxide, which remains in the atmosphere for thousands of years and in the oceans for even longer. Without tackling CO2 emissions, we can not tackle climate change and keep temperature increases to below 2°C above the pre-industrial era," he continued, referring the warming threshold that some analysts say may still bring about catastrophic effects.

This new reality, he said, necessitates a "fast-track" implementation of the Paris climate accord.

The new information from the WMO follows a prediction from NASA that, based on data through September, 2016 will likely be the hottest year on record.

According to meteorologists Jeff Masters and Bob Henson, "Temperatures would have to plummet at an almost unthinkable pace between now and December in order to keep 2016 from becoming the warmest year in global record-keeping."

With the new climate records—and "new new math" of climate change—as a backdrop, author and 350.org co-founder Bill McKibben said last month, "If we’re going to have a chance of dealing with climate change, it means mobilizing in ways that we haven't in a very long time."