New scientific data released on Monday confirmed 2015’s place as a milestone year for the Earth’s environment, with both temperatures and greenhouse gases crossing symbolic thresholds with ominous implications for future climate change.

The World Meteorological Organization, in an annual accounting of greenhouse gas concentrations in the atmosphere, reported that average levels of carbon dioxide exceeded 400 parts per million in the early months of 2015, a rise of 43 percent over pre-industrial levels.

And, in a separate report hours later, the Met Office and Climatic Research Unit at Britain’s University of East Anglia reported that the Earth’s average temperature has crossed the symbolically important 1-degree C (1.8 F) mark, with temperatures over the first nine months of the year exceeding historic norms by exactly 1.02 degrees C.

The reports are likely to add to concerns about global warming in a year that climate experts say is almost certain to surpass 2014 as the hottest year in recorded history.

“We are moving into unchartered territory at a frightening speed,” WMO Secretary General Michel Jarraud said of the report’s findings.

The WMO maintains the world’s biggest network of sensors detecting changes in the makeup of the Earth’s atmosphere. For decades it has tracked rising concentrations of greenhouse gases such as carbon dioxide, a naturally occurring chemical compound that is vital for plant life and also acts as an insulating blanket, trapping the sun’s heat and making the planet warmer than it would otherwise be.

With the burning of fossil fuels, levels of atmospheric carbon dioxide have risen steadily, soaring from about 278 ppm during pre-industrial times to above 390 ppm by the start of the current decade.

Many scientists contend that the carbon dioxide levels should remain well below 400 ppm to avoid long-term disruptions to the Earth’s climate. But since 2012, several of the WMO’s 125 individual monitoring stations have detected readings above that threshold.

The global average climbed to 397.7 ppm in 2014, the WMO report said, and then, in early 2015, it exceeded 400 ppm for the first time since record-keeping began, the organization's data shows.

The level then dipped, as usual, with the arrival of the spring growing season in the Northern Hemisphere, when trees and other plants take carbon dioxide out of the atmosphere. But WMO officials say the planetary average is expected to remain above 400 parts per million beginning in 2016.

“We will soon be living with globally averaged CO2 levels above 400 parts per million as a permanent reality,” Jarraud said.

The long-term implications for the planet, he said, include “hotter global temperatures and more extreme weather events,” as well as melting ice, rising sea levels and increased acidity in oceans.

“It is an invisible threat, but a very real one,” he said.

The WMO report, an annual compilation of monitoring data from the organization’s Global Atmospheric Watch program, shows carbon dioxide concentrations rising by 0.5 percent from 2013 to 2014, roughly on par with the average annual increase over the past decade. But two other key greenhouse gases — methane and nitrous oxide — appear to be increasing at a fast rate, the report said. Methane increased by 9 parts per billion from 2013 to 2014, compared with an average annual increase of 4.7 ppb, the report said.

The combined radiative “forcing” from all these gases — essentially the warming effect on the planet — has now risen by 36 percent since 1990, the report said. It said consequences will continue to be felt for centuries, since new emissions of carbon dioxide will remain in the atmosphere for that long..

The East Anglia report confirming the 1-degree temperature rise is new evidence of “unequivocal warming” of the Earth, said Peter Stott, head of the climate monitoring and attribution team at the British University. U.S. climate scientists say the planet is on track to break last year’s heat record — a near-certainty in the light of this year’s unusual “El Niño” weather pattern in the Pacific.

“As the world continues to warm in the coming decades, however, we will see more and more years passing the 1 degree marker — eventually it will become the norm,” Stott said.

The release of the reports comes three weeks before the start of international negotiations in Paris on a proposed treaty to reduce global emissions of greenhouse gases.

Diplomats from more than 190 countries are expected to participate in the talks, which are intended to put the planet on a path toward capping and then reducing carbon pollution. The Obama administration has pledged to reduce U.S. emissions by up to 28 percent by the year 2030, compared with the baseline year of 2005.