Greenhouse gases in our atmosphere reached record highs in 2014, prompting fears of a "permanent reality" that could threaten the health of future generations, experts say.

The World Meteorology Organization, an agency of the United Nations, says levels of carbon dioxide, the major greenhouse gas, averaged 397.7 parts per million in 2014, and even briefly hit 400 ppm.

Since CO2 levels have hit new records highs every year since recording began in 1984, the 400 ppm level is likely to be a permanent figure sooner rather than later, says WMO Secretary-General Michel Jarraud.

"It means hotter global temperatures, more extreme weather events like heat waves and floods, melting ice, rising sea levels and increased acidity of the oceans," he says. "This is happening now and we are moving into uncharted territory at a frightening speed."

CO2 has not been at a 400 ppm level in the Earth's atmosphere for millions of years, and prior to the Industrial Revolution of the late 1800s, it averaged around 280 ppm, said the WMO is its annual report of concentrations of greenhouse gases in our atmosphere.

With the Industrial Revolution came widespread emissions of such gases, including carbon dioxide and methane from the burning of coal, oil and gas for energy.

A number of scientists have warned that a sustain level of 400 ppm or above would lead to long-term disturbances of our planet's climate.

The global average will likely remain above that figure beginning in 2016, the WMO report says.

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

While carbon dioxide has been rising at a steady rate of around 0.5 percent for the last decade, two other greenhouse gases — nitrous oxide and methane — have been rising at even faster rates, the report said.

Since carbon dioxide, once emitted, remains in the atmosphere for centuries, its consequences for the globe and its people will continue for at least that long, the report authors say.

"It is an invisible threat, but a very real one," Jarraud notes.

Hot on the heels of the WMO report came another, this one from the UK's Met Office and the University of Anglia's Climatic Research Unit, saying the average temperature on the Earth during the first nine months of this year rose above historic norms by 1.02 degrees Celsius.

That rise adds to evidence of "unequivocal warming" of our planet, says Peter Stott, head of the Anglia unit.

"As the world continues to warm in the coming decades ... we will see more and more years passing the 1 degree marker — eventually it will become the norm," he says.