By Tom Miles

GENEVA, Nov 9 (Reuters) - Greenhouse gas levels in the atmosphere reached a record high in 2014 and the relentless fuelling of climate change is endangering the planet for future generations, the World Meteorological Organization said on Monday.

"Every year we say that time is running out. We have to act NOW to slash greenhouse gas emissions if we are to have a chance to keep the increase in temperatures to manageable levels," WMO Secretary-General Michel Jarraud said in a statement.

His annual plea for the world to do whatever it can to cut greenhouse gas emissions - which come mainly from burning fossil fuels and from agriculture, cement production and deforestation - comes weeks before negotiators from over 190 states convene in Paris to try to agree a new U.N. climate deal.

Graphs issued by the WMO, a U.N. agency, showed levels of carbon dioxide, the main greenhouse gas, climbing steadily towards the 400-parts-per-million (ppm) level, having hit a new record every year since reliable records began in 1984.

Carbon dioxide levels averaged 397.7 ppm in 2014 but briefly breached the 400-ppm threshold in the northern hemisphere in early 2014, and again globally in early 2015.

"Next year we will be reporting much higher concentrations because of El Nino," WMO atmospheric research chief Oksana Tarasova told Reuters, referring to the Pacific Ocean warming phenomenon.

Soon 400 ppm will be a permanent reality, Jarraud said.

"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. This is happening now and we are moving into uncharted territory at a frightening speed."

The rise in carbon dioxide levels is being amplified by higher levels of water vapour, which are in turn rising because of carbon dioxide emissions, the WMO said.

Levels of the other two major man-made greenhouse gases, methane and nitrous oxide, also continued a unrelenting annual rise in 2014, reaching 1,833 parts per billion (ppb) and 327.1 ppb, respectively. Both rose at the fastest rate for a decade.

For the Paris conference later this month, more than 150 countries, led by top greenhouse gas emitters China and the United States, have issued plans to limit emissions beyond 2020.

But the plans revealed so far will not curb emissions enough to meet a target agreed in 2010 to limit global warming to within 2 degrees Celsius (3.6 Fahrenheit) of pre-industrial levels.

"Two degrees will be bad enough but it will be better than three degrees," said Jarraud. "Of course it would have been better to have 1 degree... But 1 degree is not possible any longer. It's just not feasible. Too late." (Reporting by Tom Miles; Editing by Mark Heinrich)