This year may eclipse 2010 as the hottest since records began in the 19th century, a sign long-term global warming is being stoked by rising greenhouse gas emissions, scientists said.

The period of January to October 2014 is already among the warmest ever recorded, and a warm ending to the year could easily make it top, according to US and British data.

Skeptics who doubt the necessity of a shift away from fossil fuels to stop the Earth's climate from heating up point out that world average temperatures have not risen much since 1998, despite rising greenhouse gas emissions.

But the final ranking for 2014, due next year, may influence public and business perceptions about the severity of climate change. Almost 200 governments are due to agree a U.N. deal to combat global warming in Paris in December next year.

"2014 is more likely than not to be the warmest year," Tim Osborn, a professor at the Climatic Research Unit at the University of East Anglia, told Reuters, saying manmade greenhouse gas emissions are tending to push up temperatures.

He said there were many uncertainties about where 2014 would rank because of natural variations in temperatures late in the year. Also, a big volcanic eruption might spew out ash that dims sunshine, cooling the planet.

The U.N.'s World Meteorological Organization (WMO) will publish a preliminary ranking for 2014 on Dec. 3, during annual U.N. talks in Peru which will prepare the Paris accord.

Promises for action by China, the United States and the European Union have made a global deal more likely, but any agreement will probably be too weak to halt rising temperatures despite new scientific warnings of powerful storms, floods, desertification and rising sea levels.

Of the WMO's three main data sources, the US National Oceanic and Atmospheric Administration (NOAA) ranks January-October 2014 as the warmest such period on record, NASA as the second-warmest and the British Met Office and University of East Anglia as the third-warmest.

NOAA says 2014 is on track to be the warmest on record. The rankings differ partly because scientists use different estimates for places with few thermometers, such as the Arctic.

"It probably is a bit premature to say 2014 will be the warmest year on record," said Michael Cabbage, spokesman for Nasa's Goddard Institute for Space Studies.

The British data place 2014 third, fractionally behind 2010 and 1998, which both cooled toward the end of the year.

Despite a slowdown in the pace of warming since 1998, the WMO says 13 of the 14 warmest years on record have been in this century. – Reuters