Last year was right on track with global warming trends, tying with 2006 and 2009 for the seventh warmest year since 1880, according to a report issued by the NASA's Goddard Institute for Space Studies (GISS).

The average temperature for 2013 was 58.3 degrees Fahrenheit (14.6 C), or 1.1 F (0.6 C) warmer than the mid-20th century baseline, the researchers said, noting that, except for 1998, the 10 hottest years in the last 134 years have all occurred since 2000, with 2005 and 2010 registering as the warmest on record. What's more, it has now been 38 years since researchers have recorded a year cooler than average temperatures.

"Long-term trends in surface temperatures are unusual and 2013 adds to the evidence for ongoing climate change," GISS climatologist Gavin Schmidt said. "While one year or one season can be affected by random weather events, this analysis shows the necessity for continued, long-term monitoring."

Furthermore, just because the global average temperature was in the top ten warmest since 1880 doesn't mean that temperatures were evenly distributed throughout. For Australia, 2013 was the hottest year on record, while the continental United States experienced its 42nd warmest.

Growing levels of greenhouse gas in the atmosphere are behind the long-term rise in temperatures, the scientists said.

"Each successive year will not necessarily be warmer than the year before, but with the current level of greenhouse gas emissions, scientists expect each successive decade to be warmer than the previous," officials wrote in a statement.

The researchers singled out carbon dioxide in particular, explaining that while it occurs naturally in certain doses, current levels - driven by the burning of fossil fuels - are higher than at any other time in the last 800,000 years.

Data for the analysis was derived from more than 1,000 meteorological stations throughout the world, as well as Antarctic research station measurements and satellite observations of sea-surface temperatures.