UN World Meteorological Organisation ranks 2014 as hottest year on record

Last year was most likely the warmest year on record, the World Meteorological Organisation (WMO ) announced today. Global surface temperature in 2014 was 0.57 degrees Celsius above the 1961-1990 average, nominally beating 2010 and 2005 to the top spot.

In the last few weeks, the world’s four main meteorological agencies have all announced that 2014 topped the charts as one of the hottest year on record. Today, the WMO made it official.

Fourteen of the fifteen warmest years on record have now all occurred in the 21st century, today’s report notes.

Taking the top spot

The WMO is the United Nations’ specialist weather and climate agency. It does its own analysis about this time every year, combining three major global datasets into one definitive one.

Global surface temperature anomaly in 2014 from the three major agencies, the World Meteorological Agency (WMO) and the Japan Meteorological Agency. All figures relative to the 1961-1990 average. Source: Rosamund Pearce, Carbon Brief

In mid-January, NASA and the US National Oceanic and Atmospheric Administration (NOAA) issued a joint statement saying 2014 was the warmest year since 1880.

Last week, the UK Met Office and the Climatic Research Unit (CRU) at the University of East Anglia released joint data, announcing 2014 tied with 2010 as the hottest year on record.

A less well-known dataset, produced by the Japan Meteorological Agency (JMA), became the first to confirm that 2014 had taken the top spot in their record earlier in January.

The full temperature record

But while it’s interesting to see whether or not an individual year breaks records, it’s far more telling to look at the bigger picture. Each of the four datasets stretch back to at least the late 19th century. You can see how the different datasets compare below.

Click here for an interactive version of the graph, and here for an animated one.

How the major global surface temperature datasets compare. NASA GisTEMP (purple) shows fastest warming. JMA tends to track slightly lower than the others (orange). NOAA MLOST is green and Met Office/CRU is blue. Credit: Rosamund Pearce, Carbon Brief

Each dataset uses a different baseline to work out temperature anomalies. We’ve plotted them above to the same 1961-1990 baseline, and included the new data taking us up to 2014.

You can find more about the why there are year-to-year differences in our special briefing on how scientists take Earth’s temperature. But overall, the datasets tell a consistent story.

A continuing trend

Last year continues the warming trend by adding to a series of very hot years. But it’s notable that 2014’s high temperatures occurred without a fully-developed El Niño, says today’s report.

The Pacific weather phenomenon tends to give global temperatures a boost. Both 2005 and 2010 – the next hottest years on record – saw El-Niño events.

The WMO notes:

“High temperatures in 1998 – the hottest year before the 21st century – occurred during a strong El-Niño year.”

Even without an El-Niño, global temperature in 2014 was 0.09 degrees above the average for the past ten years (2004-2013), the WMO calculates. But only a few hundredths of a degree separates the warmest years on record.

This is less than the degree of certainty with which scientists can make measurements of this kind. That means while 2014 is nominally the warmest years on record, scientists can’t be absolutely certain which of all the very hot years was the hottest.

Secretary-General Michel Jarraud says:

“The overall warming trend is more important than the ranking of an individual year. “

We should expect the next few years to bring more of the same high temperatures, suggests the Met Office’s new decadal forecast. Jarraud echoes this in today’s report, saying:

“We expect global warming to continue, given that rising levels of greenhouse gases in the atmosphere and the increasing heat content of the oceans are committing us to a warmer future.”

Main image: Vivid sunset over the Andes Mountains and Atacama Desert, Chile.