2014 was likely Earth's hottest year since records began in 1891, according to a preliminary analysis from the Japan Meteorological Agency (JMA):
The global average temperature in 2014 was roughly 0.63°C (or 1.1°F) hotter than the average during the twentieth century, JMA found. Its preliminary analysis was based on both satellite and ground readings. The final version will be released next month.
The second hottest year in JMA's records was 1998 — a big El Niño year — followed by 2013, 2010, and 2005. All ten hottest years have come since 1998.
Climate scientists expect the Earth to get hotter over time so long as humans keep adding greenhouse gases to the atmosphere. There are lots of short-term variations here and there — for instance, El Niño years like 1998 tend to be a bit hotter, while La Niña years are a bit cooler — so not every year will necessarily set heat records. But the overall trend is up.
The JMA is one of four major government agencies worldwide keeping track of global temperature trends. The others are NASA and the National Oceanic and Atmospheric Administration (NOAA) in the United States, as well as the Met Office Hadley Centre in the United Kingdom. All four agencies analyze the data slightly differently — NASA, for instance, ranks 2010 and 2005 as hotter than 1998. But they all show the same upward trend over time.
The other agencies will release their own data in the coming weeks and months — and they may see things a bit differently than JMA does. But a preliminary NOAA analysis also found that it was very, very likely 2014 would turn out to be the hottest year on record in its dataset.
The US was cooler than average, Europe was warmer
According to JMA, much of the continental United States was actually a bit cooler than usual in 2014 (at least, compared with the climate from 1980-2010). The big exception was California, where warm temperatures have been exacerbating a brutal drought.
On the flip side, this year saw record warmth in Europe as well as record heat over most of the Pacific Ocean:
Also notable is that 2014 was a record hot year even without a major El Niño. El Niño events, which occur in the Pacific, tend to transfer heat that's stored beneath the ocean's surface up into the atmosphere. Years at the tail end of major El Niños tend to be hotter than average — that was a big reason why 1998 was unusually hot.
Forecasters say there's still a better-than-even chance that El Niño could reappear in the Pacific Ocean this winter — which would potentially push temperatures up in 2015. Still, that's not yet assured.
So is this the end of the global warming "pause"?
Assuming that 2014 does turn out to be the warmest year on record, Chris Mooney argues at Wonkblog that people should now quit saying that global warming "stopped" back in 1998 — a favorite line of climate skeptics like Senator James Inhofe (R-OK).
There are a couple of things to unpack here. The idea that global warming had "stopped" has never been very compelling — and not just because 1998 is a cherry-picked year. Scientists have assembled plenty of evidence that adding more greenhouse gases like carbon-dioxide to the atmosphere will heat up the Earth over time. The fact that the planet has been getting hotter over the last century is excellent evidence of this. Short-term blips in the temperature record don't really change this broad understanding. Nor does it ultimately matter whether 2014 is the warmest year on record or second-warmest or third-warmest. It's the long-term trends that count.
What has puzzled some scientists, however, is the fact that global average surface temperatures have risen at a slower pace over the past 15 years than they did in the 20 years before that — despite the fact that greenhouse gases are piling up in the atmosphere at a record pace. This is what's often referred to as the "pause" or "hiatus."
This is a question of some interest to climate scientists and you can see a longer rundown of possible explanations here — possible hypotheses include the idea that much of the extra heat trapped by greenhouse gases has been stored temporarily in the ocean, or that there's been an outburst of recent volcanic activity that muted the pace of warming in the 2000s.
This debate is certainly noteworthy. For instance, if a lot of the extra heat trapped by greenhouse gases did go into the ocean recently because of, say, strong trade winds in the Pacific, that might set the stage for more rapid warming in the years ahead. Similarly, analyzing short-term temperature trends might give scientists a better understanding of how quickly the Earth warms in relation to given levels carbon-dioxide in the atmosphere (a concept known as "climate sensitivity").
But, again, the big picture is the same as it ever was — regardless of year-to-year blips or where exactly 2014 ends up on the leaderboard. As we put more carbon-dioxide into the atmosphere, the Earth will get hotter. There will be short-term fluctuations here and there. Some years will be record hot years. Others won't. El Niño years will be a bit hotter. La Niña years will be a bit cooler. But over a long-enough time horizon, global warming is still with us.