Why 2014 Was The Hottest Year Ever, But The Met Office Can't Say So

Despite commendable caution from the Met Office, the evidence is very strong that 2014 really was the Earth's hottest year since records began.

The Met Office has announced that 2014 may have been the hottest on record.

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It comes after the National Oceanic and Atmospheric Administration (NOAA) and NASA both announced that 2014 definitely was the hottest year.

The Met Office's caution is interesting. Why the reluctance to say definitively?

The data show that 2014 was 0.56°C (give or take 0.1°C) above the average global temperature. That makes it the hottest year ever, tied with 2010. But the Met Office only said it's "one of" the warmest years – "We can say with confidence that 2014 is one of 10 warmest years in the series" going back to 1850, said Colin Morice, a climate monitoring scientist at the Met Office.

It's because the uncertainty range is greater than the difference between the hottest years.

NOAA / Via ncdc.noaa.gov

It's hard to say that any given year is the hottest, because the "give or take 0.1°C" mentioned above is enough to make it uncertain. The Met Office is being cautious because one of the other, almost-as-hot years, could in fact have been the hottest. "Uncertainties in the estimates of global temperature are larger than the differences between the warmest years," says Morice.

But the odds are it really was the hottest year.

"It's fairly clear that 2014 was the hottest," said Mark Lynas, the author of Six Degrees: Our Future on a Hotter Planet, because all three datasets released in the last few weeks – NASA's, the NOAA's, and the Met Office's – agree. Often in the past there have been slight discrepancies.

Lynas thinks the Met Office's caution is in part due to "blowback" from climate sceptics: After the NOAA released its data, there was criticism that it hadn't taken this sort of uncertainty into account.

What's more, it wasn't an El Niño year.

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Most of the hottest years on record have come during El Niño years – the years when the Pacific Ocean pushes vast amounts of heat energy into the atmosphere. There was one in 1998 which pushed global temperatures to an enormous high that has barely been reached since. "If there is another 1998-style El Niño now, it will push temperatures off the charts," said Lynas.

That 1998 El Niño is a large part of why people talk about a "pause" in global warming.

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Because it was so high, "you can draw a straight line" in temperatures between then and now, said Lynas, despite the warming since. "It all depends where you put your start and end points of your data."

Whether or not 2014 was the hottest, or just one of the hottest, we are in uncharted territory now.

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"We are living in a partly artificial climate," Lynas said. "You just have to look at the difference from the mid-20th-century average. I don't think there's any serious dispute over that now."

He said there's also no serious debate that there is a "huge imbalance" between the energy coming into the system and the energy going out, because so much is being trapped by man-made greenhouse gases. "What we don't know, precisely, is where that energy is going," said Lynas. "Is it going into the ocean? If so, where? All we know is that a lot of it hasn't gone into the lower atmosphere."