Last year was the warmest year in recorded history, scientists confirmed today. With global temperatures topping 1°C above preindustrial times, the world has now experienced three consecutive record-warm years for the first time since records began
January 19, 2017 — The long-term warming trend from greenhouse gas emissions received an extra boost from the tail-end of a strong El Niño but 2016 would have been a record even without it, say scientists.
The 12-month period from January to December 2016 was 0.13°C warmer than the previous record set in 2015, which was itself 0.11°C warmer than 2014, according to scientists from the US National Aeronautics and Space Administration (NASA).
The US National Oceanic and Atmospheric Administration (NOAA) also released its official data today, confirming 2016 as the hottest year on record. A third, independent record from the UK Met Office/University of East Anglia puts 2016 marginally above 2015’s record high.
You can see how the three global datasets compare in the graph below. NASA is in blue, NOAA is in red and the Met Office/UEA is in yellow.
The World Meteorological Organisation, which takes an average of all three major datasets, also confirmed 2016 as the hottest year on record today.
Role of El Niño
According to NASA’s analysis, the departing El Niño gave a boost to global temperature early in 2016, leading to a string of record-setting months. The six-month period from January to June was the warmest half-year in the modern temperature record, dating back to 1880.
As the effects of the El Niño reached a peak and began to wane, greenhouse gas warming kept global temperatures high for the rest of the year.
Overall, El Niño contributed about 0.12°C to the global temperature anomaly in 2016, with the bulk of the warming coming from greenhouse gases, according to NASA figures. The UK Met Office’s analysis echoes the small role of El Niño relative to climate change. Dr Peter Stott, acting director of the Hadley Centre, said today:
The scientists say they do not necessarily expect 2017 to be another record year, since the world is now in a weak La Niña phase – the cold counterpart to El Niño that tends to edge global temperature downwards – and scientists are expecting a slip back to “neutral” by February.
Nevertheless, continued warming from greenhouse gases will mean 2017 is still likely to be a very warm year in the context of the 136-year record, the scientists say.
Aside from El Niño, 2016 was out-of-the-ordinary for other reasons.
The Arctic, in particular, experienced an exceptional year. Persistent high temperatures saw Arctic sea ice extent drop to record lows in January, February, April, May, June, October, and November.
But observations are scarce in the remote Arctic. How the three global temperature datasets handle the absence of data is a major reason for the differences between them, says Dr Gavin Schmidt, director of NASA’s Goddard Institute for Space Science. He tells Carbon Brief:
In large part, he explains, this is why NASA’s global temperature for 2016 (blue) is so much higher than for the Met Office/UEA (yellow) in the graph above. Schmidt continues:
Margin of error
All of today’s estimates of global temperature come with a measure of uncertainty, a range above and below the estimate within which the actual value is likely to lie. This is to account for the fact that there are some uncertainties in the measurements themselves. As Schmidt explains:
Each of the global agencies takes a slightly different approach to stitching together different data sources. The difference between global temperature in 2016 and the previous record in 2015 is greater than the margins of error in the NASA and NOAA datasets, putting it beyond doubt that 2016 is the hottest year in those records. The distinction isn’t so clear cut for the Met Office/UEA record, where missing Arctic data makes for a larger margin of error. As Stott explains:
That all three datasets arrive independently at the same overall result – of exceptional warmth relative to the past – increases confidence in their conclusion. Schmidt says:
Over time, scientists develop better ways to do this “meshing” and the datasets are updated. A paper this month, for example, confirmed that a recent upgrade to the ocean temperature record that both NASA and NOAA use does a better job at capturing the pace of warming in recent decades than older versions.
Important though they are, corrections to account for changes in the way data is collected are small compared to warming we’ve seen since humans started industrialising, Schmidt notes:
Seemingly every year there’s a discussion about whether the previous year broke records or not. Does this focus on record-setting help our understanding of climate change?
Untangling the factors that can nudge global temperature up or down in any given year, such as El Niño and La Niña, is scientifically interesting, but it doesn’t alter the big picture. As Prof Jerry Meehl, senior scientist at the US National Center for Atmospheric Research, explains:
Or as Prof Dave Reay, professor of carbon management at the University of Edinburgh, puts it:
That said, the focus on momentous “events” is inevitable, to some extent, as that tends to be how humans monitor changes over time, Schmidt tells Carbon Brief:
So, while humans are tuned to pay attention to records, the bottom line is that the planet is warming and we’re in a period of exceptional warmth historically, Schmidt concludes:
— Carbon Brief (@CarbonBrief) January 18, 2017