Odds are increasing that 2016 will be the hottest year on the books, as April continued a remarkable streak of record-warm months. Last month was rated as the warmest April on record by both NASA and the National Oceanic and Atmospheric Administration, which released their data this week. In the temperature annals kept by NOAA, it marked the 12thMore
The last 13 months, including May, have all been record warm, according to the National Oceanic and Atmospheric Administration, an unprecedented streak in the record book.
The May record came despite an easing in global temperatures from their El Niño-fueled peak, and it increases the likelihood that 2016 will surpass 2015 as the hottest year in the books.
In NOAA’s dataset, May was 1.56°F (0.87°C) above the 20th century average, the first month since November 2015 in the agency’s records that wasn’t at least 1°C above average.
“That is a very large value, the largest value in the record for May,” Deke Arndt, the head of the climate monitoring division at NOAA’s National Centers for Environmental Information, said during a press briefing.
NASA put May at 1.67°F (0.93°C) warmer than the 1951-1980 average. Each agency has slightly different ways of handling the temperature data and uses different baselines for comparing temperatures, leading to small differences in the temperature numbers.
For the year-to-date, temperatures are 1.9°F (1.08°C) above the 20th century average, according to NOAA, putting it 0.43°F (0.24°C) above where 2015 was at this point.
To show how hot the last few years have been, Arndt compared two lists: One showing the 10 warmest months on record as of November 2013 and a second showing the 10 warmest months to date. On the 2013 list, the warmest months came from eight separate years, whereas today, all but one of the top 10 months were from 2016 and 2015. The exception is January 2007, which currently is tied for the 10th warmest month. In 2013, it was the warmest month on record.
The comparison shows that “we’re in a new neighborhood now in terms of global temperature,” Arndt said.
To show how far temperatures have risen from a baseline closer to pre-industrial times — before heat-trapping greenhouse gases began accumulating in the atmosphere — Climate Central has reanalyzed the temperature data, averaging the NASA and NOAA numbers and comparing them to the average from 1881-1910.
By that reckoning, the year to date was 2.5°F (1.39°C) above that average, edging closer to 1.5°C above pre-industrial temperatures. As part of international efforts to limit global warming, nations have been discussing using that threshold as an even more ambitious target than the current goal of keeping warming under 2°C (3.6°F) by end of this century.
While El Niño helped boost global temperatures this year — and helped them cross the 1°C mark for the first time — the main driver of the steady rise in global temperatures is the buildup of carbon dioxide and other greenhouse gases.
In fact, carbon dioxide reached several notable, if somewhat symbolic milestones this year. It saw the biggest year-over-year increase in concentrations on record, and the South Pole measured its first-ever recording of 400 parts per million. Pre-industrial carbon dioxide levels were about 280 ppm.
The considerably elevated temperatures through the first five months of this year increase the odds that it will take the title of hottest year on record. If it does, it will be the third record hot year in a row.
Through April, there was already a 99 percent chance that 2016 would take the title, according to Gavin Schmidt, director of NASA’s Goddard Institute for Space Studies, which keeps the agency’s temperature record.
““I would not be surprised at all if 2016 at least nominally ended up the warmest year on record,” Arndt said.
How the rest of the year plays out depends somewhat on what happens now that El Niño has officially ended. With El Niño waning, it’s unclear whether June might continue the streak of record warm months. The warmest June on record is June 2015.
“I wouldn’t rule it out. I wouldn’t say it is likely, but it certainly is a possibility,” Arndt said.
A La Niña — which tends to depress global temperatures — is favored to form by this fall, but its biggest effects tend to come in the months after it forms. That means 2017’s temperatures may be more affected than 2016.
At the same time, the oceans, particularly the Indian Ocean, are still quite warm, and they retain heat much longer than land does.
Even if 2016 doesn’t best 2015, it will be among the warmest years on record. All but one of the 10 warmest years globally have occurred in the 21st century. The outlier, 1998, was the year of an exceptionally strong El Niño. But even La Niña years now are hotter than El Niño years of decades past, meaning 2017 is likely to be quite warm when compared to the long-term average, even if La Niña develops.