As May shatters global heat records, which 2015 will we get?

Friday, June 19, 2015, 5:47 PM - The latest temperature records have May 2015 shattering a trio of heat records for the planet. What are the odds we're headed for another warmest year on record?

2015 isn't even half-way over yet, but based on global temperature records, it's looking like it may be another record-setting year.

Now using their updated and improved dataset, which contains a more complete and accurate record of global temperatures over land and ocean, NOAA - the US National Oceanic and Atmospheric Administration - just released their global analysis for May 2015, reporting three different temperature records broken during the month:

1. The combined average temperature over global land and ocean surfaces for May 2015 was the highest for May in the 136-year period of record, at 0.87^oC above the 20th century average... surpassing the previous record set just one year ago by 0.08^oC.
2. Together, the record warm March and May and fourth warmest April made the combined average temperature over global land and ocean surfaces for the March–May period the highest on record, at 0.85^oC above the 20th century average... surpassing the previous record warmth of March–May 2010 by 0.04^oC. The Northern Hemisphere had its warmest spring on record and the Southern Hemisphere had its second warmest autumn, behind 2010.
3. The first five months of 2015 were the warmest such period on record across the world's land and ocean surfaces, at 0.85^oC above the 20th century average, surpassing the previous record set in 2010 by 0.09^oC.

NOAA isn't the only agency that's seeing May break records. The Japan Meteorological Agency (JMA) also reports that May 2015 was the warmest month of May on record, at +0.74^oC above the 20th century average, and that spring (March-May) was the warmest since record keeping began in 1891, coming in at +0.73^oC above the 20th century average. Meanwhile, NASA is reporting May 2015 as the second warmest in their records, behind 2014, and spring was also second in their record books, surpassing 2014 but still behind May 2010. Neither JMA nor NASA have the new updated and corrected methodology that NOAA is using, however.

What's driving these record temperatures?

Part of it is the El Niño in the central Pacific Ocean, as this unusually early pattern is still intensifying as we press into summer, and is expected to peak in the fall (see left) as a moderate, or possibly strong event. The oceans have apparently been running warm for some time, though, according to Deke Arndt, Climate Monitoring Branch chief at the National Centers for Environmental Education (NCEI).

During a press conference on Thursday, Arndt said "The oceans have been what's really been driving the warmth that we've seen in the last year and a half to two years. We've seen really large warmth in all of the major ocean basins. So, if there's anything unusual or weird, I guess, about what we're seeing, it's the fact that the entire global ocean is participating in this really extreme warmth that we've seen in the last couple years."

This assessment agrees with what researchers have found, and what is reported by the Intergovernmental Panel on Climate Change (IPCC), that the vast majority of extra heat being accumulated in Earth's environment is going into the oceans.

How might 2015 progress from here?

It's never an easy task to say what's going to happen for the rest of the year around the globe. However, just looking at what has occurred so far in 2015, along with what has happened in previous years, we can at least get an idea of how conditions would have to develop to avoid displacing 2014 from its lofty position in the record books.

Given the trend so far through May, each month for the rest of the year - June through December - would need to rank as 6th warmest on record, at the most, for 2014 to maintain its current ranking. So, that said, how likely is it that we'll avoid a new record?

2015 is already running hot, as the maps above reveal, and with El Niño strengthening, the chances of temperatures cooling off enough (up to a tenth of a degree in some cases!) are fairly slim. Looking back to 1987, when a similar pattern to El Niño 2015 had developed, temperatures during the summer jumped significantly, followed by a warm autumn and a very warm start to winter. While it's unlikely 2015 will follow the exact same pattern, something similar could drive this year to far surpass last year, as could simply matching 2014's temperatures or having the current temperature trend (+0.85^oC from Jan-May) persist through the rest of the year.

At the very least, if temperatures match just the 5th warmest months on record for the rest of the year, 2015 will take its place as the next warmest year on record. Given the pattern that we're in, that's really not setting the bar very high.

Graph courtesy: NOAA/NCDC, with edits by author.

Sources: NOAA/NCEI | JMA | NASA | Skeptical Science