September 2015 was the warmest such month for Planet Earth since such data began in 1880, and very likely long before that, according to data released Wednesday by the National Oceanic and Atmospheric Administration (NOAA). The first nine months of the year were also record warm, increasing the likelihood — which was already 97% by one measure — that this will be the warmest year the planet has seen since at least 1880.
The superlatives for September 2015 are remarkable, and are the result of a combination of one of the top three most powerful El Niño events on record in the tropical Pacific Ocean plus long-term, manmade global warming.
The September globally averaged sea surface temperature was 1.46°F (0.81°C) above the 20th century average. This was the highest temperature for September in the 1880-2015 record, surpassing the previous September record set last year by 0.13°F (0.07°C). To date, seven months this year have been record warm, including the past five in a row, NOAA said.
Not only was September the warmest such month on record in NOAA's data set (as well as thatkept by the Japan Meteorological Agency), but it was also the greatest rise above average for any month in the 136-year historical record.
In other words, September had a global average surface temperature that was so far above normal that it set a record for the margin above average. This is sort of like a baseball player hitting a home run that travels a greater distance than any other home run on record for that particular stadium.
It reflects just how skewed the climate system is toward setting warm records.
In this case, September 2015 beat out February and March of this year for the greatest rise above average record, beating them both by 0.01 degrees Celsius, or 0.02 degrees Fahrenheit, NOAA found.
Six of the ten highest temperature departures from average have occurred in 2015, Jessica Blunden, a scientist at NOAA's National Centers for Environmental Information (NCEI) in Asheville, told Mashable in an email.
Or to put it another way, "Out of 1,629 monthly records since 1880, six months of 2015 are among the 10 highest monthly temperature departures from their respective averages," NOAA reported in its monthly climate summary.
Both land and ocean temperatures were record warm in September, as they have been for many other months this year so far. Ocean temperatures, in particular, were extremely mild, exceeding the previous record set in September 2014 by 0.13 degrees Fahrenheit, or 0.07 degrees Celsius.
This may seem like quibbling over very small differences, but consider that the discrepancy between the planet we know today and a planet with virtually zero ice cover in Greenland and Antarctica is about 10 degrees Fahrenheit, for a global average.
In short, big changes can occur as a result of relatively small differences in global average temperatures.
Typically, global average temperature records — whether they're months or years — are exceeded by far smaller margins. For example, the difference between the third warmest September and the fourth warmest September in the data set was just 0.1 degree Celsius, or 0.18 degrees Fahrenheit.
The year-to-date temperature across global land and ocean surfaces was 1.53 degrees Fahrenheit, or 0.85 degrees Celsius, above the 20th century average. This was the highest for January-September in the 1880-2015 record, NOAA said in a report posted online, surpassing the previous record set last year by 0.19 degrees Fahrenheit, or 0.12 degrees Celsius.
Again, this means that 2015 is tracking significantly above last year's temperatures, not just a small distance above that record. Both land temperatures and ocean temperatures are separately setting records for the mildest year on record so far, NOAA found.
The warm oceans have fueled a record number of Category 4 and 5 hurricanes and typhoons in the Northern Hemisphere so far this year, with 21 such storms, beating the old record of 18 set in 2004.
This is not only El Niño's doing
El Niño, which is characterized by milder-than-average ocean temperatures across the tropical Pacific Ocean, can pump more heat into the atmosphere and temporarily elevate global ocean temperatures. Such events, which typically occur every five to seven years, can temporarily boost global average temperatures, but they occur on top of longer-term trends.
As the planet warms in response to human activities, scientists say even weak El Niño events can put the planet over the edge into setting a temperature record. Since the ongoing event is unusually strong, the spike is even higher. However, it would be wrong to conclude that the entirety of the temperature spike is caused by El Niño, scientists say.
For example, so far this year, global average surface temperatures are running about 0.31 degrees Fahrenheit higher than at this point in 1998, which was a record-setting El Niño year. "This indicates that there are other factors beyond El Niño that are contributing to the warmth," Blunden said. "The fact that we continue to break records clearly shows our underlying global warming trend."
"The El Niño years keep getting warmer compared to one another, and the La Niña years keep getting warmer compared to one another. That's a clear signal that global warming underlies the variability of ENSOs and such we see over months and years," Blunden wrote, using the acronym for the larger climate cycle El Niño and La Niña events are a part of, known as the El Niño-Southern Oscillation.
Blunden also made clear that it's not just the El Niño regions of the Pacific Ocean that are record warm, either. "The northeast "Pacific Blob" has been present for the better part of two years and the entire Indian Ocean has been incredibly warm," she wrote. "And now we're starting to see more record warmth emerge in parts of the Atlantic. It truly is the global oceans driving our record heat."
The oceans absorb the vast majority of the additional heat being pumped into the climate system by skyrocketing concentrations of global warming pollutants in the atmosphere, including carbon dioxide.