2015 'unambiguously' the hottest year on record, says report

Thursday, January 14, 2016, 12:50 PM - If there were any lingering doubts that 2015 was going to top the list of hottest years on record, this first look - ahead of official reports from NOAA and NASA - will surely put them to rest.

According to a new report from Berkeley Earth, preempting the official word from agencies such as NOAA, NASA and the Japan Meteorological Agency (JMA), "2015 was unambiguously the hottest year on record."

From the report:

For the first time in recorded history, the Earth’s temperature is clearly more than 1.0 C (1.8 F) above the 1850-1900 average. 2015 was approximately 0.1 degree C (about 0.2 degrees F) hotter than 2014, which had tied with 2005 and 2010 as the previous hottest years. 2015 set the record with 99.996% confidence. The analysis covered the entire surface of the Earth, including temperatures from both land and oceans.

"Berkeley Earth has taken a cautious approach to announcing hottest years," Elizabeth Muller, Executive Director of Berkeley Earth, said in a press release. "A year ago, we announced that 2014 was not a clear record, but only in a statistical tie with 2005 and 2010. Now, however, it is clear that 2015 is the hottest year on record by a significant margin."

Based on Berkeley Earth's analysis, large swaths of the Earth's surface - mainly over the oceans but also in the northwestern United States and western Canada, eastern Europe, northern Russia, southern and eastern Africa, parts of the Middle East and northern South America - experienced their hottest temperatures ever recorded, compared to the 1951-1980 climate average*.

The near-record El Niño pattern in the equatorial Pacific Ocean had a large part to play in the temperature extremes seen in that region of the world, with "The Blob" playing a significant role in the northeastern Pacific as well.

Another conspicuous anomaly is the cold blob in the North Atlantic, just to the south of Greenland. This cold spot, which has been flagged as a potential worry for the continued functioning of the Gulf Stream in transporting heat from the equator to the North Atlantic, has its roots in the melting of Greenland's glaciers.

Global Warming is speeding up!

At the same time as Berkeley Earth comes in on the side of "unequivocal" for 2015 now ranking as the #1 hottest year on record, their analysis also shows the rate at which global warming is speeding up.

With each time-step in the animation, the period being examined gets shorter, from 165 years in the first panel to just 45 years in the final panel, and the intensity of the warming seen during each period ramps up with each step. The warming between 1970 and 2015 is nearly 3 times stronger than the warming since 1850 (when temperature records began). This trend is also shown in the graph below.

Certainties and Uncertainties

When the last official record for hottest year was posted in early 2015 by NOAA and NASA, the announcements included statements uncertainties, with NOAA listing 2014 as having a 48 per cent chance at being the hottest year and NASA listing it as 38 per cent. Also vying for the top spot were 2010, 2005, 2013 and even tenacious 1998. However, as the table below shows, by their analyses, these years were certainly not neck-and-neck in the running.

Slide #5 from "Annual Global Analysis for 2014", by Gavin Schmidt (NASA) and Thomas Karl (NOAA), January 2015. Differences are "sensitive to methodology and coverage." Credit: NASA/NOAA

From both agencies, 2014 was still the front-runner, by a fairly wide margin based on NOAA's records. So, far from casting doubt on the certainty of 2014's ranking in the record books, this solidified its place as the hottest year on record.

According to a press briefing at the time of the release, Thomas Karl, the director of NOAA's National Climate Data Center (NCDC) stated: "for the NOAA data, 2014 is two and a half times more likely than the second warmest year on record, 2010, to actually be the warmest on record, after consideration of all the data uncertainties that we take into account. And for the NASA data, that number is on the order of about one and a half times more likely than the second warmest year on their records, which again, is 2010. So clearly, 2014 in both our records were the warmest, and there’s a fair bit of confidence that that is indeed the case, even considering data uncertainties."

With Berkeley Earth's announcement that 2015 is, without a doubt, the hottest year on record, the upcoming reports from NOAA and NASA, due out next week, should make for some very interesting reading.

Sources: Berkeley Earth (pdf) | Berkeley Earth | NOAA (pdf) | NOAA/NASA (mp3)

*Berkeley Earth (along with NASA) uses a 1951-1980 climate average for their BEST (Berkeley Earth Surface Temperature) dataset, as opposed to the 1981-2010 average used by NOAA. Whereas 1981-2010 gives a comparison to the last three decades, 1951-1980 represents a more "neutral" period in the current warming trend.

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