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El Niño or no El Niño, 2015 was the hottest year on record. That's the official word from NOAA and NASA, as they confirm that global temperatures for last year were far and away the hottest ever seen in the data record.
OUT OF THIS WORLD | Earth, Space And The Stuff In Between - a daily journey through weather, space and science with meteorologist/science writer Scott Sutherland

See the graphics that lock 2015 in as hottest year on record

Scott Sutherland
Meteorologist/Science Writer

Wednesday, January 20, 2016, 3:15 PM - El Niño or no El Niño, 2015 was the hottest year on record.

That's the official word now from NOAA and NASA, as they released their findings for 2015 on Wednesday, confirming that global temperatures for last year were far and away the hottest ever seen in the data records, going back a total of 135 years.

With their different methods of analyzing the data and a different base period to compare to, the final numbers came out slightly different, but regardless, reports from both agencies point to the exact same conclusion.

According to NOAA, in 2015 "the average global temperature across land and ocean surface areas for 2015 was 0.90oC (1.62oF) above the 20th century average of 13.9oC (57.0oF), beating the previous record warmth of 2014 by 0.16oC (0.29oF). This is not only the highest calendar year temperature, but also the highest temperature for any 12-month period on record."

NOAA plot of 2015 global temperatures by percentile, showing wide swaths across the globe of "much warmer than average" or "record warmest" temperatures. Credit: NOAA NCEI

According to NASA, 2015 was 0.87oC above the 1951-1980 average, which "shattered the previous mark set in 2014 by 0.23 degrees Fahrenheit (0.13 Celsius). Only once before, in 1998, has the new record been greater than the old record by this much."

NASA temperature anomalies, compared to the 1951-80 average. Credit: NASA GISS

Based on NOAA's records, overall, the top 16 hottest years on record are the past 15 years, 2001-2015, and 1998 still hangs in there as tied with 2009 for 6th place.

Top 16 hottest years on record. Credit: NOAA NCEI

The overall chance of 2015 ranking as the hottest on record, accounting for all uncertainties in the data?

According to a NASA statement, "2015 was the warmest year with 94 percent certainty," while Thomas Karl, director of NOAA's National Centers for Environmental Information stated during a press teleconference that NOAA was over 99 per cent certain that 2015 was the new record-holder.

This is in stark contrast to 2014, which only had a 38 per cent chance of being the hottest on record according to NASA, and a 48 per cent chance at being the hottest from NOAA (although in both cases, it was still the most likely year compared to others in the running).

Comparison graph of temperature anomalies, 1880-2015. Credit: NOAA NCEI

Weather and Climate Anomalies

There were several significant weather and climate events during 2015, as shown in the graphic below:


With or without El Niño?

There's no doubt that El Niño can have a strong influence on global temperatures, but there's no way to solely blame 2015's record heat on the El Niño pattern that formed during the year.

To see part of the reason for this, we only need to look back one year, to 2014. Although there were some early indications of a developing El Niño pattern that year, ocean temperatures in the central equatorial Pacific Ocean came out roughly average. It wasn't until early 2015 that the pattern fully-formed. Yet, even without El Niño's help, 2014 still came in as the hottest year on record up to that point.

A look back to 1997 and 1998 gives us a glimpse at the last El Niño of this strength for comparison. According to NOAA:

The 2015 temperature also marks the largest margin by which an annual temperature record has been broken. Prior to this year, the largest margin occurred in 1998, when the annual temperature surpassed the record set in 1997 by 0.12°C (0.22°F). Incidentally, 1997 and 1998 were the last years in which a similarly strong El Niño was occurring. The annual temperature anomalies for 1997 and 1998 were 0.51°C (0.92°F) and 0.63°C (1.13°F), respectively, above the 20th century average, both well below the 2015 temperature departure.

Thus, while El Niño certainly helped 2015 to its current position as hottest year on record, the overall trend of global warming due to excess carbon dioxide and other greenhouse gases in the atmosphere is still the primary driver of Earth's rising temperatures.

Betting on 2016?

With 2014 and 2015 already in the top two spots on the list of hottest years on record, what can we expect for 2016?

There's been a general trend observed over the years. When it comes to El Niño events and the temperature record, the second year of the event is usually the warmer one. This was especially noticeable in the previous "super" El Niño event of 1997-98, when 1997 claimed hottest year on record, and then 1998 quickly followed up by taking over that slot by a wide margin.

In fact, 1998 was so warm that it held on to the top spot in the climate record for another seven years after, until 2005 came along to displace it. The year still retains a spot in the top 10 hottest years on record, tied with 2009 for 6th place.


Global temperature anomalies since 1975, with comparison of "super El Niño" years. Credit: NOAA NCEI, with notations by S. Sutherland

So, with 2016 being the second year of this equally (or possibly even stronger) El Nino, will it take over as the next hottest year on record?

"If you were betting, you'd bet that 2016 would be the hotter of the two years," Karl, who chairs the Subcommittee on Global Change Research for the U.S. Global Change Research Program, said during Wednesday's press teleconference.

Gavin Schmidt, director of NASA's Goddard Institute for Space Studies, agreed with Karl, saying that he gave 2016 better than 50/50 odds of at being the hotter year.

Sources: NOAA | NASA

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