2015 The Warmest Year on Record
- Category: Climate Change
- Published: Thursday, 21 January 2016 14:24
- Written by NOAA - Bernd Riebe
- Hits: 1931
The State of the Climate November 2015 report noted that in order for 2015 to not become the warmest year in the 136-year period of record, the December global temperature would have to be at least 0.81°C (1.46°F) below the 20th century average—or 0.24°C (0.43°F) colder than the current record low December temperature of 1916. In fact, December 2015 was the warmest month of any month in the period of record, at 1.11°C (2.00°F) higher than the monthly average, breaking the previous all-time record set just two months ago in October 2015 by 0.12°C (0.21°F). This is the first time in the NOAA record that a monthly temperature departure from average exceeded 1°C or reached 2°F and the second widest margin by which an all-time monthly global temperature record has been broken. (February 1998 broke the previous record of March 1990 by 0.13°C / 0.23°F.)
With the contribution of such record warmth at year's end and with 10 months of the year record warm for their respective months, including the last 8 (January was second warmest for January and April was third warmest), the average global temperature across land and ocean surface areas for 2015 was 0.90°C (1.62°F) above the 20th century average of 13.9°C (57.0°F), beating the previous record warmth of 2014 by 0.16°C (0.29°F). This is not only the highest calendar year temperature, but also the highest temperature for any 12-month period on record. The global temperatures in 2015 were strongly influenced by strong El Niño conditions that developed during the year.
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.
This marks the fourth time in the 21st century a new record high annual temperature has been set (along with 2005, 2010, and 2014) and also marks the 39th consecutive year (since 1977) that the annual temperature has been above the 20th century average. To date, including 2015, 15 of the 16 warmest years on record have occurred during the 21st century. 1998 is currently tied with 2009 as the sixth warmest year on record.
Overall, the global annual temperature has increased at an average rate of 0.07°C (0.13°F) per decade since 1880 and at an average rate of 0.17°C (0.31°F) per decade since 1970.
Sixteen Warmest Years (1880–2015)
The following table lists the global combined land and ocean annually-averaged temperature rank and anomaly for each of the 16 (two tied at #15) warmest years on record.
Much of the record warmth for the globe can be attributed to record warmth in the global oceans. The annually-averaged temperature for ocean surfaces around the world was 0.74°C (1.33°F) higher than the 20th century average, easily breaking the previous record of 2014 by 0.11°C (0.20°F). Ocean temperatures for the year started with the first three months each third warmest for their respective months, followed by record high monthly temperatures for the remainder of the year as one of the stongest El Niños in the historical record evolved.
Prior to 2015, the highest monthly anomaly on record for the global oceans was 0.74°C (1.33°F) above the 20th century average, occurring just last year in September 2014. This all-time monthly record was broken in August 2015 (+0.78°C / +1.40°F), then broken again in September (+0.83°C / +1.49°F), and then broken once more in October (0.86°C / 1.55°F)—making three all-time new monthly high global ocean temperature records set in a single calendar year. [Three all-time records (at the time) were also broken in 2014.] In 2015, the last four months of the year were more than 0.80°C higher than their respective average, the first instances in which this monthly-average threshold has been crossed.
The warmth was due to the near-record strong El Niño that developed during the Northern Hemisphere spring in the eastern and central equatorial Pacific Ocean and to large regions of record warm and much warmer-than-average sea surface temperatures in parts of every major ocean basin. Record warmth for the year was particularly notable in large parts of the northeastern and equatorial Pacific, a large swath of the western North Atlantic, most of the Indian Ocean where a positive Indian Ocean dipole prevailed, and parts of the Arctic Ocean. Similar to 2014, some of the Southern Ocean waters off the tip of South America and part of the Atlantic Ocean south of Greenland were much cooler than average, with one localized area in the Atlantic region record cold.
Separately, temperatures were record warm across land surfaces as well. The global land temperature for 2015 was 1.33°C (2.39°F) above the 20th century average, surpassing the previous records of 2007 and 2010 by 0.25°C (0.45°F). This is the largest margin by which an annual global land surface temperature has been broken. Previously, 1981 had broken the record of 1980 by 0.22°C (0.40°F).
Because land surfaces generally have low heat capacity relative to oceans, temperature anomalies can vary greatly between months. In 2015, the average monthly land temperature anomaly ranged from +0.94°C (+1.69°F) in June to +1.89°C (+3.40°F) in December, a difference of 0.95°C (1.71°F). The ocean has a much higher heat capacity than land and thus anomalies tend to vary less over monthly timescales. During the year, the global monthly ocean temperature anomaly ranged from +0.58°C (+1.04°F; February) to +0.86°C (+1.55°F; October), a difference of 0.28°C (0.51°F).