Climate facts 2015

2014 had already been the warmest year since the time series began in 1880, but it only narrowly exceeded 2005 and 2010 according to data from the NOAA. Yet substantially higher figures were recorded in 2015. According to the NOAA data published in mid-January 2016, it was by far the warmest year from a global perspective. 

The mean global temperature over land and ocean surfaces exceeded the 20th century mean of 13.9°C by 0.90°C, surpassing the 2014 record (0.74°C) by 0.16°C. In 2015, the mean global temperature climbed for the first time to 1°C above the mean for the period from 1850 to 1900, which corresponds to the pre-industrial temperature level. This means that half of the 2°C limit – or two thirds of the 1.5°C limit stipulated in the Paris Agreement (COP21) – was already reached in a single year.

One of the reasons for the high temperatures in 2015 was a very pronounced El Niño phase in the tropical Pacific that developed from March 2015; this released a large amount of thermal energy into the atmosphere, and circulation systems changed due to teleconnection patterns. It was also excessively warm in the northeast Pacific region, including the western half of North America. Eurasia and the African-Indian Ocean region likewise exhibited positive thermal anomalies. 

As regards rainfall, many regions reflected the typical influence of El Niño over the course of the year (more on this subject in the article “A strong El Niño”, page 22 to 26). This included the drought in northeastern Brazil, northern parts of South America, the Caribbean, northwestern North America, and broad swathes of southern Africa; the reduced summer monsoon in some parts of India, and the drought in parts of Southeast Asia, Indonesia, and some southern and eastern regions of Australia. Similarly, the excessive rainfall in southern and southeastern regions of North America, southern Brazil, northeastern Argentina, southern India and the British Isles corresponds to the typical El Niño pattern.

The fact that the influence of El Niño is clearly recognisable in the temperature and rainfall signal shows that the long-term climate change signal is always superimposed by the natural variability of climate on different time scales. In this way, the very strong El Niño event has not only contributed to a high mean annual temperature in 2015, but may also produce a similar effect in 2016. However, the superimposition by natural climate variability also means that there will be years in the future with a somewhat lower mean global temperature. Accordingly, a substantial portion of the temperature fluctuation in the time series for global mean annual temperatures in the past can be explained by the climate variation between El Niño and La Niña events. Nevertheless, the recent record years for mean annual temperature show that the latest data do not allow identification of an interruption in the increase in mean global temperature any more – in other words, the long-term upward trend is continuing.