Climate change and El Niño fueled 2015’s record heat

Last updated: January 20, 2016

Earth’s second consecutive record hot year signals alarming warming trend

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2015 is the second of two back-to-back record hot years, and scientists say the record heat’s primary cause is climate change. During 2015, the average temperature across global land and ocean surfaces was 1.62°F (0.90°C) above the 20th century average. This was the highest among all years in the 1880-2015 record, surpassing the previous record set in 2014 by 0.29°F (0.16°C). This is also the largest margin by which the annual global temperature record has been broken.

That heat records are now commonplace is a clear signal of the planet’s long-term warming trend. From 1880 to 2012, the Earth warmed 1.5°F (0.85°C) at a rate roughly ten times faster than the rate ending past ice-ages. Each of the last three decades has been successively warmer than any decade on record, and 13 of the 15 hottest years on record occurred since 2000, with the two exceptions (1997 and 1998) occurring during the strongest El Niño on record. 

Warming world + El Niño = record warmth

While the El Niño Southern Oscillation (ENSO) is responsible for a large part of the variation in weather we see in the global climate from one year to the next, a study conducted by scientists with the World Weather Attribution (WWA) initiative finds that climate change is the dominant cause of 2015’s record warmth.

Using well-established techniques from peer-reviewed literature, the scientists estimated 2015’s global temperature anomaly to be 1.89°F (1.05°C) above the 1850-1900 pre-industrial baseline and determined that roughly 1.8°F (1.0°C) of 2015’s temperature anomaly was due to human-caused climate change. The WWA analysis found that El Niño was responsible for 0.09°F to 0.18°F (0.05°C to 0.1°C) of 2015’s record warmth. This means, El Niño caused at most 10 percent of the warming, with the other 90 percent being due to climate change.

The influence of climate change is also apparent when comparing 2015 to past El Niño years. 2015 has seen the third-largest surface temperature warming influence from any El Niño event on record, behind 1998 and 1987. Yet its global average temperature is set to be more than 0.36°F (0.2°C) warmer than the record 1998 El Niño year. The temperature difference between 2015 and 1998 highlights the fact that in 2015, El Niño started its warming from higher baseline temperatures. Records are often broken when climate change and natural variability run in the same direction, and such was the case in 2015 when El Niño and climate change combined to create record warmth.

2015 heat records at a glance

El Niño in a warming world

Extreme heat and heat events

One of the clearest findings of climate science is that global warming amplifies the intensity, duration and frequency of extreme heat events. Even a small-seeming change in average global temperature can lead to dramatic regional changes in extreme events. Due to global warming, extreme heat events impact a percentage of the globe 10 times greater than they did from 1951-1980. Here is a list of extreme heat events that occurred during the hottest year on record: