Long-Term Global Warming Trend Continues

Earth's global surface temperatures in 2017 ranked as the second warmest since 1880. Continuing the planet's long-term warming trend, globally averaged temperatures in 2017 were 1.62 degrees Fahrenheit (0.90 degrees Celsius) warmer than the 1951 to 1980 mean, according to scientists at NASA's Goddard Institute for Space Studies in New York. That is second only to global temperatures in 2016.

In a separate, independent analysis, scientists at the National Oceanic and Atmospheric Administration (NOAA) concluded that 2017 was the third-warmest year in their record. The minor difference in rankings is due to the different methods used by the two agencies to analyze global temperatures. Both analyses show that the five warmest years on record all have taken place since 2010.

The planet's average surface temperature has risen about two degrees Fahrenheit (a little more than one degree Celsius) during the last century or so, a change driven largely by increased carbon dioxide and other human-made emissions into the atmosphere. Last year was the third consecutive year in which global temperatures were more than 1.8 degrees Fahrenheit (one degree Celsius) above late 19th-century levels.

El Niño

Global temperatures spiked during the record warm years of 2014 to 2016 largely because El Niño released an unusually large amount of heat generated by greenhouse gas emissions and stored in the Pacific Ocean, a new study has found.

By analyzing records of global temperature, sea level rise, ocean heat content and other climate data, a team of University of Arizona and University of Michigan scientists found that the 2015-2016 El Niño released excess heat from the Pacific Ocean that had accumulated over the past two decades because of global warming. They conclude this heat transfer from the ocean is largely responsible for the sharp spike in temperatures.

The record-breaking temperatures from 2014 to 2016 coincided with extreme weather events worldwide, including heat waves, droughts, floods, extensive melting of polar ice and global coral bleaching. The study authors predict that temperature spikes like the one from 2014 to 2016 and accompanying extreme weather events will become more frequent by the end of the century unless greenhouse gas emissions decline.

Their projections indicate that if greenhouse gas emissions peak by 2020 and decline thereafter, temperature jumps of at least 0.24 degrees Celsius (0.43 degrees Fahrenheit) might occur once in the 21st century or not at all. But if greenhouse gas emissions rise unabated throughout the 21st century, the projections suggest large temperature surges would occur three to nine times by 2100. Under this scenario, such events would likely be warmer and longer than the 2014-2016 spike and have more severe impacts.