Global temperatures have continued to rise, making 2016 the hottest year on the historical record and the third consecutive record-breaking year, scientists say. Of the 17 hottest years ever recorded, 16 have now occurred since 2000.
In the historical record, months early in the year, like February and March, have moved further away from the norm than the rest of the year. Scientists expect that the early months of 2017 will continue to show levels of warming beyond the norm, but likely not at the level of 2016 because a strong El Niño weather pattern is now subsiding.
The Earth’s temperature has risen since record-keeping began in the 19th century. Warming began to accelerate around the 1980s.
Human-induced climate change has made it at least 160 times more likely that three consecutive years after 2000 would be record-setting, according to Michael E. Mann, a climate scientist at Pennsylvania State University.
His findings show that if human-induced climate change was not part of the equation, the amount of warming in 2016 would have less than one-in-a-million odds of occurring.
“One could argue that about 75 percent of the warmth was due to human impact,” Dr. Mann said.
2016 was the first time that the hottest year on record occurred three times in a row.
The later months of 2015 and the first half of 2016 experienced faster warming partly due to the El Niño climate pattern in the Pacific Ocean, which sent a surge of heat into the atmosphere.
The El Niño pattern occurs irregularly, in intervals of about two to seven years, and scientists say that the most recent El Niño was among the largest in a century. The peak of the most recent El Niño occurred during winter of 2015, and temperatures were dramatically higher than normal. It began to subside over the course of 2016.
Scientists are working to understand whether climate change is also making El Niño phenomena stronger.
Historical records of global temperature are compiled by two American government agencies: the National Aeronautics and Space Administration, and the National Oceanic and Atmospheric Administration. Meteorological agencies in Britain and Japan also compile reliable datasets of global temperature.
The analyses by the agencies are based on thousands of measurements from weather stations, ships and ocean buoys around the world. Each group tracking global temperature uses different methods to take account of problems in the data, but usually reach similar conclusions about the significant long-term trend of global warming.
For 2016, the records from NASA were likely the most accurate, because of data collection in Antarctica and a more sophisticated statistical analysis in the Arctic. The combination allows NASA to have more reliable coverage in the polar regions of the world, which have been highly affected by rising temperatures. Global sea ice extent reached near record low levels late in 2016.
“We expect records to continue to be broken as global warming proceeds,” Dr. Mann said.