Scientists reported Wednesday that the earth reached its highest temperature on record in 2016 -- trouncing a record set only a year earlier, which beat one set in 2014. It is the first time in the modern era of global-warming data that temperatures have blown past the previous record three years in a row.
Temperatures are heading toward levels that many experts believe will pose a profound threat to the natural world and to human civilization.
In 2015 and 2016, the planetary warming was intensified by the weather pattern known as El Nino, in which the Pacific Ocean released a burst of energy and water vapor into the atmosphere.
But the bigger factor in setting the records was the long-term trend of rising temperature, which scientists say is being driven by increasing levels of carbon dioxide and other greenhouse gases.
"A single warm year is something of a curiosity," said Deke Arndt, chief of global climate monitoring for the National Oceanic and Atmospheric Administration. "It's really the trend, and the fact that we're punching at the ceiling every year now, that is the real indicator that we're undergoing big changes."
The heat extremes were especially pervasive in the Arctic, with temperatures in the fall running 20 to 30 degrees above normal across large stretches of the Arctic Ocean.
Sea ice in that region has been in precipitous decline for years, and Arctic communities are wrestling with the resulting problems, such as rapid coastal erosion, caused by the changing climate.
"What's going on in the Arctic is really very impressive; this year was ridiculously off the chart," said Gavin Schmidt, head of the Goddard Institute for Space Studies in Manhattan, a unit of NASA that tracks global temperatures.
But Arctic people were hardly alone in feeling the heat. Drought and starvation afflicted Africa.
On May 19, the people in the town of Phalodi lived through the hottest day in the recorded history of India, 123.8 F.
El Nino has now ended, and climate scientists almost universally expect 2017 to be cooler than the year before. But the scale of the heat burst has been startling to many of the experts, and some of them fear an acceleration of global warming over the next few years.
Even at current temperatures, billions of tons of land ice are melting or sliding into the ocean.
The sea is absorbing most of the heat trapped by human emissions.
Those factors are causing the ocean to rise at what appears to be an accelerating pace, and coastal communities in the United States are spending billions of dollars to fight increased tidal flooding. Their pleas for help from Congress have largely been ignored.
The finding that a record had been set for the third year in a row was released Wednesday by three government agencies, two American and one British, that track measurements made by ships, buoys and land-based weather stations.
They analyze the figures to correct for known problems, producing an annual average temperature for the surface of the Earth. The national meteorological agency of Japan also confirmed the findings in a preliminary analysis.
The findings about a record-warm year were also confirmed by the Berkeley Earth Surface Temperature project, a nonprofit California group set up to provide a temperature analysis independent of governments. That group, however, did not find that three records had been set in a row; in its analysis, 2010 was slightly warmer than 2014.
In addition to the surface measurements, satellites are used to measure the temperature of the atmosphere a few miles above the surface. Two groups that analyze these figures showed a record-warm 2016 in data going back to 1978, though in one data set it was a record by only a small margin.
Since 1880, NOAA's records show only one other instance when global temperature records were set three years in a row: in 1939, 1940 and 1941.
The earth has warmed so much in recent decades, however, that 1941 now ranks as only the 37th-warmest year on record.
The modern era of global warming began around 1970, after a long stretch of relatively flat temperatures, and the past three years mark the first time in that period that three records were set in a row.
Of the 17 hottest years on record, 16 have now occurred since 2000.
A Section on 01/19/2017