The announcement is no surprise to climate scientists — experts at NASA had already projected that 2016 would be a third year of record heat — and the record will not be definitive until early next year.
But the latest estimate of record-shattering heat comes as world leaders gather in Marrakesh, Morocco, for the annual United Nations talks on limiting the impact of climate change. The meeting is taking place in an atmosphere of alarm. President-elect Donald J. Trump has called human-caused climate change a “hoax” perpetrated by the Chinese; has vowed to dismantle the Environmental Protection Agency “in almost every form”; and has named Myron Ebell of the business-backed Competitive Enterprise Institute, who has deep oil industryties, to head his E.P.A. transition team.
Preliminary data shows that 2016’s global temperatures are approximately 1.2 degrees Celsius (2.16 degrees Fahrenheit) above pre-industrial levels. The landmark climate deal reached by 195 nations near Paris last December commits them to holding the increase in temperature to 2 degrees Celsius, or 3.6 degrees Fahrenheit, the point at which the world would be locked into irreversible and potentially devastating environmental changes.
Mr. Trump has vowed to withdraw from the Paris climate deal. It has entered into legal force — meaning that countries like the United States cannot legally withdraw for four years — but there are many actions the Trump administration could take to limit the execution of the agreement. That prospect has already stirred alarm among the world’s largest countries, and even a warning from China.
The meteorological organization found that global temperatures from January to September were about 0.88 degrees Celsius (1.58 degrees Fahrenheit) above the average for the years from 1961 to 1990, a period the organization uses as a baseline. Temperatures spiked early this year because of the weather phenomenon known as El Niño, which exacerbated coral reef bleaching, which is caused by water that is too warm, and a rise in sea levels.
“Preliminary data for October indicate that they are at a sufficiently high level for 2016 to remain on track for the title of hottest year on record,” the organization said. That would mean that 16 of the 17 hottest years on record have been in the 21st century. The other one was 1998.
The organization also found that concentrations of major greenhouse gases in the atmosphere continue to increase to record levels; that Arctic sea ice remained at very low levels; and that there was significant, earlier-than-usual melting of the Greenland ice sheet.
Petteri Taalas, the secretary general of the organization, noted temperatures above the long-term average of 6 to 7 degrees Celsius (10.8 to 12.6 degrees Fahrenheit), and at least 3 degrees Celsius (5.4 degrees Fahrenheit) above the long-term average in many parts of Russia, Alaska and northwest Canada.
“We are used to measuring temperature records in fractions of a degree, and so this is different,” he said. “Because of climate change, the occurrence and impact of extreme events has risen. ‘Once in a generation’ heat waves and flooding are becoming more regular. Sea level rise has increased exposure to storm surges associated with tropical cyclones.”
The organization’s statement did not mention Mr. Trump or the United States — except to note that Hurricane Matthew, in October, was the deadliest weather event this year, claiming at least 546 lives and injuring 438 people, mostly in the Caribbean.