“Obviously, a single year, even if it is a record, cannot tell us much about climate trends,” said Stefan Rahmstorf, head of earth system analysis at the Potsdam Institute for Climate Impact Research in Germany. “However, the fact that the warmest years on record are 2014, 2010 and 2005 clearly indicates that global warming has not ‘stopped in 1998,’ as some like to falsely claim.”

Such claims are unlikely to go away, though. John R. Christy, an atmospheric scientist at the University of Alabama in Huntsville who is known for his skepticism about the seriousness of global warming, pointed out in an interview that 2014 had surpassed the other record-warm years by only a few hundredths of a degree, well within the error margin of global temperature measurements. “Since the end of the 20th century, the temperature hasn’t done much,” Dr. Christy said. “It’s on this kind of warmish plateau.”

Despite such arguments from a handful of scientists, the vast majority of those who study the climate say the earth is in a long-term warming trend that is profoundly threatening and caused almost entirely by human activity.

They expect the heat to get much worse over coming decades, but already it is killing forests around the world, driving plants and animals to extinction, melting land ice and causing the seas to rise at an accelerating pace.

“It is exceptionally unlikely that we would be witnessing a record year of warmth, during a record-warm decade, during a several decades-long period of warmth that appears to be unrivaled for more than a thousand years, were it not for the rising levels of planet-warming gases produced by the burning of fossil fuels,” Michael E. Mann, a climate scientist at the Pennsylvania State University, said in an email.

NASA and the other American agency that maintains long-term temperature records, the National Oceanic and Atmospheric Administration, issued separate data compilations on Friday that confirmed the 2014 record. A Japanese agency had released preliminary information in early January showing 2014 as the warmest year.

One more scientific group, in Britain, that curates the world’s temperature record is scheduled to report in the coming weeks.