Last year was the hottest in earth’s recorded history, scientists reported on Friday, underscoring scientific warnings about the risks of runaway emissions and undermining claims by climate-change contrarians that global warming had somehow stopped.

Extreme heat blanketed Alaska and much of the western United States last year. Several European countries set temperature records. And the ocean surface was unusually warm virtually everywhere except around Antarctica, the scientists said, providing the energy that fueled damaging Pacific storms.

In the annals of climatology, 2014 now surpasses 2010 as the warmest year in a global temperature record that stretches back to 1880. The 10 warmest years on record have all occurred since 1997, a reflection of the relentless planetary warming that scientists say is a consequence of human emissions and poses profound long-term risks to civilization and to the natural world.

Of the large inhabited land areas, only the eastern half of the United States recorded below-average temperatures in 2014, a sort of mirror image of the unusual heat in the West. Some experts think the stuck-in-place weather pattern that produced those extremes in the United States is itself an indirect consequence of the release of greenhouse gases, though that is not proven.

Several scientists said the most remarkable thing about the 2014 record was that it occurred in a year that did not feature El Niño, a large-scale weather pattern in which the ocean dumps an enormous amount of heat into the atmosphere.

Longstanding claims by climate-change skeptics that global warming has stopped, seized on by politicians in Washington to justify inaction on emissions, depend on a particular starting year: 1998, when an unusually powerful El Niño produced the hottest year of the 20th century.

With the continued heating of the atmosphere and the surface of the ocean, 1998 is now being surpassed every four or five years, with 2014 being the first time that has happened in a year featuring no real El Niño pattern. Gavin A. Schmidt, head of NASA’s Goddard Institute for Space Studies in Manhattan, said the next time a strong El Niño occurs, it is likely to blow away all temperature records.

“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.”

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.

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

“Why do we keep getting so many record-warm years?” Dr. Schmidt asked in an interview. “It’s because the planet is warming. The basic issue is the long-term trend, and it is not going away.”

February 1985 was the last time global temperatures fell below the 20th-century average for a given month, meaning that no one younger than 30 has ever lived through a below-average month.

The contiguous United States set its temperature record in 2012. But, mainly because of the unusual chill in the East last year, 2014 was only the 34th warmest year on record for the lower 48 states.

That cold was brought into the interior of the country by a loop in a current called the jet stream that allowed Arctic air to spill southward. But an offsetting kink allowed unusually warm tropical air to settle over the West, large parts of Alaska and much of the Arctic.

A few recent scientific papers say that such long-lasting kinks in the jet stream have become more likely because global warming is rapidly melting the sea ice in the Arctic, disturbing longstanding weather patterns. But many leading scientists are not convinced on that point.

Whatever the underlying cause, last year’s extreme warmth in the West meant that Alaska, Arizona, California and Nevada all set temperature records. Some parts of California had basically no winter last year, with temperatures sometimes running 10 or 15 degrees above normal for the season.

Those conditions exacerbated the severe drought in California, which has been alleviated only slightly by recent rains. Some small towns have run out of water, the sort of impact that scientists fear will become commonplace as global warming proceeds in the coming decades.