The year 2014 was officially the hottest year since records began, federal scientists announced on Friday, part of a long-term warming trend driven by the burning of fossil fuels.
Ten of the warmest years ever have occurred since 1997. Global ocean and land temperatures, which have been calculated since 1880, measured 1.24 degrees Fahrenheit above the 20th century average temperature in 2014, and 1.6 degrees Fahrenheit above pre-industrial averages. December also marked the 358th consecutive month—nearly 30 years—of above-average global temperatures.
"This is the latest in a series of warm years, in a series of warm decades," said Gavin Schmidt, a climate scientist and director of NASA's Goddard Institute for Space Studies. "While the ranking of individual years can be affected by chaotic weather patterns, the long-term trends are attributable to drivers of climate change that right now are dominated by human emissions of greenhouse gases."
The warming contributed to dozens of extreme weather and climate events last year, including severe hurricanes, drought, flooding and heat waves.
Last year's record heat was confirmed by two separate analyses by the National Oceanic and Atmospheric Administration and the National Aeronautics and Space Administration. They affirmed earlier findings by the Japanese Metrological Agency.
"Natural variability has assumed a large role in the public discussion over climate change," said Richard Alley, a climate scientist at Penn State University who was not involved in the study. "But there is clearly a long-term, upward trend, driven by greenhouse gases."
Unlike several other record-breaking years, 2014's heat wasn't influenced by El Nino, a natural weather phenomenon that warms ocean waters, affecting regional climate patterns and causing temperatures to rise across the globe.
Wide swaths of the western part of the United States, from Arizona to Alaska, experienced scorching heat in 2014. California's annual average temperature, for example, was 4.1 degrees Fahrenheit hotter than its 20th century average. The eastern half of the U.S., meanwhile, had below-average temperatures, largely due to the polar vortex last winter and a changing jet stream that forced warm air into Alaska and northern Europe, but cool air into the Midwest and East Coast.
Europe experienced its hottest temperatures in 500 years, and it is expected that 2014 will be the hottest year ever for 19 countries on the continent. Africa and Asia had a similar warming trend. Morocco's October temperatures were 5 degrees Fahrenheit above average. China saw eight months of above-average heat. Elsewhere, Argentina observed its second-warmest year on record, and Australia its third.
Much of last year's warmth was attributed to the rapidly warming oceans, which averaged 1 degree Fahrenheit higher than last century. The warm waters helped fuel an above-average tropical storm season in the Pacific and Indian Oceans, accompanied by heavy rains and severe flooding.
Congressional and other advocates of climate action latched onto the NASA and NOAA findings Friday morning as more evidence for scientists' conclusion that fossil fuels, such as Canada's tar sands, should stay in the ground. As the reports were released, senators were on the floor debating a bill to approve the controversial Keystone XL oil pipeline.
"The data from NASA and NOAA is the latest scientific evidence that climate change is real, and we must act now to protect our families and future generations," California Democratic Senator Barbara Boxer said in a statement. "Deniers must stop ignoring these alarms if we are to avoid the worst impacts of climate change. The very last thing we should do is to increase dangerous carbon pollution through harmful actions like building the Keystone tar sands pipeline."