Global temperatures in 2018 were 1.5 degrees Fahrenheit (0.83 degrees Celsius) warmer than the 1951 to 1980 mean, according to scientists at NASA's Goddard Institute for Space Studies, an affiliate of Columbia University's Earth Institute.
The obvious long-term trend of steady warming makes it easier to more accurately predict near future warming, said NASA chief climate scientist Gavin Schmidt. "It's the long-term trends that are having impacts on ice, on severity of droughts, on heat waves, on sea level rise and wildfires".
While this planet has seen hotter days in prehistoric times, and colder ones in the modern era, what sets recent warming apart in the sweep of geologic time is the relatively sudden rise in temperatures and its clear correlation with increasing levels of greenhouse gases like carbon dioxide and methane produced by human activity.
There were 14 weather and climate disasters that cost more than $1 billion, for a total of $91 billion, Arndt said. But if you look at two, three, four, now five very warm years, then it is much harder to dismiss that.
NOAA and NASA each analyze temperature measurements from thousands of sites around the world, including weather stations on land and ships and buoys spread across the world's oceans.
It was also an expensive year for natural disasters. The warming trends are most evident in the Arctic, NASA said. Lower than normal temperatures are shown in blue.
The NASA and NOAA reports are consistent with analyses by other governments, including the Japan Meteorological Agency and the European Union's Copernicus Climate Change Service, both of which also concluded that 2018 was the fourth-warmest year on record.
The November report warned that climate change will intensify over the century without swift emissions cuts. Even an increase in 1.5 could be a great risk to the stability of the world.