Earth was cooling until the end of the 19th century and a hundred years later, the planet's surface was on average warmer than at any time in the previous 1,400 years, according to climate records presented on Sunday.
In a study spanning two millennia published in Nature Geoscience, scientists said a "long-term cooling trend" around the world swung into reverse in the late 19th century.
In the 20th century, the average global temperature was 0.4 degrees Celsius (0.7 degrees Fahrenheit) higher than that of the previous 500 years, with only Antarctica bucking the trend.
From 1971-2000, the planet was warmer than at any other time in nearly 1,400 years.
This measure is a global average, and some regions did experience warmer periods than that—but only for a time. Europe, for instance, was probably warmer in the first century AD than at the end of the 20th century.
The investigation is the first attempt to reconstruct temperatures over the last 2,000 years for individual continents. It seeks to shed light on a fiercely-contested aspect in the global-warming debate.