Earth's rapid warming in the late 20th century was far more widespread than any temperature variations during the previous 2,000 years, according to a study published on Wednesday that shows how profoundly humans have altered the climate.
The study crunched data covering two millennia from almost 700 sources ranging from tree rings and coral to sediments and ice cores.
Published in the journal Nature, it found that previous major climate events were confined to certain areas, and not global phenomena as scientists had previously assumed, said one of its co-authors, Columbia University climate scientist Nathan Steiger.
"The main takeaway is that climate variability in the contemporary period is very different than what's happened in the past 2,000 years," he said.
Natural phenomenon?
Some people who question whether burning coal, oil and gas is causing global warming point to evidence of prolonged shifts in climatic conditions in past centuries to argue that today's higher temperatures may also be a natural phenomenon.
Previous shifts include the "Medieval Climate Anomaly" from 800-1200 AD when temperatures rose, and the "Little Ice Age" from around the 1300s to the 1850s when Britons skated on the frozen River Thames.
But the study, which measured readings from zero to 2,000 AD, showed that some of the coldest temperatures during that period were more localized, occurring in parts of the Pacific in the 15th century and in northwestern Europe and southeastern North America in the 17th.
By contrast, the researchers found that the rapid rise in average temperatures in the closing decades of the last century affected more than 98% of the planet.
"This is definitely further evidence that fossil fuels and anthropogenic activity actually has fundamentally changed the climate," Steiger told Reuters.
Volcanic activity
Mark Maslin, professor of climatology, at University College London (UCL) said the paper should "finally stop climate change deniers claiming that the recent observed coherent global warming is part of a natural ... cycle."
A parallel study published in Nature Geoscience found that pre-industrial fluctuations in temperature were primarily driven by volcanic activity.
The studies were released less than a week after temperature data from the U.S. National Oceanic and Atmospheric Administration showed last month was the hottest June globally in 140 years.
