Average global temperatures are higher now than at any point in the last 2,000 years with the shift in climate impacting the whole world concurrently for the first time ever, studies released on Wednesday have concluded.
Depictions of the "Medieval Warm Period" (approximately 700 to 1400) and the "Little Ice Age" (from approx 1300 to 1850) in Europe and North America led scientists in the past to theorise that these events had impacted the whole world at the same time.
But a team of researchers led by Raphael Neukom from the University of Bern said that evidence from proxy data — including tree rings, corals, ice cores and lake and ocean sediments — suggest otherwise.
"It's true that during the Little Ice Age it was generally colder across the world world," Neukom said in a statement, "but not everywhere at the same time".
"The peak periods of pre-industrial warm and cold periods occurred at different times in different places," he added.
The current warming period, meanwhile, impacts 98% of the world — a first.
"What we didn't know until now is that not only average global temperatures in the 20th century are higher than ever before in at least 2,000 years, but also that a warming period is now affecting the whole planet at the same time for the first time," the statement reads.
Another study found that volcanoes, and not the sun as previously thought, shaped the climate before humankind and that the current period of warming exceeds natural variability.
"This provides strong evidence that anthropogenic (man-made) global warming is not only unparalleled in terms of absolute temperatures but also unprecedented in spatial consistency within the context of the past 2,000 years," one of the paper states.
"This represents a triple underlining of the fact that humans have caused global warming, and that what we're experiencing is unique," said Nathan Steiger, one of the climate scientists who co-authored the Nature study. "I hope it has some positive impact in this climate debate"