But what concerns many scientists is what occurred next: In just the last 100 years, the average temperature has increased by 1.3 degrees. Although global temperatures of the last decade have not exceeded peak Holocene highs, they are warmer than 75% of the epoch.
“Global temperature, therefore, has risen from near the coldest to the warmest levels of the Holocene within the past century,” the researchers wrote.
By the end of the century, climate warming models predict an additional increase of 2 to 11.5 degrees, due largely to carbon emissions, the study noted.
The Science study was not the first to use such proxies to assess the ancient climate, but it was the first to pull together so many of them from all over the world, the researchers said. Previous studies used only regional data, which may be influenced by localized events like monsoons and the cyclical ocean-warming phenomenon known as El Niño.
Michael Mann, a physicist and climatologist at Pennsylvania State University who was not involved in the study, said the paper was important because it illustrated clearly that the rate and magnitude of recent warming was unprecedented in at least the last 11,000 years.
“We know that there were periods in the past that were warmer than today — for example, the Cretaceous period 100 million years ago,” he said. “The real issue is the rate of change, because that's what challenges our adaptive capacity.”
Mann, who was among the first climate scientists to introduce the hockey stick graph a decade ago — and has been strongly criticized by climate warming skeptics ever since — said the authors should prepare themselves for similar judgment.
“I am certain that professional climate-change deniers will attack the study and the authors, in an effort to discredit this important work,” Mann said.