By 2100, the Earth will be warmer than any time during this period no matter what we do, they project.
"We already knew that on a global scale, Earth is warmer today than it was over much of the past 2,000 years," study researcher Shaun Marcott of Oregon State said in a statement. "Now we know that it is warmer than most of the past 11,300 years. This is of particular interest because the Holocene spans the entire period of human civilization."
The study was published Friday, March 8 in the journal Science. The researchers used data from 73 global sites to reconstruct Earth's temperatures back to the end of the last Ice Age. Their data came from the chemical and physical characteristics of fossils from ocean sediment cores and terrestrial archives.
During the last 5,000 years, the Earth as a whole cooled about 1.3 degrees Fahrenheit – until the past 100 years, when it warmed about 1.3 degrees. The largest changes were in the northern hemisphere, where there are more land masses and greater human populations.
"The last century stands out as the anomaly in this record of global temperatures since the end of the last ice age," said Candace Major, program director in the National Science Foundation's Division of Ocean Sciences.
Predictions indicate this trend will continue, with the Earth warming between two and up to 11.5 degrees by 2100. We will really be seeing the effects of global climate change by then: In 2100, spring will come to New York in mid-February.