Many scientific studies published lately have measured the sharp rise in Earth's temperature during the early 21st century. Now climate scientists at Harvard and Oregon State University have gone much further back in time than previous studies. They examined temperature records of the past 11,300 years using such sources as ice cores and found that the planet is hotter today than at least 70 percent of that entire time period.

The finding further underscores just how fast the climate is changing, and the recent change appears driven mainly by greenhouse gas emissions from human activities. "It is the only variable that can best explain the rapid increase in global temperatures," said the study's lead author, Shaun Marcott of Oregon State University, in a statement published Thursday.

The researchers noted that Earth's temperature still hasn't become as hot as the peak of this epoch, known as the early Holocene, but it's on track to reach those temperatures or even hotter ones by 2100, even if greenhouse gases continue to rise at the low end of projection models from the UN's Intergovernmental Panel on Climate Change. The quick pace of the the warming trend has the study's authors worried that many species will struggle to adapt well, including humans.