(CNN)The Arctic Ocean has been warming since the onset of the 20th century, decades earlier than instrument observations would suggest, according to new research. The study, published Wednesday in the journal Science Advances, found that the expansion of warm Atlantic Ocean water flowing into the Arctic, a phenomenon known as "Atlantification," has caused Arctic water temperature in the region studied to increase by around 2 degrees Celsius since 1900. Francesco Muschitiello, an author on the study and assistant professor of geography at the University of Cambridge, said the findings were worrisome because the early warming suggests there might be a...