Predictions that the 21st century is safe from major circulation changes in the North Atlantic Ocean may not be as comforting as they seem, according to a Penn State researcher.

Scientists at the University of Liverpool have found that natural variability in the earth’s atmosphere could be masking the overall effect of global warming in the North Atlantic Ocean.

A Duke University-led analysis of available records shows that while the North Atlantic Ocean’s surface waters warmed in the 50 years between 1950 and 2000, the change was not uniform. In fact, the subpolar regions cooled at the same time that subtropical and tropical waters warmed.

Scientists examining a spike in worldwide ocean temperatures 55 million years ago have linked it to massive volcanic eruptions that pushed Greenland and northwest Europe apart to create the North Atlantic Ocean.