As much of the ocean responds to the rising temperatures of today’s world, the deep, dark waters at the bottom of the Pacific Ocean appear to be doing the exact opposite. A Harvard study has found that parts of the deep Pacific may be getting cooler as the result of a climate phenomenon that occurred hundreds of years ago. Around the 17th century, Earth experienced a prolonged cooling period dubbed the Little Ice Age that brought chillier-than-average temperatures to much of the Northern Hemisphere. Though it’s been centuries since this all played out, researchers say the deep Pacific appears to lag behind the waters closer to the surface, and is still responding to the Little Ice Age. ‘Climate varies across all timescales,’ said Peter Huybers, a professor at the Harvard John A. Paulson School of Engineering and Applied Sciences. ‘Some regional warming and cooling patterns, like the Little Ice Age and Medieval Warm Period, are well known. ‘Our goal was to develop a model of how the interior properties of the ocean respond to changes in surface climate.’ The Medieval Warm Period was a period lasting between the 9th and 12th centuries during which Earth’s climate leaned on the warmer side. It was followed not long after by the Little Ice Age, which lasted from the 16th through 19th century, though some argue it began even earlier. According to researchers from the Woods Hole Oceanographic Institution and Harvard University, this long-ago cooling period could still be showing its face in the temperatures of the deep ocean. ‘If the surface ocean was generally cooling for the better part of the last millennium, those parts of the ocean most isolated from modern warming may still be cooling,’ said Jake Gebbie, a physical oceanographer at Woods Hole Oceanographic Institution. To test this, the team compared measurements taken during the 1870s by scientists on the HMS Challenger to modern data. During the study in the late 1800s, the researchers of the time dropped thermometers deep down into the ocean between 1872 and 1876, collecting more than 5,000 measurements in total. ‘We screened this historical data for outliers and considered a variety of corrections associated with pressure effects on the thermometer and stretching of the hemp rope used for lowering thermometers,’ Huybers said. As expected, the comparisons showed most of the world’s ocean has been warming up over the last century. In the deep Pacific Ocean, however, temperatures are dropping. This effect could be seen at a depth of around 2 kilometers (1.2 miles). According to the team, this could influence our understanding of how much heat the ocean has absorbed in the last century, suggesting it could be as much as 30 percent less than previously assumed. Their findings are published in a new paper in the journal Science. ‘The close correspondence between the predictions and observed trends gave us confidence that this is a real phenomenon,’ Gebbie said. ‘Part of the heat needed to bring the ocean into equilibrium with an atmosphere having more greenhouse gases was apparently already present in the deep Pacific,’ Huybers said. ‘These findings increase the impetus for understanding the causes of the Medieval Warm Period and Little Ice Age as a way for better understanding modern warming trends.’ What Was the ‘Little Ice Age’? Around the 17th century, Earth experienced a prolonged cooling period dubbed the Little Ice Age that brought chillier-than-average temperatures to much of the Northern Hemisphere. It’s said to have lasted from the 16th through 19th century, though some argue it began even earlier. It was not a true Ice Age, but brought cold temperatures in three intervals from the mid-1600s to the 1800s. In Europe and North America, this meant colder winters which in some cases destroyed farms and villages with encroaching glaciers. Rivers also froze over in many locations, and ‘frost fairs’ were held along the River Thames. Changes in sea ice disrupted travel and shipping around Iceland, and crop devastation led to years of famine in some parts of Europe. Published in Daily Times, January 7th 2019.