A new study at Scripps Institution of Oceanography comparing past and present ocean temperatures reveals the global ocean has been warming for more than a century. Not alarmingly so, however — unless the Arctic ice begins to melt at a faster pace.  “The swelling is rising slowly at one inch per decade,” said Scripps physical oceanographer Dean Roemmich. “In 1,000 years, that would be at the one-foot level. But it could accelerate if the ice begins to melt more quickly.” On average, the global increase is roughly 0.6 degrees Celsius at the surface and 0.1 degrees at depth. This analysis appeared in the journal Nature Climate Change. The research indicates that extra heat trapped by pollution from more than a century’s worth of coal and fossil fuel burning is beginning to reach depths that could impact the survival of sea life. The world’s oceans have been warming for more than 100 years — twice as long as previously believed, new research suggests. “The findings could help scientists better understand the Earth’s record of sea-level rise, which is partly due to the expansion of water that happens as it heats up,” Roemmich said. “Temperature is one of the most fundamental descriptors of the physical state of the ocean.” The first recorded research was done from 1872 to 1876, when the HMS Challenger, a British war ship, sailed on a 69,000-nautical-mile track, crossing the Atlantic, Indian and Pacific oceans. During the voyage, scientists among the 200-person crew took 300 ocean-temperature profiles — measurements at several depths in each spot — with pressure-protected thermometers. Roemmich and his colleagues have compared Challenger temperatures with data from the modern-day Argo project, which uses 3,500 free-drifting floats to measure temperature and salinity of the world’s oceans every 10 days. The comparison showed a 1.1-degree Fahrenheit (0.59-degree Celsius) temperature increase at the surface over 135 years.  Ocean warming has been previously linked to glacial melting and mass coral bleaching, but the issue of documenting it is one of magnitude, Roemmich said, calling the amount of information scientists have to work with “a huge volume of data. Much more than we could obtain from shipboard methods. “It’s an ongoing research,” he said. “But what makes this study unique from all the others is the comparison of modern-day data with the Challenger data on a much longer time scale.” Asked whether warmer water has been the cause of increased hurricanes and tornados, Roemmich was hesitant to draw any definitive deductions. “We must be cautious not to make any claims we can’t back up,” he said. “There are no conclusions. We can’t link storms to ocean warming. It’s possible but not demonstrated. We have to be careful in interpreting these things. A lot of people have doubts about climate change.” — Johnny McDonald is a longtime writer and columnist for the San Diego Community Newspaper Group. He can be reached at [email protected].