Deep Pacific Waters Are Cooling Down Due To Centuries-Ago Little Ice Age, New Study Suggests

Clouds, waves and ship trace in north Pacific.
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Most of the world’s waters may be warming as a result of climate change, but a new study shows that the deepest parts of the Pacific Ocean still appear to be cooling down hundreds of years after the period in history known as the “Little Ice Age.”

According to a report from Science Daily, a team of researchers from the Woods Hole Oceanographic Institute (WHOI) and Harvard University discovered that there has been a “lag” of a few centuries in terms of temperature change in the deep Pacific. This part of the ocean, the report stressed, is still seemingly cooling and adjusting to the temperature drops of the Little Ice Age while the rest of the Pacific gets warmer as a result of modern factors.

“These waters are so old and haven’t been near the surface in so long, they still ‘remember’ what was going on hundreds of years ago when Europe experienced some of its coldest winters in history,” commented WHOI physical oceanographer Jake Gebbie, lead author of the new study.

As documented in a paper that was published Friday in the journal Science, the researchers created a model simulating how the deep Pacific’s temperature might react to changes in climate on the surface, then compared the data from the model against two historical sources. These sources included ocean temperature data taken in the 1870s by scientists aboard the HMS Challenger and temperatures gathered over a century later, through the World Ocean Circulation Experiment in the 1990s.

Based on how these comparisons aligned, the researchers found that warming was present in most parts of the world’s oceans and consistent with the current trend of climate change. The only exception was the deep Pacific, where temperatures were cooling at around 1.25 miles (two kilometers) deep. This suggested that long-ago changes in surface climate, such as those that took place during the Little Ice Age, could still have an influence on the effect of climate change in modern times.

“The close correspondence between the predictions and observed trends gave us confidence that this is a real phenomenon,” Gebbie explained.

All in all, the researchers believe that the cooling phenomenon in the deep Pacific could force a downward revision of 30 percent for estimates of how much heat had been absorbed by the Earth over the last century.

According to the Daily Mail, it is believed that the Little Ice Age might have lasted from the 16th through the 19th century, though some scientists believe it could have started as far back as the 1250s, as reported in 2012 by BBC News. While this period was not a “true” Ice Age like the one in prehistoric times, it resulted in colder winters in Europe and North America, with many of the world’s rivers freezing over due to the unusually chilly weather.

Regardless of when the Little Ice Age started, it was preceded by the Medieval Warm Period, where global temperatures were conversely warmer than average. This period is estimated to have run from the 9th century through the 12th century.

Considering the possible effect of the Little Ice Age on deep Pacific temperatures and modern climate change, study co-author Peter Huybers, a professor of Earth and Planetary Sciences at Harvard University, said that the findings make it important to look deeper into what might have caused the Medieval Warm Period and Little Ice Age. This, he stressed, should be done in order to “better understand modern warming trends.”