The notion that global warming was slowing down at the start of this century left climate scientists stumped. They were unable to explain this so called “hiatus,” which quickly became an important weapon in the arsenals of climate skeptics. Was global warming coming to a halt? Probably not. U.S. government researchers undermined this argument last month with research that suggested that the observed pause in global warming was based on incorrect data. A recent study by NASA has another explanation for the hiatus – extra heat from greenhouse gases had been trapped in the Pacific and Indian oceans.
Throughout the 20th century, global surface temperatures were increasing as a result of an increase in greenhouse gas concentrations. While greenhouse gases continued to trap extra heat, several papers noted that global average surface temperatures had no longer been climbing since 2003, and, in some cases, temperatures were in fact cooling.
To figure out what was going on, NASA’s Jet Propulsion Laboratory analyzed direct ocean temperature measurements. Their findings showed that temperatures below the ocean’s surface had in fact been increasing.
The study, published in Science, observed two decades of data and found that the Earth’s extra heat was being redistributed by the world’s largest oceans. Researchers found that “cooling in the top 100-meter layer of the Pacific Ocean was mainly compensated by warming in the 100- to 300-meter layer of the Indian and Pacific Oceans.”
Image credit: Argo Program, Germany/IFREMER.
“Our findings support the idea that the Indo-Pacific interaction in the upper-level water (0–300 m depth) regulated global surface temperature over the past two decades and can fully account for the recently observed hiatus,” researchers wrote in the paper.
While global warming is a widely established phenomenon within the scientific community, whether this warming has been slowing down or not continues to be debated. Previous research attempting to explain the hiatus relied more heavily on climate models. This study, on the other hand, involved the use of observational data, which is why the researchers believe that it provides the “most definitive explanation of how the heat was redistributed.”