Global climate change is an observed, demonstrable scientific fact: Earth’s temperatures have risen steadily with greenhouse gas emissions, with a prominent spike occurring at the end of the last century. However, an apparent flat-lining so far in this century had scientists scratching their heads – greenhouse gasses were trapping more hot air in Earth’s atmosphere, but why weren’t surface temperatures rising? Scientists at the University of Washington believe they’ve found the answer in the Atlantic ocean: It’s absorbing heat, and trapping it below the surface in denser, saltier water.

“Every week there’s a new explanation of the hiatus,” said corresponding author Ka-Kit Tung, a UW professor of applied mathematics and adjunct faculty member in atmospheric sciences. “Many of the earlier papers had necessarily focused on symptoms at the surface of the Earth, where we see many different and related phenomena. We looked at observations in the ocean to try to find the underlying cause.”

Natural forces result in an Atlantic current that carries heat between the north and south poles, but this current has apparently increased in the past 15 years, dragging heat down nearly a miles. Earlier studies either focused on more short-term factors, or ignored the Atlantic altogether in favor of the Pacific ocean as the prime heat hoarding suspect.

The team used data from Argo floats, which collect data as deep as 2,000 meters down in the ocean. Once the rapid warming of the late 20th century slowed down, the heat sinking cycle sped up, partially counteracting the effects of greenhouse gasses and surface warming.

The key to the cyclical currents is the disparate densities of very salty and less salty water.

“When it’s heavy water on top of light water, it just plunges very fast and takes heat with it,” Tung said. Recent observations at the surface in the North Atlantic show record-high saltiness, Tung said, while at the same time, deeper water in the North Atlantic shows increasing amounts of heat.

Though climate change doubters will likely froth at the findings, research into historical data by Tung’s team indicates that the warming/cooling cycle looks less like a sine wave and more like a staircase. While it’s possible Earth will experience a cooler period for another decade or more, temperatures won’t retreat – they’ll rise even higher. It makes sense, as energy cannot be destroyed: The heat will have to go somewhere, eventually.

Tung is quick to avoid making any concrete predictions about the future.

“We are not talking about a normal situation because there are so many other things happening due to climate change,” Tung said.