Climate scientists searching for missing amounts of atmospheric heat say the Atlantic Ocean and its currents have been masking the effects of global warming, but things are preparing to heat up much more after this latest 30-year cycle alternates back to several decades of heating.
Several decades of ocean-induced cooling follow a term of heating, which lasts for a similar amount of time, according to researchers from the University of Washington. Right now, the Atlantic Ocean's currents are sending heated surface water deep within the water body's chilly depths.
It's given the illusion that the planet isn't heating in accordance with previous climate change models, but the researchers say global warming and periods of ocean heat exchanges are separate events. And when the Atlantic's cooling period ends, roughly 30 years after its 2000 start, the ocean's heating effect will only compound the global warming it is currently temporing.
The study, "Varying planetary heat sink led to global-warming slowdown and acceleration," was published in the American Association for the Advancement of Science on Aug. 22.
The researchers delved deeper in their quest to pinpoint the missing heat, literally studying the depths of the ocean instead of changes at it surface area, according to corresponding author Ka-Kit Tung, a UW professor of applied mathematics and adjunct faculty member in atmospheric sciences. With ice sheets thinning faster than ever observed in recorded history, studying sea level was a logical start to launch the search for the missing atmospheric heat.
"Every week there's a new explanation of the hiatus," says Tung. "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."
Salt drives the cycles of hot and cold. Saltier waters of the Atlantic sink into lighter regions, causing the ocean's currents to pick up speed. The temperature oscillations has been tracked for centuries and may go back millennia, based on historical records, the report suggests.
"There are recurrent cycles that are salinity-driven that can store heat deep in the Atlantic and Southern oceans," Tung says. "After 30 years of rapid warming in the warm phase, now it's time for the cool phase."
The salt-sped currents send the heated waters of the southern Atlantic up into the region around Iceland, though it remains unclear what causes the cycle to reset. However, the current cycle of cooling is slowing down and is on pace to end in sync with the duration of previous periods.
Richard Alley, a geoscientist at Pennsylvania State University, says he's unsure if study on the Atlantic is a new story or a different narrator's view of the same tale.
"Those of us who work in palaeoclimate have for a very long time had an idea that the Atlantic matters," Alley says. "The evidence from the ice ages is that there were huge North Atlantic changes that show up in climate records all over the world."