The key to the slowdown in global warming in recent years could lie in the depths of the Atlantic and Southern oceans where excess heat is being stored – not the Pacific Ocean as has previously been suggested, according to new research. But the finding suggests that a naturally occurring ocean cycle burying the heat will flip in around 15 years’ time, causing global temperature rises to accelerate again.
The slowdown of average surface temperature rises in the last 15 years after decades of rapid warming has been seized on by climate change skeptics and has puzzled scientists, who have hypothesized that everything from volcanic eruptions and sulphur from Chinese power stations to heat being trapped deep in the oceans could be the cause. Several studies have focused on the Pacific as potentially playing a major role.
A new study, published in the journal Science, concludes that the Pacific alone cannot explain the warming “hiatus” and that much of the heat being trapped by greenhouse gases at record levels in the atmosphere is being sunk hundreds of meters down in the Atlantic and Southern oceans.
A shift in the salinity of the north Atlantic triggered the effect around the turn of the century, the study says, as surface water there became saltier and more dense, sinking and taking surface heat down to depths of more than 300 meters. Using temperature data from floats across the world, Tung found the Atlantic and Southern Oceans each account for just under half the global energy storage change since 1999 at below 300m.
The study gives little room for complacency that the oceans can safely store heat caused by human activities because the cycle that buries the heat deep in the Atlantic will “inevitably” switch back. Heat would then no longer be removed deep underwater, leading to another episode of accelerated warming at the surface.
Most importantly, this paper is another a nail in the coffin of the idea that the hiatus is evidence that our projections of long-term climate change need revising down. Variability in the ocean will not affect long-term climate trends but may mean we have a period of accelerated warming to look forward to.
This February, the national science academies of the U.S. and UK said the global warming slowdown did not “invalidate” the long-term trend of rising temperatures caused by man-made climate change.