A new study published in Geophysical Research Letters, found that ocean heat content rose at its fastest rate ever recorded over the past 15 years. The study, written by Magdalena A. Balmaseda, Kevin E. Trenberth, and Erland Kallen, found that the deep ocean below 700 meters accounted for 30% of all global heat content increase over the past decade.
What this means is that total warming of the atmosphere-ocean system didn’t slow down as some global warming denier sources claim. Instead, total Earth warming accelerated.
According to the paper, the most recent period since 1999 was:
the most sustained warming trend in this record of OHC. Indeed, recent warming rates of the waters below 700m appear to be unprecedented. In the last decade, about 30% of the warming has occurred below 700 m, contributing significantly to an acceleration of the warming trend.
Over the past decade, La Nina events have predominated. And this, according to study authors, resulted in a large portion of global warming being retained in the oceans. The reason is that El Nino is a powerful mechanism of ocean heat transfer to the atmosphere. But over the past decade, El Nino events have been rare, keeping more human caused heating in the world’s oceans. Not only did upper levels of the ocean heat up, a massive amount of global warming telegraphed into the deepest regions of world ocean systems.
According to Keven Trenberth, one of the study’s authors and a leading climate scientist, “It means less short term warming at the surface but at the expense of a greater earlier long-term warming, and faster sea level rise.”
The reason is that rapidly warming oceans pump more water vapor into the atmosphere. Water vapor is a powerful greenhouse gas and a major amplifying feedback to human caused warming. In addition, rapidly warming waters leads to greater thermal expansion of the world’s oceans, accelerating sea level rise.
Bad News For Methane Hydrates
More rapid ocean heating also has another impact not directly mentioned in the new study. What it does is put more of the world’s deposits of methane hydrates at risk of destabilization.
Methane hydrate is a volatile mixture of methane and frozen water that can be found on seabeds around the world. It is estimated that as much as 10,000 gigatons of carbon lay locked in methane hydrate deposits around the globe. Methane is a powerful greenhouse gas. Over a century, it is 20 times more powerful by volume than CO2. Over ten years, it is 100 times more potent. Methane is also problematic because after it amplifies warming as methane, it then breaks down into CO2, adding to already high volumes of that gas. Were even a small fraction of this carbon to bubble up from the ocean bottom and reach the atmosphere, it would result in a powerful amplifying feedback to human caused climate change.
Over the past decade, instances of methane hydrate destabilization have been found in the Arctic, off the east coast of the United States, and in other regions around the globe. Many of these events appeared to be new. Of these, methane plumes found in the East Siberian Arctic Shelf were the most disturbing. There, plumes of methane a kilometer across were discovered. Though submerged tundra was also a likely contributor to massive methane plumes discovered on the shelf, hydrates are also known to have formed there.
Now, with oceans heating at a greater rate than the atmosphere, risks for large methane hydrate releases are also increasing.
Most Missing Heat Found, Look to Ice Sheets for Remainder
This new research finds most of the missing heat scientists have been looking for around the globe. And that heat, as previously suspected, ended up in the world’s oceans and, to great extent, in the deep oceans. That said, a much smaller measure of heat is still unaccounted for. It might not be a bad idea to look in the world’s ice sheets — which appear to be decaying at a much faster rate than expected. One speculates that the hearts of the great glaciers are more watery than anticipated and contain much of the remaining heat from human caused global warming not currently located.