Climate change: The deep ocean protects us from ourselves — for now
In the latest IPCC report, a realistic but dire situation is presented. Already, the world is experiencing some of the predictions made by the earlier reports including massive wildfires, intense heat waves, powerful storms, climate-induced migrations (by animals, plants and humans), and general weather weird-ening. And the future holds more calamities for us all. We are baked into many of the future scenarios, but the report also describes some of the changes that would be necessary to avoid further chaos. These will take a massive, coordinated, global effort, but I am still optimistic that our society is up to this grand challenge.
But there is also something missing. Buried in some of the technical sections of the report is the role that the deep ocean plays in protecting us from ourselves. I am referring to the seldom-recognized services that the deep sea, which makes up 95 percent of the habitable space on Earth, provides our society. Over 90 percent of the heat generated by the greenhouse effect in the Industrial Age is currently stored in the ocean. The atmosphere would be far hotter than it is now if that heat could not make it to the deep sea.
Furthermore, much of the CO2 pumped into the atmosphere dissolves into the ocean. Not only is the deep ocean storing our heat, but it is also preventing more heat from being trapped in the atmosphere by keeping the carbon away from us. If not for these services, all of the scenarios where we still have time to save ourselves would be long past.
So, we owe a great debt to the deep sea, but holding all of this heat has other effects. Warm water holds less oxygen, and there is no photosynthesis to generate oxygen in the deep, dark ocean. In some areas of the Pacific Ocean, the oxygen concentration is so low that no animals can survive. This oxygen minimum zone is still at depths below a few hundred feet, but it is expanding.
In the Gulf of Mexico, the warm water, along with the eutrophication caused by the runoff of fertilizer carried by the Mississippi River, causes a “Dead Zone” to form every summer extending all the way from the surface to the seafloor. This year, it covers an area over 6000 square miles, larger than the state of Connecticut. Ocean deoxygenation will increase the size of these events and the oxygen minimum zone will only get shallower until we can alter our relationship with the environment.
There are also consequences to being the Great Carbon Sink. The deep sea is the largest carbon reservoir on Earth, but only part of it is dissolved in the water or locked up in massive deep-sea coral reefs. The majority of the carbon in the deep ocean is in the form of methane hydrate. This is a solid, ice-like form of methane that occurs under very cold and/or high-pressure conditions. When it gets too warm, it becomes unstable and the large chucks of methane ice in the ocean floor go straight from a solid to a gas and bubble up to the surface. Historically, some of these gas releases have been catastrophic, leaving “pock marks” in the seafloor, some of which are miles wide.
Methane is a far more powerful greenhouse gas than CO2, although it is more short-lived. A rapid release of methane is believed to have occurred that last time the Earth was in a state like the one we are headed toward. This is referred to as the Paleocene-Eocene Thermal Maximum (PETM), about 55 million years ago. Once the temperature reached about 2 degrees Celsius higher than average, there is good evidence that massive amounts of methane were released from the hydrates, causing another 2 to 3 degrees of heating in the atmosphere. This is explained in Chapter 5 of the IPCC, about 1,000 pages into the report, and then largely dismissed as a concern about 200 pages later by (presumably) other authors of the report.
Although the potential impact of present-day methane hydrate destabilization is still debated, it may not be far off. Over the last five to 10 years, scientists have learned how to acoustically image the bubble plumes coming up from deep-sea, natural-gas, “cold seeps.” This led to the discovery of thousands of these seeps along both of the east and west coasts of the U.S. We should be watching these seeps to see if they are caused by gas release from methane hydrates and whether this rate is changing. Unfortunately, we still do not have a great way to monitor methane concentrations in the ocean over time.
The issues raised in the IPCC report are all urgent and are backed by an incredible set of data that took many brilliant people years to compile. The report does a great job of detailing what we know about our current and future situation. But we still have so little information about the deep ocean that we have trouble even identifying all of the issues. My goal here is not to add to the already-long list of things that keep you up at night. My goal is to highlight the need for more investment in the exploration of inner space and in the technological innovations required to observe and monitor these processes in the ocean so we can understand the protections we enjoy and the dangers we may find in the dark recesses of the other 95 percent of our own planet.
Erik Cordes, Ph.D., is a professor and vice chair of biology at Temple University in Philadelphia and the founder and co-lead of the Offshore Energy Working Group of the Deep Ocean Stewardship Initiative. He has worked on the ecology of the Gulf of Mexico for over 20 years, including the damage assessment following the Deepwater Horizon oil spill in the Gulf of Mexico. Follow him on Twitter: @CordesLab.