“Most of us suffer from a kind of myopia. We see only the things that fit in with our beliefs about the world.”
— TJ MacGregor
About the Ocean
The word “Ocean” (capitalized, singular, and without an adjective) refers to all four oceans and twenty seas in the world. It is enormous. It has a surface area of 196 million square miles, holds 336 million cubic miles of water, and weighs 1,320 quadrillion metric tons.
The Ocean is 1,600 times heavier than the atmosphere. Since heat storage capacity is proportional to mass, the Ocean is storing 93% of the heat retained due to greenhouse gases. The atmospheric heating we have observed is due to the other 7%. If the Ocean had stopped absorbing heat in 1970, the average global temperature of the atmosphere today would be 122 degrees F. (From the Netflix documentary “Chasing Coral”) This is too hot for life (except extremophiles) to exist.
Our Terrestrial Bias
Yet, when we speak about global temperature, we mean the temperature of the atmosphere. We ignore the heat in the Ocean. We are biased towards focusing on the atmosphere because that is the environment in which we live. Yet it is still astounding how little we know about the Ocean when it plays such an important role in climate change. According to a 2018 NOAA report, more than 80% of the Ocean remains unmapped, unobserved, and unexplored. We know more about the surface of Mars than we know about the Ocean.
If we want to survive the climate change crisis, we had better factor in the 90% of the problem we have been ignoring. As the atmosphere’s air conditioner, the Ocean has saved us from an early demise, but its capacity to absorb heat, though large, is not infinite. The warmer it gets, the more difficult it is for it to absorb more heat, and, incidentally, to absorb more carbon dioxide.
In order to understand how the Ocean absorbs heat, we need to understand how it is structured. The Ocean has three layers, as shown in this schematic:
Surface Layer: This is the top layer. It goes down to a depth of 600 feet. This is the only layer where light can penetrate. It is also where most marine plants and animals live. It is well mixed and has a relatively uniform temperature of 55 degrees Fahrenheit.
Thermocline: This is the second layer. It starts at 600 feet and goes down to 3000 feet. The temperature in this layer drops the farther down you go, from 55 degrees F to 39 degrees F. Most of the heat the Ocean absorbs remains in the Surface Layer
Deep Ocean: The Deep Ocean never freezes because of a property unique to water; it expands when it freezes. The tremendous pressures in the Deep Ocean keep the water from expanding so it can’t freeze. The temperature here ranges in the low 30’s F.
Heat is absorbed at the surface. Waves and currents mix this heat down, but most of it remains in the Surface Layer. The Ocean will not go on absorbing this much heat because the warmer the surface gets, the less able it is to absorb heat and carbon dioxide.
Interdecadal Pacific Oscillation
Then there is the Interdecadal Pacific Oscillation (IPO). The IPO is a 40 to 60 year irregular oscillation mostly in the Pacific basin but with effects on temperature around the world. The cycle has warm and cool phases. Since 1920, there have been two warm phases (1924 to 1944 and 1977 to 1998) and two cool phases (1945 to 1976 and 1999 to present).
We are now in a cool phase. During a cool phase, high winds increase the mixing of surface water with deep water. This brings colder water from the depths to the surface, which cools the atmosphere. The temperature increases we’ve seen since 1999 would have been higher but for this cool IPO phase. Colder water also absorbs carbon dioxide better than warm water, so this phase of the IPO has also helped to offset the rate at which carbon dioxide concentration is building up in the atmosphere.
We have been in the present IPO cool phase for 21 years and will return to a warm phase at any time. Since we are still burning fossil fuels at an ever-faster rate, this means that when the IPO warm phase kicks in, the global temperature and atmospheric carbon dioxide content will rise even faster. In addition to this, the Ocean may begin giving up its heat. This will further add to the rate at which the atmosphere is warming.
Consequences of Ocean Heating
The Ocean has saved us from an early demise, but it comes at a steep price.
Arctic sea ice, Antarctic ice shelves, the Greenland and Antarctic Ice Caps, and glaciers around the world are melting far faster than expected. This increases the rate at which sea levels are rising and decreases the Earth’s ability to reflect sunlight (it’s albedo) which causes even more heat to be absorbed which accelerates the melting.
As you can see from this schematic, The Thermohaline Circulation is a continuous conveyor belt that move water throughout the Ocean. A big concern is that the increasing flow of melt water from the Greenland Ice Cap will interfere with the conveyor belt where it dives down to deeper depths off the east coast of Greenland. Fresh water is lighter that saltwater, so when it flows faster than it can mix, if floats on top of the saltwater. This could slow the conveyor belt by inhibiting its dive to deeper depths, and this could slow the entire conveyor belt, with potentially huge impacts on the global climate. For example, warming Arctic waters could worsen summer heat waves in Europe and North America by lowering the temperature differential that drives mid-latitude circulation.
As for marine life, ocean heating already presents multiple, intensifying dangers.
- Most ocean organisms, from plankton to fish to whales, live in the Surface Layer, the zone where heat is building up the fastest. Making matters worse, marine heat waves have increased by more than 50 percent over the past century. During these events, temperatures near the surface of the ocean can spike up to several degrees above the average.
- Warmer water also holds less oxygen and increases ocean stratification, which blocks the movement of oxygen-rich surface waters to lower depths. The resulting low-oxygen zones are spreading. Not only are the zones inhospitable to most sea creatures, they squeeze more marine life into an increasingly crowded critical upper ocean habitat as they enlarge.
- Excess heat, acidification from excess carbon dioxide, and the increasing presence toxic microplastics (the microscopic remains of the plastic waste that gets dumped into the Ocean) are damaging sea life of all kinds. Heat, for example, is killing the algae that live in a symbiotic relationship with coral. They give coral its color, and when they die, the coral turns white. It’s called bleaching. Once the algae are gone, the coral starve and die. Half of the Great Barrier Reef has been bleached to death since 2016. Some scientists speculate that, given current trends, all coral on Earth may be gone by 2050.
- When carbon dioxide dissolves in seawater, the water becomes more acidic. The acidity of the oceans has increased by 26 % since about 1850, a rate of change roughly 10 times faster than any time in the last 55 million years. Associated chemical reactions can make it difficult for marine calcifying organisms, such as coral and some plankton, to form shells and skeletons, and existing shells become vulnerable to dissolution. The extent to which calcifying organisms are already being affected by acidification is unclear, as this is a very new area of study.
- Any damage to the base of the food chain will quickly propagate up through the food chain due to the inverted marine predator-prey ratio. There are five times as many predators as prey. This is made possible by the fast replacement rate of marine prey. If the base of the food chain is interrupted, the effects up through the food chain will be fast, broad, and lethal.
We still have a lot to learn about the Ocean, how it is affected by climate change, and how it will affect climate change. The uncertainty about the future leads skeptics to dismiss the concerns, but all the trends favor negative contingencies, not positive ones.
The 90% of the heat that has gone into the Ocean is a ticking time bomb. We do not know when the air conditioner will shut down or turn into a global heater. When it does, the game will abruptly change and the future that deniers have scoffed at will come into clear focus. But what will we do then?
Near Term v Long Term
Some of the heat in the Ocean will not return to the atmosphere for perhaps hundreds or even thousands of years. We need not be worried about that. What we need to worry about is the next three decades. If we can get to 2050 and keep the global temperature from rising more than another half degree, we will be in good shape to handle what comes after. If we can’t (or won’t), then the die will have been cast for a world in which merely surviving will be viewed as a victory.