The Sinking Ocean Sink


One of the big problems with the analysis of the oceans by climate skeptics is that they will treat the ocean as if it were a single block of ocean and carbon dioxide is absorbed uniformly throughout its volume rather than relying upon ocean circulation and diffusion before it reaches an equilibrium distribution. There are layers to the ocean, and even now anthropogenic carbon dioxide emissions have are fairly concentrated within the top two meters. Likewise, there is a skin to the ocean where due to the increased acidity that results from carbon dioxide which has already been absorbed - and creates a barrier to the absorption of additional carbon dioxide.

Then there is another common "error" in which they will assume that the carbon dioxide which is absorbed by the ocean isn't largely replaced by the carbon dioxide which is leaving the ocean. Even under equilibrium conditions, the ocean is emitting carbon dioxide, but this is balanced against that which it absorbs.

Additionally, as carbon dioxide raises results in higher temperatures in both the atmosphere and the ocean (we are able to measure the effects of global warming as far down as 1500 meters), this tends to raise the rate at which carbon dioxide is emitted by the upper layers of the ocean - just as a soda is less able to hold its fizz at higher temperatures. Absorption tends to take place by the colder waters of the Arctic and Antarctic - and these are already losing their ability to absorb the carbon dioxide which we are emitting. But the main mechanism in play currently is a little different from that which we were expecting, at least in the case of the Antarctic. However, it helps to have a little background on the structure of the atmosphere to understand why.

What's Hot and What's Cool

The lower part of the atmosphere, where we live, is called the troposphere. It is warmed principally by moist air convection. The reradiation of thermal radiation by greenhouse gases has the direct effect primarily of cooling the atmosphere. It absorbs plenty of thermal radiation, but this is more than balanced by the thermal radiation which it emits. The additional radiation which the surface receives as the result of greenhouse gases reradiating more thermal radiation (more or less in all directions - about half of which goes back to the surface will warm the surface) results in a higher humidity due to evaporation and thus more moist air convection.

The farther you go up, the drier the atmosphere becomes until finally you reach the tropopause where there is very little moisture. As a result there is less and less moist air convection with altitude within the troposphere until finally at the boundary of the troposphere there is no moist air convection at all. Consequently the temperature drops with altitude in the troposphere. But above the tropopause which marks the end of the troposphere, the temperature actually rises with altitude in the stratosphere.

More greenhouse gases will have the effect of cooling the stratosphere rather than warming it, principally because it lowers the rate at which thermal radiation is able to leave the lower layers of the troposphere and surface. As such, while the climate change that results from more greenhouse gases warms our part of the climate system, it has the effect of cooling the stratosphere - with a long term thermal equilibrium within the stratosphere coming about only as the result of thermal diffusion. And it cools the stratosphere first - even before it begins to warm the troposphere.

Fading Sunscreen

However, one exception to greenhouse gases lowering the temperature of the atmosphere is ozone. This gas is able to absorb ultraviolet radiation directly from sunlight rather than being limited to the infrared thermal radiation being radiation from the surface. However, it tends to be destroyed in moist air - as the result of OH radicals resulting from water molecules being struck by ultraviolet radiation. Consequently it tends to be limited to the upper parts of the troposphere and stratosphere.

The layer of ozone in the atmosphere has been partly damaged as the result of CFCs which were in use until the 1970s - and this damage shows up particularly near Antarctica. This has already reduced the temperature of the stratosphere to a fair extent in that area. However, the increased moisture in the troposphere is reducing it further, resulting in the stratosphere becoming cooler due to additional moisture in the lower atmosphere resulting in more water molecules reaching the stratosphere - and thus more OH radicals which destroy ultraviolet-absorbing ozone.

The Winds of Change

The lower temperature of the stratosphere and the higher temperature in the troposphere then results in increased atmospheric circulation - wind. This will carry the moisture in the troposphere higher, resulting in the destruction of more ozone - lowering the rate at which the ozone layer is able to heal.

Now given the lower temperature of the Antarctic, this is where much of the carbon dioxide gets absorbed by the ocean. However, this is also where the stratosphere tends to be closer to the surface. As a result, the warmer temperature of the troposphere and the cooler temperature of the stratosphere will result in increased wind at the surface of the ocean. This brings up organic material from the depths of the ocean - resulting in more carbon dioxide being emitted in that part of the ocean. And as a result it has been lowering the ability of the southern ocean to absorb as much of our carbon dioxide emissions.

An Important Key

Incidentally, the cooling of the stratosphere is one of the key pieces of evidence which demonstrates that what is causing the current trend towards warming in the troposphere is increased greenhouse gases - not solar radiation. More solar radiation would result in the warming of both the stratosphere and the troposphere.

Unless otherwise stated, the content of this page is licensed under Creative Commons Attribution-ShareAlike 3.0 License