Where is All the CO2 Going?

coral reef wikimediaWhen fossil fuels — coal, oil and natural gas — burn, the major combustion products are carbon dioxide (CO2) and water vapor. Water doesn’t matter since it is already everywhere and adding a little bit more to the Earth won’t tip any balances. CO2, on the other hand is considered to be a great evil by those who believe in catastrophic global warming.

It’s perfectly reasonable that adding CO2 to the atmosphere could cause some warming, probably minor. This perfectly reasonably supposition was turned into unreasonable dogma by certain scientific disciplines that sensed an opportunity. They realized that if CO2 were inflated into the great Satan, it would be very beneficial for their careers. Backwater scientists in the obscure specialty of atmospheric science became well-traveled celebrities by promoting the doomsday theory of global warming.

Radical environmentalists joined the catastrophic global warming chorus. This worked pretty well during the 70’s, 80’s and 90’s when the Earth was warming. But then the warming stopped and now, after 18 years of no warming, the theory of catastrophic global warming is falling apart. To keep the money flowing, the global warming promoters began promoting extreme weather and ocean acidification, two new and bad things that are supposed to happen if we continued burning fossil fuels. They even began jiggering the temperature data to try to bring back the 18 missing years of global warming.

In 1978, by burning fossil fuels, we were adding approximately 1.5 billion tons of CO2 to the atmosphere each month. By 2012, as China and the rest of Asia grew economically, that had doubled to about 3 billion tons per month. This may sound like a lot of CO2 unless you know that the mass of the atmosphere is 5 million, billion tons. An interesting thing happens to the CO2 that is added to the atmosphere every month. Nearly half of it disappears. Apparently it mostly disappears into the ocean, with the remainder disappearing into the land.

There are two main ways that CO2 can disappear. It can be absorbed by photosynthetic plants and turned into carbon containing plant bodies, including algae in the ocean, or it can be absorbed into the oceans directly. If a plant absorbs CO2 it is important, if there is to be long term sequestration of the carbon, that the plant not immediately die, decay, and release the CO2 it absorbed back into the atmosphere. Plants breathe CO2 and extract the carbon to form their carbon-based bodies. If the plant decays, the carbon is re oxidized into CO2. It is often the case that dead plants are buried and create a store of carbon. For example, on the land, there are peat bogs that accumulate dead plants. Or, in the ocean biological matter becomes stored carbon if it sinks into the bottom sediment.

In the ocean the removal of biologically based carbon from the surface waters to deeper waters or the bottom sediment is called the biological pump. Biological activity in the upper ocean is based on photosynthetic organisms that incorporate carbon into their bodies. The photosynthetic organisms die and decay or are eaten by other organisms that also die and decay. A small part of this food chain based on photosynthesis falls to the deep ocean or the ocean floor with the resulting removal of carbon from the upper ocean and Earth’s biosphere. The biological pump is an important part of ocean carbon sequestration. Carbon incorporated in bottom sediments is permanently sequestered, or at least for a very long time, while carbon that remains in the deep water will upwell to the ocean surface in around a thousand years.

CO2 gas can be absorbed by the oceans as a dissolved gas, much like CO2 is absorbed in carbonated soda. CO2 can also be stored in water by a chemical reaction. In the ocean, a molecule of CO2 can come apart and combine with the water. The CO2 then exists as carbonate (CO3) ions or bicarbonate (HCO3) ions. These different ways of storing carbon can dynamically change, one to the other, the proportions depending on the salinity (or alkalinity) of the water.

Potentially the oceans are a huge sink for CO2 and they could eventually absorb all the human CO2 emissions. The key is “eventually.” Global warming dogmatists say that the ability of the ocean to absorb CO2 will begin to decline soon and that it will take thousands of years for the ocean to absorb most of the human CO2. In other words nature won’t solve the “problem” and we must urgently start building windmills and electric cars. The dilemma for the global warming dogmatists is that since routine measurements of CO2 in the atmosphere began in 1958, the Earth, probably mostly the ocean, has been absorbing an increasing proportion of the CO2 emitted – now about 45%.

fossil fuel co2 emitted monthly

Exactly where and how, on the land, CO2, transformed into plant matter is stored is not well understood. We know that a lot of CO2 is emitted into the air by land clearing and forest fires, but apparently plants are also consuming CO2 as they grow, and currently, the consumption of CO2 exceeds the generation of CO2 from the land. When consumption of CO2 exceeds production of CO2 on the land we say that the land is a net sink for CO2.

In the oceans, we know that CO2 is readily absorbed in the top 100 meters. The top 100 meters, approximately, is called the mixed layer. Due to the effect of wind and waves CO2 can readily move back and forth between the ocean mixed layer and the atmosphere. It is less clear how, or if, CO2 can easily get into the deep ocean. The deep ocean, called the abyss, is vast and is a place that has the capacity to absorb all the CO2 we can generate.

CO2 can get into the abyss slowly by being mixed downward by a process called turbulent mixing. Or, in principle, CO2 can ride down to the abyss on an express train called the overturning circulation. In certain regions, near the Arctic and Antarctic, where the water is very cold and reasonably salty, the water begins to sink toward the bottom of the ocean. Every year, the top 4 meters of the world’s oceans are skimmed off and sink deep into the ocean, often to the very bottom of the abyss. The sinking water pushes the water above the abyss upward by the same 4 meters. Water that previously sank gradually rises, until thousands of years later it reemerges at the surface as upwelling ancient water.

The problem is that for the sinking water of the overturning circulation to carry significant CO2 into the abyss it has to absorb it from the atmosphere in sufficient quantities. The water that is upwelling from the abyss is warming and releasing ancient CO2 to the atmosphere, particularly in the tropics. The sinking leg of the overturning circulation is reabsorbing the CO2 and taking it back down to the abyss. Seawater releases CO2 when it gets warmed and absorbs CO2 when it cools. However, if the sinking overturning circulation simply reabsorbs the same amount of CO2 that was released in the tropics, there will be no net removal of CO2 from the atmosphere.

At this point a bugaboo called the Revelle Factor comes into play. Roger Revelle was an important scientist and an early pioneer in studying CO2 in the atmosphere and ocean. Although the ocean’s ability to store CO2 is sensitive to temperature (colder is better), it is less sensitive to the concentration of CO2 in the atmosphere. If the amount of CO2 in the atmosphere increases by 20%, we say that the partial pressure of CO2 has increased by 20%. However if the partial pressure of CO2 increases, the increase of ocean storage is reduced by the Revelle factor. If the Revelle factor is 10, then a 20% increase of CO2 in the atmosphere will only result in a 2% increase in CO2 in the ocean immediately under the atmosphere. The Revelle factor depends on salinity and is in the range of 8 to 16. Higher salinity is better and results in more CO2 storage. If the Revelle factor is low, the amount of CO2 carried to the abyss will be greater. It may help that the sinking water of the overturning circulation is associated with high salinity and thus better CO2 absorption.

The significance of CO2 disappearing into sinks is that, the more CO2 disappears, the less we have to worry about global warming (for those who are inclined toward that worry). Currently the science governing the CO2 sinks is not very solid. Work is underway to develop this area of knowledge, including the launching of satellites to measure atmospheric CO2 concentration and indirectly CO2 circulation. Given the strong bias of the scientific community toward promoting global warming catastrophism, everything establishment science says has to be critically evaluated. It will be interesting to see what the future holds.