Oxygen

Don't take for granted what you can't replace. 

This article is about the atmosphere's oxygen levels. At first this topic might appear done and dusted. It is true that burning fossil fuels depletes oxygen. However, there are significant reserves of oxygen in the atmosphere. So much so that, in the last 20 years we have only decreased it by 0.03%. But first, some technical background:

"It is roughly true that the oxygen depletion is equivalent to a displacement by carbon dioxide. But it is not exactly true. First, some of the carbon dioxide produced has been absorbed by the oceans. This process involves inorganic chemical reactions which have no effect on O2. Second, the O2:C combustion ratio of a fossil-fuel depends on the hydrogen content. The ratio varies from about 1.2 for coal, 1.45 for liquid fuels, and 2.0 for natural gas. Taking these factors together, we are losing nearly three O2 molecules for each CO2 molecule that accumulates in the air." (Dr Ralph Keeling)

".. the total estimated industrial O2 depletion on Jan 1, 2005 would have been ... 0.095% of the preindustrial amount." (article)
We have lost 0.095% of the atmospheric oxygen through the burning of fossil fuels. It is still happening (current measurements). 

From here "fossil fuel burning is depleting atmospheric oxygen at a rate of almost 1000 tons per second". If we burnt all known sources of fossil fuel we would deplete the atmosphere by 3.3%. Given the current oxygen content at 21% remove 3.3% = 17.7% of oxygen.
That is the equivalent of living at an altitude of 1524m. However, I don't expect we will burn all the fossil fuels.

So what is the problem?

Today we have 20.95% oxygen in the atmosphere, but the geological history has shown periods of 10-15% atmospheric oxygen.
"We found that particularly low oxygen levels coincided with intervals of elevated global temperatures and high carbon dioxide concentrations" (article)

Nature is a fine balance. Look at where the oxygen comes from, at least 70% of the worlds oxygen is generated by phytoplankton. Phytoplankton are one celled plants in the ocean. They use the energy from the sun, and the nutrients from the ocean and produce oxygen as a by-product of photosynthesis. These tiny plants are under threat from ocean warming and acidification. 

"... results suggest that changes in the pH at the cell surface of plankton could adversely affect cellular equilibrium, leading to poor growth if not death. "
"The implications of our research are profound," said Professor Flynn. "They suggest scope for a more serious impact of oceanic acidification upon marine plankton than previously thought."
(link)
"The new research means that ocean warming will impact plankton, and in turn drive a vicious cycle of climate change."
(link)

As stated previously phytoplankton are adversely affected by acidification, and also by Surface Sea Temperature (SST). There are many types of phytoplankton. The benign types are the food source of the ocean. But there are other toxic types. Given the right environment the toxic ones will out compete the benign ones. With the result that under warming conditions toxic algal blooms will increase.(link)

Benign phytoplankton, the good, are decreasing. Along with the declines are also decreasing Zooplankton populations. Benign phytoplankton and the Zooplankton are the basis of the ocean food chain, CO2 absorbtion, and up to 70% of the oxygen we breathe. 



The effects are starting to be seen in the food chain.

Let's make a hypothesis on where this could head to, and I admit this is speculation. Ocean acidification decreases the availability of benign phytoplankton. So less oxygen is being produced. However, the ocean is still absorbing oxygen from the atmosphere via diffusion. Ocean acidification increases toxic algal blooms, which are feeding on agricultural pollutants. When the algae die off from over population the bacteria decompose the algae and as they do that, they consume oxygen. They consume more dissolved oxygen than the algae produced. There is nothing to replace the oxygen at the rate that the ocean is consuming it. The land produces roughly 30% of the worlds oxygen. The ocean becomes an oxygen sponge. The more anaerobic it becomes the more purple and green bacteria will dominate.

Unless the land mass is generating at least the same amount of oxygen that the ocean is consuming then our atmosphere will become toxic to human life. Originally it was estimated phytoplankton has decreased 40% from 1950. (link) The original paper published in nature. Apparently new algorithms in satellite imagery meant a better detection of oceanic plankton in the Southern Ocean. So science refined its predictions. The latest is this report which is predicting 6% loss of phytoplankton, with a 2C rise, without factoring in acidification.

Significantly better than the previous estimate, but even a 6% loss would reduce the amount of oxygen coming from the ocean.
Some back of the envelope calculations...
Oxygen is 20.95% of the Earth's atmosphere. It is generated from 30% (land based) + 70% (sea based)
Decreasing the seas ability to generate oxygen by 6% would result in;
20.95/100 = x/95.8
20.07% with a 2C rise, not factoring acidification and land desertification. 

The problem with factoring acidification is that colder water absorbs higher levels of CO₂ (more acidification) than warmer water. Warmer water, also absorbs less oxygen, decreasing dissolved oxygen and increasing the oxygen minimum zones (aka dead zones). 
Same calculation, 3C rise? For now we will assume a linear effect in the ocean, that would result in a 9% reduction of oxygen generation from the ocean. 
20.95/100 = x/93.7 =>  19.63% oxygen without factoring the effects of acidification and land desertification.

 "if the oxygen level in such an environment falls below 19.5% it is oxygen deficient, putting occupants of the confined space at risk of losing consciousness and death." (OSHA rules on atmospheres in closed environments)

Obviously with the concentration of fossil fuel burning in particular areas oxygen levels are not constant. As mentioned previously between 1990 and 2008 (say 20 years), we have lost 0.0317%. Assume that was to continue at a linear rate, therefore if we hit 3C in 20 years global oxygen will be at roughly 19.6%.
This would imply that certain areas will go oxygen deficient at a 3C rise.
Compare the following images. The first from California, the other from the southern tip of Australia


The difference is pretty obvious. The difference may be from colder waters (more phytoplankton) in the southern ocean, or from increased CO2 burning in the US. Regardless, given the 19.6% estimate if 3C in 20 years is an average, then some areas are going to be more at risk than others.
That is not taking into account desertification of the land. "Due to drought and desertification each year 12 million hectares are lost (23 hectares/minute!)..." (link)
We are getting closer to localized oxygen deficiency.  My estimate would be that city centres would be the most depleted. Cities are hotter than the suburbs usually by 1-2C. A city's heat island effect creates low pressure, this pulls in air from the suburbs. The suburbs contain the most traffic during peak hours. Therefore, air being pulled towards the city centre has been subjected to fossil fuel combustion. As mentioned previously, that air would be oxygen depleted. A city, particularly one land locked, would suffer as a result.

Geological record

A number of times in history have seen ocean acidification events. It seems that when it was gradual the systems adapted. When the change was dramatic, large die-backs of plankton resulted. That coincides with our current situation. The recurring theme seems to be that higher latitudes performed better (link) in regards to plankton survival.

What's the effect of low oxygen levels on our body? 
Low oxygen levels also can have a harmful affect on brain function and physical ability. Attention span and concentration may be reduced. Memory and mood can be affected. Abstract reasoning and problem solving skills can be impaired. Speech may become affected. Simple sensory and motor skills may become difficult. Complex tasks that require gross and fine motor skills become harder. This may include tasks such as driving a car and operating equipment. Poor endurance for exercise, muscle weakness and impaired coordination also can be seen. Severe hypoxemia is lifethreatening. It can ultimately lead to confusion, coma and death. (link)

This is a potentially huge problem, it may not hit for a while, but it really seems to be gathering pace. A lot of linear assumptions have been made in coming to these conclusions, let's hope they stay that way.

A global fix would be difficult without radical geo-engineering to cool the water temperature. Initially, the following low tech ideas might help (pulled from the web I don't remember where). But possibly the better approach might be to grow your own phytoplankton. It can be used as a food source for fish and people (if untainted), and it generates oxygen. The other, more industrial, approach is to use electrolysis to generate hydrogen and oxygen from solar cells. Obviously, not for everyone.

Things You Can Do to Improve Your Air and Oxygen Intake

Use plants to reduce indoor air pollution. Plants breathe in carbon dioxide and breathe out oxygen. 
The recommended number of plants is 2 for every 100 square feet of interior space (assuming 8 to 10 feet ceilings) with groupings of plants being helpful. The more leaves the plant has, the better. Covering potting soil with a layer of aquarium gravel will help reduce mold spores. Even four or five plants in a room can make a difference in air quality. Some of the best plants for cleaning air indoors are:

• Chinese Evergreen
• Gerbera Daisy
• Aloe Vera
• English Ivy
• Bamboo
• Palm
• Banana
• Spider Plant
• Mum
• Heart-Leaf Philodendron
• Janet Craig
• Devil's Ivy
• Split-Leaf Philodendron
• Warneckie Snake Plant
• Ficus (Weeping Fig)
• Corn Plant
• Peace
• Lily Madagascar Dragon Tree
• Umbrella Plant
• Arrowhead Plant

Here is another good article on oxygen generating plants.