Unpacking the Carbon Cycle

For me an understanding of the carbon cycle and the Ocean Conveyor Belt that oxygenates our oceans – which doesn’t rely on complex measurements or computer models – has been key to getting my head around the current climate change controversy.

Thanks to the ABC documentary Crude, I now understand that there are basically four places where carbon is stored on earth: in the atmosphere and oceans as CO2, in the crust (as fossilized calcium carbonate rock, oil, coal and natural gas) and in livings plants and animals. When the earth was first formed, the vast majority of its carbon was present as atmospheric CO2 and as oceans formed, dissolved CO2 in the oceans. Then when life emerged, plants used energy from the sun to extract carbon from CO2 and combine it with oxygen and hydrogen to form the complex hydrocarbons that are characteristic of all plant and animal life. The cycle is completed when these plants and animals die and bacterial decay releases the carbon back to the atmosphere (see diagram).

The Jurassic Greenhouse

During the Jurassic Age (200 million years ago), high atmospheric CO2 levels meant the entire earth – including both poles which were ice free year round – was a massive greenhouse. Then complex ecological events occurred that caused hydrocarbons from plant and animal life to be trapped in the earth’s crust – as fossilized rock, oil, coal and natural gas. I used to believe that fossil fuels came from decaying dinosaurs. However current geological science indicates that oil, at least, derives from massive algae blooms that formed in the massive dead zones that were pervasive in the massive ocean (there were no polar ice caps) that covered three quarters of the earth’s service during the Jurassic period.

As in present day dead zones, the algae blooms sucked all the oxygen from the water and killed the fish and other animal life that ate the algae. For over 250,000 years, layer upon layer of dead algae sank to the ocean floor. And because there was no oxygen for bacteria to convert it back to CO2, the pressure build-up converted it to an even more complex hydrocarbon – namely oil.

As more and more CO2 was removed from the atmosphere, less and less heat was trapped in the Jurassic greenhouse, and the earth slowly cooled. Because cooling happened faster at the poles, ice sheets formed, and the increasing temperature differential created an Ocean Conveyer Belt that continuously moved warmer water towards the colder latitudes. And because cold water holds more oxygen, animal life gradually reappeared and the stagnant dead zones dissipated.

A Potentially Catastrophic Experiment

At this moment in history, mankind has converted roughly half the earth’s stored oil and natural gas (and 1/4 to 1/3 of the earth’s coal deposits) back to CO2. The concentration of atmospheric CO2 has risen from 280 parts per million (ppm) before large scale industrialization began in to 390.9 ppm last month. Because such a rapid increase in CO2 concentrations temperatures has never occurred before, no one can precisely predict the effect it will have on global temperatures. However climatologists can trace natural fluctuations in CO2 concentrations by studying ice cores in Antarctica. In general they find that global temperatures tend to be higher during periods of high CO2 concentration.

There is also no question that current global temperatures are rising; that extreme weather events (droughts, tropical storms and floods) are increasing; and that ice sheets in the Arctic and Greenland are receding a little more most summers than they recover in the winter. If current trends continue, the Arctic is predicted to be ice-free in summer by 2020 and totally ice-free by 2040.

The Effect of Losing the Arctic Ice Sheet

In my view, the current controversy over whether increasing global temperatures are the result of the (manmade) increase in CO2 concentrations or some natural cause is not the question we need to ask ourselves. That question, in my view, is whether we want to increase atmospheric CO2 to the level where the Arctic ice sheet totally melts.

I myself don’t need any scientists or complex measurements or computer models to come up with an answer. I think it’s a matter of common sense. If we lose the temperature differential between the equator and the Arctic, we run the risk of stopping the Ocean Conveyor Belt, which will turn the northern oceans into one massive dead zone. And no one has figured out yet how to get it going again.

(To be continued – addressing the more imminent issue of ocean acidification and why no one mentions Global Dimming in alleging solar activity as the real cause of global warming?)

Crude can be downloaded free (to show your climate skeptic neighbors) at http://www.abc.net.au/science/crude/

---