The world we live in has a volcanic history. The continents ultimately came from volcanoes, often volcanic arcs, in some cases several billions of years ago, in other cases more recently. All ocean floor is volcanic, made in mid-oceanic rifts within the past few hundred million years. And the volcanic contributions do not stop there. The air we breath is in part of volcanic origin, and in the absence of volcanoes, would quickly become unlivable. In the list of acknowledgements at the end of the movie ‘The human race’ (coming soon to a planet near you), volcanoes will feature prominently, immediately after the main actors, and in a big font; perhaps they will also feature in the funny outtakes at the end, for instance the Yellowstone eruption which was accidentally filmed supersized, wiping out all of human life and requiring a re-take, however I expect that human bloopers will provide a plethora of choice already, enough to fill up an entire youtube channel. (Thinking about it, isn’t human bloopers what most television channels already show?) We are volcanoes’ living heritage.
But not everything volcanoes do is to our benefit. The lava flows build new land but also burn down what was before. The gases that are emitted range from harmless (water) to dangerous (SO2, HF) and deadly (CO). But one of those volcanic gases has everything. CO2, which accounts for 10 per cent of the gas emitted by volcanoes, is the killer we could not live without. It keeps our Earth warm but in excess causes global heating. Is it for better or for worse? And is it true, as some have claimed, that volcanoes emit more CO2 than humans do? Ian Plimer famously stated “Over the past 250 years, humans have added just one part of CO2 in 10,000 to the atmosphere. One volcanic cough can do this in a day.” A politician, Mike Huckabee, said “The volcano that erupted over in Northern Europe actually poured more CO2 into the air in that single act of nature than all of humans have in something like the past 100 years.“ He can be forgiven for not trying the pronounce the name Eyjafjallajökull. But what is the scientific truth? How much do volcanoes contribute?
Before we continue, you may want to take a quick test, comparing human and volcanic emission per year.
And one more polling question about comparing volcanoes to humans:
The miracle of carbon
So why is carbon so important? After all, the amount of CO2 in the Earth’s atmosphere is minuscule. But carbon does much more than making CO2. The biosphere is a carbon world. Life requires organic chemistry, and organic chemistry demands carbon. It is a versatile atom which can make four bonds with other atoms. This opens up a world of possibilities. It can bond (boringly) with four hydrogens, to make methane. It can do two oxygens instead (each oxygen accounts for two bonds), making the life-giving killer CO2. Or it can mix and match bonds, say H2CO or OCS. Putting a hydrogen on the oxygen, so that only one bond is needed to weld the OH to the carbon leaves three bonds free, and allows H3COH – methanol. The real power comes, though, from carbon bonding with carbon. Immediately, H3CCH2OH becomes possible, that essential molecule for (previously) intelligent life, ethanol (alcohol). Include nitrogen, and you enter the realm of the complex molecules that define life, from the busy-bees of the amino acids to the digital information systems of DNA. The only atom that can compete in complexity is silicon, which can also do four bonds. Whilst carbon makes an unending series of different molecules, silicon instead makes crystals, equally wonderful and complex but inert. Theirs is the elegance of autism, a wonderful world, greatly rewarding the effort needed to understand its beauty. But to build an organic world, you need to interact in ways that silicon, frozen in place, just doesn’t. Carbon is the wonder that carries the gift of life.
It also carries the gift of death. The complexity of carbon molecules makes their chemistry unpredictable. One misplaced reaction can destabilize the intricate web upon which life depends. Even a molecule as simple as benzene is dangerous. The art of making pesticides is finding a molecule that kills one thing but is harmless to everything else – a dangerous dream which requires a great deal of wishful thinking. Life came out of complexity, and complexity brings with it fragility. But that is a different story. And even a molecule as simple as CO2 is a mixed blessing. Plants can’t live without it; animals can’t live with it. A few per cent of CO2 in the air stops our blood from carrying oxygen, with deadly consequences. It is used to carbonate our drinks, adding excitement to bland liquid sugar, but it is best to avoid breathing the liberated gas. Even the machines that make carbonated drinks are known to have caused fatalities.
Volcanoes are also implicated in CO2 fatalities. In February 1979, following a phreatic eruption, Dieng volcano, in Indonesia, released nearly pure CO2 gas. 142 people died in the valley below the volcano, from asphyxiation. (Such a CO2 discharge from a vent is called a mofetta.) Cameroon has also fallen victim. It contains two volcanic lakes, which capture CO2 emitted by hydrothermal springs at the bottom of the lake. These two lakes lack a regular turn-over of the water: the bottom water stays where it is, aided by the fact that adding CO2 makes water heavier. The lakes have become strongly stratified and the bottom layers eventually become saturated with the gas. Until, at some point, this stratification fails. The water at the top suddenly sinks down, the bottom water comes to the surface. the CO2 suddenly –and explosively- comes out of the solution (think a coke bottle shaken, not stirred), and is released into the atmosphere. On 21 August 1986, this happened at Lake Nyos: 1700 people died. The gas burst caused a 25-meter high lake tsunami, but the real killer was the gas. There had been an earlier warning: nearby Lake Monoun had done the same thing in August of 1984, killing 37 people. Why did it happen twice in August? August is the monsoon season, when the rains cool the surface. Cooler water is denser, and this time it became denser than the CO2-rich bottom water. Still waters can hide fizzy killers. Lake Nyos is now under control, but there may be other such ticking time bombs in Africa.
CO2 suffers from more bad press. It is implicated in the acidification of the oceans, and in the inexorable rise of worldwide temperatures. The latter is a complete accident of physics. CO2 happens to absorb radiation that would otherwise carry heat from Earth to space. The Earth acts like a room where the radiator is always on, and the temperature is regulated by opening and closing curtains. CO2 is that curtain, and as more is added to the atmosphere, the curtain becomes thicker. We are now implementing carbon budgets, and countries are slowly becoming committed to limit their emissions to amounts the Earth can cope with. But as Lake Nyos demonstrated, not all CO2 is humane. Are volcanoes in compliance with the Paris agreement? Or are we kidding ourselves by regulating our own emissions whilst ignoring the unstoppable volcanoes?
Let’s put some numbers into this discussion. The current concentration of CO2 in the atmosphere is around 400 ppm. ‘ppm’ stands for ‘parts per million’. A number of 400 means that out of every 10,000 molecules in the air (where water molecules are excluded from the count), CO2 accounts for 4. In comparison, over 2000 of those molecules are O2, and 100 are argon. If you were to buy the essential ingredients needed to make air, CO2 wouldn’t feature on the shopping list.
CO2 emissions are measured in weight rather than number of molecules. Take a square meter of ground: the air column above it contains 6.1 kilogram of CO2. To get the total amount of CO2 in the atmosphere, multiply this number by the total surface area of the Earth. It comes to 3.1 x1015 kilogram of CO2 – or 3130 gigatons, if you prefer.
To confuse things further, sometimes the total weight of carbon is quoted rather than that of CO2. The ‘C’ accounts for 32 per cent of the weight of CO2 (the rest is in the two oxygen atoms). So the total amount of carbon in the atmosphere at the present time is 996 gigatons. Adding methane (2 ppm) brings this up to almost exactly 1000 gigatons of carbon.
NASA’s view of CO2 in the air
Carbon in the biosphere
Measuring the weight of carbon rather than CO2 is useful in cases where carbon is in a different form, for instance organic molecules. This is the case in the biosphere: the sum of all living things. Let’s start with ourselves. The human body is about 18 per cent carbon by weight. If we take our average weight as 60 kg, and a current number of 7.5 billion people, humanity accounts for 83 million tons of carbon. (The CO2 equivalent would be 3.1 times larger, i.e. 250 million tons.) Domesticated animals account for perhaps twice as much as people. Wild land animals contain a sum total of 5 million tons of carbon. An interesting aside is that, since the population explosion, humanity outweighs all wild land animals combined by a factor of 15! This may give a whole new reason why, wherever people spread, large animals went extinct. We took their carbon.
But animals are a minor contribution to life. Plants account for 550 gigatons of carbon: they outweigh us by a factor of 6000! The contributions from all other types of life are quite uncertain: some papers claim that bacteria dominate everything, others dispute this. Recent research seems to favour lower numbers for the total bacterial weight, mainly because much of the oceans seem to be too nutrient-poor to support large communities.
The total amount of carbon in the biosphere is estimated at about 1000 gigatons . But the uncertainties are such that it could be twice as high or a bit less. The equivalent is 3100 gigatons of CO2. This is about the same amount as there is in the atmosphere, a curious coincidence.
As an aside, the numbers show that the majority of the carbon mass of the biosphere is on land! This is because plant life dominates, and there are very few plants in the sea. When plants colonized land, biomass exploded. The sea has much more living space than the continents do, but much of it is poor in nutrients. It may not be an accident that the Cambrian explosion coincided with the origin of land plants. They expanded the biosphere, and the sea benefited through run-off of the detritus leading to an algae bloom. To farm the sea, find fertilizer.
But life is not everything. There is also a lot of non-biological carbon in the sea: around 37.5 thousand gigatons. And around 2700 gigatons of carbon is hiding in the soil. To put this in context, remember that there is 1000 gigatons of carbon in the air (as CO2) and a similar amount in life. If we convert it to equivalent CO2 mass, the ocean, soil, air and life contain 116, 8.4, 3.1, and 3.1 thousand gigatons.
The carbon in the sea, soil, air and life (plants, mainly) is roughly in ratio 37:3:1:1. The large majority of carbon is non-biological, dissolved in sea water. Life makes quite efficient use of the carbon available to it in the air and soil (it has taken up about 20 per cent), but the huge pool of carbon in the oceans has remained largely inaccessible. The oceans are not friendly to life.
Part 2 of this post gives the detailed accounting of volcanic and humanic emissions, including identifying the most polluting volcanoes! And the answers to the poll questions.