Surviving the 21st Century - Julian Cribb
I was much further out than you thought.
And not waving but drowning – Stevie Smith, 1957
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AUTHOR
Julian Cribb AM is an Australian science writer and author of seven books on the human existential emergency. His latest book is How to Fix a Broken Planet (Cambridge University Press, 2023)
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Could that really be the fate that today’s humans, knowingly or not, are engineering for their children and grandchildren? To choke out on a planet whose atmosphere can no longer support our kind?
The scientifically attested facts make unpleasant, but necessary reading. Oxygen levels in the air and seas of our frail blue Planet have been going down slowly for eons. Then, suddenly, in a rush.
Just over ten years ago two scientists, Ralph Keeling and Andrew Manning, who had been carefully observing the sharp rise in the Earth’s atmospheric CO2 due to human burning of fossil fuels and felling of forests noticed something else: it was parallelled by a fall in oxygen levels.
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| Figure 1. Decline in Earth’s atmospheric oxygen levels, measured over the Southern Ocean at Cape Grim, Australia 1990-2024. Source: Scripps Institute. |
A steady decline over the last million years has accelerated sharply in the last 150, with 12% of the loss occurring on modern society’s brief watch (just 0.015% of the elapsed time).
The explanation is not far to seek: every CO2 molecule we create when we start a car, burn coal or light a barbecue sucks two molecules of breathable oxygen out of the air.
In a typical year our carbon emissions alone remove around 100 billion tonnes of oxygen from the atmosphere. And that does not include the CO2 or methane emitted by 8.2 billion humans and their 100 billion livestock.
But there is an added twist to the story which makes it far more scary. The world’s oceans and forests, the planet’s primary oxygen pumps, are dying – and the reason is us.
Atmosphere
Human activities and climate change are increasingly disrupting the natural oxygen cycle, which has maintained Earth’s atmosphere for hundreds of millions of years.
Deforestation, land clearing, the spread of deserts, industrial pollution and urban sprawl are reducing the number of trees and plants, which are the source of photosynthesis, the sun-powered process that produces the oxygen we breathe.
Earth’s air is not naturally rich in oxygen. It has probably only been ‘breathable’ for about 20-30% of the planet’s existence. For the first two or three billion years since life appeared there was almost no O2, much like Mars today.
The life that existed then did not need it – indeed, oxygen was the waste that they excreted – and the gas did not begin to rise sharply until the ‘Oxygen Catastrophe’ which almost obliterated life between 2400 million and 2000 million years ago.
The air itself did not become rich in oxygen until around 850 million years ago. Thereafter some living organisms adapted to using oxygen and, around 700 million years ago this gave rise to explosion of different species we know as the ‘Tree of Life’, including ourselves.
Hereafter atmospheric oxygen levels are expected to continue a slow, steady decline - unless humans do something particularly stupid to speed it up.
Oceans
Globally, the ocean has lost around 2% of its dissolved oxygen since the 1950s and is predicted to lose a further 1–7% by 2100.
Although oxygen levels vary by region, most parts of the ocean are experiencing loss. This is chiefly due to ocean warming, as warmer water holds less dissolved oxygen.
Warming also causes the oceans to stratify or form layers, meaning that oxygen is less well mixed into the deeper waters which then become hostile to life.
More than 500 ‘ocean dead zones’ have been detected around the world, generally in coastal regions close to heavy human populations or farming areas. Their numbers are increasing as humanity proliferates.
The zones are largely driven by eutrophication – the over-enrichment of sea water by fertiliser, eroded topsoil, human sewage and industrial wastes. This causes algal blooms which then die and are devoured by bacterial blooms. These bacteria then strip the oxygen out of the water, producing a ‘dead’ layer than cannot support normal sea life.
The oceans are the main source of oxygen in the air we breathe, their plankton producing more than half of what currently keeps us alive.
It should therefore come as a profound concern that Chinese scientists have recently reported that the oceans are becoming less green. The decline in greenness is due to a loss of chlorophyll, which is the chemical in plants that enables them to absorb sunlight and use it to convert CO2 to oxygen. And the chlorophyll is declining due to ocean warming.
Overall, this indicates that the major Earth process which forms a breathable atmosphere may be breaking down - and humans are to blame.
The picture is far from uniform, but as the scientists caution “Our analysis suggests widespread decline in ocean greenness”. And that spells trouble for folk who wish to breathe, not just now maybe – but certainly later.
Coupled with the decline in ocean greenness is the equally disturbing rise in ocean acidity – a factor that has now breached planetary safety limits, according to the Potsdam Institute for Climate Impact Research (PIK).
Ocean acidification is caused by CO₂ from the burning of fossil fuels dissolving into seawater, which forms carbonic acid, turning the ocean slightly more acidic. Since the 1850s, the acidity of the oceans has increased by around 30–40%.
The implications for sea life are immense: it directly affects organisms with calcium carbonate shells and skeletons, like corals, shellfish and many kinds of plankton, disrupting food webs that stretch all the way from microscopic sea life to fish, whales and, ultimately, humans. This affects the total productivity of the oceans and, ultimately, their ability to yield oxygen.
Failing forests
On land, the picture is, if anything, more disturbing. Prior to humans, 57 per cent of the Earth’s land area was cloaking in forest. Today that number is 31 per cent and falling, meaning we have nearly halved the original area of forest.
What remains is far from healthy, having been logged, thinned, fragmented and altered vastly from its natural state by human activities including roads, farms and towns. This greatly reduces its ability to generate fresh oxygen and, to make matters worse, some forests have become net emitters of CO2.
Recently some people have taken comfort in the fact that the Earth overall is becoming greener, incorrectly believing it is due to higher CO2 levels in the atmosphere. In fact, it is due to the spread of grasses in the form of crops and pastures, as humans replace forests with agriculture. And grasses produce nothing like the amount of oxygen that forests do. By feeding our vast numbers we are building a planet on which it will be harder to breathe.
Like global warming, the new ‘Oxygen Holocaust’ is starting slowly and many may pretend it is of small concern. But the power of humans to engineer vast change in the Earth has always been underestimated. Our ability to disable the oxygen machine is just the latest twist in the saga of our planetary mismanagement.
For instance, most people assume we will manage to halt global heating at +2 or at most +4 degrees. In fact, at present rates of fossil fuel use, the planet will hit +8 degrees within a century or two. The misunderstanding arises from the fact that 2100 (+4) is the furthest ahead that current IPCC forecasts look, whereas actual heating continues long after.
Coupled with reducing the Earth to a charred cinder is the fact that we are, by the same mechanisms, building a planet with an unbreathable atmosphere – one with less than 19.5 per cent of free oxygen.
Human impacts
The potential consequences of decreased oxygen levels are vast, affecting both individual health and society’s ability to function. Low oxygen availability causes lung problems, especially for the old, the very young and those with respiratory conditions.
Crucially – as any diver or mountaineer can tell you - low oxygen levels impair your ability to think, to reason, to make good decisions. This damages productivity and quality of life for the whole of a more thoughtless society.
As resources become scarcer, competition for access to clean air and water will exacerbate existing inequalities. This may heighten social unrest, geopolitical tensions and conflict, as nations struggle to exist in a disintegrating world. Two industries particularly vulnerable to lower oxygen levels are animal agriculture and fish aquaculture, our main sources of protein.
At present the decline in global oxygen is small, and no cause for panic. But the human ability to geoengineer catastrophe is large – and growing every day.
Unless we grasp the mistakes we are making with a clear mind and reverse them, we may steal the very breath of life from our grandchildren.
What kind of a parent does that?
Links
- Studies of recent changes in atmospheric O2 content
- Earth’s Atmospheric Oxygen Decline: Causes, Consequences, and Projections
- Great Oxidation Event
- The future lifespan of Earth’s oxygenated atmosphere
- What Are Ocean Dead Zones?
- How much oxygen comes from the ocean?
- Declining ocean greenness and phytoplankton blooms in low to mid-latitudes under a warming climate
- Seven of nine planetary boundaries now breached – ocean acidification joins the danger zone
- The Effects of Ocean Acidification on Phytoplankton Communities
- The Earth Uncloaked - a catastrophe in slow motion
- Vegetation greenness in 2024
- Past and future warming – direct comparison on multi-century timescales
- Minimum Oxygen Concentration For Human Breathing
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