Many believe that around 20,000 years ago, Earth was inches away from an ecological disaster. The carbon dioxide in the atmosphere fell to its lowest recorded level in 4.5 billion years, a mere 180 ppm. If it had dropped a bit lower, most plant life – and with it, animals and humans – would have gone extinct.
Rubisco
When plants first evolved on our planet, the carbon dioxide level was 10-20 times higher than today. It provided an abundance of food from which plants could grow. A key component in photosynthesis is the enzyme rubisco, which evolved 2.4 billion years ago. It is perhaps the most abundant protein in the world.
In high concentrations of carbon dioxide, rubisco works well. However, it rapidly loses its efficiency at lower levels. At the ice age level of 180 ppm, most plants are nearly suffocating. To compensate for the lack of food, the plants grow more breathing holes, called stomata. However, for every carbon dioxide molecule a plant absorbs through such a hole, it loses around 100 molecules of water. In short: It dries up.
That’s no problem in a warm and wet world with plenty of rain – but the cold climate in the ice age also meant far less precipitation. The combination of low carbon dioxide levels and dry weather 20,000 years ago rendered nearly the entire planet into deserts and grasslands.
Life could still survive under this condition, but if carbon dioxide had dropped to below 100 ppm, most plants would go extinct, including the oceanic planktons that are the food source of sea animals. Even grass species, which have evolved a specific mechanism to handle low levels, would struggle.
Lost Carbon
Carbon dioxide fell to a historical low because of fossilization and sedimentation of organic carbon. Over hundreds of millions of years, this has depleted the carbon cycle of more than 95% of its material. Paradoxically, life has been the source of its long-term starvation and inevitable extinction.
What’s worse, there was no end in sight for the downward trend. In a few million years, most life could be gone.
An Eye Blink
Fortunately, the ice age ended 10,000 years ago, and CO2 rose high enough to enable agriculture. Twenty thousand years sounds like an eternity, but in the scale of Earth’s 4.5-billion-year existence, it is barely the blink of an eye. Imagine if Earth’s history started 24 hours ago. Then our brush with extinction occurred only 0.4 seconds ago.
The current warm climate is just a brief pause until the next ice age, bringing us further on the path toward ecological disaster and mass death.
Recycling Lost Carbon
But then something unique happened: Humans discovered how to mine and burn fossilized hydrocarbons and bring them back into the atmosphere! This recycling of lost ancient carbon contributes to re-greening the Earth to its past glory and saving life from certain suffocation death in the future.
Already we see massive greening across the world. NASA has documented this greening with its satellites over many decades, and the greening continues unabated.
Hundreds of peer-reviewed scientific articles document the positive effects this added carbon has on plants, especially in deserts and steppes with little rainfall. With a higher level of carbon dioxide, plants need fewer stomata and become more water-efficient, enabling them to survive better in arid climates.
However, supporters of this theory suggest that, on a geological time scale, carbon levels are still uncomfortably low. We have a long way and a massive amount of fossil fuel burning to go before we raise carbon dioxide levels to anywhere near its historical concentration when land plant life prospered on our planet.
That is a perspective that is too often lost in the ongoing debate about anthropogenic climate change.
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Read more from Caroline Adana.
