Pyrocene: life on a blazing planet

As summer 2022 is ablaze with wildfires and heat waves, we may well have entered the Pyrocene, the age of fire. This name was coined by Stephen J Pyne, as an alternative for the Anthropocene: the era in which humanity leaves an ineradicable mark on the earth. Fire seems to play an increasingly important role in how we transform the world we live in. But fire and wildfires are not new. Let's look at fire today and in the past.

Author: Kathelijne Bonne

In recent times, forest fires are bigger, hotter and rage longer. A question then arises: Have we created a new geological time, the age of fire? So far, we already transformed the atmosphere, the ocean and the biosphere, affecting the fluxes between soil, air, life and water. Humanity interferes with earth with geological vigor.

Fire is a powerful process that quickly converts living matter into carbon dioxide and carbon. But fire cannot just burn. It needs heat (a spark), oxygen, and combustible material. Increasing drought and heat means the amount of combustible material is growing. Thirsty forests worldwide are waiting for rain, but all they do is go up in flames.

Fire specialist

I came across the term Pyrocene through Roseanne Chambers' blog post "Our age of fire: the Pyrocene", in which she mentions the work of a leading fire specialist: Professor Stephen J Pyne, the writer from Arizona who has devoted his academic career to fire. He spent 15 years fighting wildfires. "How humans created fire and fire made us human," is the title of his 2015 article in Aeon, in which he coined the term Pyrocene. 

One of his latest books is "The Pyrocene: How we created an age of fire and what happens next." He notes that not one but two worlds are burning: the living world through wildfires and the life of the past world through the burning of fossil fuels.

Start of the Pyrocene

But when did the Pyrocene begin? That is difficult to determine at this time, because Pyrocene is not an official term and thus not (yet) recognized by the special scientific committee in charge of fine-tuning the geologic time scale. Anthropocene is, and scientists are still debating whether to put the start of the Anthropocene at either the beginning of the Industrial Revolution, or sometime in the 1940s when the radioactive fallout from the first nuclear tests precipitated on Earth. 

Whether the Pyrocene will ever become an official epoch is up to us. Let's hope that we will outsmart the age of fire and can quickstart an age of recovery.

What is fire?

Fire consists of gases and soot particles that are so hot that they glow and emit light. In such heat, a chemical reaction occurs with oxygen: oxidation. Oxidation at high temperature is called burning. The gases that are released, including carbon dioxide, are visible and bright until they cool down.

Zombie fires and firestorms

Forest fires are no longer an exception but a recurring phenomenon. Heatwaves, which are becoming more frequent, pave the way for firewaves. The polar regions, such as Siberia, Alaska and Greenland, can also be ablaze. And it's not just forests that burn; steppes, peat bogs, wetlands and the permafrost can also be scourged by fire. Dormant wildfires may even smoulder under the snow, underground and unnoticed, until the right conditions cause it to flare up again above ground. They are called zombie fires.

Another phenomenon are firestorms, fierce air currents that are sucked towards the source of the fire because the oxygen has been consumed. Firestorms are life-threatening and terrorized the state of Colorado in 2018 and 2021. In war, they can occur during bombings.

First oxygen

Forests can only burn if there is oxygen. Billions of years ago, the atmosphere was oxygen-free, but at some point, 2.4 billion years ago, oxygen production started. It happened very slowly, through the action of bacteria. These bacteria performed photosynthesis: the process whereby sunlight is used to draw carbon dioxide from the air and release oxygen. The transition from an oxygen-free to an oxygen-accumulating atmosphere is called the Great Oxygenation Event. I wrote about it in my article: When did we start breathing?

This would eventually lead to the emergence of multicellular organisms that breathe oxygen, such as animals and humans. Plants also sought their way to the light, and perform photosynthesis, as do bacteria. Because one group produces oxygen, and the other consumes it, there is an equilibrium. But that balance is somewhat shaky. However, strong ecosystems and the survival instincts of each individual organism ensure that large outliers balance themselves out.

Dawn of a green planet

During the Silurian period, vegetation colonized the land. Later, during the Carboniferous (ca. 350 to 300 million years ago), giant, dense forests had developed; the Earth had become a green planet. Because of all the photosynthesis, the oxygen concentration had risen to 35%, much higher than today. All the ingredients for wildfires were present: lots of green and lots of oxygen.

Devastating forest fires sometimes raged across the continents, ignited by lightning strikes. The charred remains of life were buried under sediment in many places, forming thick coal seams that we've been using as fuel since the Industrial Revolution and are still using today. But life was persistent and the greenery kept coming back. Meanwhile, as a result of the huge biomass, lots of carbon dioxide was drawn from the air. All these profound changes eventually led to an ice age and an extinction wave at the end of the Carboniferous.

However, these climate changes occurred very gradually and would not have been noticeable during a human lifetime. Possibly there were other causes of Carboniferous climate change, such as changes in ocean currents. In any case, renewed emissions of carbon dioxide, from volcanoes, eventually led to warming and the melting of the frozen world. The age of the Permian followed, a difficult time for life, but that's another story.

Amazing fire

Hence, over the last ~350 million years, occasional wildfires were a normal part of ecosystems. But two million years ago the Pleistocene age dawned, and then something changed: humanity emerged. About one million years ago, we began to play with fire, and the discovery that fire could be "tamed" and controlled led to huge advances. It is said to have even influenced our brain size.

Control of fire allowed us to prepare food faster, kill germs, protect ourselves from dangerous animals, clear forests to hunt animals or manage livestock, and make tools. In the evenings, we gathered around the fire to muse, dream and tell stories. Even today, we still like to gaze into the dancing flames of a good fire. 

Indigenous peoples still use fire in traditional agricultural practices, but their fires are controlled and small, they do not burn the seed bank of the soil. On realtime fire maps on NASA and Copernicus websites, you can clearly see how in the tropics many small fires burn in certain seasons. Some seeds even need the heat of fire to germinate, like those of the giant sequoia in America.

Sorcerer's Apprentice

But large out-of-control forest fires that scorch everything, are extremely destructive. Besides the immediate material damage and human and animal death toll, it takes much longer for the soil and ecosystem to recover. At the same time, valuable biomass has evaporated into carbon dioxide, contributing to global warming.

Humanity is now like Goethe's Sorcerer's Apprentice. We have lost control over fire. From our ally we have made a formidable enemy. Not only is our slice of meat on the grill, but so is the earth itself. The twig of fire held by our ancestors has now become a planetary lever with which we unwittingly tilt the earth in a dangerous direction, paraphrasing Stephen Pyne. 

Fire today has lots of opportunities to start in these times of heat and drought. With every fire, ecosystems shrink and the greenhouse effect increases. One effect amplifies the other, and so we have entered a self-sustaining spiral towards life on a fire planet. 

The question is, is there a way back? Roseanne can't be clearer at the end of her article, so I cite: "measures are available to help mitigate the worst of the effects of our impact. We need to implement them."

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Related articles: 

• Anthropocene vs natural climate change: which one is faster?
• The planetary boundaries: a safe place for humans? 
• The origin of oxygen: when did we start breathing? 
• The Dust Bowl comes to Spain: desertification and soil erosion.

Article by Kathelijne Bonne, geologist and soil scientist. I also write on Good Climate News. 

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