The Blogs: If Fungi Had Eaten Trees, We’d Have No Coal, No Ice Ages and No Us (Probably!) ?

When we think of climate change today, we think of fossil fuels: coal, oil, gas. They are the compressed memory of ancient forests, buried by time and pressure, and now burned back into the sky. But what if those forests had never been entombed in the first place? What if fungi, with their quiet, patient work of decomposition, had long ago mastered the ability to break down wood completely? It is a scientific “what if” that leads us to an unsettling answer: the Earth might always have been warmer, wetter, and more unstable—long before humanity had the chance to stoke the fire.

The Carboniferous Miracle That Wasn’t

During the Carboniferous period, some 300 million years ago, Earth’s forests flourished. Towering lycopsids and ferns carpeted swamps, pulling vast quantities of carbon dioxide from the air. Yet their deaths posed a problem for the planet’s chemistry. Trees contain lignin, a complex and stubborn polymer. For millions of years, fungi had not yet evolved the enzymes to digest it. As a result, when these plants fell, they did not fully rot. Instead, they piled up, forming thick layers of peat that would, under geological pressure, harden into coal. This accident of evolution amounted to a planetary savings account: carbon was locked away underground, never to return—until the industrial age.

It was only when fungi such as white rot evolved the molecular toolkit to crack lignin that decomposition became total. From then on, the carbon in wood could be released back into the atmosphere as carbon dioxide rather than fossilized. If fungi had possessed this trick from the beginning, coal seams would never have formed, and the long-term climate trajectory of Earth would have shifted. The great drawdown of atmospheric carbon that cooled the late Paleozoic world and allowed glaciers to spread across Gondwana might never have occurred. Instead, Earth’s atmosphere might have remained rich in greenhouse gases, keeping the climate persistently hotter, more humid, and perhaps less hospitable to the ecosystems—and evolutionary experiments—that later gave rise to us.

A Hotter, More Restless World

If carbon had cycled back into the atmosphere continuously, Earth would likely have been locked into a greenhouse baseline. This would mean not just higher average temperatures, but fewer of the great ice ages that periodically sculpted our planet.

Ice sheets and sea level: Without massive carbon burial, glaciations might have been rare or weak. Sea levels could have been permanently higher by tens of meters, drowning continental shelves and shifting coastlines inland. Fertile river valleys—from the Nile to the Mekong—might never have existed in their present form.
Ocean chemistry: More carbon dioxide in the air would have meant more dissolved CO₂ in the oceans. Acidification could have been chronic rather than episodic, weakening reef-building organisms and altering the course of marine evolution. Coral reefs, as we know them today, might have been rarer or absent, with cascading effects on biodiversity.
Biodiversity and evolution: Ice ages and climate swings have been engines of speciation. The Pleistocene glaciations, for example, created the pressures that shaped modern humans. Without those pulses of cold and expansion of ice sheets, evolutionary pressures might have been softer, producing a very different biosphere. Mammals may not have gained the foothold they did after the dinosaurs, and humans may never have emerged.

Civilization Without Coal

The absence of coal would have had profound consequences for human societies. Coal was not just an energy source—it was the bedrock of industrial modernity. Without coal seams, humanity might have been forced down very different energy pathways.

Biomass dependency: We might have burned wood and peat on an even larger scale, driving earlier and more complete deforestation. This in turn would have released even more carbon and destabilized local climates.
Early oil economy: Petroleum, seeping naturally to the surface in places like Mesopotamia, might have been tapped much earlier. The fossil fuel era could have arrived centuries earlier, with its attendant carbon emissions—and perhaps its climate crisis—beginning long before the 20th century.
Renewables by necessity: Lacking coal, some regions might have innovated faster with hydropower, wind, or even solar technologies. Industrialization might have been slower but potentially cleaner. Europe’s industrial revolution might have been delayed—or relocated to parts of the world rich in other energy resources.
Nuclear acceleration: With no abundant fossil fuels, the incentive to develop nuclear power might have come much earlier, possibly by the late 19th or early 20th century. The balance of geopolitics, tied to energy availability, would have looked unrecognizable.

The Counterfactual Anthropocene

This thought experiment raises an even deeper question: would we even have had the Holocene, the 10,000-year period of relative climate stability that cradled agriculture, writing, and cities? If the Earth’s atmosphere had remained stubbornly carbon-rich, our species might have emerged into a hotter, stormier, less predictable world—one in which farming large, stable fields was impossible. In such a world, civilization might have been stunted, nomadic, or perpetually on the edge of collapse.

In a sense, the very accident that denied fungi the ability to eat lignin gave us civilization. Coal deposits cooled the Earth, stabilized the climate, and created the raw energy reserves that powered industry. Yet this gift was also a trap: once we dug it up, we began to dismantle the stability it had enabled.

Lessons for Today

Critics might argue that this is academic: tectonics, orbital wobbles, and volcanic eruptions were also powerful forces shaping Earth’s climate. True. But the lignin story illustrates something profound. Biology itself—the evolution of a single fungal enzyme—can reshape the planet’s thermostat. Life does not just adapt to climate; it engineers it.

We are now the inheritors of that fungal precedent. Unlike fungi, however, we have awareness. Unlike Carboniferous forests, our emissions will not be quietly buried for millions of years. The irony is sharp: had fungi evolved faster, we might never have had coal, and perhaps never had civilization as we know it. Yet by burning coal, we are undoing the very climate stability that fungi once failed to erase.

The Philosophical Twist

So was coal a stroke of luck or a planetary trap? If coal’s burial allowed human civilization to flourish, then the history of fungi and lignin is bound up with our own story of progress. But if coal was merely a delayed release of stored carbon, then perhaps we are simply finishing a cycle that nature postponed. The difference is that we do so knowingly, with full awareness of the costs.

That awareness is our burden—and our chance. Evolutionary accidents cannot be undone, but human choices still can. The fungi never had a choice; we do.