We are living through a climate revolution of the same magnitude as an ice age, but with flames in place of ice. An epochal shift that may have ushered us into a new era: the Pyrocene.
Anthropocene. A geological epoch in which human beings are the primary drivers of the territorial, structural and climatic changes taking place on our planet. An epoch that may have begun as early as 1945: from that date onwards, nuclear tests and the "great acceleration" of all human activities began leaving permanent traces in the geological strata of the Earth. Radionuclides, phosphorus, mercury, plastic, fossilised chicken bones — these are the traces that will bear witness to our passage for many thousands of years into the future.
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There is one trace that more than any other will tell the story of this epoch with eloquence: carbon. Those who study the history of the Earth in ten or a hundred thousand years' time, perhaps by analysing fossil air trapped in Antarctic ice (if it still exists) will discover that during the Anthropocene the concentration of carbon in the atmosphere increased vertiginously, reaching values within a few decades that the planet had not known for at least 3 million years.
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The carbon produced in the Anthropocene is not found only in the air. The beds of lakes and marshes hold another lasting trace of our existence: tiny black, opaque prisms, concentrated in thin but precise "bands" preserved in sediments in the absence of oxygen. Charcoal.
The trace of past fires, imprinted on lake beds for thousands of years. To the future scientists who will extract and analyse it under the microscope, the charcoal of the Anthropocene will tell the story of what may happen over the next fifty years: a relentless increase in the area burned by wildfires, at every latitude and in every season of the year.
A story deeply intertwined with the other defining feature of the Anthropocene: the rise in atmospheric carbon generated by our use of fossil fuels. Vegetation fires on the one hand, the combustion of fossil reserves on the other: the hallmark of a new relationship between humanity, fire and the planet. A climate revolution of the same magnitude as an ice age — but with flames in place of ice. An epochal shift that may lead us to call the period in which we live by an even more fitting name: the Pyrocene.
A climate revolution of the same magnitude as an ice age, but with flames in place of ice.Giorgio Vacchiano, Sisef
Combustion is a chain chemical reaction, fast and exothermic (meaning it releases heat). Three ingredients are needed to start it: a fuel, whose atoms are ready to break the bonds holding them together and recombine in a different form; a source of heat or ignition, which gives the atoms the initial "push" needed to break free from their chemical bonds; and oxygen, which binds irreversibly to the displaced atoms and forms new substances with them, such as water vapour or, indeed, CO2. Once started, the reaction is self-sustaining, because the heat produced drives more atoms in the fuel to break free and combine with oxygen, until one or the other is exhausted.
The oldest traces of a wildfire are fossil carbon residues dating back at least 420 million years: this was the first moment in which the Earth had enough fuel (terrestrial vegetation) and oxygen (thanks to the contribution of the first forests) to turn a spark into a fire. Volcanic eruptions and lightning provided the ignition, oxygen and biomass were abundant, and climate determined when vegetation could burn.
For example, warm, dry periods drain moisture from vegetation and, deprived of water and the ability to dissipate heat through evaporation, wood ignites more easily and burns with greater intensity. This is why prolonged drought promotes the spread of wildfires, regardless of the ignition source. Conversely, if vegetation is rich in water because there has been heavy rainfall, a spark is unlikely to generate a chain combustion reaction.
On longer time scales, over centuries or millennia, the dynamics depend not only on climate but also on interactions with vegetation: for instance, long rainy epochs favour the growth of forests, which become flammable only during rare but dramatic drought episodes that transform "potential fuel" into "available fuel".
The Earth's vegetation has coexisted with fire for many millions of years: like a sieve, fire has favoured the persistence of those species that had by chance developed traits of resistance or resilience to fire. The "invention" of bark and the emergence of the ability to produce new shoots from a damaged stump are today considered the result of natural selection imposed by fire as an evolutionary agent. Many species and communities have gone even further, developing forms and tissues that promote combustion: paired with effective and inventive post-fire reproduction strategies, high flammability can be the secret of success for those capable of persisting after a fire when all competing species are destroyed.
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One example of how vegetation can in turn influence the frequency and intensity of fires at a global scale is the expansion of savannahs and grasslands, which began 25 million years ago due to a prolonged reduction in rainfall at a global scale and culminated around 6–7 million years ago. When grass became the dominant component of many ecosystems, fire was able to spread more quickly and across larger territories. The grassland regenerated effectively after fire, extending its presence. In turn, fire released large quantities of CO2 into the atmosphere, which contributed to causing a "natural" climate change (much slower than the contemporary one), with a further reduction in rainfall and the expansion of grasslands at the expense of forests in the tropical zone.
The climate and vegetation continued to be the main drivers of fires around the world even after the emergence of the genus homo. Three million years ago, the natural expansion of savanna at the expense of rainforest in eastern Africa brought humanoid primates closer to fire. Terror gave way to reverence, then came the discovery that burned areas were good ground for sourcing food and moving across, and finally the domestication of fire.
Over the past 100,000 years, humans have used fire continuously, not only for cooking and keeping warm, but above all to clear large stretches of land for hunting or settlement. Nevertheless, the greater or lesser prevalence of fires during that period still depended closely on the climate — until the beginning of the 19th century, when human fire "decoupled" from natural processes.
Charcoal residues tell us that, following a reduction during the Little Ice Age, over the past 200 years fire activity has undergone three enormous shifts. From 1800 onwards, the expansion of humans into still-uninhabited territories (Australia, the American West, South America), the increase in human activities capable of producing sparks (cars, railways, agricultural work) and the growing use of fire to clear unwanted vegetation caused a first peak in fire activity, reflected in the sudden increase in the quantity of carbonaceous residues in recent sediments.
A century later, having become aware of the threat, human communities organised themselves to tackle it: the emergence and spread of fire control and firefighting techniques and technologies, public information campaigns, and regulatory instruments banning the use of fire proved effective in reducing fires to their historical minimum, with reference to the last millennium at a global scale.
Today, by contrast, we are witnessing the third major shift in fire activity — perhaps the beginning of the Pyrocene. The increase in greenhouse gases in the atmosphere and the alteration of the climate on a planetary scale risk generating a new rise in fires across the world, fires that we are no longer able to control. An increase that we are already observing in various parts of the world (those most exposed to worsening droughts), and that is set to continue according to all current climate models, leading, for example, to an increase of between 40 and 100 per cent in the area burned by fire in Mediterranean Europe by the end of this century (Italy included), and an extension of the fire season by two weeks.
From 2017 to the early months of 2020, the forests of many countries were struck by vast fires. From Italy to Portugal, from Greece to California, from Sweden to Siberia all the way to Greenland, from the Amazon to Indonesia (where, however, there was a strong interaction with deforestation practices), and then in recent months in Australia: events that have affected tens of millions of hectares of land, caused hundreds of fatalities, and released into the atmosphere large quantities of CO2, equivalent to the annual emissions of entire states.
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In several cases these fires were described as "unprecedented" phenomena, either because they occurred in areas historically little vulnerable to fire, or because of the unusual time of year in which they broke out, or for characteristics (extent, intensity, rate of spread, involvement of areas already recently burned) never observed before. The extremity of these fires, their simultaneity across a vast geographical scale and their persistence over several weeks raise fears of long-term repercussions on ecosystem services, and unpredictable impacts on plant and animal biodiversity.
The broad resilience strategies of communities that have evolved in territories periodically swept by fire are, in fact, severely tested when fire activity exceeds the "historical range of variability" — that is, the conditions under which the phenomenon has manifested itself over the long period in which plants and animals evolved their adaptation and response strategies.
In Italy too, some fires in the 2017 season displayed extreme behaviour, such as the event that affected the Val di Susa between October and November, which turned out to be one of the most extensive fires in living memory in the countries of the Alpine arc (over 4,000 hectares). All these recent events attracted considerable media attention, both because of the growing global sensitivity to the climate crisis, and because they affected densely populated areas, with effects even at great distances due to the transport of smoke over urban areas, as occurred in the Amazon.
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In many of the affected places, the area burned by fires over the past two years exceeds the average of recent decades, as in some Australian states (over 5 million hectares in New South Wales, the highest in fifty years), California (766,000 hectares in the 2018 season, the highest since 1970), and Russia (9 million hectares against an average of under 5 million, although with even higher peaks in the past twenty years).
In the Amazon the situation appears more complex: the number of fires was higher than in recent years, but did not represent an all-time record; the area burned, according to the first scientific study to examine the situation, was above average in Bolivia, Paraguay and Venezuela, but not in Brazil (where, nonetheless, an increase on the previous year was recorded, rising from 800,000 to 1,800,000 hectares burned: not a good sign, given that these fires are closel