The Anthropocene is the name scientists proposed to give to the present epoch in Earth’s history, one that is driven by human impacts like climate change. In their study, theoretical physicist Professor Orfeu Bertolami of the University of Porto and his colleagues modelled the arrival of the Anthropocene as a so-called phase transition. The concept of phase transitions is something that the average person might associate with materials — like, for example, how water changes phase from liquid to solid when it freezes, or from liquid to gas when it evaporates. Other systems can also undergo phase transitions as well, however. As far as the Earth system goes, a given climate produces a regular pattern of seasons and weather, while a phase transition would lead to a different climate and new patterns as a result.
In the past, changes to the climate have been driven by factors like shifts in the Earth’s orbit, or periods of intense volcanic activity.
The future of the climate system, however, is highly dependent on the nature of human activity — in particular, the extent of our greenhouse gas emissions — over the next few decades.
To explore all the possibilities, the researchers used a mathematical tool called a logistic map, which is particularly useful when considering variables that can grow, but that also has a natural limit.
Logistic maps, for example, are often used to model the growth of animal populations — while they can keep giving birth, maximum population sizes tend to be constrained by factors like predators and the availability of resources like food.
In a similar fashion, humanity at present has the capacity to continue to increase its impact on the environment, but at some point will have to stop, either because the Earth reaches its population limit or because we max out our possible carbon-releasing activities.
The team used their logistic map to explore how our carbon output might evolve based on various factors like the population size, carbon reduction strategies and technological advances — and from that, how the Earth’s climate will respond.
In the best-case scenario, the researchers found, the Earth’s climate will stabilise at a new, higher temperature than before once humanity has reached the limit of its carbon output.
Such would not be positive for us — the temperature increase will cause sea levels to rise, submerging some of the world’s currently most occupied areas.
This will be accompanied by an increase in extreme weather events.
On the other hand, however, the climate system would at least be stable — while warmer, the Anthropocene would have a climate that resembled those of the past, replete with regular and repeatable weather patterns.
The researchers’ worst-case scenario, meanwhile, is chaos — both figuratively and, from a mathematical standpoint, literally.
A truly chaotic system has no repeated patterns and no equilibrium point around which it settles, and thus a chaotic climate would have seasons whose nature would shift from decade-to-decade — or, worse still, perhaps even on a yearly basis.
Years of quiet weather in a chaotic world would give way to those beset by frequent spells of extreme weather, for example, while the average world temperature could shift suddenly in directions it would be nearly impossible to predict.
As Prof Bertolami told Live Science: “A chaotic behavior means that it will be impossible to predict the behavior of the Earth system in the future — even if we know with great certainty its present state.
“It will mean that any capability to control and to drive the Earth system towards an equilibrium state that favors the habitability of the biosphere will be lost.”
According to the researchers, if the Earth’s atmosphere passes a certain threshold temperature, it could cause a positive feedback cycle from which a chaotic outcome would be inevitable.
Prof Bertolami concluded: “The implications of climate change are well known — droughts, heat waves, extreme phenomena, etc.”
“If the Earth System gets into the region of chaotic behavior, we will lose all hope of somehow fixing the problem.”
A preprint of the article, which has not yet been peer-reviewed, can be read on the arXiv repository.