The Earth’s vegetation is changing at a faster rate today than it has over the last 18,000 years – and humans may be largely responsible, according to scientists.
Researchers have found that changes in biodiversity and ecosystems stabilised around 4,000 years ago before beginning to accelerate, coinciding with the rise of human civilisations that led to agriculture and deforestation.
In their study, published in the journal Science, an international team of experts say that rates of change in the planet’s vegetation will continue to pick up pace over the coming decades, fuelled by human-induced climate change.
“This work suggests that 3,000 to 4,000 years ago, humans were already having an enormous impact on the world (and) that continues today," said Jack Williams, professor of geography at the University of Wisconsin-Madison in the US and one of the study authors.
As part of their study, the researchers analysed more than 1,100 fossil pollen records from The Neotoma Paleoecology Database, which collects data on past ecosystems spanning all continents except Antarctica.
The records allowed the researchers to understand how the Earth’s vegetation has changed since the end of the last Ice Age – about 18,000 years ago – and how quickly this transformation took place.
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They found the Earth’s ecosystems underwent drastic changes at record pace following the end of the last Ice Age, as ice sheets retreated and the climate warmed, with plants racing to colonise formerly frozen landscapes. Then as the climate began to settle, this rate of change peaked somewhere between 8,000 and 16,000 years ago, depending on the continent.
Analysis showed that ecosystems then stabilised until about 4,000 years ago, before beginning “a meteoric rise that continues today”.
“There were a lot of dynamic things happening over the last 11,000 years," said Sarah Ivory, an assistant professor of geosciences at Pennsylvania State University in the US, and also one of the study authors.“Ecosystems were reorganising. Many of the megafauna went away. It’s hard to explain all that without climate.
“However, during the later part of this period, there aren’t major climate changes, so it is more likely human technology that is responsible.”
The researchers believe the more recent dramatic changes in the planet’s vegetation from around 4,000 years ago coincides with a time when humans became more dominant.
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They said the findings suggest that the acceleration of biodiversity change observed over the last two centuries likely began thousands of years before – long before the Industrial Revolution in the mid-1700s and the rise of fossil fuels in the early 1900s.
They warn that as intensified land use continues, and global temperatures rise due to greenhouse gases, future rates of ecosystem transformation may yet again break new records.
In a related article also published in the journal Science, climate scientists Dr Jonathan Overpeck and Dr David Breshears, from the universities of Michigan and Arizona in the US, wrote: “Humans continue the inexorable pace of deforestation to grow more crops and animals for food, fibre, and energy. Additional climate-driven change is also a sure bet.
“Even in a world where climate change is soon halted, global temperature rise will likely reach between 1.5°C and 2°C above preindustrial levels.
“This means that global vegetation will likely face climate change effects that are substantially worse than already experienced.”