Scientists say climate change, not humans, wiped out Ice Age mammals

New research hopes to shed light on the hotly debated question of whether human expansion or a rapidly changing climate was to blame for mass extinctions of large mammals in the Earth's 'recent' past.

Between 50,000 and 3,000 years ago, almost two thirds of mammal species larger than 44kg – about the size of a Labrador dog – were wiped out.

While 47,000 years seems like a long time, it is an evolutionary blink of an eye and a much briefer period than that over which dinosaurs are thought to have met their end.

There are two schools of thought about why these animals disappeared, with one holding mankind’s rapid rise responsible while the other suggests that a climatic shift was the principle culprit.

While both doubtless played some part in the demise of a huge number of species, an international team has recently published research that they claim will lend weight to the climate change theory.

“Until now global evidence to support the climate change argument has been lacking, a large part of existing evidence was based on local or regional estimates between numbers of extinctions, dates of human arrivals and dates of climate change,” said Dr David Nogues-Bravo of the University of Copenhagen.

“Our approach is completely different. By dealing with the issue at a global scale we add a new dimension to the debate by showing that the impact of climate change was not equal across all regions, and we quantify this to reveal each continent’s “footprint of climate change.”

Put simply, the team looked at how climate change had affected different continents and compared this with how the mammals had fared.

Historically hard-hit continents with a low human population, such as North America, saw a rapid loss of species whereas those that saw more temperate times and a much denser human population, such as Africa, recorded a lower loss of species.

A key piece of evidence in the humans versus climate debate is the size of the extinct mammals.

It has always been assumed that humans mainly impacted on populations of large mammals, while if climate change played the key role there should be evidence of large impacts on small mammals as well as the larger animals.

The team’s results show that continents which saw bigger climate change impacts also experienced more extinctions of small mammals, further strengthening the idea that climate was a key factor in controlling past extinctions on a global scale.

The researchers claim the work has important implications for the current study of climate change, not only in revealing the role of the climate in causing extinction in mammals, but also by demonstrating how the effect will be different across regions and continents.

Sam Bond

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