/ 22 June 2015

Humans driving sixth mass extinction

Humans Driving Sixth Mass Extinction

The world is witnessing extinction rates unseen in the last 65-million years. That was when dinosaurs died off – thanks to a mixture of an asteroid impact on Mexico and massive volcanic outbursts elsewhere. The four mass extinctions before that were also caused by natural disasters.

But this time it is down to human activity, say a group of scientists writing in the journal Science Advances. 

Looking at data from the International Union for the Conservation of Nature, the researchers looked at the rate of extinction of animals over the last 500 years. The union runs a Red List of critically endangered animals. 

They found that normally two species per 10 000 species go extinct every 100 years. That is the baseline, or natural rate of extinction without disaster events.   

Human intervention – they said in the release on Friday – has accelerated this rate by up to a hundred times. This has been during “the period during which Homo sapiens truly became a major force on the biosphere”.    

However, the number of up to a 100% increase in extinctions is conservative. The researchers said it would be hard to accurately predict extinction rates when numbers had only been effectively recorded in recent years. And even these numbers only scratch the surface. 

Their paper – “Accelerated modern human–induced species losses: Entering the sixth mass extinction.” – said only around 16 000 of the estimated 1.4-million invertebrates worldwide were catalogued. 

This meant species are going extinct without people knowing it. And the species that are going extinct are so small that they are hardly noticeable, the researchers said. 

The conservative scenario found that 111 mammal species have gone extinct between 1500 and 1900. Sixty-nine more have gone extinct in the last century. The same acceleration is evident in other species: 477 vertebrate species have gone extinct in the last century, compared to 617 in the four preceding centuries.   

In the five hundred years that they looked at, the researchers found that 130 000 species have been lost – 7% of the world’s biodiversity. “The particularly high losses in the last several decades accentuate the the increasing severity of the modern extinction crisis.” 

If nothing is done to stem the rate of extinction, the researchers said 75% of the species in existence today could vanish. “We have the potential for making massive change … and the bottom line is that we can’t be the generation responsible for wiping out three-fourths of life forms on the Earth.”

They are however hopeful that urgent action – if taken soon – will stem the rate of extinction. “Avoiding a sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species.”