Evidence is mounting for the notion that humans are causing a mass extinction event.

New modelling has found that species are dying-off as much as 1,000 times more frequently now than they did before modern humans arrived.

It was often considered to be about 100 times more frequent, but that number has now be revised much higher.

It would be impossible to understand the current rate of global species extinction without knowing what it was before people came along. The new estimates from Brown University in the US indicate that the pre-human rate was 10 times lower than thought, which means the current level is 10 times worse.

Orders of magnitude, rather than precise numbers are about the best any method can do for a global extinction rate, researchers say.

“That’s just being honest about the uncertainty there is in these type of analyses,” lead author of the new paper, Jurriaan de Vos said.

The new estimate improves on prior efforts by going beyond the fossil record.

Fossils have been vital sources of information on evolution and extinction, but they tend to bring disproportionate representation of hard-bodied sea animals. Also, fossils usually only allow identification of the animal or plant’s genus, but not its exact species.

The Brown model includes phylogenies; constructed by studying DNA to trace how groups of species have changed over time.

By adding new genetic lineages and losing unsuccessful ones, they provide rich details of how species have diversified over time.

“The diversification rate is the speciation rate minus the extinction rate,” said co-author Lucas Joppa, a scientist at Microsoft Research.

“The total number of species on earth has not been declining in recent geological history. It is either constant or increasing. Therefore, the average rate at which groups grew in their numbers of species must have been similar to or higher than the rate at which other groups lost species through extinction.”

By comparing the rise of the number of species from the as-yet unchecked speciation rate with the historical trend evident in the phylogenies, de Vos was able to create a predictive model of what the counteracting historical extinction rate must have been.

The models were tested with simulated data for which the team knew an actual extinction rate, and found they yielded accurate results.

The combined data approach showed a normal background extinction rate squarely in the order of 0.1 extinctions per million species per year.

The new paper expands on previous studies to track where species are threatened or confined to small ranges around the globe.

In most cases, the main cause of extinctions is human population growth and per capita consumption.