From the journal Science Advances:
The evidence is incontrovertible that recent extinction rates are unprecedented in human history and highly unusual in Earth’s history. Our analysis emphasizes that our global society has started to destroy species of other organisms at an accelerating rate, initiating a mass extinction episode unparalleled for 65 million years. If the currently elevated extinction pace is allowed to continue, humans will soon (in as little as three human lifetimes) be deprived of many biodiversity benefits. On human time scales, this loss would be effectively permanent because in the aftermath of past mass extinctions, the living world took hundreds of thousands to millions of years to rediversify. Avoiding a true sixth mass extinction will require rapid, greatly intensified efforts to conserve already threatened species and to alleviate pressures on their populations—notably habitat loss, overexploitation for economic gain, and climate change (31–33). All of these are related to human population size and growth, which increases consumption (especially among the rich), and economic inequity (6). However, the window of opportunity is rapidly closing. (emphasis added)
It's refreshing to see such blunt language in a peer-reviewed article. As most of you know, scientists tend to be a reticent lot. Have you ever heard about coaches who tend to understate player injuries? For example, if coach says it's just turf toe, then the player may very well have a broken foot. If coach says it's a sprain, then surgery is probably just around the corner. If coach says the player will be out for a few games, well, you might want to consider sending flowers. While I'm not sure if that's a fair comparison, I can't help but wonder: if scientists say we're in trouble, are we in fact doomed? Only time will tell, I suppose.
A bit more about the article is below the fold.
The authors make it clear in the abstract that they are intentionally using "extremely conservative" assumptions to avoid criticisms aimed at earlier work. They use a more recent (and higher) estimate for the background extinction rate and only count species currently listed as extinct, relying heavily on IUCN data. While the IUCN Red List is tremendously important, I think it goes without saying that it gives an incredibly conservative estimate of total vertebrate extinctions. The criteria which have to be met can be found in this 87 page document.
The IUCN has three categories for extinct animals: Extinct in the Wild (EW), Extinct (E), and Possibly Extinct (PE). The authors use both "conservative" (EW, E, and PE) as well as "highly conservative" (E only) in their analysis. The following figure shows the cumulative observed extinctions compared to the expected numbers using the background rates. A is "highly conservative", B is "conservative".
In the end, using their conservative assumptions, they find that the current extinction rate is up to 114 times higher than the expected background rate. This is lower than
other studies have found using different methods, as expected, but the message is clear:
The analysis we present here avoids using assumptions such as loss of species predicted from species-area relationships, which can suggest very high extinction rates, and which have raised the possibility that scientists are “alarmists” seeking to exaggerate the impact of humans on the biosphere (26). Here, we ascertain whether even the lowest estimates of the difference between background and contemporary extinction rates still justify the conclusion that people are precipitating a global spasm of biodiversity loss.
I don't see anything in this work that is particularly groundbreaking. It seems to me a fairly straightforward analysis using existing data sets. It's the message that's important: even using conservative numbers, we have a serious problem that we are not currently addressing. If we want to save our biosphere and our future, then we will have to act quickly.