Lots of feels, not a whole lot of science behind this Greta Thunberg girl's shtick. "We are in the beginning of a mass-extinction." Oh, really? That's flat out fearmongering and far from scientific consensus. Sure, some quick searches of scientific literature and skimming the abstracts of a search titled "holocene mass-extinction" will reveal catchy points she can pontificate about and adults with zero education in that background will accept as fact. But, mass-extinctions are quite complicated and clearly not understood by the masses. She, being one.
First off, mass extinctions are the result of a combination of bad luck. No, seriously, it is. Combinations of cataclysmic events are the precursors of these mass extinctions. Usually requires the perfect combination of sudden changes in the chemical composition of the atmosphere/ocean, extra-terrestrial impact, sea level, etc. Rarely does one or two single factors trigger it. Add in the complexity of the trophic levels, that is a whole different level of unraveling needed. I like to think of the progression of mass-extinctions as a cascade failure of a network. It is often the combo of cataclysmic events that sets the chain moving. Once that trophic level is removed, it cascades up the chain. It usually doesn't start with the vertebrate megafauna we've seen go extinct and even that number is very, very small.
And some times we don't know what causes mass extinctions, just that they've happened. So, how do we know about these mass extinctions? Well, the fossil record of course. Not the big vertebrate megafauna, it's the smaller, invertebrate and even microorganisms that set the base of our ecosystem and often signal mass extinction events. Given that we have the greatest biodiversity of our planet has ever seen (looking in the past fossil record) and the number of classified genera today, the hard-evidence of extinction of species we've seen during the Holocene has been a fraction of 1%. IF that. And I'm being generous. So, how about we reel in this hyperbole. You'll see estimates of 10 or 20% loss of biodiversity (still a far cry of >50% loss in previous), but that is based on modeling of our ecosystem...and rarely does it act in a linear fashion.
Does that mean we aren't headed toward one, well I don't know. What I do know is we don't have any semblance of what the heck is actually going on or a clear path to ecosystem sustainability.
