During the last few hundred years, species extinctions primarily occurred due to habitat loss and predator introduction on islands. Extinctions have not been linked to a warming climate or higher CO2 levels. In fact, since the 1870s, species extinction rates have been plummeting.
Image Sources: Loehle & Eschenbach (2012), BBC, Wrightstone, 2019
In the past it has been widely reported that high and abruptly changing CO2 concentrations led to climate conditions that were “too hot for complex life to survive” on the planet.
More recently, though, scientists have determined that the opposite may have been true: mass extinction events occurred during periods of global cooling, expansive ice sheet growth, and marine-habitat-destroying sea level drops of more than 100 meters.
In fact, of the 5 previous mass extinctions, glaciation (triggered by volcanism) is thought to be responsible for the 1st, 3rd, and 4th events, with the 2nd unknown and the 5th from an aseteroid impact. None of these explanations have ties to CO2 concentrations or sudden warming.
Images Source: Jones et al., 2017, Phys.Org
Image Source: Creveling et al., 2018
Image Source: Isozaki and Servais, 2018
Image Source: Wu et al., 2014
Image Source: Kani et al., 2018
In most cases, scientists attribute the mass extinction glaciation events to the same mechanism previously thought to cause sudden-onset warming: widespread volcanic eruptions.
More volcanism means more sulfate aerosols blocking out solar heat from penetrating into the ocean. With “repeated clusters” of volcanic events gradually accumulating over time, decades to centuries of cooling can ensue.
Image Source: McGregor et al., 2015
Image Source: UPI.com
New (2019) research suggests that the global cooling extinction events could have been triggered by a solar-astronomical influence.
Again, this suggests no clear link between mass extinctions and CO2-induced or sudden-onset warming events.
Image Source: Isozaki, 2019
Image Source: Fang et al., 2018
May 16, 2019 at 10:06AM