Abstract
The Paleocene–Eocene Thermal Maximum (PETM) around 56 million years ago was a 5–6°C global warming event that lasted for approximately 200 kyr. A warming-induced loss and a 70–100 kyr lagged recovery of biospheric carbon stocks was suggested to have contributed to the long duration of the climate perturbation. Here, we use a trait-based, eco-evolutionary vegetation model to test whether the PETM warming exceeded the adaptation capacity of vegetation systems, impacting the efficiency of terrestrial organic carbon sequestration and silicate weathering. Combined model simulations and vegetation reconstructions using PETM palynofloras suggest that warming-induced migration and evolutionary adaptation of vegetation were insufficient to prevent a widespread loss of productivity. We conclude that global warming of the magnitude as during the PETM could exceed the response capacity of vegetation systems and cause a long-lasting decline in the efficiency of vegetation-mediated climate regulation mechanisms.
Very interesting finding on page 10 where they identify 4° global heating as a special limit. Below 4° plants can adapt or migrate. When you go above 4°, it’s so different that plants have to evolve into new kinds of plants.
I think one way to read this paper was that in the PETM event, this tipping point was breached and the biosphere was no longer able to sequester carbon (big plant die off) and so the hysteresis of the climate system basically broke. And then it takes 75,000 years or something for new plants to evolve and reset the system.
I think the latest estimates put 2° at 2050 and +0.27 per decade at current rates assuming no new tipping points. Meaning 4°would be coming no later than year 2130.