The experiment has been done several times right here on Earth, involving the whole of the Earth's atmosphere and biosphere. Just because the source of the GHGs was natural in no way changes the physics of the situation. Several times there have been rapid increases and decreases in GHGs, and each time there has been an extinction event, large or small.
Extinction and Climate « ClimateSight
There have been five major extinction events in the Earth’s history, which biologists refer to as “The Big Five”. The Ordovician-Silurian, Late Devonian, Permian-Triassic, Late Triassic, Cretaceous-Tertiary…they’re a bit of a mouthful, but all five happened before humans were around, and all five are associated with climate change. Let’s look at a few examples.
The most recent extinction event, the Cretaceous-Tertiary (K-T) extinction, is also the most well-known and extensively studied: itÂ’s the event that killed the dinosaurs. Scientists are quite sure that the trigger for this extinction was an asteroid that crashed into the planet, leaving a crater near the present-day Yucatan Peninsula of Mexico. Devastation at the site would have been massive, but it was the indirect, climatic effects of the impact that killed species across the globe. Most prominently, dust and aerosols kicked up by the asteroid became trapped in the atmosphere, blocking and reflecting sunlight. As well as causing a dramatic, short-term cooling, the lack of sunlight reaching the Earth inhibited photosynthesis, so many plant species became extinct. This effect was carried up the food chain, as first herbivorous, then carnivorous, species became extinct. Dinosaurs, the dominant life form during the Cretaceous Period, completely died out, while insects, early mammals, and bird-like reptiles survived, as their small size and scavenging habits made it easier to find food.
However, life on Earth has been through worse than this apocalyptic scenario. The
largest extinction in the Earth’s history, the Permian-Triassic extinction, occurred about 250 million years ago, right before the time of the dinosaurs. Up to 95% of all species on Earth were killed in this event, and life in the oceans was particularly hard-hit. It took 100 million years for the remaining species to recover from this extinction, nicknamed “The Great Dying”, and we are very lucky that life recovered at all.