It's not just that a few species go extinct. Whole ecosystems change. In 100 years the environment might not be suitable for the species anymore (e.g. reintrodu

It's not just that a few species go extinct. Whole ecosystems change. In 100 years the environment might not be suitable for the species anymore (e.g. reintroduction of wooly mammoths would be a disaster today) due to global issues (temperature, co2, acidity/salinity), but also local issues such as losing food sources, breeding grounds or some other species already filling the empty niche.