Alarmists say we are losing our biodiversity and that our ecosystem will be destroyed because of human activity. This will cause mass extinctions that will eventually lead to our own.
The rate at which species go extinct versus the rate of speciation (divergence of lineage to a new species) would be difficult to arrive at, considering that our knowledge of those species that existed in the past and present is still incomplete. Similarly it would be difficult to figure what net effect the amount of extinctions human activity is directly responsible for versus the ones we prevented by breeding species for farming and other purposes.
For the most part extinctions and speciation are natural events from a geological perspective. Climate change and habitat destruction can be part of this natural process. There is no evidence to support that habitat destruction due to human activity will cause a significant amount of extinctions, or that this has caused permanent damage to the ecosystem.
Life continues to thrive on earth and it is more diverse than ever. After all 4.5 billion years ago there was no life on earth, 3.5 billion years ago there were only Prokaryotes. Earth’s history shows we've had much climate change and ever changing conditions defining ecosystems. It's these conditions that allowed for evolution of the species and allowed for the level of biodiversity we have today.