The world will be just fine. (It was just fine for the 4.5 billion years before we arrived on the scene).

Sure, some species will be extinct, but others will flourish. Miami may be in the ocean, so people who currently own the less desirable inland properties will be able to have beach-front condos!

What seems to be ignored is what I consider to be the real problem -that there are only a finite number of resources to support a finite number of organisms. As long as we humans continue to over-populate this planet, the other species will be crowded out. A global effort at human birth control would go a long ways to helping insure that there is enough resources for all living creatures on this planet.