The Earth has been around for a long time. During that time it has been through quite a lot. It has been struck by multiple asteroids. It was once struck so violently that
Even during times when life existed, the Earth has been far warmer than it is today. The global climate was much warmer when the dinosaurs roamed the Earth than it is now. It was the global cooling that occurred after another asteroid strike around 65.5 million years ago that gave rise to warm-blooded mammals.
This graph shows estimated global temperatures during the Phanerozoic Eon, the period during which abundant animal life has existed on Earth. Notice that we are in one of the cooler periods.
Global warming is primarily a threat to mammals. (Remember, humans are mammals.) Under global warming, vegetation will thrive. So will cold-blooded animals such as insects and reptiles. Rising ocean levels will benefit fish as well. It is us, the mammals, who are at risk. As far as humans are concerned, it is primarily a risk to people in poor countries. Therefore, the environmentalist message shouldn't be "Save the Earth," it should be "Save the Mammals."
Minimizing global climate change may save many mammals, perhaps even humans. But fear not for the Earth! Regardless of its climate, it will continue to happily orbit the sun for billions of years to come.