Here are the possible choices:
- Like how life ended on Mars.
- If all the stars in our universe die out and we enter a drastic permanent ice age.
- Nuclear war
- Black hole ends up sucking everything in our solar system.
- Meteor
- As you know, the earth and its moon have some sort of magnetic attraction which weakens every moment. After some time, the earth will be at a certain distance which can no longer receive the moon's force and so the earth will be thrown into the abyss.
- The devil isn't satisfied with daily human sufferings and decides to take everyone to hell.
I'm a bit skeptical about the existence to global warming. Climate fluctuations have happened before man has stepped foot on this world. Then again, historians say that volcanic smog had something to do with the temporary temperature risings during the period when all the landmass was located in the southern part of the globe.