Antonyms are cornucopian, humanist, realist.
Doomers hold a faith based belief that humanity is incapable of resolving human-society created global issues, e.g. by replacing oil with other energy sources.
I used to be a doomer, but then I remembered how to add.
Doomers hold an unshakable faith that the planet is inevitably doomed because of anthropogenic global warming and that nothing can reverse earth's ultimate destruction. In particular, doomers seem to take joy in discussing and contemplating a global doomsday.
Used by the peak oil community to refer to those who believe that the end of the oil age will also mean the end of human society.
You're doomerosity is only so high 'cos you're suffer from apocophilia.