Scifi pessimists say - we'll never be able to feed 8 billion people. Scifi optimists invent algae which can fix nitrogen from the air, generate fertilizer, and live in a symbiotic relationship with roots of food plants in airborne greenhouses.
Scifi pessimists say - global warming will kill us all.
Scifi optimists invent CO2 scavenging algae which generate carbon nanotube filaments used for building space elevators.
Scifi pessimists say - the sunspots won't come back and we'll all freeze in another ice age.
Scifi optimists invent CO2 storage bins which absorb or release tons of CO2 every day for precision climate control.
Scifi pessimists say the ozone layer will disappear and we'll all fry.
Scifi optimists invent airborne ozone replenishing units staffed by extremely attractive people.
It's too bad there are so few scifi optimists.