Asteroids

At some point a huge asteroid will hit earth. We won't be able to do anything about it--it's probably on it's way right now. There already have been some near misses, and evidence of asteroid collisions with earth in the past. People have surmised that firing nukes at an asteroid will break it apart, but what if you miss? Where will the pieces go? What if they hit earth? The scale of destruction will be huge. Extinction of the human race will be inevitable due to an inhospitable atmosphere, unless we start digging down and construct massive underground networks and shelters immediately. Wow--we really need to get on this, now that I think about it. So many things need to be taken into consideration. Living underground we'll be deprived of sunlight, a necessary life ingredient which processes nutrients/vitamins in the body as well as bolsters the spirit. While we can mimic sunlight with UV lamps, everyone knows it's not the same thing. We won't be able to grow fresh produce without fertilizers and hydroponics. Food will not be produced fast enough for all the people underground unless we begin this endeavor now, and it definitely won't be organic or wholesome. We'll be miserable. And pale, and probably have very poor skin and develop nutrient deficiencies which will make our hair and nails disgusting. No one will want to have sex because we will all look horrendous. The human population will die out slowly, or we'll go bonkers and kill each other within the first few months. So the human race will become extinct anyway, I guess no matter what we do.

Killjoy
Party Pooper
Spoilsport
Fuss-budget
Fusspot
Worrywort
Persona non grata
Aguafiestas
Rabat-joie
Guastafeste
Spielverderber

Seriously--Spielverderber.