Oops, an ice age is on its way. According to this guy
Now that we're doom-mongering, let's go for it:
The earth is warming until mankind gives up fire.
We're also overdue for a new ice age which will make most of the world's land masses inhabitable.
The earth's magnetic field has been weakening for 2,000 years and we're overdue for one of earth's periodic axis shifts, which will obviously destroy most life on the planet.
We're gonna get hit by an asteroid, which will obviously destroy most life on the planet.
The star Betelgeuse may have already gone supernova, and will hit us with three days of continual X-rays some time in the next 500 years, severely degrading most life.
A big volcano will blow up and darken the world for years, killing most life.
Earthquakes, tsunamis, flood, famine, mass death.
Pestilence, manmade or otherwise, accidental or on purpose, terrorist or state-sponsored warfare.
Antibiotics are only one step ahead of stronger, more powerful bacteria that will wipe out a large percentage of mankind.
We're running out of fuel.
We're overpopulating the earth.
We're running out of fresh water.
Ruinous wars over declining resources are inevitable.
Technology is getting close to the point where a small cadre of humans with a grudge can create mass murder on a scale imaginable only by nation-states a few decades ago. Stealing a nuke and using it to blow up a nuclear power plant could render thousands of square miles inhabitable for decades or centuries.
Even if a small group of people don't do it, rogue nation-states may still blow up a good part of the world and cause nuclear winter.
Even if we don't blow ourselves up on purpose, we may still do on accident.
The 12th Imam may come back. The anti-Christ and the beast may show up. The Jewish messiah may finally show up. Siva, the god of death, may return.
Even if none of this happens, we may still build a technological dystopia based on entertainment, distraction and consumerism that numbs what remains of our souls so that we'd wish all the above had happened a long time ago.
And worst of all, if and when any of this happens, someone's last words will be, "I told you so."
Bottom line: You want negative. That's negative.