100 years.... Sure sure.... This is yet another one of those doomsday prophecies like Y2K, 2012, etc.
Just add it to the list:
A Brief History of the Apocalypse
^ and it's a very long list.
Humans won't go extinct any time soon. When the crap looks like it's hitting the fan, people will head into their bomb shelters or hide out in the forests and caves to wait it out while everybody kills themselves off fighting wars over jarred pickles and processed hot dogs.
Worst case scenario and his predictions are accurate?
Nuke a couple of third world nations and drop the population down a chunk or two, problem solved.
Target the ones where people keep living in deserts and places they can't grow crap in, who keep begging for donations and food supplies from charities and governments because they're too damn lazy to learn how to grow their own food, or dig their own wells (or move) while their kids get money from middle class families halfway around the world to go to school, learn their ABC's in clean looking clothes, only to graduate and end up like their parents who keep begging for donations and handouts because they're too lazy and ignorant to do anything for themselves.
Nuke em Ricco, solve the world's problems, stop the vicious cycle and save humanity in the process.
Yeah I know, me being weed free for three years has turned me into such a loving bowel of sunshine and cupcakes...... I love you all.