Mankind clearly doesn't have much time left - how long more do you give?

I say 500 long, miserable more years and we're outta here. On the news it read that by 2050 the food production has to DOUBLE to sustain the world's growing population. We're practically being fed SH*T that makes us fat and gives us cancer. On the other hand, we're starving to death by the millions. I don't even have to mention pollution, depleting of natural resources, the threat of nuclear war, etc. How long more?