The problem confronting humanity is called global "warming" for a reason.  The fact that increasing year-over-year global temperatures is unsustainable is self-evident.  Increased temperatures create drier soil conditions that bring about crop withering, and crop withering has huge social implications, e.g. rural populations moving into overcrowded cities.  Crop withering in Syria linked to climate change caused such a migration and contributed significantly to the chaos in Syria.  

Climate change -> drought -> civil unrest -> conflict -> mass deaths is a vicious sequence playing out today in real time throughout Africa (http://www.africanews.com/2017/03/17/depth-of-the-worst-drought-since-1945-peaking-in-parts-of-africa//).   Your observation "In short, more food" for Sub-Sahara Africa sounds quite hollow when compared to the present reality.