Allah, the almighty Subhanah Wa Taala (SWT) measured the sustenance in two days when he created the universe, and it is not acceptable nor thinkable to say that the earth will not be sufficient for the people in the future. In  some countries sustenance from land is very limited because of the rain shortness but they withdraw their sustenance from the sea. This could be seen in the icy regions as well as in the desert regions. This is the creation of God and this is a sign of the God’s creation and power. The theory saying that the earth will not be sufficient for people if the demographic pattern is not reduced or stopped is false. No one can predict the sustenance needed by the world in the next future, it should be at least assumed that the food amount produced now trough out the world is widely higher than the population.