war and plankton

The world's population will keep on growing until it hits a peak of 9 billion round about the year 2050. Most arable land in the world is already being used so how are all these new people going to eat bearing in mind that 1 billion people are currently undernourished? Increasing the efficiency of food distribution is one way - a lot of food is destroyed when harvested, spilt while being transported or allowed to go moldy in storage. Increasing people's wealth is another solution: many city dwellers simply don't have the money to buy food so producing more food or increasing the efficiency of its distribution will have no effect on them. Using non-arable land is another solution but this comes with heavy environmental costs: poor quality land needs a large input of fertilisers which consume fossil fuels and in the long term kill the soil. Another solution which I have already banged on about in the past is to grow plants hydroponically. I am still a little sceptical about the cost of this but with some government support who knows? Two more possibilities: one is to harvest plankton. Plankton are protein rich and need very little apart from sunlight in order to grow. There are a wide variety of plankton suited to different water conditions so presumably all parts of the world could find a plankton to suit their local waters. Don't know what plankton tastes like or how much you need to make a decent meal but with 9 million bellies to feed we can't afford to be picky. The other possibility is to wait for a third world war to cull our numbers.