i think the major cause of overpopulation is being caused by fossil fuel.

fossil fuels made the industrial revolution possible hence farming and food production had since became more and more efficient.

according to one guy in the documentary "the 11th hour", the actual human population that earth can sustain is less than 1 billion if we rely on the daily sunlight (plants, and everything). what we are doing now is actually tapping on ancient sunlights (ancient plants and animals which has become fossil fuels) to enhance our food production and thus leading to fossil fuel addiction.

can you imagine that back in the 60s, our population was only 3 billion. i took us just 40 years to double ourselves. what happened in those 40 years was the introduction of hypermarkets. with the introduction of hypermarkets, food can be distributed much more readily to the population. so there are no worries when it comes to food and hence there are no any worries for the human population to continue growing.

the nightmare will come when alternative forms of energies are not found if fossil fuels are depleted in the future. without fossil fuels, combine harvesters cant work and trucks that transport food cant work. this will force them farmers to use traditional farming techniques which are not as productive as the modern ones. this will lead to a shortage of food and many might die because of a massive famine.

thats why i'm not a big fan of using my own tupperware for take aways and all those stuffs because i dont think it would help much. the only solution to save the earth is to reduce ourselves i think.