- Using too much energy from fossil fuel – fossil fuel produces air pollutions when converting to usable energy, sometimes too much energy is used to gain only a little yield increases. This figure can be used to show that more energy used doesn’t give out the same ratio to the product yields; “Between 1910 and 1983, corn yields in the US increased by 346% (on a per area basis), which the energy inputs increased by 810%, also on a per area basis!”