A hydrogen vehicle is a vehicle that uses hydrogen as its on-board fuel for motive power. The term may refer to a personal transportation vehicle, such as an automobile, or any other vehicle that uses hydrogen in a similar fashion, such as an aircraft. The power plants of such vehicles convert the chemical energy of hydrogen to mechanical energy (torque) in one of two methods combustion, or electrochemical conversion in a fuel cell .some car mamufcture are makind hydrogen cars like bmw ant tyota. these cars will no co2 emissions and this then will help to stop the ice caps from melting and this will help stop the greenhouse effect.