- the fuel used to heat the water for running a steam engine was usually coal - burning the fuel emitted carbon-di-oxide into the atmosphere - thick, black smoke irritated the respiratory tract and caused itchiness in the eyes - there was significant air and noise polution caused by steam engine - furthermore, railroads supported many industries, thus indirectly causing more pollution - hybrid engines definitely helped to cut down pollution levels - since diesel-electric power is used in most hybrid engines, pollution has not been eliminated completely - burning diesel still emits pollutants, and the residue heat after charging the batteries is also emitted into the atmosphere

- pollution has led to ecological imbalance, global warming, health problems