(i)    Burning of fossil fuels to meet increasing demand for energy causes air-pollution.
(ii)    Construction of dams on rivers to generate hydroelectricity destroys large ecosystems which get submerged under water in the dams. Further, large amount of methane (which is a greenhouse gas) is produced when submerged vegetation rots under anaerobic conditions.
(iii)     Continuous whirling and whistling of windmills cause noise-pollution and plays havoc with the lives of migratory birds.
(iv)     Heavy energy structures to exploit wave energy affect marine mammal and seabird population.
(v)     Using wood as fuel results in deforestation which affects environment.
In order to reduce energy consumption:
(i)    Fossil fuels should be used with care and caution to derive maximum benefit out of them.
(ii)    Fuel saving devices such as pressure cookers etc. should be used.
(iii)    Efficiency of energy sources should be maintained by getting them regularly serviced.
(iv)    Last of all, we should be economical in our energy consumption as energy saved is energy produced.