Cremation is the accepted practice for disposing of dead bodies for a number of religious groups in India, including Hindus, Sikhs, Buddhists and Jains. Some 85 per cent of the country's 1-billion-plus population cremate their dead. Beyond the Indian subcontinent, Hinduism is also a significant religion in Mauritius, Guyana and Fiji.Many people from other religions, including Taoism and Shinto practised in China, Japan and Indo-China, also choose to cremate their dead. Cremation is not just limited to religious custom; it is also practised by many people in Europe and America for reasons other than religion.A conservative estimate for the number of people around the world who would opt for cremation is around 1.2 billion. Taking an annual death rate of 1.5 per cent, that means roughly 18 million cremations annually.It takes about 100 kilograms of wood to create a fire that is hot enough to cremate an average human body, so that adds up to 1.8 million tonnes of wood. If we take the energy value of wood as 17 megajoules per kilogram, this works out at about 30 million gigajoules.In some places, electric furnaces replace wood. These tend to have a capacity of between 75 and 100 kilowatts, and they can cremate a body in 30 minutes or so, consuming somewhere between 0.13 and 0.18 megajoules for each body.However, most bodies worldwide are simply buried. Coffins consume wood, of course, and the quantity can be substantial in prosperous western societies.There are many factors to consider regarding the environmental impact of these various practices. While cremation consumes wood and generates smoke and carbon dioxide, burial also generates CO2, methane and other substances as bodies decompose, although this is spread over a longer time period.In addition, burial also occupies land, and in some societies such land is considered sacred and so cannot be used again. At one time, families in China reserved the most fertile patch of their farmland for burials, thus blocking land use forever.Apart from burial and cremation, there are some unusual practices in some parts of the world. Some Tibetans hack up bodies and feed the pieces to vultures. In India and Iran, Zoroastrians also allow their dead to be consumed by vultures, placing the bodies on a circular structure called a tower of silence. Tibetans and Zoroastrians believe that the body should serve a useful purpose after death - and the environmental impact is zero. Burial at sea, as practised by sailors, also works in the same way, although the motives are more practical.Some people in other societies have the same thought regarding usefulness when they donate their bodies to medical research. However, the remains have to be disposed of later, normally by incineration.Dileep Paranjpye, Lucknow, India

The most recently available global figures for cremation are from 2006 and they put the figure at 7,838,353. As with most global statistics, the heavyweights are China, which cremates more than 4 million people a year. In places with little spare land, such as Japan, nearly everyone is cremated, while in the US only 33 per cent of people are. These figures are likely to increase as the Catholic population becomes more comfortable with cremation.Calculating the amount of energy used in cremations worldwide is nearly impossible because of differences in fuel types and costings.Cremation is, of course, becoming untenable. The gas used is a fossil fuel creating heat and pollution, and the vapours emitted, despite increasingly sophisticated and expensive filters, release toxins such as mercury.Susanne Wiigh Masak, a Swedish biologist and keen gardener, has invented a process she calls Promessa, in which liquid nitrogen is used to freeze-dry bodies into what she describes as a perfect compost.Another alternative, marketed by Sandy Sullivan, is called Resomation. This is a form of speeded up anaerobic digestion using heated alkalines. Both are hugely improved methods of disposal, which have interesting possible environmental applications. The major obstacle is, of course, the squeamishness of the public.The most environmentally sound method of cremation is on an open air pyre using wood. Not only would this be carbon neutral, but it would be much more spiritually and psychologically nourishing than the current industrial conveyor belt approach that is used in most modern crematoriums. It is my company's most-requested "fantasy funeral".Rupert Callender, The Green Funeral Company, Dartington Hall Estate, Devon, UK

100kW for 30 minutes is 180MJ of course, not 0.18.Still seems remarkably efficient compared to requiring 100kg of wood at 17MJ a kilo.

Then again, as has been shown in investigations on spontaneous human combustion (using pigs) - with a suitable fabric covering to create a wick, a reasonably chubby individual can self-cremate remarkably well.