Friday, 17 August 2012

How green is my crematorium?

In my last post (Energy Saving in Business - Cambridge City Council) I mentioned that in Cambridge the crematorium is responsible for 5% of the council's carbon emissions; this got me thinking about different kinds of funerals. Traditional burials involve hardly any energy consumption (though some for digging) but they do result in carbon emissions over time as our bodies are broken down in the soil. Below the top 20cm or so there is little oxygen available and so biological processes will release methane, a very powerful greenhouse gas. I have made some estimates to compare these emissions with those from the crematorium and another potentially large source: the cars the mourners arrive in.

This post has been edited 24/Sep/2013 to correct the proportion of carbon in the body which is converted to methane and how much is oxidised as it passes through the soil.

Methane is much more powerful than CO2 but it does not last so long in the atmosphere so how bad it is (the 'Global Warming Potential' or GWP) depends on the timescale you are looking at. Over a 20 year timescale methane is 72 times worse than the same amount of CO2. Over a 100 year timescale it is only 25 times as bad [1]. Since it takes a few years anyway, let's use the 100 year timescale.

Carbon emissions from a burial compared to cremation and to the emissions from mourners' car travel 10 x 30km. The IPCC recommends the assumption for landfill sites that 10% of methane generated is oxidised but other field studies have suggested the average is 35%

The chart shows the results of my calculations assuming:
  • Average weight 70 kg
  • Carbon content 18% [2]
  • In burial, half of the carbon converts to CO2 and half to methane but some of this is oxidised in the soil
    • For landfill sites IPCC assumes that 10% of methane is oxidised [3]
    • Other field studies suggest this is very conservative and the average is 35% [4]
  • 250 kWh gas needed for cremation [3], 185g CO2/kWh gas [5]
  • There are 10 cars of mourners each driving a 30km round trip, 193 g CO2/km [5]

The emissions from the cremation come from burning the gas and all the carbon in the body to CO2. The emissions from burial are from converting some of the carbon in the body to methane, from anaerobic processes, and the rest to CO2. Some methane will oxidise to CO2 as it passes through the soil, depending on soil conditions and temperature. For example in damp clay there will be little oxidation but in warm loamy soil a good deal of the methane will be converted. Cremation and burial would have equal emissions if 75% of the methane were oxidised. However, if burial is similar to landfill then field studies suggest 35% is typical.

The emissions from the cremation are rather less than those from a typical burial and not that much more than the mourners' cars. If you were to use the 20 year timescale for the global warming potential the burials would be even worse. Cremation would be even better if a renewable fuel was used instead of natural gas.

There are other options for burial under development such as 'promession' or 'cryomation'[7]. Both of these involve freezing the body, breaking it into pieces and drying out most of the water resulting in a material which can be naturally composted in aerobic conditions. There is still some energy required for the freezing and drying. Another alternative now available in some parts of the USA is resomation [8] which is a chemical process, claimed to be low in carbon emissions and in energy use compared to cremation.

Cremation can be made greener by making better use of the waste heat. Heat recovery is usually limited by the lack of uses for the heat as crematoriums are usually some way out of town, but heat can also be used to generate electricity and a Durham crematorium is installing turbines to do just that [9].

Finally, to put these figures into perspective, the average UK person is responsible for around 26 kg CO2 emissions per day [10]. The mourners' cars and the cremation together come to only 6 days worth of ordinary life. The burial (including mourners) is only about 9 days worth.

By the way, I have now revised the instructions from my funeral - a cremation please in a lightweight coffin.



[1] Climate Change 2007: Working Group I: The Physical Science Basis 2.10.2 Direct Global Warming Potentials IPCC
[2] What are the elements in the human body chemistry.about.com
[3] 2006 IPCC Guidelines for National Greenhouse Gas Inventories volume 5 Waste IPCC
[4] Under the covers Tarek Abichou, Ph.D., P.E., and Jeffrey Chanton, Ph.D. | Waste Age
[5] Benefits of the FTI FTII and FTIII Cremators (www.incineratorspecialists.com)
[6] Guidelines to Defra /DECC GHG Conversion Factors for Company Reporting, average petrol/diesel car emissions
[7] Novaterium solutions
[8] New 'Green cremation' machine opens in Minnesota (BBC August 2012)
[9] A dead heat - crematorium to sell power to the National Grid (Daily Telegraph Nov 2011)
[10] Energy and Carbon Emissions: the way we live today Nicola Terry

5 comments:

  1. Nicola,
    The methane arising from anaerobic decomposition in the ground is absorbed by micro-organisms in the soil and is not released into the atmosphere. Please could you revisit your figures which give the false impression that polluting, energy consuming cremation is OK - it isn't. It uses up finite fossil fuels, it pollutes the atmosphere with toxins and CO2 and then many choose to have their ashes interred in a memorial garden beneath an imported stone alien to the local environment in a garden which continues to need mowing and strimming in perpetuity. Cremation is damaging to the environment.

    ReplyDelete
  2. Please can you give a reference which describes the process whereby the methane is absorbed - or at least explain further how this happens and to what degree. It certainly doesn't always happen or we would not be worrying about methane released from landfill sites.

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  3. Methane Oxidation in Landfill Cover Soil: http://www.ipcbee.com/vol6/no1/61-F00119.pdf
    Based on this study, CH4 emission from solid waste disposal sites could
    be significantly reduced by the utilization of appropriate cover soil.

    It would also be worth examining the environmental cost of cut flowers. Regular funerals consume a great many flowers, which are often grown overseas, plastic trays, Oasis foam blocks, ribbons and acetate sheet wrapping. The production of hot-house flowers use up valuable water and fuel resources and contribute significantly to CO2 emissions. After the funeral regular cemeteries and crematoria gardens are festooned with cut flowers, week after week - cemeteries struggle to separate the compostable material from the plastics.

    We should also look at the environmental cost of gravestones - the majority are imported from overseas where the environmental impact is enormous (but largely unseen); the conditions for workers are often very poor; and shipping the heavy goods around the oceans is hugely polluting.

    At a natural burial ground there are no gravestones, no vases for flowers on graves and do not attract such regular grave tending visits, reducing not only the waste associated with flowers, but also the number of car journeys. The slow release of molecules into the soil where they are broken down into beneficial compounds is without doubt far less environmentally damaging than cremation and conventional cemetery burial.

    ReplyDelete
  4. Methane Oxidation in Landfill Cover Soil: http://www.ipcbee.com/vol6/no1/61-F00119.pdf
    Based on this study, CH4 emission from solid waste disposal sites could
    be significantly reduced by the utilization of appropriate cover soil.

    It would also be worth examining the environmental cost of cut flowers. Regular funerals consume a great many flowers, which are often grown overseas, plastic trays, Oasis foam blocks, ribbons and acetate sheet wrapping. The production of hot-house flowers use up valuable water and fuel resources and contribute significantly to CO2 emissions. After the funeral regular cemeteries and crematoria gardens are festooned with cut flowers, week after week - cemeteries struggle to separate the compostable material from the plastics.

    We should also look at the environmental cost of gravestones - the majority are imported from overseas where the environmental impact is enormous (but largely unseen); the conditions for workers are often very poor; and shipping the heavy goods around the oceans is hugely polluting.

    At a natural burial ground there are no gravestones, no vases for flowers on graves and do not attract such regular grave tending visits, reducing not only the waste associated with flowers, but also the number of car journeys. The slow release of molecules into the soil where they are broken down into beneficial compounds is without doubt far less environmentally damaging than cremation and conventional cemetery burial.

    ReplyDelete
    Replies
    1. The study you cite is from Thailand and it suggests methane oxidation factors range from 10% to 58%. I found a source which has wider geographic coverage and found an average of 35% so I have revised the text to use that. It seems the IPCC assumption of 10% is conservative.

      I think that the rate of return visits to burial grounds is very varied and depends on the feelings of the bereaved more than the nature of the burial.

      Also, cremation does not require a gravestone. My father's ashes were scattered at a place of sentimental significance to my mother and I hope something similar happens to mine.

      Delete