Saturday, March 27, 2010

Household Energy Emissions and Climate Change

LPG Tanks Photo Bharat Tanks
Not being a climate change specialist myself, I have been wondering why biomass energy burned as fuel in households generally does not show up in the climate change calculations. For instance typical families burning 0.18 tons LPG for cooking per year actually gets included in the estimates of greenhouse gas emissions and yet a similar family burning close to 2 tons of fuelwood per year is not considered as producing any greenhouse gas emissions.

According to my back of the envelope calculations people mostly in developing counties burn about 730 million tons of biomass per year for cooking and this amounts to about 1 billion tons of CO2 emitted into the atmosphere. This burning emits about 3%-4% of the world’s total CO2 emissions which according to some estimates is about 28 billion tons per year coming mostly from developed countries. World experts generally do not include the emissions from burning fuelwood, straw or dung because they are renewable. Thus, putting black carbon, health and other benefits aside, from a climate perspective the emissions from burning biomass are generally are considered to be climate neutral.

Continue reading and comment or take the poll below....

Cooking Emissions India: Photo Barnes
Perhaps oversimplifying there seems to be three perspectives on the recognition of emissions from biomass household fuels as a factor in climate change. The first scenario recognizes all emissions from cooking with biomass energy as greenhouse gases. Does it really matter whether CO2 comes from a coal plant or from fuelwood or straw burning? There are very few programs in the world that grow wood, straw or dung specifically for burning as a household fuel. It mostly comes from local commons, farm fields or in the case of dung from farm animals. Thus, the CO2 absorbed by local woodlands and farms is not directly related to fuel production as is the case for biofuels such as alcohol fuels, fuel from oil seed production and others. There is a tremendous amount of biomass growth naturally in the world including areas remote from populations. But that biomass growth absorbs CO2 from any source that produces it.

The second option that is commonly accepted by climate specialists is that burning biomass from resources that are renewed every year involves a balanced cycle. For example, as indicated previously ethanol comes from various biomass sources that are regrown every year and the greenhouse gases produced by burning it are in balance because presumably they are absorbed by the next years growth. Similarly CO2 from fuelwood burned from sustainable forests is not counted as a climate threat because of the balanced cycle of CO2 production and absorption. Thus, only fuelwood from non-sustainable production—which of course is very difficult to measure or document—should be considered as increasing greenhouse gases. This position links the burning of the fuel with the source of the fuel production.

The third possibility is that all biomass is potentially renewable and therefore should not count in the climate change debate. A cow eats biomass and produces dung and this dung falls to the ground and facilitates further biomass production. But what if this dung is burned in an inefficient a stove for cooking? I know this also is complicated by the fact that gases are emitted even when the dung sits in the field and it might be better to burn it in a digester. However, the general principle is that wood, dung and straw are all renewable energy and should not be counted as producing adverse climate emissions.

Anyway I really just want to find out what people think about how burning biomass energy as a household fuel fits into the climate change discussions. This is an important issue because it impacts the way carbon emissions are viewed for mitigating climate change. Please give comments or at least answer the attached poll on household energy and greenhouse gas emissions.


Unknown said...

You are right when you say that biomass growth absorbs CO2 independently from where it comes from, either from burning fossil fuels, burning renewable biomass or from any other source. Therefore, at first glance, it seems legitimate to consider that more efficient cooking stoves would reduce CO2 emissions from biomass and that this should count the same way than reducing CO2 from fossil fuel combustion. However, this is only half of the story: one should look at what would have been the fate of the carbon located in the fuel - either fossil or renewable biomass - if not used as a fuel. In the case of fossil fuels, the carbon would eventually remain in oil/gas fields or coal beds. In the case of biomass, it would have been released any way in the atmosphere, even if not burnt in a cooking stove, as part of the normal cycle of biomass degradation. Therefore, in a first aproximaiton, saving renewable biomass by using for instance more efficient cooking stove, would not prevent that the carbon located in the saved biomass to be emitted soon or late. Of course, a more detailed analysis would have to take into account the nature of the combustion (if incomplete, it generated methane, which GHG potential is considered 21 times higher than the CO2 released by a perfect combustion) and the nature of the natural degradation of the biomass (aerobic, or anaerobic,the latter generating methane. Therefore, depending on the conditions of the carbon released in both cases (anthropogenic burning or natural degradation cycle, the balance may not be always zero. However, this is not such a clear cut like for fossil fuels, for which the balance is trivial (eihter it is not emitted at all if saved and therefore eventually not extracted or there is a clear net addtion to the atmosphere stock if extracted and emitted).

Unknown said...

Eccles said...
The annual growth of wood is three to five times annual consumption of wood for fuel, timber, paper etc. Therefore, burning wood for fuel does not generally lead to increased atmospheric CO2. Most deforestation is caused by clearing land for agricultural expansion mainly as a result of population increase and the desire to improve living standards. If wood is burnt from clearing forests, without replanting or natural regeneration then in theory this wood is adding to atmospheric CO2. However, this is already accounted for in land use changes and if it was not put to a 'useful' purpose it would either rot or be burnt in situ and return to the atmosphere mainly as CO2.
Every year, plants capture about a net 100 billion tonnes of atmospheric carbon (net primary production [NPP]) and every year, the same amout is returned to the atmosphere (the carbon cycle). Of the 100 billion t of C about half is from land plants - the other half is from water biomass. So potentially about half of the NPP is available for use as energy. At present, only about 5 billion t C is used for food and energy so much more could be used as a substitute for fossil fuel. But of course the financial cost of using this renewable carbon fuel is probably more than the coat of existing fosile fuels, especially if they are subsidized. However, if account is taken of the CO2 that is added to the atmosphere and a 'carbon tax' is put on fossil fuels, then renewable carbon fuels may become cost competitive!

ConnieS said...

I agree with Christophe. It depends on the alternative "fate" of the stuff not burned and the rate of decomposition. If rapid, then probably it is a "wash." If very long (decades), burning it should be counted as having an impact. But present methods are not sophisticated enough to capture these fine points.