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Biomass vs. Fossil Fuels: Thinking of CO2 Emissions in Terms of Nature’s “Battery”

One of the reasons governments have been pushing biomass burning is the notion that it would displace fossil fuels and thereby reduce CO2 emissions. Biomass is renewable and displaces fossil fuels. But would it reduce CO2 emissions?

Fossil Fuels: Ancient Storage

In Batteries from the Carboniferous, I noted that fossil fuels are Nature’s ancient method of storing solar and photosynthetic energy in the ground. Inadvertently, fossil fuels have served as a multimillion year old storage battery, which sat in the ground because no species had learned to use it efficiently until human beings figured out how in recent centuries.

Because using it releases a number of pollutants, however, fossil fuels are a somewhat imperfect battery.  These pollutants are: particulate matter, sulfur dioxide, nitrogen oxides, various hydrocarbons and carbon monoxide (the latter two if combustion is less than 100% efficient). [Note: CO2 is not in my list of pollutants. It is the stuff of life, rather than a pollutant. You, dear reader, are 18% carbon, virtually all of which originates in CO2 in the atmosphere. Don’t try to go without carbon!]

An Analogy

In order to figure out whether burning biomass rather than fossil fuels would reduce atmospheric CO2 emission, consider the following analogy.

Whether you pay your electricity bill out of your savings account (analogous to carbon in fossil fuels) or your checking account (analogous to carbon in newer biomass), your total wealth (checking + savings, analogous to total carbon in fossil fuels and newer biomass) is the same assuming the bill is paid out with equal efficiency, i.e., all fees are equal, whichever account you use.

From the electrical company’s point of view, its revenues are also the same.

Although paying it from your checking account makes your savings account larger, you are no better or worse off, on net. So, it makes no difference which account you use, either to your net wealth or the electrical company.

What willmake a difference is being able to decrease your electricity bill or increasing the amount you bring in to your checking account. But if the total bill is the same, it makes no difference which account you use.

Similarly, what carbon is no longer tied up in fossil fuels and in newer biomass ends up in the atmosphere (minus what is dissolved in the oceans and re-used in photosynthesis). Thus, it makes little or no difference to the atmosphere whether one uses new biomass or old biomass (aka fossil fuels).

That using biomass is any more sustainable than using coal, for instance, is based on compartmentalization (between checking and savings accounts). What is more “sustainable” (or “sustainable” for a longer time) — note the quotes, I use the word advisedly, but that’s another story — is either to reduce the use of energy or to generate biomass more rapidly (without displacing something else that would generate equal or more biomass).

Finally, note that for the combustion phase, it is possible to burn fossil fuels more efficiently than biomass. Hence, the former ought to reduce CO2 emissions overall. But a more sophisticated analysis ought to consider life-cycle consequences (including CO2 released in extraction, preparation, transportation, etc., of the two forms of biomass).

Conclusion

Biomass may be renewable, politically correct, and fossil-fuel displacing. But it is unlikely to reduce atmospheric CO2 concentrations much, if at all.

9 comments

1 Jim Clarkson { 09.21.11 at 7:35 am }

The enviromentalist argument is that biomass is going to decompose and put CO2 in the atmosphere anyway with no net increase in CO2 levels while coal has carbon locked up.

I’m not sure you addressed their argument enough to refute it.

2 john { 09.21.11 at 9:05 am }

@ Jim, the decomposition would produce methane, which is a more significant greenhouse gas. If you burn it then it will be converted to CO2.

3 Chip Knappenberger { 09.21.11 at 10:13 am }

Indur,

It seems to me that you have this framed wrong. Biofuels are not supposed to displace CO2 emissions but rather the CO2 source (and hence reduce CO2 build-up in the atmosphere).

What is of concern, is not the total amount of carbon in the system (i.e. checking+savings), but the total amount in the atmosphere. As long as you keep releasing carbon from your savings account, the atmospheric concentration will grow (absent additional sequestration actions). This not so much the case when using your checking account.

If energy from biofuels were to replace all energy from fossil fuels, CO2 emissions would be similar and yet the atmospheric concentration would cease to increase (or at least roughly so, without working through all the details). Just as the CO2 in the breath from 1 human or 7 billion doesn’t impact the atmospheric CO2 concentration (assuming your are not eating coal or drinking oil).

-Chip

4 Indur M. Goklany { 09.21.11 at 8:05 pm }

Jim – Decomposition is a valid concern if you are interested in reducing the CO2 in the atmosphere. To figure out the full effect one needs to do a life-cycle analysis (as suggested above).

Remember that if you don’t burn the new biomass, not all the new carbon in the biomass has to be returned to the atmosphere, nor does it have to return immediately. In fact, it is possible to sequester the biomass for hundreds of years if one wants to. It can, for instance, be incorporated into the soil (as is the fate of much of the biomass from photosynthesis) or into long lived products (e.g., building materials, furniture, or even trees), assuming these products are not disturbed or burned subsequently.

When one does these life-cycle analyses one should also discount the emissions if they are emitted 50 or 100 or 200 years from today as opposed to right now (assuming that CO2 concentrations continue to grow). This is because the relationship between temperature increase and CO2 concentrations is logarithmic and is subject to a law of “diminishing returns” for each additional molecule. One also has to consider whether the carbon is returned to the atmosphere as CO2 or methane (as John notes). But one has to consider this for the fossil fuel as well.

Chip – I am not sure I agree. There are two ways to look at this. First, consider the situation just AFTER the biomass has been created (and before it is burned). At this point, the carbon in the biomass is no longer in the atmosphere. It is in my “checking account”. So if one wants to use energy, one can either burn the biomass or an equivalent amount of fossil fuel. Either way, the same amount of CO2 would be added back to the atmosphere.

The other way to look at this is that the conservation of mass (for carbon) applies. So what is not in my checking account (new biomass) and the savings account (fossil fuel) is in the atmosphere (assuming no change in the oceanic carbon). So if the sum of carbon in fossil fuel and new biomass is the same, then so is the carbon in the atmosphere.

5 Indur Goklany: Biomass vs. Fossil Fuels: Thinking of CO2 Emissions in Terms of Nature’s “Battery” | JunkScience Sidebar { 09.21.11 at 11:54 pm }

[...] Biomass vs. Fossil Fuels: Thinking of CO2 Emissions in Terms of Nature’s “Battery” by Indur Goklany September 21, 2011 [...]

6 Chip Knappenberger { 09.22.11 at 11:14 am }

Indur,

Thanks for the response.

You are correct that on very short times scales (like during the growing season), you could see a drawdown of atmospheric CO2 from growing biofuels. But assuming the biofuels are used to produce energy as soon as they are harvested, the CO2 that was stored as carbohydrates is immediately returned to the atmosphere. So on an annual basis, the net carbon exchange between the biofuels and the atmosphere is near zero. In essence this is a closed carbon system with a turnover time of about a year or so.

This is not the case for using fossil fuels (at least not on human timescales). The carbon flow is only in one direction–into the atmosphere (not accounting for the boost to terrestrial sinks that additional atmospheric CO2 provides for).

-Chip

7 Indur M. Goklany { 09.22.11 at 7:32 pm }

But if instead of burning the new biomass you burn fossil fuel, the amount of CO2 in the atmosphere will be approximately the same for a long time in the future (assuming one sequesters the biomass in some fashion — see the response to Jim above).

In fact, since it should be possible to burn fossil fuels more efficiently than new biomass, you’ll end up with somewhat less atmospheric CO2.

8 cknappenberger { 09.23.11 at 10:28 am }

Indur,

Technically you are correct, assuming energy can be extracted from fossil fuels more efficiently than biofuels AND biofuels aren’t used for fuel, but instead are sequestered for hundreds of years…of course, in that case, they wouldn’t be called biofuels, but biosinks. And we wouldn’t be having this discussion. But, given that the plan is to develop biofuels to replace some energy from fossil fuels, then if it were to be done on a large enough scale, it would slow the atmospheric build-up of CO2 (not that I think this is a good idea for a plethora of other reasons).

-Chip

9 jeb { 06.06.14 at 8:53 am }

We assume that only biomass fuels can use the carbon sinks i.e. forest areas; yet at present the fossil fuels are also using these green sinks. Is it not a matter of preserving these green areas for carbon sinks whatever fuel we burn? Back to industry paying carbon quotas for green forest area conservation.

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