Science magazine mentioned this study, below is my summary of it
26 Jul 2012. Bioenergy — Chances and Limits. German National Academy of Science (Leopoldina Nationale Akademie der Wissenschaften). Page 30-56 English Version.
A major motivations for using bioenergy is to reduce climate change from carbon dioxide (CO2) emissions by substituting biomass for fossil fuels.
But biomass is NOT CO2 neutral because:
- Plants need more than carbon to survive. They also need water, nitrogen, phosphorus, sulfur, and soil minerals. When you remove plants, you have to put the soil nutrition back with fertilizer, which releases nitrogen-based greenhouse gases (GHGs) with a much higher global warming potential than CO2.
- Plowing and harvesting releases carbon dioxide, nitrous oxide, and methane (livestock husbandry). Nitrous oxide is 300 times, and methane 25 times more potent in GHG than CO2.
- Forest biomass has carbon amassed over centuries and this CO2 is released when wood is harvested and burned at higher rates than it can be regrown.
- Using abandoned cropland in Eastern Europe might release more CO2 if it’s converted to growing biomass crops.
Other major problems with growing plants for biofuels are:
- Environmental damage from reduced soil quality, reduced biodiversity, soil salinization, contaminated groundwater, lakes and rivers from nitrates and phosphates.
- Limited phosphate reserves. Intensive agriculture will not be able to continue and therefore crops produced will eventually decline, not increase to provide more biofuel
- High yielding crops use more water than others. In dry areas, this has to be done with irrigation, yet all over the world, groundwater levels are dropping.
- Desalinization of ocean water is not a solution (see p 36 for details).
- The idea that we can genetically modify plants to increase production can only go so far: all plants are limited by the laws of physics — there is an upper limit of production set by available photons (light conversion efficiency into biomass), nutrients, water, and plant structure that can’t be exceeded, no matter how much fertilizer, pesticide, or bioengineering is applied.
Use of Algae.
Current life cycle analyses indicate that the energy return on investment (EROI) is less than one.
Use of Oceans to grow biofuels
Although the gross primary production of the oceans is similar to the magnitude on land, the difference between the amount of biomass in each is astounding. Land plants have orders of magnitude more tonnes of C bound up in biomass
- Land: 650,000,000,000
- Ocean: 3,000,000,000
This is because ocean phytoplankton die so fast from zooplankton consumption and other causes, which makes oceans unsuitable as a source of large-scale biofuel production.
There’s not enough biomass in Germany to make fuel with
There’s not enough biomass. Germany is already using 75% of the productivity of forests, agriculture, grass, and pasture (the remaining land is infrastructure — cities, roads, factories, etc). That leaves just 25% for all other creatures, hardly inline with Germany’s conservation of nature and biodiversity regulations.
The 14 million tonnes of wood harvested per year has the amount of energy contained in about 4% of the energy in current oil, coal, gas, nuclear, and renewable energy consumed per year. 40% of the wood is burned for energy, 60% wood products (that may end up getting burned later). Not only would harvesting more wood increase CO2, it wouldn’t increase energy production and forests might not be sustainable any more.
90% of the 53 million tones of biomass harvested from crop and grasslands are used for human or animal food and industrial products. The remaining 10% residue is less than 1.5% of Germany’s energy consumption. Increasing crops means more fertilizer, pesticide, machinery, transportation, and so on that use fossil fuels, reducing further the net energy gain and increasing CO2.
20 million tonnes of straw are produced: 13 million tonnes are left on the fields and even so, 3% of the soil carbon is lost per year — more straw should remain on the fields, but an additional 4 million tonnes are used for animal bedding rather than soil enhancement.
Although 7% of Germany’s energy came from biofuels, most of this energy came from imported biofuels. At most Germany could produce 3% of energy from sustainably grown biomass (mainly renewable wastes).
Importing biomass is simply taking it away from somewhere else, creating problems in other nations where the soil isn’t renewed sustainably, as well as potentially destroying forests and taking food away from people and animals in these nations.
The German population could theoretically get by on 9 million tonnes C of biomass, but in reality more than 70 million tonnes of C are eaten (40 million tons of C for animal feed and 20 million tons of C from grasses grazed by animals with 10 million tons C of that lost via manure). Also humans can’t digest up to 50% of plants due to the cellulose and lignin. And somewhere between 30 to 50% of plant material is consumed by pests or discarded.
A better way than biofuels to reduce CO2 is to eat a more vegetarian diet — the biomass eaten by animals and the enormous amount of methane released by animals would contribute far more to climate change mitigation than the production of bioenergy.
Don’t bet on Second Generation Biofuels either
“Use of cellulose and lignocellulose constituents of plant material (wood, straw etc.) for bioethanol or biobutanol production is limited by the high stability of lignocelluloses. Mechanical and thermochemical treatment help to overcome this limitation, but these treatments in turn are highly energy-intensive.”
Biogas is best at small to medium scale in rural areas
It’s not a large-scale solution since centralization would take too much energy to transport the raw waste material.
Biofuels burned in combustion engines release toxic products
In the unlikely event biofuels are ever actually used on a substantial scale, new engine exhaust catalysts will be needed to filter out aldehydes, sulfur and nitrogen compounds, as well as unforseeable compounds because of the complex diversity of the biofuel derived from different plants (gasoline is much simpler, it’s just saturated hydrocarbons).
Biomass as a feedstock for chemicals as fossil fuels decline
Oil is used in 500,000 products. Many scientists feel it’s crazy to be burning this precious substance to hurl 3,000 pound vehicles to the nearest fast food joint. So really the main use of biomass should be to replace oil in chemicals, medicines, and so on, but it will be hard to do, because plants are much more complex than oil, so many new common chemical production processes will need to be adapted or fundamentally changed.
With the exception of the use of biogenic waste the larger scale use of biomass as energy source is not a real option for countries like Germany.