Farmer in a field of Miscanthus at harvest time.
Technical Summary

Perennial Biomass Production

Project Drawdown defines perennial biomass production as: the use of perennial grasses and coppiced woody plants for bioenergy feedstock, instead of annual crops like corn. This solution replaces grazing or annual cropping.

Bioenergy from annual crops has a poor life cycle analysis in terms of climate impact, but some perennial bioenergy crops have modest potential. Perennial grasses and re-sprouting woody plants have naturally high productivity, need fewer inputs and water, and are not food crops; hence, many governments worldwide are choosing them as future energy farming systems. They have the advantage of sequestering modest amounts of soil carbon while producing bioenergy (energy impacts are accounted for in the biomass Energy Sector solution). Though not modeled here, they are also an ideal feedstock for clean cookstoves.

This study focuses on two types of perennial energy crops: herbaceous crops (in this case mostly giant grasses) and short rotation coppice, in which the aboveground biomass of re-sprouting woody crops is harvested mechanically on a 2-3 year rotation.

Bio-based energy cannot hope to replace fossil fuels. However, perennial biomass production crops can sequester carbon while restoring degraded land. Their contribution to climate change may be most important in the next few decades, as clean energy gradually comes to dominate the energy sector. Though not modeled here, perennial biomass production can be used as feedstock for many other uses, from paper and cardboard to insulation and bioplastics.

Methodology

Total Land Area[1]

The total land suitable for perennial biomass production is 265 million hectares, representing degraded grassland areas.[2] This area is lower than many estimates, as Drawdown prioritizes food and reforestation over bioenergy. Current adoption[3] of perennial biomass production is estimated at 0.3 million hectares, based on 13 data points from 7 sources.

Adoption Scenarios[4]

Five custom scenarios were developed based on the estimation of low, medium, and high adoption rates for the future growth of perennial biomass cultivation based on 15 data points from 7 sources. .

Impacts of increased adoption of perennial biomass production from 2020-2050 were generated based on two growth scenarios, which were assessed in comparison to a Reference Scenario where the solution’s market share was fixed at the current levels.

  • Scenario 1: Scenario analysis shows the adoption of perennial biomass production on 106.9 million hectares of the allocated area by 2050.
  • Scenario 2: Scenario analysis shows the adoption of perennial biomass production on 189.9 million hectares of the allocated area by 2050.

Sequestration Model

Sequestration rate is 1.1 tons of carbon per hectare per year, based on 19 data points from 9 sources. It is assumed that all sequestered carbon that is not harvested for energy production is re-emitted at the end of productive life, when fields are plowed up and re-planted. Perennial bioenergy crops were assumed to have a productive lifespan of 20 years based on meta-analysis of 7 data points (reporting averages) from 5 sources.

Financial Model

First cost is US$1,294.34 per hectare,[5] based on meta-analysis of 9 data points from 6 sources. It is assumed that first costs for the land use that perennial bioenergy crops are replacing have already been paid, as the land is already in production. Net profit per hectare is calculated at US$363 per year for the solution (based on meta-analysis of 13 data points from 6 sources), compared to US$154.12per year for the conventional practice (based on 20 data points from 15 sources).[6] Annual operational cost per hectare is calculated at US$599.51 for the solution (based on meta-analysis of 11 data points from 6 sources), compared to US$328.42 for the conventional practice (based on 9 data points from 7 sources).[7]

Integration[8]

Drawdown’s Agro-Ecological Zone model allocates current and projected adoption of solutions to the planet’s forest, grassland, rainfed cropland, and irrigated cropland areas. Despite very broad climactic suitability, perennial bioenergy crops were given low priority so as to reduce impacts on food production.

The solution was relegated to degraded grasslands, where it was the third (and lowest) priority, as Drawdown rates food production and ecological restoration as higher priorities than energy.

Results

Total adoption in the Scenario 1 is 106.9 million hectares in 2050, representing 40 percent of the total suitable land. Of this, 106.65 million hectares are adopted from 2020-2050. The impact of this scenario is 4.0 gigatons of carbon dioxide-equivalent emissions reduced by 2050. Marginal first cost is US$230.3billion and lifetime operational cost is US$1.5 trillion. Lifetime savings is US$0.9 trillion.

Total adoption in the Scenario 2 is 189.9  million hectares in 2050, representing 72 percent of the total suitable land. Of this, 189.68 million hectares are adopted from 2020-2050. The impact of this scenario is 7.04 gigatons of carbon dioxide-equivalent by 2050. Marginal first cost is US$399.9 billion and lifetime operational cost is US$2.7 trillion. Lifetime savings is US$1.6 trillion.

Discussion

Benchmarks

This solution is somewhat challenging to benchmark, as few projections are available. Leymus and Lal, 2005 project the biosequestration of 0.06 gigatons of carbon dioxide-equivalent per year by 2050 from perennial biomass production. The Drawdown study calculates 0.14-0.28 gigatons of carbon dioxide-equivalent per year in 2050; thus, it is in alignment with Leymus and Lal.

Limitations

Many factors limit this study, as the industry is in its infancy. Current adoption, projected future adoption, and financials would all benefit from additional data points.

Conclusions

Perennial biomass production may never be as central a solution as afforestation or multistrata agroforestry. Nonetheless, it offers a productive and carbon-sequestering use of degraded lands, farm borders, riparian edges, and other spaces. As wind, solar, and other energy sources come to meet civilization's energy needs, use of perennial biomass production may shift to clean cookstoves and feedstock for paper, bioplastic, and other bio-based products.

 

[1] To learn more about the Total Land Area for the Land Use Sector, click the Sector Summary: Land Use link below.

[2] Determining the total available land for a solution is a two-part process. The technical potential is based on the suitability of climate, soils, and slopes, and on degraded or non-degraded status. In the second stage, land is allocated using the Drawdown Agro-Ecological Zone model, based on priorities for each class of land. The total land allocated for each solution is capped at the solution’s maximum adoption in the Optimum Scenario. Thus, in most cases the total available land is less than the technical potential.

[3] Current adoption is defined as the amount of functional demand supplied by the solution in the base year of study. This study uses 2018 as the base year due to the availability of global adoption data for all Project Drawdown solutions evaluated.

[4] To learn more about Project Drawdown’s three growth scenarios, click the Scenarios link below. For information on Land Use Sector-specific scenarios, click the Sector Summary: Land Use link.

[5] All monetary values are presented in US2014$.

[6] Tropical staple trees are not as labor-efficient as annual crops, in a mechanized context. However, 175 million hectares of the world’s farms are smallholders with little mechanization. The net profit per hectare figure shows that these crops are economically viable despite higher labor costs.

[7] Tropical staple trees are not as labor-efficient as annual crops, in a mechanized context. However, 175 million hectares of the world’s farms are smallholders with little mechanization. The net profit per hectare figure shows that these crops are economically viable despite higher labor costs.

[8] For more on Project Drawdown’s Land Use integration model, click the Sector Summary: Land Use link below.