Evaluation and comparison of CO2 mitigation possibilities of the complete bio-energy chain from two model frameworks

Introduction

With increasing pressure to reduce greenhouse gasses for the combustion of fossil fuels, there has recently been significant interest in the use of biomass as a primary source of energy (bio-energy). However, a number of open questions remain: What are the main primary sources of biomass (crops, forests, residues)? What bioenergy technologies can help with emission mitigation? What is the total emission mitigation contribution? Does increased use of biomass limit land-based mitigation?

A number of integrated assessment models (IAMs) have attempted to answer these questions. However, different IAMs have different representations of land and energy systems, leading to varying results. This project attempts

1. to understand the contribution bio-energy may have as an emission mitigation measure, including land and energy system emissions, and
2. to compare the results of two IAMs in order to see how system representation affects the results.

Methodology

The two IAMs included in this study are GLOBIOM-MESSAGE and IMAGE. First, a qualitative assessment of the models was conducted to understand the system representation in each IAM. After this, a scenario analysis was conducted. Each IAM was run with a baseline and a mitigation scenario (4.5W/m²). The growth in biomass use as well as changes in CO₂ sources/since were assessed. A final scenario with the carbon price of the mitigation scenario and no biomass use was also run. The tradeoff between biomass production and land-based mitigation, as well as the resulting emissions gap, provided insight into the contribution of biomass to reduction of emissions. Results from the two IAMs were compared and agreements or disagreements  explained.

Results

Despite vastly different land-energy system representations between the IAMs, they both broadly agree on the importance of bio-energy in reducing emissions. Areas of agreement include primary biomass use projection (60-80EJ/yr by 2100, approx. 10% of TPES), growth of biomass use in mitigation scenario (110-130EJ/yr), the importance of bio-energy with carbon capture and storage (CCS), and the importance of fuel switching, as opposed to land-based mitigation, to reduce emissions. Most importantly, the models agreed that the resulting emissions gap, where there is no bio-energy, is approximately 15%. The models disagree on the potential of land-based mitigation; this disagreement is due to differences in land-system representation. 

Conclusions

Bioenergy can play a significant role in reducing anthropogenic emissions. Depending on system representation, there may be a tradeoff between biomass availability and land-based mitigation. However, both models agree that the potential emission reduction from displacing fossil fuels, as well as using CCS technology, vastly outweighs the potential for land-based mitigation.

Please note these Proceedings have received limited or no review from supervisors and IIASA program directors, and the views and results expressed therein do not necessarily represent IIASA, its National Member Organizations, or other organizations supporting the work.

Last edited: 19 August 2015