We present an overview of results from 11 integrated assessment models (IAMs) that participated in the 33 rd study of the Stanford Energy Modeling Forum (EMF-33) on the viability of large-scale deployment of bioenergy for achieving long-run climate goals. The study explores future bioenergy use across models under harmonized scenarios for future
We have compiled historical greenhouse gas emissions and their uncertainties on country and sector level and assessed their contribution to cumulative emissions and to global average temperature increase in the past and for a the future emission scenario. We find that uncertainty in historical contribution estimates differs between countries due to different shares of greenhouse gases and time development of emissions. Although historical emissions in the distant past are very uncertain, their influence on countries' or sectors' contributions to temperature increase is relatively small in most cases, because these results are dominated by recent (high) emissions. For relative contributions to cumulative emissions and temperature Climatic Change (2011) 106:359-391 rise, the uncertainty introduced by unknown historical emissions is larger than the uncertainty introduced by the use of different climate models. The choice of different parameters in the calculation of relative contributions is most relevant for countries that are different from the world average in greenhouse gas mix and timing of emissions. The choice of the indicator (cumulative GWP weighted emissions or temperature increase) is very important for a few countries (altering contributions up to a factor of 2) and could be considered small for most countries (in the order of 10%). The choice of the year, from which to start accounting for emissions (e.g. 1750 or 1990), is important for many countries, up to a factor of 2.2 and on average of around 1.3. Including or excluding land-use change and forestry or non-CO 2 gases changes relative contributions dramatically for a third of the countries (by a factor of 5 to a factor of 90). Industrialised countries started to increase CO 2 emissions from energy use much earlier. Developing countries' emissions from land-use change and forestry as well as of CH 4 and N 2 O were substantial before their emissions from energy use.
This paper evaluates the role of land in long-run climate stabilization mitigation scenarios. The details of land modeling for common stabilization policy scenarios are, for the first time, presented, contrasted, and assessed. While we find significant differences in approaches across modeling platforms, all the approaches conclude that land based mitigationagriculture, forestry, and biomass liquid and solid energy substitutescould be a steady and significant part of the cost-effective portfolio of mitigation strategies; thereby, reducing stabilization cost and increasing flexibility for achieving more aggressive climate targets. However, large fossil fuel emissions reductions are still required, and there are substantial uncertainties, with little agreement about abatement magnitudes. Across the scenarios, land mitigation options contribute approximately 100 to 340 GtC equivalent abatement over the century, 15 to 40% of the total required for stabilization, with bioenergy providing up to 15% of total primary energy. Long-run land climate modeling is rapidly evolving with critical challenges to address. In characterizing current capability, this paper hopes to stimulate future research and the next generation of land modeling and provide a point of comparison for energy and climate policies considering bio-energy, reduced deforestation and degradation, and cost containment.
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