Cumulative Radiative Forcing Research Articles

Evaluating cotton apparel with dynamic life cycle assessment: The climate benefits of temporary biogenic carbon storage

Static life cycle assessment (LCA) methodologies fail to consider the temporal profiles of system inputs and outputs (including emission timing), such that they underestimate the benefits of temporarily stored biogenic carbon in bioproducts, such as cotton. This research focuses on greenhouse gas emission timing and applies dynamic emission accounting to the life cycle of cotton woven pants. The significance of temporary biogenic carbon storage and emission timing is illustrated by converting the 2017 Cotton Incorporated static LCA to a dynamic model using the Dynamic Carbon Footprinter (baseline scenario). A reduction in cumulative radiative forcing for dynamic relative to static modeling of 22%, 5%, and 2% are observed at 10-years, 30-years, and 100-years, respectively. Alternative scenarios analyzed include converting cotton woven pants at end of life to bioenergy, to compost, or to building insulation, an alternative cotton production scenario using regenerative agricultural practices, and two pants extended lifetime scenarios. The regenerative agricultural practice scenario provides reductions in cumulative impacts compared to the baseline scenario of 96%, 69%, and 105% after 10, 30, and 100-years, respectively. A 3x extension in the lifetime of pants provides a benefit in reduced cumulative impacts of 31%, 40%, and 41%, after 10, 30, and 100-years, respectively. This case study with cotton demonstrates that dynamic LCA is a useful tool for assessing the benefits of biobased products, and it allows for more nuanced analysis of reductions in climate impacts in both the short- and long-term time horizons.

The climate benefits from cement carbonation are being overestimated

Rapid decarbonization of the cement industry is critical to meeting climate goals. Oversimplification of direct air capture benefits from hydrated cement carbonation has skewed the ability to derive decarbonization solutions. Here, we present both global cement carbonation magnitude and its dynamic effect on cumulative radiative forcing. From 1930–2015, models suggest approximately 13.8 billion metric tons (Gt) of CO2 was re-absorbed globally. However, we show that the slow rate of carbonation leads to a climate effect that is approximately 60% smaller than these apparent benefits. Further, we show that on a per kilogram (kg) basis, demolition emissions from crushing concrete at end-of-life could roughly equal the magnitude of carbon-uptake during the demolition phase. We investigate the sensitivity of common decarbonization strategies, such as utilizing supplementary cementitious materials, on the carbonation process and highlight the importance of the timing of emissions release and uptake on influencing cumulative radiative forcing. Given the urgency of determining effective pathways for decarbonizing cement, this work provides a reference for overcoming some flawed interpretations of the benefits of carbonation.

Volcanic forcing of high-latitude Northern Hemisphere eruptions

High-latitude explosive volcanic eruptions can cause substantial hemispheric cooling. Here, we use a whole-atmosphere chemistry-climate model to simulate Northern Hemisphere (NH) high-latitude volcanic eruptions of magnitude similar to the 1991 Mt. Pinatubo eruption. Our simulations reveal that the initial stability of the polar vortex strongly influences sulphur dioxide lifetime and aerosol growth by controlling the dispersion of injected gases after such eruptions in winter. Consequently, atmospheric variability introduces a spread in the cumulative aerosol radiative forcing of more than 20%. We test the aerosol evolution’s sensitivity to co-injection of sulphur and halogens, injection season, and altitude, and show how aerosol processes impact radiative forcing. Several of these sensitivities are of similar magnitude to the variability stemming from initial conditions, highlighting the significant influence of atmospheric variability. We compare the modelled volcanic sulphate deposition over the Greenland ice sheet with the relationship assumed in reconstructions of past NH eruptions. Our analysis yields an estimate of the Greenland transfer function for NH extratropical eruptions that, when applied to ice core data, produces volcanic stratospheric sulphur injections from NH extratropical eruptions 23% smaller than in currently used volcanic forcing reconstructions. Furthermore, the transfer function’s uncertainty, which propagates into the estimate of sulphur release, needs to be at least doubled to account for atmospheric variability and unknown eruption parameters. Our results offer insights into the processes shaping the climatic impacts of NH high-latitude eruptions and highlight the need for more accurate representation of these events in volcanic forcing reconstructions.

Climate effects of post-use wood materials from the building sector in a system perspective

This study investigates the climate change effects in terms of greenhouse gas emissions and radiative forcing resulting from different pathways of processing wood materials when they reach the end-of-life stage. The shares of combustion, landfill, recycling, and reuse, which vary with the pathways of post-use wood, influence the material and energy production systems. The dynamics of CO2 and CH4 emissions, together with the cumulative radiative forcing of each pathway, are evaluated from various regional system perspectives. The results show that the choice of a treatment pathway for post-use wood could strongly influence the profile of greenhouse gas emissions and, consequently, the global warming potential. Taking into account the situation of the reference material and energy production systems, the post-use wood can have unfavorable consequences for the climate, as in the case when the material and energy production systems are based on the low-carbon energy of natural gas. However, from the perspective where the treatment of post-use wood influences the quantity of forest biomass on the forest floor, the increased share of reuse and recycling contributes positively to the climate change mitigation, but only during the early stage. Under such a context, options relying on carbon capture and storage to handle biogenic CO2 emissions at energy conversion facilities could cause a cooling effect on the Earth's atmosphere.

Orphan No More—Federal Funds Begin Flowing to State Coffers for Orphan Well Remediation

Billions of dollars in federal funding secured under the 2021 Bipartisan Infrastructure Investment and Jobs Law (BIL) has started flowing into US state coffers for the plugging and remediation of orphan oil and gas wells. Signed into law in November 2021, the BIL is a $1.2 trillion “once-in-a-generation investment” that includes $4.7 billion in funding to plug and remediate orphan wells across the nation. According to the US Department of the Interior (DOI), these legacy pollution sites are environmental hazards and jeopardize public health and safety by contaminating groundwater, emitting noxious gases and methane, littering the landscape with rusted and dangerous equipment, and harming wildlife. The US Environmental Protection Agency (EPA) estimated in a 2020 inventory of greenhouse gas emissions that, on average, each unplugged abandoned oil and gas well emits 0.13 tons of methane per year. When multiplied by an estimated 2.1 million unplugged, abandoned oil and gas wells, the EPA estimated methane emissions of 276,472 tons in 2019, equivalent to roughly 9.5 mtpa of carbon dioxide (CO2) assuming a 100-year global warming potential (GWP) of 34. This is roughly 2.6% of total US energy-related methane emissions or roughly 0.2% of total US energy-related greenhouse gas emissions in 2019, assuming a 100-year GWP for methane of 34, according to a report published in Environmental Science & Technology. The Intergovernmental Panel on Climate Change defines GWP as the cumulative radiative forcing, both direct and indirect effects, over a specified time horizon resulting from the emission of a unit mass of gas related to some reference gas. While the EPA pegs the number of orphaned wells in the millions, there are variations in the count, depending on how each state or organization defines what is and is not an orphaned well. A survey, for example, by the Interstate Oil and Gas Compact Commission in 2018 put the range of orphaned and idle wells at around 560,000 to 1.1 million. According to the Railroad Commission of Texas (RRC), the regulatory body that oversees Texas oil and natural gas development, an orphan well is an inactive and unplugged well that has not produced oil or natural gas for a minimum of 12 months. But the Colorado Oil & Gas Conservation Commission defines an orphan as a well which has no owner or operator that can be found, or where the owner or operator is unwilling or unable to plug and abandon such a well. This JPT article described the hunt for the potentially hundreds of thousands of unknown, undocumented orphans across the country. In October 2021, the Environmental Defense Fund (EDF) released a map showing the location of more than 81,000 documented orphan wells in 28 states that are eligible for funding under the BIL. In the spring of 2022, thanks in part to states documenting more than 40,000 additional orphan wells, EDF released an updated map showing more than 120,000 documented orphan wells in 30 states (Fig. 1).

Lifecycle climate impact and primary energy use of electric and biofuel cargo trucks

AbstractHeavy trucks contribute significantly to climate change, and in 2020 were responsible for 7% of total Swedish GHG emissions and 5% of total global CO2emissions. Here we study the full lifecycle of cargo trucks powered by different energy pathways, comparing their biomass feedstock use, primary energy use, net biogenic and fossil CO2emission and cumulative radiative forcing. We analyse battery electric trucks with bioelectricity from stand‐alone or combined heat and power (CHP) plants, and pathways where bioelectricity is integrated with wind and solar electricity. We analyse trucks operated on fossil diesel fuel and on dimethyl ether (DME). All energy pathways are analysed with and without carbon capture and storage (CCS). Bioelectricity and DME are produced from forest harvest residues. Forest biomass is a limited resource, so in a scenario analysis we allocate a fixed amount of biomass to power Swedish truck transport. Battery lifespan and chemistry, the technology level of energy supply, and the biomass source and transport distance are all varied to understand how sensitive the results are to these parameters. We find that pathways using electricity to power battery electric trucks have much lower climate impacts and primary energy use, compared to diesel‐ and DME‐based pathways. The pathways using bioelectricity with CCS result in negative emissions leading to global cooling of the earth. The pathways using diesel and DME have significant and very similar climate impact, even with CCS. The robust results show that truck electrification and increased renewable electricity production is a much better strategy to reduce the climate impact of cargo transport than the adoption of DME trucks, and much more primary energy efficient. This climate impact analysis includes all fossil and net biogenic CO2emissions as well as the timing of these emissions. Considering only fossil emissions is incomplete and could be misleading.

A lifecycle comparison of natural resource use and climate impact of biofuel and electric cars

Here we compare the biomass feedstock use, primary energy use, net CO2 emission, and cumulative radiative forcing of passenger cars powered by different energy pathways. We consider the full lifecycle of the vehicles, including manufacture and operation. We analyze battery electric vehicles (BEVs) powered by standalone electricity generation using woody biomass, with and without CCS, and with integration of wind electricity. We analyze internal combustion vehicles (ICVs) powered by fossil gasoline and by biomethanol derived from woody biomass, with and without carbon capture and sequestration (CCS). Our system boundaries include all fossil and biogenic emissions from technical systems, and the avoided decay emissions from harvest residue left in the forest. We find that the pathways using electricity to power BEVs have strongly lower climate impacts, compared to the liquid-fueled ICV pathways using biomethanol and gasoline. The pathways using bioelectricity with CCS result in negative emissions leading to global cooling. The pathways using gasoline and biomethanol have substantial climate impact, even with CCS. Regardless of energy pathway, smaller cars have consistently lower climate impact than larger cars. These findings suggest that accelerating the current trend toward vehicle electrification, together with scaling up renewable electricity generation, is a wise strategy for climate-adapted passenger car transport.

Influence of material choice, renovation rate, and electricity grid to achieve a Paris Agreement-compatible building stock: A Portuguese case study

The thermal retrofit of buildings plays a key role to limit global warming. However, the spatial and temporal dynamics of urban-scale renovation are not well understood. This paper proposes a new methodology that is based on a bottom-up building stock model. It links dynamic Material Flow Analysis with dynamic Life Cycle Assessment to include the temporal dynamics of emissions and renovation activity, and the spatial dynamics of the building stock. Alternative renovation scenarios for a Lisbon neighborhood are analyzed over the next 100 years. Thee scenarios include renovation rates, electricity grid transformation and material choice: Conventional renovation systems are compared to bio-based systems (using cork, wood and straw). A need-based prioritization of poorly insulated buildings is suggested and the effect of different energy grid transitions analyzed. The results show that bio-based systems, especially made with fast-rotation biomass, are beneficial regarding radiative forcing. The straw- and wood-based system ("TES"), combined with an increased renovation rate, result in a cumulative radiative forcing of −45.4 * 10−8 kW/m2 for embodied impacts in 2050, compared to 3.5* 10−8 kW/m2 with a conventional system and a business-as-usual renovation rate. A fast and radical transition of the energy grid is crucial to meet the carbon budget to limit global warming to 2 °C.

Life-cycle assessment of climate change impact on time-dependent carbon-footprint of asphalt pavement

This study aims to quantify life-cycle carbon footprint of asphalt pavement due to warming temperatures under climate change scenario.Pavement Mechanistic-Empirical (ME) Design Method was used to simulate long-term pavement performance with historic and projected temperature inputs. Life-cycle assessment (LCA) was conducted to calculate CO2emissions in pavement life cycle including phases of raw materials, plant production, transportation, field construction, traffic delay, and use. In particular, time-dependency of CO2emission was considered with physical decay to increase the accuracy in estimating cumulative radiative forcing. It was found that warming temperatures would lead to faster structural deterioration of pavement, resulting in earlier or more frequent overlay treatments. Pavement rehabilitation treatments generate more CO2 emission in material and construction related stages but cause the reduction of CO2 emission in pavement use phase. The LCA results show that climate change causes greater CO2 emission abundance over the years during the study period.

Climate effects of forestry and substitution of concrete buildings and fossil energy

Forests can help mitigate climate change in different ways, such as by storing carbon in forest ecosystems, and by producing a renewable supply of material and energy products. We analyse the climate implications of different scenarios for forestry, bioenergy and wood construction. We consider three main forestry scenarios for Kronoberg County in Sweden, over a 201-year period. The Business-as-usual scenario mirrors today's forestry while in the Production scenario the forest productivity is increased by 40% through more intensive forestry. In the Set-aside scenario 50% of forest land is set-aside for conservation. The Production scenario results in less net carbon dioxide emissions and cumulative radiative forcing compared to the other scenarios, after an initial period of 30–35 years during which the Set-aside scenario has less emissions. In the end of the analysed period, the Production scenario yields strong emission reductions, about ten times greater than the initial reduction in the Set-aside scenario. Also, the Set-aside scenario has higher emissions than Business-as-usual after about 80 years. Increasing the harvest level of slash and stumps results in climate benefits, due to replacement of more fossil fuel. Greatest emission reduction is achieved when biomass replaces coal, and when modular timber buildings are used. In the long run, active forestry with high harvest and efficient utilisation of biomass for replacement of carbon-intensive non-wood products and fuels provides significant climate mitigation, in contrast to setting aside forest land to store more carbon in the forest and reduce the harvest of biomass.

Evaluating climate change pathways through a building's lifecycle based on Dynamic Life Cycle Assessment

Climate change impact of a building was evaluated through a Dynamic Life Cycle Assessment (DLCA) methodology with the aim at demonstrating the feasibility of DLCA and the usefulness of such approach in the building sector. The methodology uses dynamic thermal simulation for energy consumption, databases for the building sector, a new developed database for temporal parameters of buildings, DyPLCA tool for dynamic LCI calculation. Clime change indicators were obtained in function of time for 500 years time span: radiative forcing, cumulated radiative forcing and global mean temperature change. Results revealed that each building component has its own climate footprint from which mitigation actions can be deduced. Results should always be placed in the climate context, in this case, the critical period 2030–2050, a turning point for limiting the temperature increase at 1.5 °C, with an objective of zero net emission beyond 2050. Dynamic indicators are well adapted for accounting the effect of biogenic CO2 and can be used to simulate strategies for GHGs neutralization. The main outcome of the comparison DLCA – LCA is that the results can be greatly different, especially when biogenic carbon is present (case of bio-based materials): i) the ranking and proportion of the contributors can change according to the time horizon for a given dynamic indicator (cumulative radiative forcing and global mean temperature change), ii) the ranking and proportion of the contributors can be different between the considered indicators, demonstrating the need of a more detailed assessment in the context of the imminent climate target.

Trends and patterns in the contributions to cumulative radiative forcing from different regions of the world

Different regions of the world have had different historical patterns of emissions of carbon dioxide, other greenhouse gases, and aerosols as well as different land-use changes. One can estimate the net cumulative contribution by each region to the global mean radiative forcing due to past greenhouse gas emissions, aerosol precursors, and carbon dioxide from land-use changes. Several patterns stand out from such calculations. Some regions have had a common historical pattern in which the short-term offsets between the radiative forcings from carbon dioxide and sulfate aerosols temporarily led to near-zero radiative forcing during periods of exponential emissions growth with few emission controls. This happened for North America and Europe in the mid-20th century and China in the 1990s and 2000s. However, these same periods lead to a commitment to future radiative forcing from the carbon dioxide and other greenhouse gases that stay in the atmosphere long after the aerosols. For every region, this commitment to future radiative forcing (2018-2100) from emissions already in the atmosphere is larger than the cumulative radiative forcing to date (1900-2017). This comparison again highlights how the full radiative forcing from greenhouse gases is unmasked once the aerosol emissions are reduced to improve air quality. The relative contributions from various regions to global climate forcing depends more on the time the contributions are compared (e.g., now or 2100) and future development scenarios than on whether cumulative radiative forcing, ocean heat content, or temperature is used to compare regional contributions.

Climate effects of electricity production fuelled by coal, forest slash and municipal solid waste with and without carbon capture

We analyse the climate implications of producing electricity in large-scale conversion plants using coal, forest slash and municipal solid waste with and without carbon capture and storage (CCS). We calculate the primary energy, carbon dioxide (CO2) and methane (CH4) emission profiles, and the cumulative radiative forcing (CRF) of different systems that produce the same amount of electricity. We find that using slash or waste for electricity production instead of coal somewhat increases the instantaneous CO2 emission from the power plant, but avoids significant subsequent emissions from decaying slash in forests or waste in landfills. For slash used instead of coal, we find robust near- and long-term reductions in total emissions and CRF. Climate effects of using waste instead of coal are more ambiguous: CRF is reduced when CCS is used, but without CCS there is little or no climate benefits of using waste directly for energy, assuming that landfill gas is recovered and used for electricity production. The application of CCS requires more fuel, but strongly reduces the CO2 emissions. The use of slash or waste together with CCS results in negative net emissions and CRF, i.e. global cooling.

A climate rationale for research and development on photovoltaics manufacture

Photovoltaic (PV) power generation is critical to many climate policy goals, as PV electricity results in little or no greenhouse gas (GHG) emissions during use, utilities and governments view PV installations as a way to accelerate progress towards emissions reduction targets. However, typical analyses of the GHG implications of the PV lifecycle ignore inter-temporal effects, in which the initial GHGs emitted in PV manufacturing phase must be offset by avoided fossil-fuel combustion emissions during use. Thus, the overall climate benefits of PV are a function of both GHG efficiency of PV manufacture, and electricity generation efficiency of deployed modules during use. Improvements to PV manufacture result in immediate climate benefits, in contrast with improvements in module efficiency which may offset greater GHG emissions, albeit over decades of useful life.This study presents a novel framework using the cumulative radiative forcing (CRF) metric to demonstrate the significant climate benefit of improving PV manufacturing processes predominantly located in GHG-intensive geographies and determines the equivalent increase in module efficiency that provide the same climate benefit. The findings show low-carbon PV manufacturing increases the life-cycle climate benefit by 20% and is equivalent to increasing the module efficiency from a baseline value of 17% to 21.7% and 16% to 18.7% for mono-Si and multi-Si modules, respectively. With commercial module efficiency having increased annually by only 0.25% over the last 12years, the implication is that improving PV manufacturing may be more effective than module efficiency improvements for increasing the climate benefit of terawatt scale PV installations.

Beyond Global Warming Potential: A Comparative Application of Climate Impact Metrics for the Life Cycle Assessment of Coal and Natural Gas Based Electricity

SummaryIn the ongoing debate about the climate benefits of fuel switching from coal to natural gas for power generation, the metrics used to model climate impacts may be important. In this article, we evaluate the life cycle greenhouse gas emissions of coal and natural gas used in new, advanced power plants using a broad set of available climate metrics in order to test for the robustness of results. Climate metrics included in the article are global warming potential, global temperature change potential, technology warming potential, and cumulative radiative forcing. We also used the Model for the Assessment of Greenhouse‐gas Induced Climate Change (MAGICC) climate‐change model to validate the results. We find that all climate metrics suggest a natural gas combined cycle plant offers life cycle climate benefits over 100 years compared to a pulverized coal plant, even if the life cycle methane leakage rate for natural gas reaches 5%. Over shorter time frames (i.e., 20 years), plants using natural gas with a 4% leakage rate have similar climate impacts as those using coal, but are no worse than coal. If carbon capture and sequestration becomes available for both types of power plants, natural gas still offers climate benefits over coal as long as the life cycle methane leakage rate remains below 2%. These results are consistent across climate metrics and the MAGICC model over a 100‐year time frame. Although it is not clear whether any of these metrics are better than the others, the choice of metric can inform decisions based on different societal values. For example, whereas annual temperature change reported may be a more relevant metric to evaluate the human health effects of increased heat, the cumulative temperature change may be more relevant to evaluate climate impacts, such as sea‐level rise, that will result from the cumulative warming.

Climate change impacts of power generation from residual biomass

The European Union relies largely on bioenergy to achieve its climate and energy targets for 2020 and beyond.We assess, using Attributional Life Cycle Assessment (A-LCA), the climate change mitigation potential of three bioenergy power plants fuelled by residual biomass compared to a fossil system based on the European power generation mix. We study forest residues, cereal straws and cattle slurry.Our A-LCA methodology includes: i) supply chains and biogenic-CO2 flows; ii) explicit treatment of time of emissions; iii) instantaneous and time-integrated climate metrics.Power generation from cereal straws and cattle slurry can provide significant global warming mitigation by 2100 compared to current European electricity mix in all of the conditions considered.The mitigation potential of forest residues depends on the decay rate considered. Power generation from forest logging residues is an effective mitigation solution compared to the current EU mix only in conditions of decay rates above 5.2% a−1. Even with faster-decomposing feedstocks, bioenergy temporarily causes a STR(i) and STR(c) higher than the fossil system.The mitigation potential of bioenergy technologies is overestimated when biogenic-CO2 flows are excluded. Results based solely on supply-chain emissions can only be interpreted as an estimation of the long-term (>100 years) mitigation potential of bioenergy systems interrupted at the end of the lifetime of the plant and whose carbon stock is allowed to accumulate back.Strategies for bioenergy deployment should take into account possible increases in global warming rate and possible temporary increases in temperature anomaly as well as of cumulative radiative forcing.

Time-dependent global warming impact of tree stump bioenergy in Sweden

Tree stump harvesting could significantly increase the amount of bioenergy feedstock that forestry can supply to substitute for fossil alternatives. However, the climate mitigation potential of using stumps for bioenergy has been debated due to their often long residence time in the forest caused by slow decomposition. This study evaluated the climate effect over time of utilising stumps for bioenergy using ecosystem forest carbon modelling and time-dependent LCA methodology, including uncertainties in soil carbon changes. Different climate impact metrics were used (global mean temperature change, global warming potential and cumulative radiative forcing) and evaluations were made for single harvest as well as continuous supply over a landscape. Stump harvesting scenarios for spruce forests across Sweden were simulated and the forest net carbon balance was estimated as the difference compared with a reference scenario where the stumps were left to decompose in the forest.The results showed that using stump residues from commercial forestry in Sweden gives a climate benefit when they substitute for fossil fuel, even in a shorter perspective of around two decades. The temperature impact from using stumps for bioenergy at the stand level peaked after 10–15years and then declined steadily to ∼15% of the maximum level during the following 4–5 decades. The remaining long-term climate impact was small compared to using fossil fuel. An immediate climate benefit was achieved when replacing fossil coal, whereas the parity time, i.e. the time to reach climate benefit was 12–16years (±2years) when replacing natural gas, depending on geographical location. For continuous supply of stump bioenergy over a landscape, the corresponding parity time was 22–28years. There was a higher impact on global climate for northern Sweden, although the absolute difference was small. Sensitivity analysis indicated a moderate additional climate warming effect from the soil disturbance caused by stump harvesting.

Using Common Boundaries to Assess Methane Emissions: A Life Cycle Evaluation of Natural Gas and Coal Power Systems

SummaryThere is consensus on the importance of upstream methane (CH4) emissions to the life cycle greenhouse gas (GHG) footprint of natural gas systems, but inconsistencies among recent studies explain why some researchers calculate a CH4 emission rate of less than 1% whereas others calculate a CH4 emission rate as high as 10%. These inconsistencies arise from differences in data collection methods, data collection time frames, and system boundaries. This analysis focuses on system boundary inconsistencies. Our results show that the calculated CH4 emission rate can increase nearly fourfold not by changing the magnitude of any particular emission source, but by merely changing the portions of the supply chain that are included within the system boundary. Our calculated CH4 emission rate for extraction through pipeline transmission is 1.2% for current practices. Our model allows us to identify GHG contributors in the upstream supply chain, but also allows us to tie upstream findings to complete life cycle scenarios. If applied to the life cycles of power systems and assessed in terms of cumulative radiative forcing, the upstream CH4 emission rate can be as high as 3.2% before the GHG impacts from natural gas power exceed those from coal power at any point during a 100‐year time frame.

The climate effect of increased forest bioenergy use in Sweden: evaluation at different spatial and temporal scales

Bioenergy from boreal forests managed for productive purposes (e.g., pulp, timber) is commonly held to offer attractive options for climate change mitigation. However, this view has been challenged in recent years. Carbon balances, cumulative radiative forcing, and average global temperature change have been calculated for a variety of bioenergy management regimes in Swedish forests, and the results support the view that an increased use of forest biomass for energy in Sweden can contribute to climate change mitigation, although methodological (e.g., spatial scales) and parameter value choices influence the results significantly. We show that the climate effect of forest‐based bioenergy depends on the forest ecosystems and management, including biomass extraction for bioenergy and other products, and how this management changes in response to anticipated market demands; and on the energy system effects, which determine the fossil carbon displacement and other greenhouse gas (GHG) mitigation effects of using forest biomass for bioenergy and other purposes. The public and private sectors are advised to consider information from comprehensive analyses that provide insights about energy and forest systems in the context of evolving forest product markets, alternative policy options, and energy technology pathways in their decision‐making processes. WIREs Energy Environ 2016, 5:351–369. doi: 10.1002/wene.178This article is categorized under: Bioenergy > Climate and Environment

Climate effects of bioenergy from forest residues in comparison to fossil energy

Forest residues can be left at the harvest site to gradually decompose, or can be collected for energy purposes. This study analyzes the primary energy and climate impacts of bioenergy systems where forest residues are collected and used for electricity, heat and transportation, compared to fossil-based energy systems where fossil fuels provide the same services while forest residues are left on site to decompose. Time profiles are elaborated of primary energy use and carbon dioxide emissions from various energy applications fulfilled by bioenergy or fossil energy systems. Different biological decay functions are considered based on process-based modeling and inventory data across various climate zones. For all scenarios, the changes in cumulative radiative forcing (CRF) are calculated over a 300-year period, to evaluate the short- and long-term contributions of forest residue to climate change mitigation. A life cycle perspective along the full energy chains is used to evaluate the overall effectiveness of each system. The results show largest primary energy and climate benefits when forest residues are collected and used efficiently for energy services. Using biomass to substitute fossil coal provides greater climate change mitigation benefits than substituting oil or fossil gas. Some bioenergy substitutions result in positive CRF, i.e. increased global warming, during an initial period. This occurs for relatively inefficient bioenergy conversion pathways to substitute less carbon intensive fossil fuels, e.g. biomotor fuel used to replace diesel. More beneficial bioenergy substitutions, such as efficiently replacing coal, result immediately in reduced CRF. Biomass decay rates and transportation distance have less influence on climate benefits.