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Biogenic vs. geologic carbon emissions and forest biomass energy production
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n the current debate over the CO2 emissions implications of switching from fossil fuel energy sources to include a substantial amount of woody biomass energy, many scientists and policy makers hold the view that emissions from the two sources should not be equated. Their rationale is that the combustion or decay of woody biomass is simply part of the global cycle of biogenic carbon and does not increase the amount of carbon in circulation. This view is frequently presented as justification to implement policies that encourage the substitution of fossil fuel energy sources with biomass. We present the opinion that this is an inappropriate conceptual basis to assess the atmospheric greenhouse gas (GHG) accounting of woody biomass energy generation. While there are many other environmental, social, and economic reasons to move to woody biomass energy, we argue that the inferred benefits of biogenic emissions over fossil fuel emissions should be reconsidered.
Keywords: bioenergy emissions, biogenic carbon, carbon debt, forest biomass, greenhouse gas accounting
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The outcome is in the assumptions: analyzing the effects on atmospheric CO2 levels of increased use of bioenergy from forest biomass
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Recently, several studies have quantified the effects on atmospheric CO2 concentration of an increased harvest level in forests. Although these studies agreed in their estimates of forest productivity, their conclusions were contradictory. This study tested the effect of four assumptions by which those papers differed. These assump- tions regard (1) whether a single or a set of repeated harvests were considered, (2) at what stage in stand growth harvest takes place, (3) how the baseline is constructed, and (4) whether a carbon-cycle model is applied. A main finding was that current and future increase in the use of bioenergy should be studied considering a series of repeated harvests. Moreover, the time of harvest should be determined based on economical principles, thus taking place before stand growth culminates, which has implications for the design of the baseline scenario. When the most realistic assumptions are used and a carbon-cycle model is applied, an increased harvest level in forests leads to a permanent increase in atmospheric CO2 concentration.
Keywords: atmosphere, bioenergy, carbon, climate change, Faustmann, impulse response functions
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Mineral soil carbon fluxes in forests and implications for carbon balance assessments
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Forest carbon cycles play an important role in efforts to understand and mitigate climate change. Large amounts of carbon (C) are stored in deep mineral forest soils, but are often not considered in accounting for global C fluxes because mineral soil C is commonly thought to be relatively stable. We explore C fluxes associated with forest management practices by examining existing data on forest C fluxes in the northeastern US. Our findings demonstrate that mineral soil C can play an important role in C emissions, especially when considering inten- sive forest management practices. Such practices are known to cause a high aboveground C flux to the atmo- sphere, but there is evidence that they can also promote comparably high and long-term belowground C fluxes. If these additional fluxes are widespread in forests, recommendations for increased reliance on forest biomass may need to be reevaluated. Furthermore, existing protocols for the monitoring of forest C often ignore mineral soil C due to lack of data. Forest C analyses will be incomplete until this problem is resolved.
Keywords: carbon accounting, deep soil mineral carbon, Forest carbon pool assessments, forest soil, stand level carbon dynamics
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Methane emissions from sheep pasture, measured with an open-path eddy covariance system
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Methane (CH4) is an important greenhouse gas, contributing 0.4–0.5 W m␣2 to global warming. Methane emissions originate from several sources, including wetlands, rice paddies, termites and ruminating animals. Previous measure- ments of methane flux from farm animals have been carried out on animals in unnatural conditions, in laboratory chambers or fitted with cumbersome masks. This study introduces eddy covariance measurements of CH4, using the newly developed LI-COR LI-7700 open-path methane analyser, to measure field-scale fluxes from sheep grazing freely on pasture. Under summer conditions, fluxes of methane in the morning averaged 30 nmol m␣2 s␣1, whereas those in the afternoon were above 100 nmol m␣2 s␣1, and were roughly two orders of magnitude larger than the small methane emissions from the soil. Methane emissions showed no clear relationship with air temperature or photo- synthetically active radiation, but some diurnal pattern was apparent, probably linked to sheep grazing behaviour and metabolism. Over the measurement period (days 60–277, year 2010), cumulative methane fluxes were 0.34 mol CH4 m␣2, equating to 134.3 g CO2 equivalents m␣2. By comparison, a carbon dioxide (CO2) sink of 819 g CO2 equivalents m␣2 was measured over the same period, but it is likely that much of this would be released back to the atmosphere during the winter or as off-site losses (through microbial and animal respiration). By dividing methane fluxes by the number of sheep in the field each day, we calculated CH4 emissions per head of livestock as 7.4 kg CH4 sheep␣1 yr␣1, close to the published IPCC emission factor of 8 kg CH4 sheep␣1 yr␣1.
Keywords: agriculture, carbon sink, closed path, CO2 flux, global warming potential, grassland, grazing, grazing system
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Temperature-growth divergence in white spruce forests of Old Crow Flats, Yukon Territory, and adjacent regions of northwestern North America
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We present a new 23-site network of white spruce ring-width chronologies near boreal treeline in Old Crow Flats, Yukon Territory, Canada. Most chronologies span the last 300 years and some reach the mid-16th century. The chro- nologies exhibit coherent growth patterns before the 1930s. However, since the 1930s, they diverge in trend and exhibit one of two contrasting, but well-replicated patterns we call Group 1 and Group 2. Over the instrumental per- iod (1930–2007) Group 1 sites were inversely correlated with previous-year July temperatures while Group 2 sites were positively correlated with growth-year June temperatures. At the broader northwestern North America (NWNA) scale, we find that the Group 1 and Group 2 patterns are common to a number of white spruce chronolo- gies, which we call NWNA 1 and NWNA 2 chronologies. The NWNA 1 and NWNA 2 chronologies also share a sin- gle coherent growth pattern prior to their divergence (ca. 1950s). Comparison of the NWNA 1/NWNA 2 chronologies against gridded 20th-century temperatures for NWNA and reconstructed northern hemisphere sum- mer temperatures (AD 1300–2000) indicates that all sites responded positively to temperature prior to the mid-20th century (at least back to AD 1300), but that some changed to a negative response (NWNA 1) while others maintained a positive response (NWNA 2). The spatial extent of divergence implies a large-scale forcing. As the divergence appears to be restricted to the 20th century, we suggest that the temperature response shift represents a moisture stress caused by an anomalously warm, dry 20th-century climate in NWNA, as indicated by paleoclimatic records. However, because some sites do not diverge and are located within a few kilometres of divergent sites, we specu- late that site-level factors have been important in determining the susceptibility of sites to the large-scale drivers of divergence.
Keywords: boreal treeline, dendroclimatology, divergence, Old Crow Flats, ring-width, white spruce, Yukon Territory
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Fragmentation and thermal risks from climate change interact to affect persistence of native trout in the Colorado River basin
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Impending changes in climate will interact with other stressors to threaten aquatic ecosystems and their biota. Native Colorado River cutthroat trout (CRCT; Oncorhynchus clarkii pleuriticus) are now relegated to 309 isolated high- elevation (>1700 m) headwater stream fragments in the Upper Colorado River Basin, owing to past nonnative trout invasions and habitat loss. Predicted changes in climate (i.e., temperature and precipitation) and resulting changes in stochastic physical disturbances (i.e., wildfire, debris flow, and channel drying and freezing) could further threaten the remaining CRCT populations. We developed an empirical model to predict stream temperatures at the fragment scale from downscaled climate projections along with geomorphic and landscape variables. We coupled these spa- tially explicit predictions of stream temperature with a Bayesian Network (BN) model that integrates stochastic risks from fragmentation to project persistence of CRCT populations across the upper Colorado River basin to 2040 and 2080. Overall, none of the populations are at risk from acute mortality resulting from high temperatures during the warmest summer period. In contrast, only 37% of populations have a ! 90% chance of persistence for 70 years (simi- lar to the typical benchmark for conservation), primarily owing to fragmentation. Populations in short stream frag- ments <7 km long, and those at the lowest elevations, are at the highest risk of extirpation. Therefore, interactions of stochastic disturbances with fragmentation are projected to be greater threats than warming for CRCT populations. The reason for this paradox is that past nonnative trout invasions and habitat loss have restricted most CRCT popula- tions to high-elevation stream fragments that are buffered from the potential consequences of warming, but at risk of extirpation from stochastic events. The greatest conservation need is for management to increase fragment lengths to forestall these risks.
Keywords: climate change, cutthroat trout, fragmentation, multiple stressors, native fish, stream temperature model, stream warming
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Comparing carbon sequestration in temperate freshwater wetland communities
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High productivity and waterlogged conditions make many freshwater wetlands significant carbon sinks. Most wet- land carbon studies focus on boreal peatlands, however, with less attention paid to other climates and to the effects of hydrogeomorphic settings and the importance of wetland vegetation communities on carbon sequestration. This study compares six temperate wetland communities in Ohio that belong to two distinct hydrogeomorphic types: an isolated depressional wetland site connected to the groundwater table, and a riverine flow-through wetland site that receives water from an agricultural watershed. Three cores were extracted in each community and analyzed for total carbon content to determine the soil carbon pool. Sequestration rates were determined by radiometric dating with 137Cs and 210Pb on a set of composite cores extracted in each of the six communities. Cores were also extracted in uplands adjacent to the wetlands at each site. Wetland communities had accretion rates ranging from 3.0 to 6.2 mm yr␣1. The depressional wetland sites had higher (P < 0.001) organic content (146 ± 4.2 gC kg␣1) and lower (P < 0.001) bulk density (0.55 ± 0.01 Mg m␣3) than the riverine ones (50.1 ± 6.9 gC kg␣1 and 0.74 ± 0.06 Mg m␣3). The soil carbon was 98–99% organic in the isolated depressional wetland communities and 85–98% organic in the riv- erine ones. The depressional wetland communities sequestered 317 ± 93 gC m␣2 yr␣1, more (P < 0.01) than the river- ine communities that sequestered 140 ± 16 gC m␣2 yr␣1. The highest sequestration rate was found in the Quercus palustris forested wetland community (473 gC m␣2 yr␣1), while the wetland community dominated by water lotus (Nelumbo lutea) was the most efficient of the riverine communities, sequestering 160 gC m␣2 yr␣1. These differences in sequestration suggest the importance of addressing wetland types and communities in more detail when assessing the role of wetlands as carbon sequestering systems in global carbon budgets.
Keywords: 137Cs, 210Pb, carbon accumulation, Gahanna Woods, Nelumbo lutea, Old Woman Creek, Phragmites australis, Quercus palustris, wetland community, wetland hydrgeomorphology
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Linking forest fires to lake metabolism and carbon dioxide emissions in the boreal region of Northern Quebec
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Natural fires annually decimate up to 1% of the forested area in the boreal region of Que ́bec, and represent a major structuring force in the region, creating a mosaic of watersheds characterized by large variations in vegetation structure and composition. Here, we investigate the possible connections between this fire-induced watershed heterogeneity and lake metabolism and CO2 dynamics. Plankton respiration, and water–air CO2 fluxes were measured in the epilimnia of 50 lakes, selected to lie within distinct watershed types in terms of postfire terrestrial succession in the boreal region of Northern Que ́ bec. Plankton respiration varied widely among lakes (from 21 to 211lgCL1day1), was negatively related to lake area, and positively related to dis- solved organic carbon (DOC). All lakes were supersaturated in CO2 and the resulting carbon (C) flux to the atmosphere (150 to over 3000 mg C m2 day1) was negatively related to lake area and positively to DOC concentration. CO2 fluxes were positively related to integrated water column respiration, suggesting a biological component in this flux. Both respiration and CO2 fluxes were strongly negatively related to years after the last fire in the basin, such that lakes in recently burnt basins had significantly higher C emissions, even after the influence of lake size was removed. No significant differences were found in nutrients, chlorophyll, and DOC between lakes in different basin types, suggesting that the fire-induced watershed features influence other, more subtle aspects, such as the quality of the organic C reaching lakes. The fire-induced enhancement of lake organic C mineralization and C emissions represents a long-term impact that increases the overall C loss from the landscape as the result of fire, but which has never been included in current regional C budgets and future projections. The need to account for this additional fire-induced C loss becomes critical in the face of predictions of increasing incidence of fire in the circumboreal landscape.
Keywords: boreal, carbon dioxide flux, climate, forest fire, lakes, organic carbon, plankton respiration, watershed
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Climate change, income and happiness: An empirical study for Barcelona
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The present article builds upon the results of an empirical study exploring key factors which determine life satisfaction in Barcelona. Based on a sample of 840 individuals we first look at the way changes in income, notably income reductions, associated with the current economic situation in Spain, affect subjective well-being. Income decreases which occur with respect to one year ago have a negative effect on happiness when specified in logarithmic terms, and a positive one when specified as a dummy variable (and percentage change). The divergence in results is discussed and various explanations are put forward. Both effects are however temporary and do not hold for a period longer than a year, probably for reasons of adaptation and a downward adjustment of reference consumption and income levels. Next, we examine the implications of experiencing forest fires and find a lasting negative effect on life satisfaction. Our results suggest that climate policy need not reduce happiness in the long run, even when it reduces income and carbon-intensive consumption. Climate policy may even raise life well- being, if accompanied by compensatory measures that decrease formal working hours and reference consumption standards, while maintaining employment security.
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Potential of geoengineering highly uncertain
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1st paragraph: Despite having the knowledge and tools to dial back greenhouse gas emissions from fossil fuel burning and land-use change, humanity seems on track to continue with business as usual, concludes Geoengineering the climate: Science, governance and un- certainty, a report from the U.K.’s Royal Society. The report emphasizes that emissions reductions re- main the first priority for mitigating global warming, but geoengineering could play a role as a tool of last resort in the face of a future climate crisis. And so, we’d better learn something about it.
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