Increased Transparency in Accounting Conventions Could Benefit Climate Policy

Allocation issues in LCA methodology: a case study of corn stover-based fuel ethanol

Implications of removing straw from soil for bioenergy: An LCA of ethanol production using total sugarcane biomass

<p>For the 1960-2000 period, the latest generation of climate models (CMIP6) shows less global mean surface temperature change relative to pre-industrial than that seen in observations. In contrast, the previous generation of models (CMIP5) warmed in line with observations over this period. It has been hypothesised that this suppressed late-20th Century warming seen in CMIP6 is caused by a stronger aerosol effective radiative forcing (ERF) than in CMIP5. We investigate the role that historical ERF plays in historical global mean warming. </p><p>To diagnose the historical ERF we determine the climate feedback parameter from regression of top-of-atmosphere energy imbalance against temperature in abrupt-4xCO<sub>2</sub> runs and use the diagnosed climate feedback values in the historical simulations from the same models. We evaluate the historical ERF in 35 CMIP6 and 27 CMIP5 models. We show that this method to estimate ERF is a fairly good approximation to more accurate estimates using atmosphere-only integrations from the Radiative Forcing Model Intercomparison Project (RFMIP). The agreement with RFMIP is best in those models with little or no time dependence (curvature) in their climate feedback parameter. However, the historical ERF estimate can be improved by considering the non-linearity in climate feedbacks. To do this we repeat the process using a three time-constant regression model, showing that this method gives results that are much closer to RFMIP in those models that perform poorly with the one-parameter model.</p><p>Under both the one- and three-parameter methods, we show that total historical ERF is lower in CMIP6 than in CMIP5 for 1960-2000. This lower forcing at first appears to explain the differences in warming between the CMIP6 and CMIP5 ensembles. To dive deeper into the contribution to historical forcing we also estimate ERF contributions from greenhouse gases, other anthropogenic forcers (including aerosols), and natural forcing in the subset of CMIP6 and CMIP5 models that performed experiments from the Detection and Attribution Model Intercomparison Project (DAMIP). The causes are a stronger negative aerosol ERF and weaker positive greenhouse gas ERF in CMIP6 compared to CMIP5. However, these forcing differences are amplified by differences in climate sensitivity between the CMIP5 and CMIP6 ensemble, which leads to both a stronger aerosol cooling over 1960-1990 and a stronger greenhouse gas induced warming from 1990 in CMIP6.</p>

Soil–air greenhouse gas fluxes influenced by farming practices in reservoir drawdown area: A case at the Three Gorges Reservoir in China

Net exchanges of CO2, CH4 and N2O between marshland and the atmosphere in Northeast China as influenced by multiple global environmental changes

Abstract. The concept of Global Warming Potentials (GWPs) has been extensively used in policy consideration as a relative index for comparing the climate impact of an emitted greenhouse gas (GHG), relative to carbon dioxide with equal mass emissions. Ozone depletion due to emission of chlorinated or brominated halocarbons leads to cooling of the climate system in the opposite direction to the direct warming contribution by halocarbons as GHGs. This cooling is a key indirect effect of the halocarbons on climatic radiative forcing, which is accounted for by indirect GWPs. With respect to climate, it is critical to understand net influences considering direct warming and indirect cooling effects especially for Halons due to the greater ozone-depleting efficiency of bromine over chlorine. Until now, the indirect GWPs have been calculated using a parameterized approach based on the concept of Equivalent Effective Stratospheric Chlorine (EESC) and the observed ozone depletion over the last few decades. As a step towards obtaining indirect GWPs through a more robust approach, we use atmospheric models to explicitly calculate the indirect GWPs of Halon-1211 and Halon-1301 for a 100-year time horizon. State-of-the-art global chemistry-transport models (CTMs) were used as the computational tools to derive more realistic ozone depletion changes caused by an added pulse emission of the two major Halons at the surface. The radiative forcings on climate from the ozone changes have been calculated for indirect GWPs using an atmospheric radiative transfer model (RTM). The simulated temporal variations of global average total column Halons after a pulse perturbation follow an exponential decay with an e-folding time which is consistent with the expected chemical lifetimes of the Halons. Our calculated indirect GWPs for the two Halons are much smaller than those from past studies but are within a single standard deviation of WMO (2007) values and the direct GWP values derived agree with the published values. Our model-based assessment of the Halon indirect GWPs thus confirms the significant importance of indirect effects on climate.

Global warming and mitigation potential of milk and meat production in Lombardy (Italy)

Agricultural land use and management practices affect the global climate due to greenhouse gas (GHG) fluxes and changes in land surface properties. Increased albedo has the potential to counteract the radiative forcing and warming effect of emitted GHGs. Thus considering albedo could be important to evaluate and improve agricultural systems in light of climate change, but the albedo of individual practices is usually not known. This study quantified the albedo of individual crops under regional conditions, and evaluated the importance of albedo change for the climate impact of current crop production using life cycle assessment (LCA). Seven major crops in southern Sweden were assessed relative to a land reference without cultivation, represented by semi-natural grassland. Crop-specific albedo data were obtained from a MODIS product (MCD43A1 v6), by combining its spatial response pattern with geodata on agricultural land use 2011–2020. Fluxes of GHGs were estimated using regional data and models, including production of inputs, field operations, and soil nitrogen and carbon balances. Ten-year mean albedo was 6–11% higher under the different crops than under the reference. Crop-specific albedo varied between years due to weather fluctuations, but differences between crops were largely consistent. Increased albedo countered the GHG impact from production of inputs and field operations by 17–47% measured in GWP100, and the total climate impact was warming. Using a time-dependent metric, all crops had a net cooling impact on global mean surface temperature on shorter timescales due to albedo (3–12 years under different crops), but a net warming impact on longer timescales due to GHG emissions. The methods and data presented in this study could support increasingly comprehensive assessments of agricultural systems. Further research is needed to integrate climatic effects of land use on different spatial and temporal scales, and direct and indirect consequences from a systems perspective.

The effective radiative forcing (ERF) is a robust predictor of future equilibrium warming. It is generally assumed that the ERF depends only on changes in atmospheric constituents and is independent of the background climate state. Building on recent work demonstrating that, in contrast, the instantaneous radiative forcing (IRF) for CO2 is strongly state-dependent, we show that the ERF for CO2 also increases in warmer climate states. We analyse a 4×CO2 atmosphere-only forcing in both control and warmer climate states in eight CMIP6-era models. Four models participated in the Cloud Feedback Model Intercomparison Project (CFMIP) which used pre-industrial SSTs in its control state and SSTs from near the end of the same model’s coupled abrupt-4×CO2 run in its warm state. In the other four models we used an AMIP climatology as the control state and a uniform increase in SSTs of 4 K above this AMIP climatology in the warm state. All eight models show an increase in 4×CO2 ERF, ranging from 0.1-0.5 W m-2, translating to a relative increase of 0.02-0.09 W m-2 K-1 or 0.2-1.1 % K-1. The increase is statistically significant in five of the eight models.Our findings have implications for derivation of simplified relationships of climate warming, for instance in the calculations of global warming metrics and in economic models, from which future climate change risks being underpredicted without a temperature adjustment.We also run aerosol forcing experiments under the +4 K climate, for which there is less agreement between models, but some show large changes in aerosol ERF under the warmer climate state, with potential implications for our ability to discern transient warming even with a more accurate understanding of present-day aerosol forcing. 

Effective radiative forcing (ERF) is evaluated in the ACCESS1.0 General Circulation Model (GCM) with fixed land and sea‐surface‐temperatures (SST) as well as sea‐ice. The 4xCO 2 ERF is 8.0 W m −2 . In contrast, a typical ERF experiment with only fixed SST and sea‐ice gives rise to an ERF of only 7.0 W m −2 . This difference arises due to the influence of land warming in the commonly used fixed‐SST ERF experimental design, which results in: (i) increased emission of longwave radiation to space from the land surface (−0.45 W m −2 ) and troposphere (−0.90 W m −2 ), (ii) reduced land snow‐cover and albedo (+0.17 W m −2 ), (iii) increased water‐vapor (+0.49 W m −2 ), and (iv) a cloud adjustment (−0.26 W m −2 ) due to reduced stability and cloudiness over land (positive ERF) counteracted by increased lower tropospheric stability and marine cloudiness over oceans (negative ERF). The sum of these radiative adjustments to land warming is to reduce the 4xCO 2 ERF in fixed‐SST experiments by ∼1.0 W m −2 . CO 2 stomatal effects are quantified and found to contribute just over half of the land warming effect and adjustments in the fixed‐SST ERF experimental design in this model. The basic physical mechanisms in response to land warming are confirmed in a solar ERF experiment. We test various methods that have been proposed to account for land warming in fixed‐SST ERFs against our GCM results and discuss their strengths and weaknesses.

Review of comparative LCAs of food waste management systems – Current status and potential improvements

Identifying rice varieties for mitigating methane and nitrous oxide emissions under intermittent irrigation

<p>It is crucial to reduce uncertainties in our understanding of the climate impacts of short‐lived climate forcers, in the context that their emissions/concentrations are anticipated to decrease significantly in the coming decades worldwide. Using the Community Earth System Model (CESM1), we performed time‐slice experiments to investigate the effective radiative forcing (ERF) and climate respons to 1970–2010 changes in well‐mixed greenhouse gases (GHGs), anthropogenic aerosols, and tropospheric and stratospheric ozone. Once the present‐day climate has fully responded to 1970–2010 changes in all forcings, both the global mean temperature and precipitation responses are twice as large as the transient ones, with wet regions getting wetter and dry regions drier. The temperature response per unit ERF for short‐lived species varies considerably across many factors including forcing agents and the magnitudes and locations of emission changes. This suggests that the ERF should be used carefully to interpret the climate impacts of short‐lived climate forcers. Changes in both the mean and the probability distribution of global mean daily precipitation are driven mainly by GHG increases. However, changes in the frequency distributions of regional mean daily precipitation are more strongly influenced by changes in aerosols, rather than GHGs. This is particularly true over Asia and Europe where aerosol changes have significant impacts on the frequency of heavy‐to‐extreme precipitation. Our results may help guide more reliable near‐future climate projections and allow us to manage climate risks more effectively.</p>

To date there is still a lack of reliable data on greenhouse gas emissions from drained fens needed to determine the climatic relevance of land use and land use change on peatlands and to supply the National Inventory Report for the German Greenhouse Gas Inventory. In this study we present the results of monthly‐based multiyear measurements of CO2, N2O and CH4 flux rates in two drained agriculturally used fen ecosystems in NW Germany (cropland and grassland) over a period of 4.5 y using transparent and opaque closed chambers. CO2 exchange was modelled at high resolution with temperature and photosynthetic active radiation. The measured and modelled values fit very well (R2 ≥ 0.93). Annual GHG and Global Warming Potential (GWP) balances were determined. Net CO2 emissions at the cropland and grassland sites were similarly high, taking into account changes in management; net ecosystem C balance amounted to about 4.0 to 5.0 Mg C ha−1 y−1. Emissions of N2O and CH4 were low at both sites. The mean GWP balance for a time frame of 100 y (GWP100) amounted to about 17.0 to 19.0 Mg CO2‐eq. ha−1 y−1. The unexpectedly low greenhouse gas emissions from the cropland site are attributed to the high water table and a change in crop management. The change from corn for silage to corn‐cob mix lead transiently to rather small greenhouse gas emissions. The study confirms the need for multiyear measurements taking climatic and management variation into account.

Characterizing greenhouse gas (GHG) emissions and global warming potential (GWP) has become a key step in the estimation of atmospheric GHG concentrations and their potential mitigation by cropland management. However, the impacts of organic amendments on GHG, GWP, and yield-scaled GWP on cropland have not been well documented. Here, we investigate four amendment treatments (no amendment, mineral fertilizers, and pig slurry or crop residue combined with mineral fertilizers) during a two-year field experiment in rain-fed wheat-maize cropping systems. The results show that the average annual cumulative methane (CH4) flux ranged from −2.60 to −2.97 kg·C·ha−1 while nitrous oxide (N2O) flux ranged from 0.44 to 4.58 kg·N·ha−1 across all four treatments. N2O emissions were significantly correlated with soil inorganic nitrogen (i.e., NH4+-N and NO3−-N), and soil dissolved organic carbon (DOC) during both the winter wheat and summer maize seasons. On average, organic amendments combined with mineral fertilizers increased the annual GWP by 26–74% and yield-scaled GWP by 19–71% compared to those under only mineral fertilizers application. This study indicates that the fertilization strategy for Eutric Regosols can shift from only mineral fertilizers to organic amendments combined with mineral fertilizers, which can help mitigate GHG emissions and GWP while maintaining crop yields.