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The severe impacts associated with recent record‐setting annual global temperatures elevate the need to accurately predict the hottest conditions that could occur even if the most ambitious decarbonization goals are achieved. We use convolutional neural networks (CNNs) to predict peak global warming from recent observed temperature maps and future cumulative CO2 emissions. For the SSP1‐1.9 decarbonization scenario there is >99% probability that mean global warming exceeds 1.5°C, approximately even odds that it reaches 2°C, and ∼90% probability that the hottest year globally exceeds 2023 by at least 0.5°C. Further, for the SSP2‐4.5 decarbonization scenario, there is >90% probability that the hottest annual global temperature anomaly is twice the 2023 anomaly. That our framework makes highly accurate out‐of‐sample predictions of the hottest historical year provides confidence in the predicted future probabilities, suggesting substantial risks from the extreme local conditions that are likely to result from globally hot years during rapid decarbonization. Plain Language Summary: Calendar year 2023 was the hottest year on record globally, reaching ∼1.5°C above the pre‐industrial. Many national, sub‐national and non‐state actors have articulated ambitious decarbonization goals to stabilize the global temperature. However, the intensifying impacts as individual years have approached 1.5°C have heightened the need to more accurately predict not just the mean warming but also the hottest years that could occur even in the context of rapid decarbonization. We train neural networks on an ensemble of global climate models and then use historical observations as input to the trained networks, thus constraining the uncertainty in climate model projections by using the current state of the climate system as the basis for a truly out‐of‐sample prediction. For the historical period, we find that, despite a wide range of climate sensitivities across global climate models, the neural networks make highly accurate predictions of the hottest historical year when given observed climate patterns as out‐of‐sample inputs. Predicting future warming under different cumulative emissions, we find that even if net‐zero emissions are achieved mid‐century, mean warming is virtually certain to exceed 1.5°C and has even odds of reaching 2°C, with high likelihood of individual years that are at least 0.5°C hotter than 2023. Key Points: We train CNNs to predict peak global warming given the map of recent annual temperatures and total additional CO2 emissionsEven if net‐zero emissions are reached mid‐century, mean warming is virtually certain to exceed 1.5°C, with even odds of 2°CThere is high likelihood of individual years that are at least 0.5°C hotter than 2023 even in the most ambitious decarbonization scenario [ABSTRACT FROM AUTHOR]

Agricultural waste can have a catastrophic impact on climate change, as it contributes significantly to greenhouse gas (GHG) emissions if not managed sustainably. Swine-digestate-manure-derived biochar may be one sustainable way to manage waste and tackle GHG emissions in temperate climatic conditions. The purpose of this study was to ascertain how such biochar could be used to reduce soil GHG emissions. Spring barley (Hordeum vulgare L.) and pea crops in 2020 and 2021, respectively, were treated with 25 t ha−1 of swine-digestate-manure-derived biochar (B1) and 120 kg ha−1 (N1) and 160 kg ha−1 (N2) of synthetic nitrogen fertilizer (ammonium nitrate). Biochar with or without nitrogen fertilizer substantially lowered GHG emissions compared to the control treatment (without any treatment) or treatments without biochar application. Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions were directly measured using static chamber technology. Cumulative emissions and global warming potential (GWP) followed the same trend and were significantly lowered in biochar-treated soils. The influences of soil and environmental parameters on GHG emissions were, therefore, investigated. A positive correlation was found between both moisture and temperature and GHG emissions. Thus, biochar made from swine digestate manure may be an effective organic amendment to reduce GHG emissions and address climate change challenges. [ABSTRACT FROM AUTHOR]

Agricultural waste can have a catastrophic impact on climate change, as it contributes significantly to greenhouse gas (GHG) emissions if not managed sustainably. Swine-digestate-manure-derived biochar may be one sustainable way to manage waste and tackle GHG emissions in temperate climatic conditions. The purpose of this study was to ascertain how such biochar could be used to reduce soil GHG emissions. Spring barley (Hordeum vulgare L.) and pea crops in 2020 and 2021, respectively, were treated with 25 t ha−1 of swine-digestate-manure-derived biochar (B1) and 120 kg ha−1 (N1) and 160 kg ha−1 (N2) of synthetic nitrogen fertilizer (ammonium nitrate). Biochar with or without nitrogen fertilizer substantially lowered GHG emissions compared to the control treatment (without any treatment) or treatments without biochar application. Carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) emissions were directly measured using static chamber technology. Cumulative emissions and global warming potential (GWP) followed the same trend and were significantly lowered in biochar-treated soils. The influences of soil and environmental parameters on GHG emissions were, therefore, investigated. A positive correlation was found between both moisture and temperature and GHG emissions. Thus, biochar made from swine digestate manure may be an effective organic amendment to reduce GHG emissions and address climate change challenges.

Energy for sustainable development requires replacing fossil fuel use by renewables. Such substitution is the kingpin of climate action. As per IPCC AR6 WG I latest report "limiting human-induced global warming requires limiting cumulative CO 2 emissions" and "every tonne of CO 2 emissions adds to global warming". In other words, climate action should focus on cumulative emissions and not on annual emissions. We need to shift the discourse from annual emissions to cumulated emissions. For example, in the Paris Agreement instead of the final level of emissions in 2030 as goals emphasis should have been on the cumulated emissions of the pathways till 2030. Responsibility for finance needs to be in that proportion. Moreover, an annual fee of even US$1 per ton from all countries big and small on their cumulated emissions from 1990 onwards incentivises them to reduce and postpone their emissions. Such a fee can currently raise annually at least US$ 733 billion for climate finance. Moreover, focusing on annual emissions can lead to a false sense of comfort that climate change is under control, whereas warming will continue even after net-zero is attained. • Cumulated emissions is a better scientific indicator to guide climate action and discourse than annual emissions. • It should be the measure for a country's mitigation responsibility and climate finance obligations. • A fee of one US$ per tCO2 from all countries for their cumulative emissions since 1990 can raise US$ 733 billion in 2020. • It would incentivize countries to postpone, reduce and increase negative emissions. • It can raise finance for domestic action, transfer resources to countries and purchase technology license for global goods. [ABSTRACT FROM AUTHOR]

Numerous local authorities are committed to constructing buildings to net-zero carbon emissions performance, and have declared carbon emergency, striving to reach carbon neutrality well before 2050. However, buildings in the UK are currently being designed and constructed to current building regulations which do not require net-zero performance, and these buildings will last well beyond 2050. This paper presents a case study of a housing development in Hertfordshire, UK, where a structured approach for achieving net-zero carbon performance homes was developed. The methodology was based on dynamic simulation modelling to design buildings which achieve net-zero operational emissions, and an industry standard inventory of carbon and energy database was used to evaluate embodied emissions in building materials. The approach comprised of developing dynamic simulation models to investigate the improvement in energy performance of the development through fabric-first approach, focusing on building envelope design prior to introducing renewable energy systems, in order to achieve operational net-zero carbon performance. Carbon emissions (operational and embodied) were investigated to assess the appropriateness of the deployed strategies. Dynamic simulation results combined with embodied emissions analysis illustrated that, by combining embodied and operational emissions, a net-zero carbon performance would be achievable by the 2050 target only if alternative building materials based on photosynthetic bio-composites are used. This analysis also highlighted the limitations of conventional retrofit interventions carried out 10 years after the construction as they resulted in increased embodied carbon emissions, thus lengthening the time period well beyond the 2050 target for achieving net-zero carbon performance. As the use of conventional materials appeared to delay the achievement of net-zero emissions by several decades, the only way to achieve net-zero targets before 2050 is to design new buildings to be carbon negative from the operational point of view and to use photosynthetic materials for their construction.

The idea of a global "carbon budget"—the cumulative amount of "allowable" carbon emissions to meet a global temperature target—has become established as a central concept in climate science and policy. As a concept explicitly aimed at mediating between scientific knowledge and policymaking, the carbon budget has always been actively positioned in relation to ongoing policy debates, but the specific forms this concept has taken have varied. This article reviews key contributions to the carbon budget literature from the 1980s until today, in order to identify how scientists have positioned the concept between the worlds of science and policy. Three main shifts are identified in how the policy relevance of the carbon budget is envisaged in the scientific literature. The shifts can be related in part to developments in climate science, and in part to changes in international climate policy. The history of the carbon budget thus illustrates how science and policy interacts to shape dominant understandings of how climate change can be known and governed. This article is categorized under:Climate, History, Society, Culture > Ideas and Knowledge [ABSTRACT FROM AUTHOR]

We exploit recent advances in climate science to develop a physically consistent, yet surprisingly simple, model of climate policy. It seems that key economic models have greatly overestimated the delay between carbon emissions and warming, and ignored the saturation of carbon sinks that takes place when the atmospheric concentration of carbon dioxide rises. This has important implications for climate policy. If carbon emissions are abated, damages are avoided almost immediately. Therefore it is optimal to reduce emissions significantly in the near term and bring about a slow transition to optimal peak warming, even if optimal steady-state/peak warming is high. The optimal carbon price should start relatively high and grow relatively fast. [ABSTRACT FROM AUTHOR]

During composting, a large number of odorous substances were produced, mainly containing ammonia, hydrogen sulfide and TVOCs (total volatile organic compounds). In order to control the odor produced during the composting process, composting experiment of pig manure and straw under different ventilation modes was carried out. The experiment has 3 treatments with the ventilation intensity of 0.1 m3/(min·m3), ventilated 5min every other 30 min (T1), ventilated 5min every other 15 min (T2), continuous ventilation (T3) in a forced ventilation device with 50 L compost materials. Pig manure and straw were mixed in a mass ratio of 5:2. The C/N ratio of the composting materials was 29 and moisture content was 63%. The static chamber method was used to monitor the emission concentration of ammonia, hydrogen sulfide, TVOCs, dimethyl disulfide and dimethyl trisulfide during the composting. Data acquisition was started after 25 minutes of ventilation in T1, after 10 minutes of ventilation in T2, and data acquisition completed within 5 minutes. The optimal ventilation frequency for reducing odor in composting was studied. The study showed that under the 3 treatments, the maximum emission concentration of ammonia in compost exceeded 150 mg/m3 for 22, 20 and 9 days; The maximum emission concentrations of hydrogen sulfide were 29.4, 18.89 and 10.3 mg/m3; The maximum emission volume fractions of TVOCs were 420.3×10-6, 382.7×10-6 and 326.5 ×10-6; The maximum emission concentrations of dimethyl disulfide were 1 730.1, 3 646.2 and 3 971.8 ng/L; The maximum emission concentrations of dimethyl trisulfate were 991.4, 6 678.8 and 1 883.4 ng/L, respectively. At the same time, the cumulative emissions of hydrogen sulfide per kilogram of dry pig manure and straw were 14.3, 13.5, 31.5 mg; The cumulative emissions of TVOCs per kilogram of dry materials were 1.26, 2.00 and 6.08 L; The cumulative emissions of dimethyl disulfide per kilogram of dry materials were 1.5, 4.3 and 10.6 mg; The cumulative emissions of dimethyl trisulfate per kilogram of dry materials were 0.37, 4.37 and 4.94 mg, respectively. Increasing the frequency of ventilation during composting can reduce the maximum concentrations of hydrogen sulfide and TVOCs. However, high frequency ventilation can increase the cumulative emissions of hydrogen sulfide, TVOCs, dimethyl disulfide and dimethyl trisulfide, compared with the concentration of odor emission, the cumulative amount of odor emission can better characterize the degree of odor harm to the environment. In this experiment, the reduction of cumulative odor emissions was used as the optimization objective. It was found that the optimal ventilation modes was ventilated 5 min every other 30 min. This study provides a reference for controlling odor in organic fertilizer production by changing ventilation mode. [ABSTRACT FROM AUTHOR]

Focusing on global mitigation pathways masks key aspects of technical, political, and social feasibility, which play out at the country level. We illustrate the dilemma between a "carbon law" (halving emissions every decade) at the global level and the nationally determined contributions submitted at the country level. Our results suggest that even if the United States, European Union, China, and India could strengthen their nationally determined contributions by 2050, the rest of the world is required to immediately change from their current course to a very rapid decrease in emissions reaching almost zero emissions by 2030, to achieve the Paris 2015 goal. The greatest mitigation challenges lie in the developing world. Real progress toward the Paris Agreement goal awaits an effective commitment by leading countries to undertake breakthrough research and development of low‐, zero‐, or even negative‐carbon‐emissions energy technologies that can be deployed at scale in the developing world. Key Points: Focusing on global mitigation pathways masks key aspects of technical, political, and social feasibility at the country levelEven if the United States, European Union, China, and India could strengthen their NDCs, the RoW would need to reach zero emissions by 2030 to achieve the Paris goal [ABSTRACT FROM AUTHOR]

Limiting global warming to 'well below' 2°C above pre-industrial levels and pursuing efforts to limit the temperature increase even further to 1.5°C is an integral part of the 2015 Paris Agreement. To achieve these aims, cumulative global carbon emissions after 2016 should not exceed 940 - 390 Gt of CO2 (for the 2°C target) and 167 - -48 Gt of CO2 (for the 1.5°C target) by the end of the century. This paper analyses the EU's cumulative carbon emissions in different models and scenarios (global models, EU-focused models and national carbon mitigation scenarios). Due to the higher reductions in energy use and carbon intensity of the end-use sectors in the national scenarios, we identify an additional mitigation potential of 26-37 Gt cumulative CO2 emissions up to 2050 compared to what is currently included in global or EU scenarios. These additional reductions could help to both reduce the need for carbon dioxide removals and bring cumulative emissions in global and EU scenarios in line with a fairness-based domestic EU budget for a 2°C target, while still remaining way above the budget for 1.5°C. [ABSTRACT FROM AUTHOR]

Urban areas represent key opportunities for mitigation efforts through supporting renewable energy systems, improving urban planning, and increasing resource efficiency. This research work develops two types of urban emissions scenarios in green growth-oriented contexts with and without local ambitions. These scenarios are further coupled with improvements in existing land use efficiencies and multi-dimensional analyses. The method is applied to 45 urban areas, including 15 cities that are selected as Mission Cities in Europe. Different urban emissions scenarios indicate possibilities for reducing 135.80 ± 0.87 MtCO 2 eq of annual urban consumption-based emissions in 2020 by 58.72 MtCO 2 eq in 2030 along a 100% renewable energy pathway. Urban land use efficiency scenarios are used to determine annual carbon dioxide sequestration penalties that range between 8.25 and 14.95 MtCO 2 in 2050 due to more built-up area in local biomes. Monte Carlo simulations support the analyses of urban emissions and sequestration penalties on a cumulative basis. Among illustrative scenario combinations, net cumulative urban emissions are 1725.93 MtCO 2 eq in the most favourable scenario that is 50.6% lower than those in the least favourable scenario. Multi-dimensional analyses based on a city index for benchmarking indicate an average improvement of 11.500 for Mission Cities with the quickest response for mitigation. The results have implications for guiding bold policy action and integrated urban planning to increase mitigation efforts for climate neutrality and sustainability. • 45 urban areas represent 135.80 ± 0.87 MtCO 2 eq of consumption-based emissions • Cumulative emissions can differ by 1.74 times in 2050 among green-growth scenarios • Built-up area can differ by up to 193.72 km2 in 2050 based on land use efficiencies • Annual sequestration penalties are ranging between 8.25 and 14.95 MtCO 2 in 2050 • Net cumulative urban emissions vary by up to 2.03 times among scenario combinations [ABSTRACT FROM AUTHOR]

A stylised analytical framework is used to show how the global carbon tax and the amount of untapped fossil fuel can be calculated from a simple rule given estimates of society's rate of time impatience and intergenerational inequality aversion, the extraction cost technology, the rate of technical progress in renewable energy and the future trend rate of economic growth. The predictions of the simple framework are tested in a calibrated numerical and more complex version of the integrated assessment model (IAM). This IAM makes use of the Oxford carbon cycle of Allen et al. (2009), which differs from DICE, FUND and PAGE in that cumulative emissions are the key driving force of changes in temperature. We highlight the importance of the speed and direction of technological change for the energy transition and how time impatience, intergenerational inequality aversion and expected trend growth affect the time paths of the optimal global carbon tax and the optimal amount of fossil fuel reserves to leave untapped. We also compare these with the adverse global warming trajectories that occur if no policy actions are taken. [ABSTRACT FROM AUTHOR]

Cofiring biomass with coal for power generation is an affordable and ready-to-deploy technology to help reduce carbon emissions and resolve residual biomass. Cofiring has not been widely applied in China primarily because of some practical limitations, i.e., biomass accessibility, technological and economic constraints, and lack of policy support. We identified the benefits of cofiring with consideration of these practical limitations based on Integrated Assessment Models. We found that China produces 1.82 Bts/year of biomass residues, 45% of which is waste. 48% of the unused biomass can be utilized without fiscal intervention and 70% can be utilized with the subsidized Feed-in-Tariffs for biopower and carbon trading. The average Marginal Abatement Cost of cofiring is twice that of China's current carbon price. Cofiring can help China create 153 billion yuan of farmers' income annually and reduce 5.3 Bts of Committed Cumulative Carbon Emissions (CCCEs, 2023-2030), contributing to the needed CCCE mitigations to China's overall sector and the power sector by 32 and 86%, respectively. About 201 GW of coal-fired fleets are not compliant with China's 2030 carbon-peaking goals, and 127 GW can be saved by implementing cofiring, representing 9.6% of the total fleets in 2030.

This paper defines the ‘2°C capital stock’ as the global stock of infrastructure which, if operated to the end of its normal economic life, implies global mean temperature increases of 2°C or more (with 50% probability). Using IPCC carbon budgets and the IPCC’s AR5 scenario database, and assuming future emissions from other sectors are compatible with a 2°C pathway, we calculate that the 2°C capital stock for electricity will be reached by 2017 based on current trends. In other words, even under the very optimistic assumption that other sectors reduce emissions in line with a 2°C target, no new emitting electricity infrastructure can be built after 2017 for this target to be met, unless other electricity infrastructure is retired early or retrofitted with carbon capture technologies. Policymakers and investors should question the economics of new long-lived energy infrastructure involving positive net emissions. [ABSTRACT FROM AUTHOR]

This paper explores the underlying development outcomes and cumulative emissions trajectories of 20 middle-income countries from Eastern Europe, Latin America, North Africa and South Asia. First, well-being outcomes are assessed, defined in terms of access to education, democratic and legal rights, and the infrastructures that support physical health. Second, emissions trajectories are estimated to 2050, taking into account current trends in energy consumption and carbon intensity, a likely start-date for stringent climate policy arising from the Paris Agreement (2020), and maximum feasible rates of mitigation. Comparing these estimates to a per capita allocation from the global carbon budget associated with 2 °C, ten countries have low-carbon development trends that will not exceed their allocation. Of these, Costa Rica and Uruguay are achieving very high well-being outcomes, while many more are delivering good outcomes in at least two domains of human need. However, most are seriously deficient in terms of social well-being (education, democratic and legal rights). These results call into question the socio-economic convergence of developing countries with industrialised countries; but they also reaffirm the low-emissions cost of extending good infrastructure access and physical health outcomes to all, demonstrated by the existence of multiple countries that continue to avoid carbon-intensive development. [ABSTRACT FROM AUTHOR]

Bioenergy is given an important role in reaching national and international climate change targets. However, uncertainties relating to emission reductions and the timeframe for these reductions are increasingly recognised as challenges whether bioenergy can deliver the required reductions. This paper discusses and highlights the challenges and the importance of the real greenhouse gas (GHG) reduction potential of bioenergy systems and its relevance for a global 450 ppm COe stabilisation target in terms of uncertainties and temporal aspects. The authors aim to raise awareness and emphasise the need for dynamic and consequential approaches for the evaluation of climate change impacts of bioenergy systems to capture the complexity and challenges of their real emission reduction potential within a 2 °C target. This review does not present new research results. This paper shows the variety of challenges and complexity of the problem of achieving real GHG emission reductions from bioenergy systems. By reflecting on current evaluation methods of emissions and impacts from bioenergy systems, this review points out that a rethinking and going beyond static approaches is required, considering each bioenergy systems according to its own characteristics, context and feedbacks. With the development of knowledge and continuously changing systems, policies should be designed in a way that they provide a balance between flexibility to adapt to new information and planning security for investors. These will then allow considering if a bioenergy system will deliver the required emission saving in the appropriate timeframe or not. [ABSTRACT FROM AUTHOR]

Carbon budgets provide a useful tool for policymakers to help meet the global climate targets, as they specify total allowable carbon emissions consistent with limiting warming to a given temperature threshold. Non-CO _2 forcings have a net warming effect in the Representative Concentration Pathways (RCP) scenarios, leading to reductions in remaining carbon budgets based on CO _2 forcing alone. Carbon budgets consistent with limiting warming to below 2.0 °C, with and without accounting for the effects of non-CO _2 forcings, were assessed in inconsistent ways by the Intergovernmental Panel on Climate Change (IPCC), making the effects of non-CO _2 forcings hard to identify. Here we use a consistent approach to compare 1.5 °C and 2.0 °C carbon budgets with and without accounting for the effects of non-CO _2 forcings, using CO _2 -only and RCP8.5 simulations. The median allowable carbon budgets for 1.5 °C and 2.0 °C warming are reduced by 257 PgC and 418 PgC, respectively, and the uncertainty ranges on the budgets are reduced by more than a factor of two when accounting for the net warming effects of non-CO _2 forcings. While our overall results are consistent with IPCC, we use a more robust methodology, and explain the narrower uncertainty ranges of carbon budgets when non-CO _2 forcings are included. We demonstrate that most of the reduction in carbon budgets is a result of the direct warming effect of the non-CO _2 forcings, with a secondary contribution from the influence of the non-CO _2 forcings on the carbon cycle. Such carbon budgets are expected to play an increasingly important role in climate change mitigation, thus understanding the influence of non-CO _2 forcings on these budgets and their uncertainties is critical.

The Environmental Research Letters focus issue on ‘Cumulative Emissions, Global Carbon Budgets and the Implications for Climate Mitigation Targets’ was launched in 2015 to highlight the emerging science of the climate response to cumulative emissions, and how this can inform efforts to decrease emissions fast enough to avoid dangerous climate impacts. The 22 research articles published represent a fantastic snapshot of the state-or-the-art in this field, covering both the science and policy aspects of cumulative emissions and carbon budget research. In this Review and Synthesis, we summarize the findings published in this focus issue, outline some suggestions for ongoing research needs, and present our assessment of the implications of this research for ongoing efforts to meet the goals of the Paris climate agreement.

Russia is the fifth highest emitter of carbon dioxide, having been in the top five for at least six decades. However, thus far no in-depth study has estimated Russia's cumulative emissions in the context of the global 2°C constraint. This is despite the IPCC reiterating the importance of cumulative emissions. Translating the global 2°C temperature commitment into a meaningful national context, this paper derives and evaluates 2°C-compatible carbon budgets for Russia, based on a range of apportionments. The work contributes to the debate by providing a deeper analysis of the principles of allocating carbon emissions to Russia. This analysis demonstrates how, if Russia is to make a fair contribution to global emission reductions in line with 2°C, its 2011–2100 cumulative emissions should stay within 20-26 Gt CO2, commensurate with a 37–52% probability of exceeding 2°C. If Russia continues to emit carbon dioxide at current annual levels, this budget will be “spent” by the mid-2020s. The carbon budget estimated here for Russia appears technically feasible, if extremely challenging. Despite continuing to assert itself as a fossil fuel superpower, Russia has a wealth of opportunities for full and early decarbonization, including the potential to become a net exporter of renewable energy. [ABSTRACT FROM AUTHOR]

For over 20 years, Parties to the UN Framework Convention on Climate Change have struggled with the normative significance of history for the differentiation of responsibilities. Negotiations on ‘historical responsibility’ have been marked by considerable conflict between developed and developing countries. However, in 2010, the Parties acknowledged the concept in a consensus decision. This article analyses UN Climate Change Conference delegates' agreement with the decision, whether it reconciled conflict between interpretations of historical responsibility, and the significance that delegates ascribe to the decision for future agreements. The decision has not eliminated conflict between different interpretations. Delegates who understand historical responsibility as linking countries' historical contributions to climate change to their responsibilities to act agree more with the decision and foresee it having a stronger influence on future agreements than do those viewing the concept in more conceptual terms. The decision marks the start of negotiations concerninghowrather thanwhetherhistorical responsibility should guide operative text. This article demonstrates that (1) the divergent interpretations pose clear challenges for a necessary but demanding agreement on operationalization, and (2) focusing on an ambiguous version of proportionality between contribution to change and responsibility can become a first step for convergence between divergent positions. [ABSTRACT FROM PUBLISHER]

Understanding how the emergence of the anthropogenic warming signal from the noise of internal variability translates to changes in extreme event occurrence is of crucial societal importance. By utilising simulations of cumulative carbon dioxide (CO _2 ) emissions and temperature changes from eleven earth system models, we demonstrate that the inherently lower internal variability found at tropical latitudes results in large increases in the frequency of extreme daily temperatures (exceedances of the 99.9th percentile derived from pre-industrial climate simulations) occurring much earlier than for mid-to-high latitude regions. Most of the world’s poorest people live at low latitudes, when considering 2010 GDP-PPP per capita; conversely the wealthiest population quintile disproportionately inhabit more variable mid-latitude climates. Consequently, the fraction of the global population in the lowest socio-economic quintile is exposed to substantially more frequent daily temperature extremes after much lower increases in both mean global warming and cumulative CO _2 emissions.

We investigate the extent to which global mean temperature, precipitation, and the carbon cycle are constrained by cumulative carbon emissions throughout four experiments with a fully coupled climate–carbon cycle model. The paired experiments adopt contrasting, idealised approaches to climate change mitigation at different action points this century, with total emissions rising to more than two trillion tonnes of carbon (TtC). For each pair, the contrasting mitigation approaches—capping emissions early versus reducing them to zero a few decades later—cause their cumulative emissions trajectories to diverge initially, then converge, cross, and diverge again. We find that global mean temperature is linear with cumulative emissions across all experiments, although differences of up to 1.5 K exist regionally when the trajectories of total carbon emitted during the course of the two scenarios coincide, for both pairs of experiments. Interestingly, although the oceanic precipitation response scales with cumulative emissions, the global precipitation response does not, due to a decrease in precipitation over land above emissions of around one TtC. Most carbon fluxes are less well constrained by cumulative emissions as they reach two trillion tonnes. The opposing mitigation approaches have different consequences for the Amazon rainforest, which affects the linearity with which the carbon cycle responds to cumulative emissions. The average Transient Climate Response to cumulative carbon Emissions (TCRE) is 1.95 K TtC ^−1 , at the upper end of the Intergovernmental Panel on Climate Change’s range of 0.8–2.5 K TtC ^−1 .

Recent research has demonstrated that global mean surface air warming is approximately proportional to cumulative CO _2 emissions. This proportional relationship has received considerable attention, as it allows one to calculate the cumulative CO _2 emissions (‘carbon budget’) compatible with temperature targets and is a useful measure for model inter-comparison. Here we use an Earth system model to explore whether this relationship persists during periods of net negative CO _2 emissions. Negative CO _2 emissions are required in the majority of emissions scenarios limiting global warming to 2 °C above pre-industrial, with emissions becoming net negative in the second half of this century in several scenarios. We find that for model simulations with a symmetric 1% per year increase and decrease in atmospheric CO _2 , the temperature change (Δ T ) versus cumulative CO _2 emissions (CE) relationship is nonlinear during periods of net negative emissions, owing to the lagged response of the deep ocean to previously increasing atmospheric CO _2 . When corrected for this lagged response, or if the CO _2 decline is applied after the system has equilibrated with the previous CO _2 increase, the Δ T versus CE relationship is close to linear during periods of net negative CO _2 emissions. A proportionality constant—the transient climate response to cumulative carbon emissions (TCRE)− can therefore be calculated for both positive and net negative CO _2 emission periods. We find that in simulations with a symmetric 1% per year increase and decrease in atmospheric CO _2 the TCRE is larger on the upward than on the downward CO _2 trajectory, suggesting that positive CO _2 emissions are more effective at warming than negative emissions are at subsequently cooling. We also find that the cooling effectiveness of negative CO _2 emissions decreases if applied at higher atmospheric CO _2 concentrations.

Abstract: We study the effect of the substrate material (ceramic versus metallic) on the steady-state and transient performance of monolith reactors using a one-dimensional two-phase model with position dependent transfer coefficients. When the operation of the reactor is on the ignited branch, it is shown that monoliths with metallic substrate clearly lead to a superior steady-state performance compared to those with ceramic substrate. In such cases, the ignited branch extends to lower inlet gas temperatures (typically 60–100°C in after-treatment applications) for the same catalyst loading. For transient operation where the time to light-off is important, it is shown that for the case of back-end ignition (corresponding to low inlet temperatures or low catalyst loading), metallic substrates are again superior. However, for the case of front-end ignition, ceramic converters may lead to lower cumulative emissions at lower inlet gas velocities while the converse is true at higher velocities. It is shown that the transient heating time and hence the cumulative emissions decrease with decrease in the channel hydraulic diameter and thermal capacitance of the substrate but are not monotonic with the inlet gas velocity. We present mathematical analysis and simulations to support these conclusions. Some novel results on the effect of substrate conductivity on the number of steady-states and upstream propagation of temperature fronts are also presented. [Copyright &y& Elsevier]

Abstract: In current policies, targets for GHG (greenhouse gas) and more specifically CO2 emissions are set on the basis of annual emissions. However, warming effects associated with global average temperature rise depend on accumulation of GHG in the atmosphere. Due to the quantity and longevity of CO2 in the atmosphere there is increasing awareness that taking into account cumulative CO2 emissions in defining targets for restraining the growth of CO2 emissions would be particularly effective. The notion of effectiveness is linked to measuring the degree of achievement of the objectives. Considering CO2 emissions targets set over a few decades, the path of emissions reduction contains relevant information that cannot be captured by a classical measure like the distance to the target. The main contribution of this paper is the definition of an original measure of carbon dioxide reduction effectiveness, which allows comparison of specified CO2 reduction paths expressed in deterministic or probabilistic ways. Appropriate metrics are used to illustrate the proposed measure which in particular captures the importance of early action. The measure is applied to simple what-if scenarios for the EU27 electricity and heat sector to 2050, evaluating the impact of each scenario with respect to a reference case. [Copyright &y& Elsevier]

There is much discussion within the sustainable development community regarding climate stabilization and particularly, finding environmentally equitable ways to address emission reductions. Knowing the current level of emission is only one variable in this complex picture. While the rate of emissions is clearly a problem, the overall increase in GHG concentration in the atmosphere is ultimately the main driver of anthropogenic warming. Therefore, it is also important to understand the cumulative emissions, those which have taken us to the current condition. This research presents a case study of six countries to compare the emissions per capita and cumulative emissions during the past 200 years. It is known that carbon emissions are closely related to economic activities, but here we show that some countries have reached per capita emissions plateaus at different levels while others are still rising. Specifically, one approach toward socioeconomic development, in terms of energy-economy, reaches a plateau at 10 Mt carbon per person, which the United Kingdom and South Korea have attained. The US occupies another emission regime at 20 Mt carbon per person. Developing economies such as India and China are considerably below these levels, and unless they follow other integrated economic/environmental solutions, they will continue to increase their per capita emissions during development. [ABSTRACT FROM AUTHOR]

Abstract: A transient one-dimensional two-phase model is used to obtain an explicit light-off criterion and to estimate the transient time and cumulative cold-start emissions from a catalytic monolith for the case of nonuniform catalyst loading. The light-off criterion can predict the nature of ignition (front-end, middle or back-end). For a fixed amount of metal loading, redistribution of the catalyst appropriately (with more catalyst near the inlet) favors front-end ignition in the monolith and reduces the cumulative cold-start emissions substantially. It is also found that there exists an optimal washcoat thickness and/or metal loading, above which the performance of the converter does not improve significantly while below this optimum, the transient time and cumulative emissions can be reduced by increasing the washcoat thickness or metal loading. For the case of front-end ignition, it is also found that the total transient time is the sum of ignition and the front-propagation times. We present analytical expressions for both these times and show how they may be used to estimate cumulative cold-start emissions. Numerical simulations validate the analytical design criteria presented. Finally, some strategies for minimizing cumulative cold-start emissions are discussed. [Copyright &y& Elsevier]

A one-dimensional two-phase model is used to derive an analytical light-off criterion for a straight channeled catalytic monolith with washcoat, in which the flow is laminar. For the case of uniform catalyst loading and a first order reaction, the light-off criterion is given by1/f(δckv(Tf,in)/De)ERΩδc(ΔTad)kv(Tf,in)/Tf,in2Rgg(Peh)L/RΩ2u¯+4eρfcpf/kfNuH,∞) ERΩδc(ΔTad)kv(Tf,in)/Tf,in2Rgg(Peh)L/RΩ2u¯+4eρfcpf/kfNuH,∞g(Peh)L/RΩ2u¯+4eρfcpf/kfNuH,∞+4eρfcpf/kfNuH,∞>1.Here, Tf,in is the inlet fluid temperature, ΔTad is the adiabatic temperature rise, RΩ is one-half the channel hydraulic radius (RΩ=AΩ/PΩ, AΩ, PΩ=channel cross-section area, perimeter), L is the channel length, u¯ is the fluid velocity, De is the reactant effective diffusivity in the washcoat, δc is the effective washcoat thickness, kf is the fluid thermal conductivity and kv(Tf,in) is the first order rate constant per unit washcoat volume at the inlet fluid temperature. NuH,∞ is the asymptotic Nusselt number in the channel. The function f accounts for diffusional limitations in the washcoat and is given by f(ϕ)=1 for ϕ<0.5 and f(ϕ)=2ϕ for ϕ>0.5. The factor g(Peh) depends on the solid conductivity, or more precisely, the heat Peclet number, Peh=u¯LρfcpfRΩ/δwkw, where δw(kw) is the effective wall thickness (thermal conductivity). The function g(Peh) decreases monotonically from 2.718 for Peh=0 to unity for Peh=∞. We also show that if the second term is negligible and the first exceeds unity, then ignition occurs at the back-end. If the second term exceeds unity then ignition occurs at the front-end. If the sum exceeds unity with the second term less than unity and not negligible compared to the first term then ignition occurs in the middle of the channel. This analytical ignition criterion is verified by numerical simulations using an accurate transient model that uses position dependent heat and mass transfer coefficients.We show that the plot of exit concentration versus time consists of two regions: kinetically controlled transient region and the mass transfer controlled steady-state asymptote. For the case of high solid conductivity, we present an analytical expression for the transient time at which the monolith shifts from the kinetically controlled to the mass transfer controlled regime. We also determine the influence of various parameters such as the washcoat thickness, channel dimensions, catalyst loading and initial solid temperature on this transient time and the cumulative emissions. Examination of the influence of solid conduction and channel geometry on cumulative emissions showed that designs that are optimum for steady-state operation lead to higher transient emissions and vice versa. Finally, we discuss the transient and steady-state behavior of the monolith for the special case of Lef<1 (hydrogen oxidation). [Copyright &y& Elsevier]

In this paper, the authors have calculated the cumulative energy demand and cumulative greenhouse effect for three renewable energy technologies, namely, wind energy, solar photovoltaic, and solar water heating (SWH) system, corresponding to typical climatic conditions in India. The life cycle assessment of these systems (1.5 MW windmill, 35WP SPV, 2 m[sup 2] and 100 lt. SWH systems) has yielded the parameters energy yield ratio (EYR) and emission coefficient. EYR for these three technologies are found to be from 9.59 to 31.11, 0.58 to 0.91, and 2.32 to 7.14, respectively. Variation of emission coefficients is from 2.40 to 7.86, 83.72 to 133.10, and 19.88 to 61.06 kg CO[sub 2] per GJ delivered from the three technologies, respectively. Their corresponding correlation has been fitted with an algebraic expression having a correlation coefficient of 0.91. [ABSTRACT FROM AUTHOR]

Recent estimates of the global carbon budget, or allowable cumulative CO _2 emissions consistent with a given level of climate warming, have the potential to inform climate mitigation policy discussions aimed at maintaining global temperatures below 2 °C. This raises difficult questions, however, about how best to share this carbon budget amongst nations in a way that both respects the need for a finite cap on total allowable emissions, and also addresses the fundamental disparities amongst nations with respect to their historical and potential future emissions. Here we show how the contraction and convergence (C&C) framework can be applied to the division of a global carbon budget among nations, in a manner that both maintains total emissions below a level consistent with 2 °C, and also adheres to the principle of attaining equal per capita CO _2 emissions within the coming decades. We show further that historical differences in responsibility for climate warming can be quantified via a cumulative carbon debt (or credit), which represents the amount by which a given country’s historical emissions have exceeded (or fallen short of) the emissions that would have been consistent with their share of world population over time. This carbon debt/credit calculation enhances the potential utility of C&C, therefore providing a simple method to frame national climate mitigation targets in a way that both accounts for historical responsibility, and also respects the principle of international equity in determining future emissions allowances.

Artificial removal of CO _2 from the atmosphere (also referred to as negative emissions) has been proposed as a means to restore the climate system to a desirable state, should the impacts of climate change become ‘dangerous’. Here we explore whether negative emissions are indeed effective in reversing climate change on human timescales, given the potentially counteracting effect of natural carbon sinks and the inertia of the climate system. We designed a range of CO _2 emission scenarios, which follow a gradual transition to a zero-carbon energy system and entail implementation of various amounts of net-negative emissions at technologically plausible rates. These scenarios are used to force an Earth System Model of intermediate complexity. Results suggest that while it is possible to revert to a desired level of warming (e.g. 2 °C above pre-industrial) after different levels of overshoot, thermosteric sea level rise is not reversible for at least several centuries, even under assumption of large amounts of negative CO _2 emissions. During the net-negative emission phase, artificial CO _2 removal is opposed by CO _2 outgassing from natural carbon sinks, with the efficiency of CO _2 removal—here defined as the drop in atmospheric CO _2 per unit negative emission—decreasing with the total amount of negative emissions.

International climate mitigation efforts are focused on limiting increase in global mean temperature, which has been shown to be proportional to cumulative CO _2 emissions. However, the ability of natural and human systems to successfully adapt to climatic changes depends on both the magnitude and rate of change, the latter of which will depend on how quickly a given level of cumulative emissions occurs. We show that cumulative CO _2 emissions of 4620 Gt CO _2 (reached in 2100 in RCP4.5 and 2057 in RCP8.5) produce globally averaged warming rates that are nearly twice as fast in RCP8.5 than RCP4.5 (0.34 ± 0.08 °C per decade versus 0.19 ± 0.05 °C per decade, respectively). Similarly, the globally averaged velocity of climate change calculated according to the ‘nearest equivalent climate’ is greater by a factor of ∼2 in RCP8.5 than in RCP4.5 (2.51 ± 0.67 km yr ^−1 versus 1.32 ± 0.39 km yr ^−1 , respectively), despite equivalent cumulative emissions. These differences in the projected velocity of climate change represent uncertainty for ecosystems that may be unable to adapt to the faster changes. Particularly at risk are boreal forests, of which 48% are projected to experience rates of change beyond their expected adaptive capacity (i.e. >0.3 °C per decade) in RCP4.5, compared with 95% in RCP8.5. Thus, the same budget of cumulative carbon emissions may result in critically different impacts on natural and human systems, depending on the amount of time over which that budget is expended.

Long-term climate experiments up to the year 2300 have been conducted using two full-scale complex Earth system models (ESMs), CESM1(BGC) and MIROC-ESM, for a CO _2 emissions reduction pathway, termed Z650, where annual CO _2 emissions peak at 11 PgC in 2020, decline by 50% every 30 years, and reach zero in 2160. The results have been examined by focusing on the approximate linear relationship between the temperature increase and cumulative CO _2 emissions. Although the temperature increase is nearly proportional to the cumulative CO _2 emissions in both models, this relationship does not necessarily provide a robust basis for the restriction of CO _2 emissions because it is substantially modulated by non-CO _2 forcing. CO _2 -induced warming, estimated from the atmospheric CO _2 concentrations in the models, indicates an approximate compensation of nonlinear changes between fast-mode responses to concentration changes at less than 10 years and slow-mode response at more than 100 years due to the thermal inertia of the ocean. In this estimate, CESM1(BGC) closely approximates a linear trend of 1.7 °C per 1000 PgC, whereas MIROC-ESM shows a deviation toward higher temperatures after the emissions peak, from 1.8 °C to 2.4 °C per 1000 PgC over the range of 400–850 PgC cumulative emissions corresponding to years 2000–2050. The evolution of temperature under zero emissions, 2160–2300, shows a slight decrease of about 0.1 °C per century in CESM1(BGC), but remains almost constant in MIROC-ESM. The fast-mode response toward the equilibrium state decreases with a decrease in the airborne fraction owing to continued CO _2 uptake (carbon cycle inertia), whereas the slow-mode response results in more warming owing to continued heat uptake (thermal inertia). Several specific differences are noted between the two models regarding the degree of this compensation and in some key regional aspects associated with sustained warming and long-term climate risks. Overall, elevated temperatures continue for at least a few hundred years under zero emissions.

Policy makers have called for a ‘fair and ambitious’ global climate agreement. Scientific constraints, such as the allowable carbon emissions to avoid exceeding a 2 °C global warming limit with 66% probability, can help define ambitious approaches to climate targets. However, fairly sharing the mitigation challenge to meet a global target involves human values rather than just scientific facts. We develop a framework based on cumulative emissions of carbon dioxide to compare the consistency of countries’ current emission pledges to the ambition of keeping global temperatures below 2 °C, and, further, compare two alternative methods of sharing the remaining emission allowance. We focus on the recent pledges and other official statements of the EU, USA, and China. The EU and US pledges are close to a 2 °C level of ambition only if the remaining emission allowance is distributed based on current emission shares, which is unlikely to be viewed as ‘fair and ambitious’ by others who presently emit less. China’s stated emissions target also differs from measures of global fairness, owing to emissions that continue to grow into the 2020s. We find that, combined, the EU, US, and Chinese pledges leave little room for other countries to emit CO _2 if a 2 °C limit is the objective, essentially requiring all other countries to move towards per capita emissions 7 to 14 times lower than the EU, USA, or China by 2030. We argue that a fair and ambitious agreement for a 2 °C limit that would be globally inclusive and effective in the long term will require stronger mitigation than the goals currently proposed. Given such necessary and unprecedented mitigation and the current lack of availability of some key technologies, we suggest a new diplomatic effort directed at ensuring that the necessary technologies become available in the near future.

Recent years have witnessed unprecedented interest in how the burning of fossil fuels may impact on the global climate system. Such visibility of this issue is in part due to the increasing frequency of key international summits to debate emissions levels, including the 2015 21st Conference of Parties meeting in Paris. In this perspective we plot a timeline of significant climate meetings and reports, and against metrics of atmospheric greenhouse gas changes and global temperature. One powerful metric is cumulative CO _2 emissions that can be related to past and future warming levels. That quantity is analysed in detail through a set of papers in this ERL focus issue. We suggest it is an open question as to whether our timeline implies a lack of progress in constraining climate change despite multiple recent keynote meetings—or alternatively—that the increasing level of debate is encouragement that solutions will be found to prevent any dangerous warming levels?