123 results found
Rogelj J, Schleussner C-F, 2021, Reply to Comment on 'Unintentional unfairness when applying new greenhouse gas emissions metrics at country level', ENVIRONMENTAL RESEARCH LETTERS, Vol: 16, ISSN: 1748-9326
Grassi G, Stehfest E, Rogelj J, et al., 2021, Critical adjustment of land mitigation pathways for assessing countries’ climate progress, Nature Climate Change, Vol: 11, Pages: 425-434, ISSN: 1758-678X
Mitigation pathways by Integrated Assessment Models (IAMs) describe future emissions that keep global warming below specific temperature limits and are compared with countries’ collective greenhouse gas (GHG) emission reduction pledges. This is needed to assess mitigation progress and inform emission targets under the Paris Agreement. Currently, however, a mismatch of ~5.5 GtCO2 yr−1 exists between the global land-use fluxes estimated with IAMs and from countries’ GHG inventories. Here we present a ‘Rosetta stone’ adjustment to translate IAMs’ land-use mitigation pathways to estimates more comparable with GHG inventories. This does not change the original decarbonization pathways, but reallocates part of the land sink to be consistent with GHG inventories. Adjusted cumulative emissions over the period until net zero for 1.5 or 2 °C limits are reduced by 120–192 GtCO2 relative to the original IAM pathways. These differences should be taken into account to ensure an accurate assessment of progress towards the Paris Agreement.
Jones CD, Hickman JE, Rumbold ST, et al., 2021, The Climate Response to Emissions Reductions Due to COVID-19: Initial Results From CovidMIP, Geophysical Research Letters, Vol: 48, ISSN: 0094-8276
Many nations responded to the corona virus disease-2019 (COVID-19) pandemic by restricting travel and other activities during 2020, resulting in temporarily reduced emissions of CO2, other greenhouse gases and ozone and aerosol precursors. We present the initial results from a coordinated Intercomparison, CovidMIP, of Earth system model simulations which assess the impact on climate of these emissions reductions. 12 models performed multiple initial-condition ensembles to produce over 300 simulations spanning both initial condition and model structural uncertainty. We find model consensus on reduced aerosol amounts (particularly over southern and eastern Asia) and associated increases in surface shortwave radiation levels. However, any impact on near-surface temperature or rainfall during 2020–2024 is extremely small and is not detectable in this initial analysis. Regional analyses on a finer scale, and closer attention to extremes (especially linked to changes in atmospheric composition and air quality) are required to test the impact of COVID-19-related emission reductions on near-term climate.
Rogelj J, Geden O, Cowie A, et al., 2021, Net-zero emissions targets are vague: three ways to fix, Nature, Vol: 591, Pages: 365-368, ISSN: 0028-0836
Matthews HD, Tokarska KB, Nicholls ZRJ, et al., 2020, Opportunities and challenges in using remaining carbon budgets to guide climate policy, NATURE GEOSCIENCE, Vol: 13, Pages: 769-779, ISSN: 1752-0894
Gibson MF, Rao ND, Slade RB, et al., 2020, The role of energy in mitigating grain storage losses in India and the impact for nutrition, Resources, Conservation and Recycling, Vol: 163, ISSN: 0921-3449
Globally, India's population is amongst the most severely impacted by nutrient deficiency, yet millions of tonnes of food are lost along the supply chain before reaching consumers. Across food groups, grains represent the largest share of daily calories and overall losses by mass in India. This study quantifies energy input to minimise storage losses across India, responsible for up to a quarter of grain losses. In doing so, we explore links between three Sustainable Development Goals-SDG2, SDG7, and SDG12-, and provide insight for development of joined up agriculture and health policy in the country. Focusing on rice, wheat, maize, bajra, and sorghum, we quantify one route to reduce losses in supply chains, by modelling the energy input to maintain favourable climatic conditions in modern silo storage. We quantify key nutrients (calories, protein, zinc, iron, vitamin A) contained within these losses, and calculate roughly how much deficiency in these dietary components could be reduced if grain losses were eliminated. Our modelling indicates that maize has the highest energy input intensity for storage, at 110 (18) kWh per tonne of grain (kWh/t), and wheat the lowest, at 72 (14) kWh/t. This energy cost represents 8%-16% of the energy input required in grain production. We estimate if grain losses across the supply chain were saved and targeted to India's nutritionally deficient population, average protein deficiency could reduce by 46±4%, calorie by 27±2%, zinc by 26±2% and iron by 11±1%.
Lamboll RD, Nicholls ZRJ, Kikstra JS, et al., 2020, Silicone v1.0.0: an open-source Python package for inferring missing emissions data for climate change research, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 13, Pages: 5259-5275, ISSN: 1991-959X
Graven H, Keeling RF, Rogelj J, 2020, Changes to Carbon Isotopes in Atmospheric CO2 Over the Industrial Era and Into the Future, GLOBAL BIOGEOCHEMICAL CYCLES, Vol: 34, ISSN: 0886-6236
Nicholls ZRJ, Meinshausen M, Lewis J, et al., 2020, Reduced Complexity Model Intercomparison Project Phase 1: introduction and evaluation of global-mean temperature response, GEOSCIENTIFIC MODEL DEVELOPMENT, Vol: 13, Pages: 5175-5190, ISSN: 1991-959X
Andrijevic M, Schleussner C-F, Gidden MJ, et al., 2020, COVID-19 recovery funds dwarf clean energy investment needs., Science, Vol: 370, Pages: 298-300, ISSN: 1095-9203
Tokarska KB, Arora VK, Gillett NP, et al., 2020, Uncertainty in carbon budget estimates due to internal climate variability, Environmental Research Letters, Vol: 15, Pages: 1-12, ISSN: 1748-9326
Remaining carbon budget specifies the cap on global cumulative CO2 emissions from the present-day onwards that would be in line with limiting global warming to a specific maximum level. In the context of the Paris Agreement, global warming is usually interpreted as the externally-forced response to anthropogenic activities and emissions, but it excludes the natural fluctuations of the climate system known as internal variability. A remaining carbon budget can be calculated from an estimate of the anthropogenic warming to date, and either (i) the ratio of CO2-induced warming to cumulative emissions, known as the Transient Climate Response to Emissions (TCRE), in addition to information on the temperature response to the future evolution of non-CO2 emissions; or (ii) climate model scenario simulations that reach a given temperature threshold. Here we quantify the impact of internal variability on the carbon budgets consistent with the Paris Agreement derived using either approach, and on the TCRE diagnosed from individual models. Our results show that internal variability contributes approximately ±0.09 °C to the overall uncertainty range of the human-induced warming to-date, leading to a spread in the remaining carbon budgets as large as ±50 PgC, when using approach (i). Differences in diagnosed TCRE due to internal variability in individual models can be as large as ±0.1 °C/1000 PgC (5%–95% range). Alternatively, spread in the remaining carbon budgets calculated from (ii) using future concentration-driven simulations of large ensembles of CMIP6 and CMIP5 models is estimated at ±30 PgC and ±40 PgC (5%–95% range). These results are important for model evaluation and imply that caution is needed when interpreting small remaining budgets in policy discussions. We do not question the validity of a carbon budget approach in determining mitigation requirements. However, due to intrinsic uncertainty arising from interna
Andrijevic M, Schleussner C-F, Gidden MJ, et al., 2020, climate-analytics/covid_recovery: Data and analysis scripts
This is the (final) version of the code for Andrijevic et al. 2020, "COVID-19 recovery funds dwarf clean energy investment needs"Built on v1.0 with a bit of spring cleaning
Smith SJ, Chateau J, Dorheim K, et al., 2020, Impact of methane and black carbon mitigation on forcing and temperature: a multi-model scenario analysis, Climatic Change, Vol: 163, Pages: 1427-1442, ISSN: 0165-0009
The relatively short atmospheric lifetimes of methane (CH4) and black carbon (BC) have focused attention on the potential for reducing anthropogenic climate change by reducing Short-Lived Climate Forcer (SLCF) emissions. This paper examines radiative forcing and global mean temperature results from the Energy Modeling Forum (EMF)-30 multi-model suite of scenarios addressing CH4 and BC mitigation, the two major short-lived climate forcers. Central estimates of temperature reductions in 2040 from an idealized scenario focused on reductions in methane and black carbon emissions ranged from 0.18–0.26 °C across the nine participating models. Reductions in methane emissions drive 60% or more of these temperature reductions by 2040, although the methane impact also depends on auxiliary reductions that depend on the economic structure of the model. Climate model parameter uncertainty has a large impact on results, with SLCF reductions resulting in as much as 0.3–0.7 °C by 2040. We find that the substantial overlap between a SLCF-focused policy and a stringent and comprehensive climate policy that reduces greenhouse gas emissions means that additional SLCF emission reductions result in, at most, a small additional benefit of ~ 0.1 °C in the 2030–2040 time frame.
Fofrich R, Tong D, Calvin K, et al., 2020, Early retirement of power plants in climate mitigation scenarios, Environmental Research Letters, Vol: 15, Pages: 1-12, ISSN: 1748-9326
International efforts to avoid dangerous climate change aim for large and rapid reductions of fossil fuel CO2 emissions worldwide, including nearly complete decarbonization of the electric power sector. However, achieving such rapid reductions may depend on early retirement of coal- and natural gas-fired power plants. Here, we analyze future fossil fuel electricity demand in 171 energy-emissions scenarios from Integrated Assessment Models (IAMs), evaluating the implicit retirements and/or reduced operation of generating infrastructure. Although IAMs calculate retirements endogenously, the structure and methods of each model differ; we use a standard approach to infer retirements in outputs from all six major IAMs and—unlike the IAMs themselves—we begin with the age distribution and region-specific operating capacities of the existing power fleet. We find that coal-fired power plants in scenarios consistent with international climate targets (i.e. keeping global warming well-below 2 °C or 1.5 °C) retire one to three decades earlier than historically has been the case. If plants are built to meet projected fossil electricity demand and instead allowed to operate at the level and over the lifetimes they have historically, the roughly 200 Gt CO2 of additional emissions this century would be incompatible with keeping global warming well-below 2 °C. Thus, ambitious climate mitigation scenarios entail drastic, and perhaps un-appreciated, changes in the operating and/or retirement schedules of power infrastructure.
Forster PM, Forster HI, Evans MJ, et al., 2020, Current and future global climate impacts resulting from COVID-19 (vol 82, pg 613, 2020), Nature Climate Change, Vol: 10, Pages: 971-971, ISSN: 1758-678X
Forster PM, Forster HI, Evans MJ, et al., 2020, Current and future global climate impacts resulting from COVID-19, Nature Climate Change, Vol: 10, Pages: 913-919, ISSN: 1758-678X
The global response to the COVID-19 pandemic has led to a sudden reduction of both GHG emissions and air pollutants. Here, using national mobility data, we estimate global emission reductions for ten species during the period February to June 2020. We estimate that global NOx emissions declined by as much as 30% in April, contributing a short-term cooling since the start of the year. This cooling trend is offset by ~20% reduction in global SO2 emissions that weakens the aerosol cooling effect, causing short-term warming. As a result, we estimate that the direct effect of the pandemic-driven response will be negligible, with a cooling of around 0.01 ± 0.005 °C by 2030 compared to a baseline scenario that follows current national policies. In contrast, with an economic recovery tilted towards green stimulus and reductions in fossil fuel investments, it is possible to avoid future warming of 0.3 °C by 2050.
MacDougall AH, Frölicher TL, Jones CD, et al., 2020, Is there warming in the pipeline? A multi-model analysis of the zero emissions commitment from CO2, Biogeosciences, Vol: 17, Pages: 2987-3016, ISSN: 1726-4170
The Zero Emissions Commitment (ZEC) is the change in global mean temperature expected to occur following the cessation of net CO2 emissions and as such is a critical parameter for calculating the remaining carbon budget. The Zero Emissions Commitment Model Intercomparison Project (ZECMIP) was established to gain a better understanding of the potential magnitude and sign of ZEC, in addition to the processes that underlie this metric. A total of 18 Earth system models of both full and intermediate complexity participated in ZECMIP. All models conducted an experiment where atmospheric CO2 concentration increases exponentially until 1000 PgC has been emitted. Thereafter emissions are set to zero and models are configured to allow free evolution of atmospheric CO2 concentration. Many models conducted additional second-priority simulations with different cumulative emission totals and an alternative idealized emissions pathway with a gradual transition to zero emissions. The inter-model range of ZEC 50 years after emissions cease for the 1000 PgC experiment is −0.36 to 0.29 ∘C, with a model ensemble mean of −0.07 ∘C, median of −0.05 ∘C, and standard deviation of 0.19 ∘C. Models exhibit a wide variety of behaviours after emissions cease, with some models continuing to warm for decades to millennia and others cooling substantially. Analysis shows that both the carbon uptake by the ocean and the terrestrial biosphere are important for counteracting the warming effect from the reduction in ocean heat uptake in the decades after emissions cease. This warming effect is difficult to constrain due to high uncertainty in the efficacy of ocean heat uptake. Overall, the most likely value of ZEC on multi-decadal timescales is close to zero, consistent with previous model experiments and simple theory.
Pfleiderer P, Schleussner C-F, Mengel M, et al., 2020, global mean temperature indicators linked to warming levels avoiding climate risks (vol 13, 064015, 2018), Environmental Research Letters, Vol: 15, Pages: 1-1, ISSN: 1748-9326
Rogelj J, Forster PM, Kriegler E, et al., 2020, Estimating and tracking the remaining carbon budget for stringent climate targets (vol 571, pg 335, 2019), Nature, Vol: 580, ISSN: 0028-0836
Correction to: Nature https://doi.org/10.1038/s41586-019-1368-z Published online 17 July 2019
Duan H, Rogelj J, Veysey J, et al., 2020, Modeling deep decarbonization: Robust energy policy and climate action, Applied Energy, Vol: 262, Pages: 1-3, ISSN: 0306-2619
Höhne N, den Elzen M, Rogelj J, et al., 2020, Emissions: world has four times the work or one-third of the time., Nature, Vol: 579, Pages: 25-28, ISSN: 0028-0836
McCollum DL, Gambhir A, Rogelj J, et al., 2020, Energy modellers should explore extremes more systematically in scenarios, Nature Energy, Vol: 5, Pages: 104-107, ISSN: 2058-7546
Tokarska KB, Zickfeld K, Rogelj J, 2019, Path independence of carbon budgets when meeting a stringent global mean temperature target after an overshoot, Earths Future, Vol: 7, Pages: 1283-1295, ISSN: 2328-4277
Emission pathways that are consistent with meeting the Paris Agreement goal of holding global mean temperature rise well below 2 °C often assume a temperature overshoot. In such overshoot scenarios, a given temperature limit is first exceeded and later returned to, under the assumption of large‐scale deliberate carbon dioxide removal from the atmosphere. Here we show that although such strategy might result in a reversal of global mean temperature, the carbon cycle exhibits path dependence. After an overshoot, more carbon is stored in the ocean and less on land compared to a scenario with the same cumulative CO2 emissions but no overshoot. The near‐path independence of surface air temperature arises despite the path dependence in the carbon cycle, as it is offset by path dependence in the thermal response of the ocean. Such behavior has important implications for carbon budgets (i.e. the total amount of CO2 emissions consistent with holding warming to a given level), which do not differ much among scenarios that entail different levels of overshoot. Therefore, the concept of a carbon budget remains robust for scenarios with low levels of overshoot (up to 300 Pg C overshoot considered here) but should be used with caution for higher levels of overshoot, particularly for limiting the environmental change in dimensions other than global mean temperature rise.
Tokarska KB, Schleussner C-F, Rogelj J, et al., 2019, Recommended temperature metrics for carbon budget estimates, model evaluation and climate policy, Nature Geoscience, Vol: 12, Pages: 964-971, ISSN: 1752-0894
Recent estimates of the amount of carbon dioxide that can still be emitted while achieving the Paris Agreement temperature goals are larger than previously thought. One potential reason for these larger estimates may be the different temperature metrics used to estimate the observed global mean warming for the historical period, as they affect the size of the remaining carbon budget. Here we explain the reasons behind these remaining carbon budget increases, and discuss how methodological choices of the global mean temperature metric and the reference period influence estimates of the remaining carbon budget. We argue that the choice of the temperature metric should depend on the domain of application. For scientific estimates of total or remaining carbon budgets, globally averaged surface air temperature estimates should be used consistently for the past and the future. However, when used to inform the achievement of the Paris Agreement goal, a temperature metric consistent with the science that was underlying and directly informed the Paris Agreement should be applied. The resulting remaining carbon budgets should be calculated using the appropriate metric or adjusted to reflect these differences among temperature metrics. Transparency and understanding of the implications of such choices are crucial to providing useful information that can bridge the science–policy gap.
Schleussner C-F, Nauels A, Schaeffer M, et al., 2019, Inconsistencies when applying novel metrics for emissions accounting to the Paris agreement, Environmental Research Letters, Vol: 14, ISSN: 1748-9326
Addressing emissions of non-CO2 greenhouse gases (GHGs) is an integral part of efficient climate change mitigation and therefore an essential part of climate policy. Metrics are used to aggregate and compare emissions of short- and long-lived GHGs and need to account for the difference in both magnitude and persistence of their climatic effects. Different metrics describe different approaches and perspectives, and hence yield different numerical estimates for aggregated GHG emissions. When interpreting GHG emission reduction targets, being mindful of the underlying metrical choices thus proves to be essential. Here we present the impact a recently proposed GHG metric related to the concept of CO2 forcing-equivalent emissions (called GWP*) would have on the internal consistency and environmental integrity of the Paris Agreement. We show that interpreting the Paris Agreement goals in a metric like GWP* that is significantly different from the standard metric used in the IPCC Fifth Assessment Report can lead to profound inconsistencies in the mitigation architecture of the Agreement. It could even undermine the integrity of the Agreement's mitigation target altogether by failing to deliver net-zero CO2 emissions and therewith failing to ensure warming is halted. Our results indicate that great care needs to be taken when applying new concepts that appear scientifically favourable to a pre-existing climate policy context.
Gambhir A, Cronin C, Matsumae E, et al., 2019, Using futures analysis to develop resilient climate change mitigation strategies, Grantham Briefing Paper, Publisher: Imperial College London, 33
Waisman H, De Coninck H, Rogelj J, 2019, Key technological enablers for ambitious climate goals: insights from the IPCC special report on global warming of 1.5 degrees C, Environmental Research Letters, Vol: 14, Pages: 1-4, ISSN: 1748-9326
Fujimori S, Rogelj J, Krey V, et al., 2019, A new generation of emissions scenarios should cover blind spots in the carbon budget space, Nature Climate Change, Vol: 9, Pages: 798-800, ISSN: 1758-678X
Future emissions scenarios for the IPCC Sixth Assessment Report should explore the carbon budget space in a systematic manner, which would be robust to the updates of latest climate science, so that policy implications can be adequately assessed.
Rogelj J, Schleussner C-F, 2019, Unintentional unfairness when applying new greenhouse gas emissions metrics at country level, Environmental Research Letters, Vol: 14, Pages: 1-9, ISSN: 1748-9326
The 2015 Paris Agreement sets out that rapid reductions in greenhouse gas (GHG) emissions are needed to keep global warming to safe levels. A new approach (known as GWP*) has been suggested to compare contributions of long- and short-lived GHGs, providing a close link between cumulative CO2-equivalent emissions and total warming. However, comparison factors for non-CO2 GHGs under the GWP* metric depend on past emissions, and hence raise questions of equity and fairness when applied at any but the global level. The use of GWP* would put most developing countries at a disadvantage compared to developed countries, because when using GWP* countries with high historical emissions of short-lived GHGs are exempted from accounting for avoidable future warming that is caused by sustaining these emissions. We show that when various established equity or fairness criteria are applied to GWP* (defined here as eGWP*), perceived national non-CO2 emissions vary by more than an order of magnitude, particularly in countries with high methane emissions like New Zealand. We show that national emission estimates that use GWP* are very sensitive to arbitrary choices made by countries and therewith facilitate the creation of loopholes when CO2-equivalent emissions based on the GWP* concept are traded between countries that use different approaches. In light of such equity-dependent accounting differences, GHG metrics like GWP* should only be used at the global level. A common, transparent and equity-neutral accounting metric is vital for the Paris Agreement's effectiveness and its environmental integrity.
Hilaire J, Minx JC, Callaghan MW, et al., 2019, Negative emissions and international climate goals-learning from and about mitigation scenarios, Climatic Change: an interdisciplinary, international journal devoted to the description, causes and implications of climatic change, Vol: 157, Pages: 189-219, ISSN: 0165-0009
For aiming to keep global warming well-below 2 °C and pursue efforts to limit it to 1.5 °C, as set out in the Paris Agreement, a full-fledged assessment of negative emission technologies (NETs) that remove carbon dioxide from the atmosphere is crucial to inform science-based policy making. With the Paris Agreement in mind, we re-analyse available scenario evidence to understand the roles of NETs in 1.5 °C and 2 °C scenarios and, for the first time, link this to a systematic review of findings in the underlying literature. In line with previous research, we find that keeping warming below 1.5 °C requires a rapid large-scale deployment of NETs, while for 2 °C, we can still limit NET deployment substantially by ratcheting up near-term mitigation ambition. Most recent evidence stresses the importance of future socio-economic conditions in determining the flexibility of NET deployment and suggests opportunities for hedging technology risks by adopting portfolios of NETs. Importantly, our thematic review highlights that there is a much richer set of findings on NETs than commonly reflected upon both in scientific assessments and available reviews. In particular, beyond the common findings on NETs underpinned by dozens of studies around early scale-up, the changing shape of net emission pathways or greater flexibility in the timing of climate policies, there is a suite of “niche and emerging findings”, e.g. around innovation needs and rapid technological change, termination of NETs at the end of the twenty-first century or the impacts of climate change on the effectiveness of NETs that have not been widely appreciated. Future research needs to explore the role of climate damages on NET uptake, better understand the geophysical constraints of NET deployment (e.g. water, geological storage, climate feedbacks), and provide a more systematic assessment of NET portfolios in the context of sustainable development goals.
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