National emissions targets are collectively insufficient to align with the Paris Agreement. The fair-share literature assesses whether these targets are fair and ambitious in comparison to emissions trajectories based on equity principles. Such emissions trajectories commonly start at present-day emissions levels. Here we show that these continuous trajectories inherently reward past inaction and increasingly do so with their iterative updates. We provide an approach to allocating emissions trajectories based on equity principles applied with immediate effect. The resulting discontinuous national trajectories not starting at current emissions levels imply significant immediate international support to fund rapid mitigation globally. Modelling allocations with or without continuity has remarkable consequences for the relative implied contributions to international support among high-income countries. We find that emissions targets of G7 countries, Russia and China are responsible for most of the global 2030 ambition gap, while only some countries align with their 1.5 °C allocation.

Crop yield and the availability of arable land are impacted by climate change, leading to effects on global patterns of production and trading. To gain more precise insights in how future climate change might lead to redistributing productive crop areas, we developed a new method to assess climatic crop suitability, which combines temperature and precipitation suitability through water balance calculations. We applied the method to evaluate the effects of climate change under two climatic scenarios (SSP2-4.5 and SSP5-8.5), using an ensemble of five general circulation models, for nine crops (Arabica coffee, cassava, common beans, common wheat, maize, plantain, rice, sorghum and sugarcane) for four periods of time: past (1995-2014), present day (2015-2034), medium term (2040-2059), long term (2080-2099). We observed that the fraction of area with optimal suitability might be on a downward trajectory for coffee, cassava, beans, wheat and plantain, and could be halved by the end of the century. The tropics and sub-tropics are negatively affected for all crops, while mid-latitudes see large decreases in suitability for beans, wheat and maize. Global patterns show that suitability decreases at local levels (in about 30% of the global area for bean and wheat) are not compensated by increases in suitability elsewhere (in about 19% of the area for bean and wheat). As relocation and expansion of production areas are constrained by available arable land, other strategies might be considered to improve suitability, such as irrigation, which would increase the area of optimal suitability from 5%-25% to 40%-50% of total arable land for the nine crops. Drainage could improve the optimal suitability area fivefold for maize and sorghum, while shading increases suitability for coffee (by up to 20% in both cases). The increased risk of food supply shortages led by climatic suitability loss may trigger increased deforestation if adaptation measures are not implemented.

Abstract National emissions targets are collectively insufficient to align with the Paris Agreement. The literature quantifying national emissions trajectories based on equity principles will inform the Global Stocktake on the ambition of national 2030 targets. Ambition assessments based on trajectories that start at present-day emissions levels inherently reward past inaction thus far, and increasingly do so into the future. Here we quantify emissions trajectories based on equity principles applied with immediate effect. We find national targets of G7 countries, Russia and China responsible for most of the global ambition gap, while only those of some countries in the Global South align with their 1.5°C allocation. Discontinuous trajectories not starting at current emissions levels imply stronger international support that can mobilize the capital needed to implement the 1.5°C trajectory globally. The difference between allocation with or without discontinuity has remarkable consequences for the relative implied contributions among high-income countries to international support.

Scientifically rigorous guidance to policy makers on mitigation options for meeting the Paris Agreement long-term temperature goal requires an evaluation of long-term global-warming implications of greenhouse gas emissions pathways. Here, we present a uniform and transparent methodology to evaluate the climate outcome, and hence the Paris Agreement consistency of influential institutional emission scenarios from the grey literature, including those from the International Energy Agency1,2, BP3, and Shell4. We first identify challenges to performing such an assessment and then proceed to outline a sequence of steps to address these challenges by harmonizing5 all emissions to a consistent base-year (2010), extending all pathways to 2100, and filling in missing emission species6. We employ two simple climate models, MAGICC7 and FaIR8,9 to assess peak and end-of-century temperatures, and find that few published scenarios that claim to be compatible with the Paris Agreement are so. References 1. International Energy Agency. World Energy Outlook 2020. (2020). 2. International Energy Agency. Net Zero by 2050 - A Roadmap for the Global Energy Sector. (2021). 3. BP. Global Energy Outlook 2020. (2020). 4. Shell. The Energy Transformation Scenarios. (2021) 5. Gidden, M. J. et al. A methodology and implementation of automated emissions harmonization for use in Integrated Assessment Models. Environ. Model. Softw. 105, 187–200 (2018) 6. Lamboll, R. D., Nicholls, Z. R. J., Kikstra, J. S., Meinshausen, M. & Rogelj, J. Silicone v1.0.0 : an open-source Python package for inferring missing emissions data for climate change research. Geosci. Model Dev 13, 5259–5275 (2020) 7. Meinshausen, M., Raper, S. C. B. & Wigley, T. M. L. Emulating coupled atmosphere-ocean and carbon cycle models with a simpler model, MAGICC6 - Part 1: Model description and calibration. Atmos. Chem. Phys. 11, 1417–1456 (2011). 8. Smith, C. J. et al. FAIR v1.3: A simple emissions-based impulse response and carbon cycle model. Geosci. Model Dev. 11, 2273–2297 (2018) 9. Millar, J. R., Nicholls, Z. R., Friedlingstein, P. & Allen, M. R. A modified impulse-response representation of the global near-surface air temperature and atmospheric concentration response to carbon dioxide emissions. Atmos. Chem. Phys. 17, 7213–7228 (2017).

Climate change is expected to bring higher temperatures, changes to rainfall patterns and in many places increased frequency and severity of extreme weather. Climate change is slated to affect the global food equation both on the supply and demand side as well as local level food systems where small farm communities often depend on local and their own production. As climate change has become more pronounced, the risk to land-based food security faced by many of the world’s poor, such as rural communities in Ethiopia and Niger, seems to have become more intense and less predictable. To avoid food insecurity in response to climatic and other stressors, adaptation by small-scale, subsistence farms needs to be accelerated. To effectively intervene to do so, there is a need to understand adaptive behavior in terms of its drivers and its relation with welfare outcomes such as food security. In this paper, we develop a conceptual framework of risk and adaptation, use regression and cluster analysis and the most recent version of the Living Standards Measurement Surveys data for rural areas in Ethiopia and Niger, to advance our understanding. We find that adaptation is associated with lower food insecurity in Ethiopia but not in Niger. Formal education appears as a central element of adaptive capacity and is associated with both adaptive production and income strategies. Female-headed households are much less adapted to a changing climate. Perceived risk based on past hazard experience is crucial for adaptation. Results from the cluster analysis confirm that spatial poverty traps exist. To maintain or enhance welfare in the short term and resilience in the long run in the face of a changing climate, policy makers would do well to focus on micro-regions identified as highly food insecure and build adaptive capacity through, for example, gender inclusive education interventions.

Scientifically rigorous guidance to policy makers on mitigation options for meeting the Paris Agreement long-term temperature goal requires an evaluation of long-term global-warming implications of greenhouse gas emissions pathways. Here we employ a uniform and transparent methodology to evaluate Paris Agreement compatibility of influential institutional emission scenarios from the grey literature, including those from Shell, BP, and the International Energy Agency. We compare a selection of these scenarios analysed with this methodology to the Integrated Assessment Model scenarios assessed by the Intergovernmental Panel on Climate Change. We harmonize emissions to a consistent base-year and account for all greenhouse gases and aerosol precursor emissions, ensuring a self-consistent comparison of climate variables. An evaluation of peak and end-of-century temperatures is made, with both being relevant to the Paris Agreement goal. Of the scenarios assessed, we find that only the IEA Net Zero 2050 scenario is aligned with the criteria for Paris Agreement consistency employed here. We investigate root causes for misalignment with these criteria based on the underlying energy system transformation.

Equity is one of the key principles underpinning the global climate regime and is all the more essential given the heterogenous, self-differentiated nature of the Paris Agreement. The scientific community has proposed several effort-sharing schemes to operationalise equity – reflecting not only the multi-faceted nature of the problem but also a long history of disagreement that continues to date. We outline a synthesis framework that draws on existing estimates in the literature to develop a “fair share range” for each country within which we identify a common position, which, when applied to the ranges of all countries, results in the collective achievement of the desired temperature goal. A series of methodological choices regarding the treatment of the underlying literature and translation into a temperature equivalence are tested. We demonstrate the consistency of this framework (across different methodological choices) with the principle of “Common but Differentiated Responsibilities” – members of the OECD have the most stringent allocations, while only a few African and Asian countries (including India) have emission allocations that are above their 2010 emission levels. A few OECD members, including the European Union and Great Britain, have emission allocations in 2030 that are either close to, or less than zero. Consistency with their fair share of mitigation will require them to provide appropriate levels of international finance and support to facilitate emission reductions in developing countries. These conclusions are robust to various methodological choices.

Abstract Scientifically rigorous guidance to policy makers on mitigation options for meeting the Paris Agreement long-term temperature goal requires an evaluation of long-term global-warming implications of greenhouse gas emissions pathways. Here we employ a uniform and transparent methodology to evaluate Paris Agreement compatibility of influential “institutional” emission scenarios from the grey literature. We compare a selection of these scenarios analyzed with this methodology to the Integrated Assessment Model scenarios assessed by the Intergovernmental Panel on Climate Change. We harmonize emissions to a consistent base-year and account for all greenhouse gases and aerosol precursor emissions, ensuring a self-consistent comparison of climate variables. An evaluation of peak and end-of-century temperatures is made, with both being relevant to the Paris Agreement goal. We find that few published scenarios that claim to be compatible with the Paris Agreement are so, and investigate root causes based on the underlying energy system transformation.

Parties to the UNFCCC and Paris Agreement have agreed to pursue efforts to limit the global average temperature increase to 1.5 ° C. To meet this goal, the international community will have to aggressively reduce emissions and also remove CO 2 from the atmosphere on an unprecedented scale, through an array of biological and technical Carbon Dioxide Removal (CDR) options. This paper considers governance challenges that arise from the need to rely on CDR to meet the Paris Agreement ’ s long-term temperature goal. It looks at how heavy this reliance may have to be, over what timeframe, involving what options and, crucially, how best to ensure that CDR does not, while trying to address one problem, create many other challenges for sustainable development. After identifying the potential scale and pace of CO 2 removal needed to meet the 1.5 ° C goal, we identify key governance gaps and challenges that arise from large-scale CDR implementation and propose a series of policy responses to be addressed by policy makers as a matter of priority, to enable CDR to contribute to 1.5 ° C-consistent pathways at the scale and pace required.

Climate change is projected to detrimentally affect African countries' economic development, while income inequalities across economies is among the highest on the planet. However, it is projected that income levels would converge on the continent. Hitherto there is limited evidence on how climate change could affect projected income convergence, accelerating, slowing down, or even reversing this process. Here, we analyze convergence considering climate-change damages, by employing an economic model embedding the three dimensions of risks at the country-level: exposure, vulnerability and hazards. The results show (1) with historical mean climate-induced losses between 10 and 15 percent of GDP per capita growth, the majority of African economies are poorly adapted to their current climatic conditions, (2) Western and Eastern African countries are projected to be the most affected countries on the continent and (3) As a consequence of these heightened impacts on a number of countries, inequalities between countries are projected to widen in the high warming scenario compared to inequalities in the low and without warming scenarios. To mitigate the impacts of economic development and inequalities across countries, we stress (1) the importance of mitigation ambition and Africa's leadership in keeping global mean temperature increase below 1.5 degrees C, (2) the need to address the current adaptation deficit as soon as possible, (3) the necessity to integrate quantitatively climate risks in economic and development planning and finally (4) we advocate for the generalization of a special treatment for the most vulnerable countries to access climate-related finance. The analysis raises issues on the ability of African countries to reach their SDGs targets and the potential increasing risk of instability, migration across African countries, of decreased trade and economic cooperation opportunities as a consequence of climate change exacerbating its negative consequences. (C) 2019 Elsevier Ltd. All rights reserved.

Given limited scientific agreement on approaches and methodologies, estimates of climate-change adaptation costs vary widely. Here, we present a meta-analysis of aggregate adaptation costs in developing countries, across three roughly homogeneous groups of estimates, i.e. national plan-based, bottom-up science-based, and global top-down estimates. We show that the level of global warming, a country's economic status, and methodology applied, are the main determinants for the estimated costs of adaptation. Not surprisingly, adaptation costs are much higher at high levels of global warming by 2050 and 2100, diverging from low levels of warming from the 2030s. Consequently, strong global mitigation action could reduce the adaptation costs by three quarters by 2100. Next, adaptation costs are higher for high-income countries in absolute dollar value, but costs are higher relative to gross domestic product for low-income countries. The integrated assessment model based estimates are at the higher end of the range at the global scale, but the estimates based on the sectoral impacts aggregation approach are higher in case of bottom-up estimates. Regardless of the methodology applied, current climate finance pledges of USD100 billion by 2020 - for both mitigation and adaptation - would fall far short of estimated global adaptation costs.

Current global mitigation ambition up to 2030 under the Paris Agreement, reflected in the National Determined Contributions (NDCs), is insufficient to achieve the agreement's 1.5 ∘C long-term temperature limit. As governments are preparing new and updated NDCs for 2020, the question as to how much collective improvement is achieved is a pivotal one for the credibility of the international climate regime. The recent Special Report on Global Warming of 1.5 ∘C by the Intergovernmental Panel on Climate Change has assessed a wide range of scenarios that achieve the 1.5 ∘C limit. Those pathways are characterised by a substantial increase in near-term action and total greenhouse gas (GHG) emission levels about 50 % lower than what is implied by current NDCs. Here we assess the outcomes of different scenarios of NDC updating that fall short of achieving this 1.5 ∘C benchmark. We find that incremental improvements in reduction targets, even if achieved globally, are insufficient to align collective ambition with the goals of the Paris Agreement. We provide estimates for global mean temperature increase by 2100 for different incremental NDC update scenarios and illustrate climate impacts under those median scenarios for extreme temperature, long-term sea-level rise and economic damages for the most vulnerable countries. Under the assumption of maintaining ambition as reflected in current NDCs up to 2100 and beyond, we project a reduction in the gross domestic product (GDP) in tropical countries of around 60 % compared to a no-climate-change scenario and median long-term sea-level rise of close to 2 m in 2300. About half of these impacts can be avoided by limiting warming to 1.5 ∘C or below. Scenarios of more incremental NDC improvements do not lead to comparable reductions in climate impacts. An increase in aggregated NDC ambition of big emitters by 33 % in 2030 does not reduce presented climate impacts by more than about half compared to limiting warming to 1.5 ∘C. Our results underscore that a transformational increase in 2030 ambition is required to achieve the goals of the Paris Agreement and avoid the worst impacts of climate change.

New synthesis shows what a wasted decade means for the climate pact made in Paris. New synthesis shows what a wasted decade means for the climate pact made in Paris.

Given limited scientific agreement on approaches and methodologies, estimates of climate-change adaptation costs vary widely. Here, we present a meta-analysis of aggregate adaptation costs in developing countries, across three roughly homogeneous groups of estimates, i.e. national plan-based, bottom-up science-based, and global top-down estimates. We show that the level of global warming, a countryu0027s economic status, and methodology applied, are the main determinants for the estimated costs of adaptation. Not surprisingly, adaptation costs are much higher at high levels of global warming by 2050 and 2100, diverging from low levels of warming from the 2030s. Consequently, strong global mitigation action could reduce the adaptation costs by three quarters by 2100. Next, adaptation costs are higher for high-income countries in absolute dollar value, but costs are higher relative to gross domestic product for low-income countries. The integrated assessment model based estimates are at the higher end of the range at the global scale, but the estimates based on the sectoral impacts aggregation approach are higher in case of bottom-up estimates. Regardless of the methodology applied, current climate finance pledges of USD100 billion by 2020 - for both mitigation and adaptation - would fall far short of estimated global adaptation costs.

To achieve the Paris Agreement’s long-term temperature goal, current energy systems must be transformed. Australia represents an interesting case for energy system transformation modeling: with a power system dominated by fossil fuels and, specifically, with a heavy coal component, there is at the same time a vast potential for expansion and use of renewables. We used the multi-sectoral Australian Energy Modeling System (AUSeMOSYS) to perform an integrated analysis of implications for the electricity, transport, and selected industry sectors to the mid-century. The state-level resolution allows representation of regional discrepancies in renewable supply and the quantification of inter-regional grid extensions necessary for the physical integration of variable renewables. We investigated the impacts of different CO2 budgets and selected key factors on energy system transformation. Results indicate that coal-fired generation has to be phased out completely by 2030 and a fully renewable electricity supply achieved in the 2030s according to the cost-optimal pathway implied by the 1.5 °C Paris Agreement-compatible carbon budget. Wind and solar PV can play a dominant role in decarbonizing Australia’s energy system with continuous growth of demand due to the strong electrification of linked energy sectors.

Nationally Determined Contributions (NDCs) submitted so far under the Paris Agreement are not in line with its long-term temperature goal. To bridge this gap, countries are required to provide regular updates and enhancements of their long-term targets and strategies, based on scientific assessments. The goal of this paper is to demonstrate a policy-support approach for evaluating NDCs and guiding enhanced ambition. The approach rests on deriving national targets in line with the Paris Agreement by downscaling regional results of Integrated Assessment Models (IAMs) to the country level. The method of downscaling relies on a reduced complexity IAM: SIAMESE (Simplified Integrated Assessment Model with Energy System Emulator). We apply the approach to an EU28 member state - Finland - with the aim of providing useful insights for policy makers to consider cost-effective mitigation options. Results over the historical period confirm that our approach is valid when national policies are similar to those across the larger IAM region, but must include country-specific circumstances. Strengths and limitations of the approach are discussed. We assess the remaining carbon budget and analyse the different implications of 2 degrees C and 1.5 degrees C global warming limits for the emissions pathway and energy mix in Finland over the 21st century.

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.

Integrated Assessment Models (IAMs) models are used to evaluate the technological and economic feasibility of climate goals such as the Paris Agreement’s long-term temperature goal to hold global warming well below 2 ̊C and pursue efforts to limit this warming to 1.5 ̊C above pre-industrial. The results of these models are assessed in Intergovernmental Panel on Climate Change (IPCC) reports, and play a central role in the IPCC Special Report “Global Warming of 1.5°C” (SR1.5).