This article identifies and quantifies the 10 most important benchmarks for climate action to be taken by 2020–2025 to keep the window open for a 1.5°C-consistent GHG emission pathway. We conducted a comprehensive review of existing emissions scenarios, scanned all sectors and the respective necessary transitions, and distilled the most important short-term benchmarks for action in line with the long-term perspective of the required global low-carbon transition. Owing to the limited carbon budget, combined with the inertia of existing systems, global energy economic models find only limited pathways to stay on track for a 1.5°C world consistent with the long-term temperature goal of the Paris Agreement. The identified benchmarks include: Sustain the current growth rate of renewables and other zero and low-carbon power generation until 2025 to reach 100% share by 2050; No new coal power plants, reduce emissions from existing coal fleet by 30% by 2025; Last fossil fuel passenger car sold by 2035–2050; Develop and agree on a 1.5°C-consistent vision for aviation and shipping; All new buildings fossil-free and near-zero energy by 2020; Increase building renovation rates from less than 1% in 2015 to 5% by 2020; All new installations in emissions-intensive sectors low-carbon after 2020, maximize material efficiency; Reduce emissions from forestry and other land use to 95% below 2010 levels by 2030, stop net deforestation by 2025; Keep agriculture emissions at or below current levels, establish and disseminate regional best practice, ramp up research; Accelerate research and planning for negative emission technology deployment. Key policy insights These benchmarks can be used when designing policy options that are 1.5°C, Paris Agreement consistent. They require technology diffusion and sector transformations at a large scale and high speed, in many cases immediate introduction of zero-carbon technologies, not marginal efficiency improvements. For most benchmarks we show that there are signs that the identified needed transitions are possible: in some specific cases it is already happening.

The current project-based carbon market mechanisms such as the Clean Development Mechanism (CDM) and the Joint Implementation (JI) do not have a direct impact on global greenhouse gas emission levels, because they only replace or offset emissions. Nor do they contribute to host country's national greenhouse gas emission reduction targets. Contributions to net emission reductions in host countries is likely to become mandatory in new mechanisms under development such as in the framework for various approaches, a new market-based mechanism and even in a reformed JI. This research analysed the question if approaches for carbon market-based mechanisms exist that allow the generation of net emission reductions in host countries while keeping project initiation attractive. We present a criteria-based assessment method and apply it for four generic options in existing mechanisms and derive implications for future mechanism frameworks. We identified the application of "discounts" on the amount of avoided emissions for the issuance of carbon credits and "standardisation below business as usual" as most promising options over "limiting the crediting period" and "over-conservativeness". We propose to apply these options differentiated over project types based on internal rate of return to ensure cost-efficiency and attractiveness.

This paper discusses methodological issues relevant to the calculation of historical responsibility of countries for climate change ('The Brazilian Proposal'). Using a simple representation of the climate system, the paper compares contributions to climate change using different indicators: current radiative forcing, current GWP-weighted emissions, radiative forcing from increased concentrations, cumulative GWP-weighted emissions, global-average surface-air temperature increase and two new indicators: weighted concentrations (analogue to GWP-weighted emissions) and integrated temperature increase. Only the last two indicators are at the same time 'backward looking' (take into account historical emissions), 'backward discounting' (early emissions weigh less, depending on the decay in the atmosphere) and 'forward looking' (future effects of the emissions are considered) and are comparable for all gases. Cumulative GWP-weighted emissions are simple to calculate but are not 'backward discounting'. 'Radiative forcing' and 'temperature increase' are not 'forward looking'. 'Temperature increase' discounts the emissions of the last decade due to the slow response of the climate system. It therefore gives low weight to regions that have recently significantly increased emissions. Results of the five different indicators are quite similar for large groups (but possibly not for individual countries): industrialized countries contributed around 60% to today's climate change, developing countries around 40% (using the available data for fossil, industrial and forestry CO₂, CH₄ and N₂O). The paper further argues including non-linearities of the climate system or using a simplified linear system is a political choice. The paper also notes that results of contributions to climate change need to be interpreted with care: Countries that developed early benefited economically, but have high historical emission, and countries developing at a later period can profit from developments in other countries and are therefore likely to have a lower contribution to climate change.