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To reach net-zero greenhouse gas targets, carbon dioxide removal (CDR) technologies are required to compensate for residual emissions in the hard-to-abate sectors. However, dependencies on CDR technologies involve environmental, technical and social risks, particularly related to increased land requirements for afforestation and bioenergy crops. Here, using scenarios consistent with the 1.5 °C target, we show that demand and technological interventions can substantially lower emission levels in four hard-to-abate sectors (industry, agriculture, buildings and transport) and reduce reliance on the use of bioenergy with carbon capture and storage. Specifically, demand measures and technology-oriented measures could limit peak annual bioenergy with carbon capture and storage use to 0.5–2.2 GtCO2e per year and 1.9–7.0 GtCO2e per year, respectively, compared with 10.3 GtCO2e per year in the default 1.5 °C scenario. Dietary change plays a critical role in the demand measures given its large share in residual agricultural emissions.

National net zero emission targets could, if fully implemented, reduce best estimates of projected global average temperature increase to 2.0–2.4 °C by 2100, bringing the Paris Agreement temperature goal within reach. A total of 131 countries are discussing, have announced or have adopted net zero targets, covering 72% of global emissions. These targets could substantially lower projected warming as compared to currently implemented policies (2.9–3.2 °C) or pledges submitted to the Paris Agreement (2.4–2.9 °C).

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

Forest-based climate mitigation may occur through conserving and enhancing the carbon sink and through reducing greenhouse gas emissions from deforestation. Yet the inclusion of forests in international climate agreements has been complex, often considered a secondary mitigation option. In the context of the Paris Climate Agreement, countries submitted their (Intended) Nationally Determined Contributions ((I)NDCs), including climate mitigation targets. Assuming full implementation of (I)NDCs, we show that land use, and forests in particular, emerge as a key component of the Paris Agreement: turning globally from a net anthropogenic source during 1990–2010 (1.3 ± 1.1 GtCO2e yr−1) to a net sink of carbon by 2030 (up to −1.1 ± 0.5 GtCO2e yr−1), and providing a quarter of emission reductions planned by countries. Realizing and tracking this mitigation potential requires more transparency in countries’ pledges and enhanced science-policy cooperation to increase confidence in numbers, including reconciling the ≍3 GtCO2e yr−1difference in estimates between country reports and scientific studies.

Many countries are formulating a long-term climate strategy to be submitted to the United Nations Framework Convention on Climate Change by 2020. Model-based, multi-disciplinary assessments can be a key ingredient for informing policy makers and engaging stakeholders in this process.

The Paris climate agreement aims at holding global warming to well below 2 degrees Celsius and to “pursue efforts” to limit it to 1.5 degrees Celsius. To accomplish this, countries have submitted Intended Nationally Determined Contributions (INDCs) outlining their post-2020 climate action. Here we assess the effect of current INDCs on reducing aggregate greenhouse gas emissions, its implications for achieving the temperature objective of the Paris climate agreement, and potential options for overachievement. The INDCs collectively lower greenhouse gas emissions compared to where current policies stand, but still imply a median warming of 2.6–3.1 degrees Celsius by 2100. More can be achieved, because the agreement stipulates that targets for reducing greenhouse gas emissions are strengthened over time, both in ambition and scope. Substantial enhancement or over-delivery on current INDCs by additional national, sub-national and non-state actions is required to maintain a reasonable chance of meeting the target of keeping warming well below 2 degrees Celsius.

Achieving the collective goal of limiting warming to below 2 °C or 1.5 °C compared to pre-industrial levels requires a transition towards a fully decarbonized world. Annual greenhouse gas emissions on such a path in 2025 or 2030 can be allocated to individual countries using a variety of allocation schemes. We reanalyse the IPCC literature allocation database and provide country-level details for three approaches. At this stage, however, it seems utopian to assume that the international community will agree on a single allocation scheme. Here, we investigate an approach that involves a major-economy country taking the lead. In a bottom-up manner, other countries then determine what they consider a fair comparable target, for example, either a ‘per-capita convergence’ or ‘equal cumulative per-capita’ approach. For example, we find that a 2030 target of 67% below 1990 for the EU28, a 2025 target of 54% below 2005 for the USA or a 2030 target of 32% below 2010 for China could secure a likely chance of meeting the 2 °C target in our illustrative default case. Comparing those targets to post-2020 mitigation targets reveals a large gap. No major emitter can at present claim to show the necessary leadership in the concerted effort of avoiding warming of 2 °C in a diverse global context.

Abstract This article describes the policy decision-support tool, FAIR, to assess the environmental and abatement costs implications of international regimes for differentiation of future commitments. The model links long-term climate targets and global reduction objectives with regional emission allowances and abatement costs, accounting for the Kyoto Mechanisms used. FAIR consists of three sub-models: a simple climate model, an emission-allocation model and a cost model. The article also analyses ten different rule-based emission allocation schemes for two long-term concentration stabilisation targets for greenhouse gases. This analysis shows that evaluating regimes requires not only an assessment of the initial allocation, but also of the distribution of abatement costs and the impacts from emissions trading. The Multi-Stage approach (with a gradual increase of Parties adopting emission intensity or reductions targets) and the Triptych approach (with sectoral targets for all Parties) seem to provide the best prospects for most of the Parties when compared to the other allocation schemes analysed.

AbstractIn this paper we argue that the discussion on how to get to an equitable global climate change regime requires a long-term context. Some key dimensions of this discussion are responsibility, capability and development needs. Each of these, separately or in combination, has been used in designing schemes for differentiation of commitments to limit or reduce greenhouse gas emissions. Many implementation problems of these proposals are often side-stepped. In particular, some proposals may be incompatible with Article 2 of the United Nations Framework Convention on Climate Change (UNFCCC), i.e. they are unlikely to keep the option open of long-term stabilisation of atmospheric greenhouse gas concentrations at relatively low levels. We present some evidence that shifting the emphasis from emission reduction to sustainable development needs can contribute significantly to relieving the threat of human-induced climate change.