Emission pathways consitent with 2C global temperature limit

The role of negative CO2 emmissions for reaching 3 C-insights form integrated assessment modelling

Mitigation implications of remaining carbon budget allocation rules for Mediterranean countries

The Mediterranean Basin is a climate change hotspot, experiencing accelerated warming and strong environmental vulnerability. Mediterranean Sea surface temperatures have increased by approximately 1.5 °C over the past four decades, underscoring the urgency of coordinated mitigation efforts. In this context, this study examines how alternative allocation criteria for distributing the remaining carbon budget compatible with the Paris Agreement (well below 2 °C) affect emission pathways among the 21 signatory countries of the Barcelona Convention. Using a mitigation pathway derived from the Global Change Analysis Model, the analysis evaluates emissions trajectories from 2030—anchored in current Nationally Determined Contributions—through 2100. Five allocation principles are assessed: Grandfathering, Per Capita, Per Capita Convergence, Equal Cumulative Per Capita, and Ability to Pay, each reflecting different trade-offs between equity and feasibility. Results indicate that, irrespective of the allocation rule, rapid and sustained decarbonisation is unavoidable. At current emission levels, the regional carbon budget would be exhausted by 2035, requiring average annual reductions of approximately 6% between 2030 and 2050 to meet global targets. While population-based criteria yield the largest regional budget and are more equitable, they imply more disruptive transitions. In contrast, emissions-based approaches are more feasible but risk reinforcing existing inequalities. These findings highlight significant implications for fossil fuel-dependent economies and stress the importance of regional cooperation. The Barcelona Convention emerges as a key platform to facilitate equitable burden-sharing and coordinated climate action in the Mediterranean region.

A scenario assessment of the global mitigation effort in the light of the 2035 climate finance goal

The United Nations Framework Convention on Climate Change (UNFCCC) agreed in 2024 to boost finance for climate change in developing countries to USD 300 billion by 2035. In this study, we assess how much mitigation of greenhouse gases (GHGs) is possible by generating this amount of revenues from carbon pricing in industrialized regions. We assess a scenario that considers carbon prices differentiated for industrialized, transition and developing regions. We find that such scenario provides 16% more GHG emissions reductions by 2035 compared to a scenario where the existing national mitigation targets (represented by the nationally determined contributions as of 2022) are achieved. Despite this, a considerable gap remains in terms of the revenues needed to achieve emissions reductions aligned with a pathway securing the climate target of 1.5 °C global warming above pre-industrial levels. Therefore, these outcomes suggest that considerably larger climate mitigation actions are needed beyond the climate finance goal agreed by nations under the UNFCCC. In addition, we highlight by means of additional scenarios the implications (in terms of emissions reductions, carbon price revenues and consumption losses) of the absence in the carbon pricing scheme of the major GHG emitters from industrialized regions (USA) and from developing regions (China).

Establishing SI in space for climate action

The Earth is unequivocally warming with consensus mankind is the major cause. The potential for societal catastrophe is second to none!. The ‘Paris Agreement’ (2015) seeks to contain the rise in mean Earth temperature to <2°C above pre-industrial levels with a target of <1.5°C and led to the establishment of ‘NetZero’ emissions targets for the 2050s. Even if NetZero goals are met, the world still faces significant consequences from embedded climate change. There is thus an urgency to establish a robust integrated (satellite/local) global climate observing system to monitor the Essential Climate Variables (ECV’s) of GCOS, especially the anthropogenic forcing agents e.g. Green House Gases and results of their mitigation. However, understanding decadal: climate signatures, feedbacks and potential tipping points together with complexities and interdependencies of Earth-system-cycles is also critical to ensure mitigation and adaptation strategies are timely and fit-for-purpose. The magnitude of the signals/trends that need to be detected are at the level of a few tenths %/decade, commensurate with observational noise from natural variability and current instrument performance. Minimising the time to unequivocal detection of trends requires improved sensitivity/uncertainty and be considered, ‘throwing a gauntlet’. to the observational community from climate modellers and policy makers. This challenge, ultimately rests with the metrology community to tailor and/or enhance the principles and infrastructure of the SI, that has served society for 150yrs, to facilitate trust in long-time-base data-sets of bio/geo-physical variables, derived from multiple observing systems. Remote sensing of Earth from space, is the primary means to obtain the global data/knowledge needed to inform our understanding of climate sensitivity. Two thirds of the 55 ECVs require observations from space. The worlds space-agencies have long understood the need for robust calibration and validation, particularly post-launch, seeking to correct degradation caused by the harsh environments of launch and space. Difficult to quantify biases and uncertainties to SI, limit confidence in climate understanding and hesitancy in action. To address this challenge space-agencies have embraced metrology and the SI. Embedding key principles: evidence of SI-traceability, comprehensive uncertainty budgets, comparisons, documented methods, within an international framework to facilitate independent assessment of satellite data quality against, ‘independent Fiducial Reference Measurements’ (FRMs). In addition to trust/confidence it allows harmonisation of different data-sets. The ultimate FRM needs to be established in space and this paper will also describe the ESA satellite mission, TRUTHS, under development for launch in 2030. TRUTHS will, for the first time, establish a ‘metrology institute in space’. Flying a primary standard of the SI, the satellite will not only establish direct observations of Earth and Sun at uncertainties needed for climate (~10X improvement on current instruments) but will also serve as a ‘gold standard’ reference to provide in-flight calibrations of instruments on-board other satellites, improving their performance and robustly anchoring them to SI. This symbiotic partnership of metrology and space-agencies firmly extends the reach of SI into space addressing the challenge placed upon the observational community to deliver trustworthy data with the fidelity needed by policy makers to undertake ‘fit-for-purpose' climate action.

Analysis and Outlook on Actions to Address Climate Change in 2025

The World Meteorological Organization (WMO) has confirmed that 2024 was the warmest year on record. Global warming is moving increasingly closer to the [Formula: see text]C temperature limit set by the Paris Agreement. Against a background of global economic uncertainty and geopolitical instability, international efforts to address climate change continued to move forward in 2025. The 30th session of the Conference of the Parties to the United Nations Framework Convention on Climate Change (COP30), held in Belém, Brazil, in November 2025, achieved positive outcomes on a range of key issues. As a responsible major country, China has actively responded to a complex international environment and multiple challenges, remained firmly committed to a green and low-carbon development path, and made important contributions to promoting the global transition toward green and low-carbon development.

Limiting warming by CO2 and methane mitigation in an expanded scenario space

Anthropogenic methane (CH4) currently contributes more than 0.6 ∘C to global warming, and CH4 mitigation is a powerful option to limit near-term warming. Assessments of greenhouse gas (GHG) mitigation rely on Integrated Assessment Model scenarios with typically non-linear emission trajectories (due to economic optimization) and similar mitigation ambition for CO2 and CH4. However, climate targets are often linear and focused primarily on CO2. Here, we present a complementary scenario generation approach to systematically map peak warming resulting from two political choices: the net zero emissions year for CO2 or GHG after linear reductions, and the simultaneous change in CH4 emissions. We show that without CH4 mitigation, peak warming exceeds 1.7 ∘C (50% likelihood), and the likelihood of keeping warming below 2 ∘C drops below 50% with net zero CO2 emissions after 2050. Irrespective of CH4 mitigation stringency, limiting warming to 1.5 ∘C is no longer plausible. An additional sustained linear 10% reduction in CH4 emissions ( ~ 35 MtCH4/year) until 2050 increases the 2 ∘C-compatible remaining carbon budget by ~ 165 GtCO2. These results emphasize the benefit of near-term CH4 mitigation. Systematically mapping peak warming across two main choices for climate policy – when carbon dioxide reaches net zero emissions and how fast methane emissions are cut – shows that near-term methane mitigation is essential for keeping warming below 2 °C, as suggested by climate model experiments under mitigation scenarios.