Sustainability Delivering long-term energy security and climate resilience hinges on the ability of energy systems to decouple growth from environmental degradation. A truly sustainable energy transition prioritizes low- emission, resource-efficient pathways that protect ecosystems, minimize pollution and support global net-zero goals. The ETI’s sustainability dimension evaluates system performance in terms of energy efficiency, emissions intensity, environmental impact and the share of clean energy sources in the overall energy mix. Sustainability over the past 10 years Over the past decade, the sustainability dimension was the strongest and most consistent of the three system performance components, with a steady but incremental upward trend (Figure 8). Clean electricity reached 49% of global generation in 2023,51 signalling meaningful progress towards the 90% target needed by 2050 for net zero.52 This momentum in the power sector contrasted with lagging progress across other parts of the energy system. Overall, the world remained off-track for 1.5-2.0°C pathways, and rising global temperatures underscored the urgency of more systemic and accelerated action to bend the emissions curve. –From 2016 to 2022, sustainability scores improved gradually, driven by gains in energy efficiency, modest emissions intensity reductions and a rising share of clean energy sources in the energy mix. –In 2023, a temporary reversal in progress occurred, as economic and industrial activity rebounded after disruptions related to the COVID-19 pandemic, prompting many countries to prioritize energy security and equity, which in turn led to increased fossil fuel use in some regions. –In 2024-2025, scores resumed their upward path. For instance, a 1.2% gain was seen in 2025, supported by a rebound in renewable energy deployment and reduced emissions intensity in several large economies. Despite this improvement, long-term structural challenges persisted: –Despite a growth in average global scores of 15.8% over the decade, the average share of clean energy in the primary energy mix across ETI countries remained just 14.8% – highlighting slow progress in the decarbonization of heating, transport and industry. –Energy efficiency progress was uneven. Average global energy intensity scores improved by nearly 8% over the decade, but momentum slowed. IEA reported a drop in improvement to 1.3% in 2023 from 2% in 202253 (far below the 4% annual improvement needed to meet net-zero targets).54 2016 2017 2018 2019 2020 2021 2022 2023 2024 2025Dimension score (0-100) 54.055.0 53.056.057.058.0 56.1 55.856.256.9 55.1 54.7 54.4 54.3 54.3 54.0Sustainability dimension trend, 2016-2025 FIGURE 8 Source: World Economic Forum. Over the past decade, the sustainability dimension was the strongest and most consistent of the three system performance components. Fostering Effective Energy Transition 2025 29