Global energy, costs, and emissions from reverse osmosis desalination under future water scarcity

• We quantify the energy, cost, and emissions trade-offs of reverse osmosis desalination under various climate scenarios and salinity levels. • We assess the interdependencies between desalination feasibility, climate uncertainty, and sustainability outcomes. • Desalination can alleviate water scarcity, but this study shows it poses major energy, emissions, and cost challenges under future scenarios. Desalination can help address water scarcity, but its sustainability is limited by high energy use and dependence on fossil fuels. Using a multi-model analysis, we quantify the energy, cost, and emissions trade-offs of reverse osmosis desalination under various climate scenarios and salinity levels. Under 3°C of warming, addressing global water scarcity through desalination could require up to 1,669 TWh of electricity per year and result in annual emissions of 1 billion tons of CO₂ – accounting for ∼1% of global energy use and 2.5% of emissions – with costs exceeding $130 billion. As salinity rises from 15 to 40 ppt – the typical range from brackish to saline water – energy demand increases by 74%, underscoring the central role of salinity in determining desalination's economic and environmental viability. We find that climate model variability often outweighs differences between warming scenarios, highlighting the importance of incorporating climate uncertainty into water resources planning. In terms of geographical distribution, low-income, water-stressed countries in North and East Africa, the Middle East, Central Asia, and South Asia face the greatest challenges, as limited financial and energy resources hinder the viability of widespread desalination. Without rapid grid decarbonization or dedicated renewable energy, desalination risks locking countries into a high-emissions water future. Ensuring its long-term sustainability will require low-carbon energy transitions and targeted economic support, especially for nations most vulnerable to energy insecurity and climate inequality.