Balanced trends and pathways for future global coastal and interior areas in the context of population ageing

Population ageing is increasingly exerting a profound influence on global regional balance and overall development. This study is the first to integrate Shared Socioeconomic Pathways (SSPs) with pension-related policy simulations—such as delayed pension disbursement and postponed retirement ages—to identify the long-term developmental trajectories of global coastal and interior areas from 2030−2060, and to explore potential optimal development pathways. Findings indicate that by 2060, 1) global ageing could substantially exceed the United Nations’ projections, and both SSP1 and SSP5 can significantly narrow the coastal–interior gap; however, taking into account ageing pressures, balanced trends, and environmental costs, SSP1 is better aligned with the long-term win–win and sustainable development objectives of both regions; 2) under SSP1 and SSP5, the developmental gap between global coastal and interior areas will decrease to a ratio of approximately 1.6, reaching a point of balance and potentially maximising economic output; 3) pension expenditures under SSP1 and SSP5 could exceed 40% of global GDP, with every five-year delay in pension disbursement reducing the global pension scale by US $ 4 trillion; and 4) postponing the retirement age could further narrow regional developmental gaps and enhance regional economic output. Extending the retirement age to 65 years, under SSP1 and SSP5, could increase the cumulative global economic output by approximately 14% between 2030 and 2060 and add approximately 1.9 billion people to the labour force, potentially contracting the developmental gap ratios between global coastal and interior areas to 1.624 and 1.594, respectively. Extending the retirement age to 70 years would add a 12% marginal contribution to the economy and approximately 1.7 billion workers, further reducing the respective developmental gap ratios to 1.607 and 1.574.