Income inequality remains one of the most important indicators of economic wellbeing, social justice and everyday quality of life. Unlike wealth inequality, which is often challenging to uncover and track reliably, income inequality can be measured with far greater precision, making it especially relevant for understanding immediate economic pressures, social mobility and living standards. Its importance has become even clearer following the recent G20 assessment of global wealth inequality, which delivered a bleak outlook and reinforced the need for policy tools that can provide both short- and long-term impact.

A major new international study led by Aalto University and the University of Cambridge now provides the most comprehensive subnational picture of income inequality to date. Mapping three decades of data across 151 countries from 1990 to 2023, the research moves beyond national averages to reveal what is happening within regions themselves. While the results confirm that income inequality is worsening for around half of the world’s population, they also reveal striking ‘bright spots’ where inequality has stabilised or declined, particularly in parts of Latin America. These regions account for roughly a third of the global population and demonstrate that well-designed policy can make a measurable difference.

Professor Matti Kummu of Aalto University, one of the study’s lead authors, explains that this regional focus fundamentally changes how inequality should be interpreted. National data often suggests little long-term movement, but subnational analysis reveals sharply uneven trajectories within the same country. Some regions have seen rising prosperity and improved social outcomes, while others have fallen further behind. Co-lead author Dr Daniel Chrisendo, now at the University of Cambridge, adds that income data is far more complete than wealth data and offers a more practical route for short-term policy intervention. Because income inequality feeds directly into wealth inequality over time, tackling income disparities remains one of the most effective immediate levers available to governments.

Published in Nature Sustainability on 5 December, the study also introduces the open-access Subnational Gini (SubNGini) dataset, accompanied by an online visualisation tool that allows users to explore annual inequality trends worldwide and download the data for further analysis. The platform is designed to help policymakers and researchers link shifts in inequality to particular policy environments and historical moments. India, China and Brazil emerge as especially influential case studies. In India, relative success in several southern states is closely linked to long-term investment in health, education, infrastructure and economic development. In China, rapid growth since the 1990s lifted millions out of poverty but unfolded unevenly, shaped in part by the Hukou system, which restricts rural migrants’ access to urban services; recent reforms aim to reduce these divides. In Brazil, declining regional inequality appears to be linked to a major conditional cash transfer programme that supports low-income families through education and health incentives.

Despite these regional success stories, the overall global outlook remains troubling. One of the UN’s Sustainable Development Goals calls for faster income growth among the poorest 40 per cent of the world’s population. Yet, the study confirms that progress remains far off track and that upward pressure on inequality is more substantial than previously assumed. The research team now plans to expand the dataset to include broader socio-economic and environmental indicators, from ageing and life expectancy to education and access to clean water. For Kummu, the long-term value of the project lies in its ability to move beyond simple correlations and towards a deeper understanding of how inequality, development and environmental change interact — providing the evidence base needed for more informed and effective policymaking.

More information: Daniel Chrisendo et al, Rising income inequality across half of global population and socioecological implications, Nature Sustainability. DOI: 10.1038/s41893-025-01689-4

Journal information: Nature Sustainability Provided by Aalto University