(July 2014) Throughout human history, people have been on the move—exploring new places; pursuing work opportunities; fleeing conflict; or involuntarily migrating due to changing political, social, or environmental conditions.

Today there are an estimated 230 million international migrants, a number that is projected to double to over 400 million by 2050.1 Beyond the people who cross international borders, probably more than two to three times as many are internal migrants, people who have moved within their own countries.2

The reasons for moving are complex, but over the past decade, as the evidence of global climate change has accumulated, academics, policymakers, and the media have given more attention to migration as a result of environmental change.

A major concern is whether climate change will displace large numbers of vulnerable people around the world. For example, because of rising sea levels, the population exposed to flooding during extreme storms is expected to grow dramatically over the coming decades.

The impacts of climate change will vary widely across the globe—some regions will experience drought and increased temperatures while others will experience more extreme weather such as hurricanes. But people in rural areas, where households rely daily on their local environment, will feel these effects most intensely. A widely cited article estimated that more than 25 million people were displaced by environmental factors in 1995 and claimed that as global warming takes hold, more than 200 million people could be affected by future climate change.3 Many, however, disputed these numbers and rightly clarified that scientists, particularly experts in migration, have little understanding of migration-environment relationships.4

In spite of dozens of academic publications and several international conferences, well-documented cases of environmentally induced migration are mostly limited to large-scale events such as Hurricane Katrina in the United States or the tsunami that affected Indonesia, in which millions of people were displaced due to rapid and dramatic change. The still unclear long-term consequences of these types of events, as well as slower-acting forms of environmental change such as long-term droughts and soil degradation, limit our ability to predict the scale and nature of future human migration under accelerating global environmental change. New research, however, continues to shed light on the relationships between migration and the environment.

This Population Bulletin explores the relationship between migration and the environment and highlights innovative research from the Population Centers funded by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. This research uses new approaches to link demographic, social, and environmental science methods, enabling researchers to more explicitly link people to the environment on which they depend. This linking, combined with following people over time, permits researchers to determine how environmental change contributes to people’s mobility and how migration results in environmental change.

The research suggests that the popular narrative of “environmental refugees” is oversimplified and inaccurate; rather, environmentally induced migration can be temporary, and is often within a country and over relatively short distances. Smaller numbers of people move across international borders.

Also, because of the variety of ways in which migration is a response to environmental change, policies on migration are unlikely to be adaptable enough to different situations and environmental pressures. Resilience policies and programs, however, present an opportunity to reduce the impacts of disasters and environmental change, and to assess environmental migration in context.

Jason Bremner is associate vice president in International Programs at PRB, and director of PRB's Population, Health, and Environment Program. Lori M. Hunter is an associate professor of sociology, Institute of Behavioral Science, Programs on Population, Environment and Society, at the University of Colorado, Boulder. She is also editor-in-chief of Population and Environment. Funding for this Population Bulletin was provided by Grant 5R24HD042839 to the Center for Public Information on Population Research at PRB by the Eunice Kennedy Shriver National Institute of Child Health and Human Development. Lori Hunter's effort on this Population Bulletin was supported by Grant 5R24HD066613 to the University of Colorado's Population Center by the Eunice Kennedy Shriver National Institute of Child Health and Human Development.


  1. Philip Martin, "The Global Challenge of Managing Migration," Population Bulletin 66, no. 2 (2013).
  2. Neli Esipova, Anita Pugliese, and Julie Ray, "The Demographics of Global Internal Migration," Migration Policy Practice 3, no. 3 (2013): 3-5.
  3. Norman Myers, "Environmental Refugees: A Growing Phenomenon of the 21st Century," Philosophical Transactions of the Royal Society of London B 357, no. 1420 (2002): 609-13.
  4. Richard Black, "Environmental Refugees: Myth or Reality"? Working Paper No. 34 (Geneva: United Nations High Commissioner for Refugees, 2001).