Climate change is making some regions of the world less habitable for humans, influencing where and why people move. According to the Internal Displacement Monitoring Centre (IDMC), 46.9 million new internal displacements were recorded in 2023, out of which 26.4 million (approximately 56%) were due to climate extreme events. As a result, there is growing scholarly and policy interest in the intersection between climate change and human mobility.
Defining climate migration is a nuanced and contested subject, as migration decisions rarely stem from environmental factors alone. In 2007, the International Organisation for Migration (IOM) defined environmental migrants as people who move due to “sudden or progressive environmental changes that adversely affect their lives or living conditions.” Yet, recent research increasingly shows that relatively few migrants attribute their decision solely to climate change, even when environmental pressures are significant. In most instances, economic hardship, conflict, governance, and demographic conditions—often interacting with environmental and climate stressors—collectively shape mobility outcomes.
Recently, the term “climate mobility” has gained prominence as a more inclusive, human-centered term that accounts for the various ways movement may be influenced by climate change impacts. Mobility can range from voluntary migration as an adaptation strategy or forced displacement in response to life-threatening hazards. It can be permanent, seasonal, or temporary, and can occur within or across national borders. Conversely, “immobility”—when people choose not to leave or are forced to stay—can occur depending on factors like place attachment, livelihood dependencies, limited social networks, or inadequate governance.
The Overlooked Link Between Slow-Onset Events and Mobility
A prominent factor that shapes migration responses is the type of environmental hazard: whether slow-onset or rapid-onset. Rapid-onset events, such as hurricanes, floods, and wildfires, occur suddenly and cause immediate disruption, typically resulting in short-term displacement. Responses often focus on humanitarian aid, temporary shelter, and reconstruction.
On the other hand, slow-onset events are phenomena that are often caused or intensified by climate change that occur over prolonged periods of time. The Cancun Adaptation Framework lists these as sea level rise, increasing temperatures, ocean acidification, glacial retreat, salinization, land and forest degradation, biodiversity loss, and desertification. These phenomena can permanently alter livelihoods, food security, housing, and resource availability, prompting migration that is more gradual but equally consequential. Effective policy responses may include long-term planning for relocation, migration pathways, and adaptive infrastructure in at-risk communities.
Despite this, most national and international policies that address climate mobility continue to focus primarily on sudden-onset disasters and hazards. As early as 2009, Frank Laczko and Christine Aghazarm from the IOM noticed this pattern in the academic field, calling for a greater focus on slow-onset impacts. Although data on slow-onset events and mobility is limited, a review of the existing literature showed that most research centers on climate variability (such as changes in temperature and precipitation), drought, and sea level rise. Additionally, most movement linked to slow-onset events remains within a country’s borders: of 89 studies reviewed, 64% examined internal migration, 19% international, and 17% both.
Patterns of mobility also differ widely across regions. Studies from Latin America and the Caribbean found that during droughts, younger individuals often move short distances to nearby rural towns, driven by off-farm job opportunities and lower relocation costs. Drought-related migration in Ghana was mostly seasonal, while in rural Zambia it was often permanent. In coastal Bangladesh, migration linked to sea level rise was found to be temporary in many cases, challenging assumptions that such movement is always permanent.
When migration is framed solely as a response to sudden disasters, policymakers risk overlooking the millions who move—or are unable to move—because of slow-onset changes. Incorporating this dimension into research and policy can improve anticipatory planning, ensure safer migration pathways, and help communities adapt in place where possible.
Case Study: Eastern Caribbean
The Eastern Caribbean offers a compelling example of how countries are beginning to address climate mobility at the national level. The region encompasses an area including the Gulf of Mexico, the Caribbean Sea, and adjacent areas of the Atlantic Ocean. Eastern Caribbean countries face multiple slow-onset impacts—sea level rise, salinization, increased temperatures, and desertification—which threaten infrastructure, agriculture, and coastal livelihoods. Most populations and economic centers lie within 1.5 km of the coast, making them highly exposed. Rising seas and saltwater intrusion have damaged infrastructure and marine ecosystems, while declining rainfall and rising temperatures have caused crop failures and rural-to-urban migration.
Governments in the region have started to acknowledge these risks, and the Caribbean more broadly has taken a forward-looking approach to climate policy. Eastern Caribbean countries have incorporated climate mobility concerns into their national frameworks, such as National Adaptation Plans (NAPs) and Nationally Determined Contributions (NDCs). Several members of the Organisation of Eastern Caribbean States (OECS) have voted in favor of the Global Compact for Safe, Orderly, and Regular Migration, an international agreement that outlines measures for addressing climate migration. Additionally, Antigua and Barbuda and Saint Lucia approved the 2014 Brazil Declaration and Plan of Action, a road map to address displacement trends.
Still, national frameworks remain fragmented and often focus on rapid-onset events. Between 2020 and 2021, IOM conducted policy assessments across six Eastern Caribbean countries—Antigua and Barbuda, Dominica, Grenada, Saint Kitts and Nevis, Saint Lucia, and Saint Vincent and the Grenadines—under the Regional Dialogue to Address Human Mobility and Climate Change Adaptation in the Eastern Caribbean project. Across the six countries studied, there were 25 policies referencing climate mobility, but only 13 explicitly mentioned slow-onset events. Saint Lucia led with seven climate mobility policies, four of which reference slow-onset impacts. Others acknowledge the issue to varying degrees, often emphasizing planned retreat and adaptation, though their implementation strategies remain unclear.
Most recently, OECS member states signed a 2023 Ministerial Declaration on Migration, Environment, and Climate Change, recognizing the need to address both sudden- and slow-onset impacts. Ministers of National Security and Immigration from the OECS convened in Dominica to express concern over the growing displacement caused by environmental degradation and to call for improved cooperation, data collection, financing, and policy coordination. This declaration marks a promising step toward a more comprehensive approach to climate mobility—one that future research should continue to monitor.
Implications for Policy
As countries continue to develop and update national frameworks and policies related to climate change, there is a crucial opportunity to give equal consideration to the impacts of slow- and rapid-onset events. Integrating these concerns into National Adaptation Plans (NAPs), Nationally Determined Contributions (NDCs), and disaster risk reduction strategies would help ensure that migration linked to gradual environmental change is anticipated, rather than reacted to.
Equally important is the need for more research and better data. Many countries lack reliable systems to monitor internal migration, especially movements driven by gradual and cumulative environmental pressures. Strengthening institutional capacity, improving inter-agency coordination, and establishing dedicated funding mechanisms for planned relocation and resilience-building will be key steps forward.
Aside from prioritizing different environmental hazards, considering the human dimensions of mobility—why people move, where they go, and what barriers they face—should remain at the center of policy design. Collecting data at the household and community levels can help governments identify emerging migration patterns and engage receiving communities in adaptation planning. In doing so, countries can better prepare for the realities of climate mobility while ensuring that responses to slow-onset events are equitable, inclusive, and forward-looking.
Finally, all planning and policymaking should uphold the principles of migration with dignity. First advanced by then-President of Kiribati Anote Tong, Migration with Dignity was a concept developed to give Kiribati people power and choice over whether, when, and how they migrated. The framework emphasizes that all persons have a right to dignity regardless of circumstances, and that countries should help migrants transition to an equal or better life.
The Environmental Law Institute has contributed to this dialogue through its partnership with the Dignity Rights Initiative, Delaware Law School, the UN International Organization for Migration, and the Ocean Policy Research Institute. Together, these partners co-authored Migration with Dignity: A Legal and Policy Framework and The Methodology and Application of a Migration with Dignity Framework. To learn more about ELI’s work on environmental displacement and migration, click here.