Increasing heat likely a major factor in human migration

Rising temperatures due to climate change are likely influencing human migration patterns, according to a new study by Rita Issa of University College London and colleagues, published May 24 in the open-access journal PLOS Climate.

In the last decade, heatwaves were frequent, and surface temperatures were the warmest on record. As the planet warms, many people are expected to leave their homes to escape extreme temperatures. However, the exact role of heat in human migration is not yet understood. To illuminate this relationship, Issa’s team conducted a review of research documents, annual reports, working papers, government documents and scientific literature that examined the impact of heat on human migration or the heat that migrants experience along their journey.

Of the 32 studies that considered how heat impacts migration, half found a correlation between exposure to heat and the likelihood that a person will migrate. The vast majority of the 18 studies that assessed the effects of heat on migrants as they travel reported negative health impacts, such as heat related illnesses, heat stress and early death. The research also reports that people suffered more greatly from the heat when they lived in regions with poor infrastructure, or had insufficient workplace adaptations, lower educational level and low socioeconomic status.

The new study’s findings suggest that heat likely influences human migration patterns, including the timing of when people move, the risks they face along the way and the heat they may experience once they settle. However, the fact that only half of the included studies found a correlation between heat and migration suggests that heat is not the only factor driving migration. The researchers point out that no literature has reported a “temperature threshold” above which people are certain to migrate. Instead, they propose the development of accepted ways to compare temperature measurements, heat impacts and environmental factors that cause migration, which they believe would support future efforts to study climate migrants and enact policies that protect them from harm.

The authors add: "Migration is a valid adaptive response to extreme heat. Part of the reason there is no certain temperature at which people will migrate is instituting adaptive measures that limit the consequences of extreme heat, as we see in places like the UEA where air conditioning is widely used. However, often the poorest and most marginalised remain vulnerable to temperature extremes, including migrants. These findings offer a dual opportunity for action: decisive policy to limit global heating upstream, through reducing carbon and other greenhouse gas emissions; and adaptive strategies that take into account human vulnerability - spanning urban planning, occupational adaptations, household modification and more - to assist in lessening the impacts of heat on human health, wellbeing and productivity."

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Press-only preview: https://plos.io/43i9SZT

In your coverage please use this URL to provide access to the freely available article in PLOS Climate: https://journals.plos.org/climate/article?id=10.1371/journal.pclm.0000214

Contact: Rita Issa, rita.issa@ucl.ac.uk

Citation: Issa R, Robin van Daalen K, Faddoul A, Collias L, James R, Chaudhry UAR, et al. (2023) Human migration on a heating planet: A scoping review. PLOS Clim 2(5): e0000214. https://doi.org/10.1371/journal.pclm.0000214

Author Countries: France, The Netherlands, Norway, Spain, Switzerland, UK

Funding: KRvD receives funding by the Gates Cambridge Scholarship (OPP1144) for her PhD research and for the publication fees from the Bill & Melinda Gates Foundation. This paper was completed as part of the Lancet Countdown project (Tracking the connections between public health and climate change) at www.lancetcountdown.org which is supported by an unrestricted grant from the Wellcome Trust (200890/Z/16/Z). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

Competing Interests: The authors have declared that no competing interests exist.