In-depth Q&A: How does climate change drive human migration?

The once-stable climate that people have lived in for millennia is now rapidly shifting.

Extreme weather events, such as droughts and floods, are forcing many people to flee their homes.

Meanwhile, in the face of slow-onset changes, such as sea level rise and droughts, others are making the difficult decision to leave in search of a better life.

Climate change can interact with other factors, such as conflict, economic opportunity and politics, to drive migration. If managed well, migration can be a valuable adaptation strategy to reduce peoples’ vulnerability to a warming climate and increase resilience to further changes.

Most migration happens within borders. However, the media focus is frequently on cross-border migration, often framing migrants as a threat to national security – despite the large body of research showing that, in the round, migration actually benefits societies.

In this in-depth Q&A, Carbon Brief explores how climate change is already leading to displacement and migration, what future changes in human movement might look like, and the measures that are being taken to protect displaced people.

Carbon Brief has spoken to experts in climate change and migration, including scientists, lawyers, NGO leaders and communications experts. This article also pulls together case studies from around the world, offering a range of examples of climate-driven migration and displacement.

How is human migration linked to the climate historically?

Life on Earth has been shaped by the climate. Species have evolved to survive and thrive in their surroundings and, if conditions change, they must either adapt to their new environment or move to find more hospitable conditions. The history of human evolution shows this clearly.

Changes in temperature and rainfall – largely driven by fluctuations in the Earth’s orbital pattern – have influenced the global distribution of homo sapiens and other hominid species for millions of years.

Experts estimate that the first homo sapiens evolved in Africa some 200,000 years ago during a geological period called the “Pleistocene” – a climatically unstable epoch marked by repeated ice ages during which the global average temperature could change by up to 15C in a few decades.

It is unclear exactly when people first left Africa and spread around the world – a phenomenon often called the “peopling of the Earth”. Some of the earliest estimates suggest that there were homo sapiens living outside Africa some 180,000 years ago. But experts generally agree that the main waves of migration out of Africa began some 60,000-90,000 years ago and lasted for tens of thousands of years.

Map showing human migration paths out of Africa. The numbers indicate the number of years ago that humans reached different parts of the world. Adapted from Peter Hermes Furian / Alamy Stock Photo.

The largest waves of migration were roughly every 20,000 years, when the cold and dry conditions of the early Pleistocene were punctuated by warm summers in the northern hemisphere, caused by the wobble of Earth’s axis. These warm periods created green “corridors” between Africa and Eurasia which allowed humans to move in both directions between the two continents.

Similarly, variations in the strength of the Atlantic Meridional Overturning Circulation – a major pattern of ocean circulation – brought “wet phases” that made the normally “inhospitable” Saraha and Sahel “amenable” for human passage at certain times.

Even changing ice sheets may have influenced human migration patterns, as “early people may have taken advantage of winter sea ice that connected islands and coastal refugia” to move between them, according to one study.

Throughout the Pleistocene, the human population rose and fell in line with the climate, growing when temperatures were warm and plummeting when ice ages hit.

Around 12,000 years ago, the planet entered a new geological phase called the Holocene, characterised by “unusually stable” climatic conditions. The regular temperatures and freshwater availability “maintained the conditions that enabled human development”, according to a feature article in the journal Nature.

In the newly stable climate, nomadic groups settled in regions with hospitable climates – typically near fertile land and reliable water sources – to form the first settlements. Agricultural practices quickly developed and, today, only a small proportion of humankind still practise nomadic lifestyles.

A study on the “human climate niche” finds that “for thousands of years, humans have concentrated in a surprisingly narrow subset of Earth’s available climates”. The authors note that most people – as well as their crops and livestock – clustered in areas with an average annual temperature of 11-15C, while a small group also lived in tropical regions with average annual temperatures of 20-25C.

The stable climate allowed the human population to surge from some five million people to more than seven billion in around 10,000 years. Research suggests that the scale of the civilisations today would have been impossible without the climatic stability of the Holocene.

Homo sapiens are the only species to have populated and adapted to every continent on Earth. Instead of evolving into different species to suit the climate, as has happened with many other animals, humans have adapted their behaviour and immediate environment to suit them.

Reliable seasons have also allowed people to develop patterns of seasonal migration. For example, many communities practise transhumance – a seasonal movement of livestock between fixed summer and winter pastures.

Others move for formal jobs that last the season and return home for the rest of the year. For example, the UK has relied on seasonal labour to pick crops for many years.

Romanian fruit pickers working in an English vineyard. Source: Jeff Gilbert / Alamy Stock Photo.

However, experts warn that the planet is now leaving its safe climatic space. Many scientists argue that the world has entered a new geological epoch known as the Anthropocene, which is characterised by the human influence on the climate. In this new climate epoch, areas of the planet where people have lived for thousands of years may become uninhabitable.

How is climate change making regions less habitable?

The stable climate that humanity has relied upon for millennia is shifting. Global average surface temperatures over 2011-20 were around 1.1C warmer than pre-industrial levels due to human activity.

One study identifies an average annual temperature of 29C as the upper limit of the “human climate niche”. Above this temperature threshold, regions may become unlivable, the paper warns.

The authors find that, over 1960-90, only around 12 million people, accounting for less than 1% of the global population, lived outside of this climate niche. In today’s climate, more than 600 million people – 9% of the global population – live in areas that have been pushed above this threshold temperature.

The paper warns that if warming reaches 2.7C above pre-industrial temperatures – in line with current emission pledges – around one-third of people could be pushed outside of this niche. “Exposure outside the niche could result in increased morbidity, mortality, adaptation in place or displacement,” the paper says.

As the planet warms, “record-shattering” heatwaves are already becoming more likely and hundreds of thousands of additional deaths are recorded every year due to extreme heat. Around 61,000 people across Europe died due to intense heat during the summer of 2022 alone.

High temperatures are particularly dangerous when the air is humid, because it makes sweating – the body’s most important mechanism to combat the heat – less effective. “Extreme humid heat” has more than doubled in frequency since 1979, as warmer air is able to hold more moisture.

The Intergovernmental Panel on Climate Change (IPCC) warns that parts of India, the Persian Gulf, the Gulf of California and the southern Gulf of Mexico are “already experiencing heat stress conditions approaching the upper limits of labour productivity and human survivability”. It adds that the risk of heat stress is particularly high in cities.

Around 50-75% of the global population could be exposed to periods of “life-threatening climatic conditions” due to extreme heat and humidity by 2100, the IPCC says.

Poorer, tropical regions suffer the greatest economic damage from heatwaves. Extreme heat has already suppressed per-person gross domestic product (GDP) in tropical countries, such as Brazil, Venezuela and Mali, by more than 5% per year. In contrast, high-latitude nations, such as Canada and Finland, have seen only a 1% per year GDP reduction.

Climate change is also making a range of other extreme weather events, such as floods, droughts, storms and fires, more intense and likely.

Hot, dry conditions are driving widespread crop failures, as well as killing livestock and harming aquaculture. More than one-third of crop and livestock loss in low- and middle-income countries is due to drought.

Climate extremes, such as storms and flooding, can also wipe out crops, while rising temperatures are allowing pests to expand into new regions.

Between 1970 and 2019, the number of weather, climate and water-related disasters – including droughts, floods and wildfires – reported globally increased fivefold. In this time, extreme weather events killed more than two million people and caused US$4.3tn in economic losses.

The aftermath of extreme weather events can see outbreaks of diseases, a spike in violence against women and girls and disruption to basic services, such as education and healthcare.

As the planet continues to warm, exposure to climate extremes will increase. Younger generations from low-income countries in the Middle East and North Africa, where populations are generally rising, will face greater exposure to extremes than children in high-income countries.

The interactive map below shows country-level exposure to heatwaves, wildfires, river flooding, crop failure, drought and tropical cyclones. It compares the lifetime exposure to these extremes of a person who turned 60 in the year 2020 to that of a child born in 2020. This is shown for future scenarios where the climate pledges made under the Paris Agreement (known as “nationally determined contributions”, or “NDCs”) are met and a 1.5C warming pathway. (Note that the NDC scenario uses pledges updated until 2020, which is consistent with around 2.5C of global warming.)

The orange and red shading indicates that newborns in 2020 will have a greater exposure to the climate extremes, while blue indicates less exposure. Note that the scale on the heatwave map is different from the scale on the other extremes.

Slow-onset changes in the climate can also make regions less habitable.

For example, the freshwater storage is shrinking as the climate warms. Two-thirds of the global population live under conditions of “severe water scarcity” for at least one month of the year – nearly half of whom live in India and China.

Sea level rise is another threat to habitability – especially for small island nations. Average global sea level has already risen by around 0.2 metres, forcing residents of some small island nations to move.

The Maldives is the lowest-lying nation in the world, with more than 80% of its 1,190 coral islands sitting less than one metre above sea level. Mohamed Nasheed – the first democratically elected president of the Maldives – told Carbon Brief that the coral bleaching is impacting fisheries, pushing people to “migrate to the capital” and leave their “traditional ways of living”.

Mohamed Nasheed – ex-president of the Maldives - explains how climate change is impacting migration patterns on the islands. Video credit: Ayesha Tandon.

By 2050, more than a billion people living in low-lying cities and settlements will be at risk from “coastal-specific climate hazards”, the IPCC says with “high confidence”.

The burden of current coastal flood risk and future sea level rise falls disproportionately on tropical regions, especially in Asia. In this region, tropical storms are frequent and a higher sea level can allow storm surges to sweep further inland.

The figure below shows risks to people, land and infrastructure from a one-in-100 year coastal flood event – where yellow indicates no sea level rise and purple indicates two metres of additional sea level rise, compared to 2020 levels.

The size of the circle indicates the magnitude of the impact. The top-left quadrant of each circle shows the number of people affected, top right shows the number of flights disrupted, bottom left shows the kilometres of coastline affected, and bottom right indicates whether sea level rise will have a positive or negative impact on wetlands.

Risks to cities and settlements from sea level rise, compared to 2020 levels. The top left, top right, bottom left and bottom right quadrants of each circle show the number of people affected, number of flights disrupted, kilometres of coastline affected, and impact on wetlands. Source: IPCC (2022) Figure CCP2.3.

Is climate-driven migration already happening?

Lake Chad – a vast body of freshwater lake on the edge of the Sahara desert – provides water to more than 30 million people. However, it has been shrinking for decades, due to human-caused climate change, as well as development increasing human demand for freshwater and the development of irrigation systems.

Lake Chad. Source: Robert Harding / Alamy Stock Photo.

Conducting fieldwork in the region, Amali Tower – the founder and executive director of the not-for-profit organisation Climate Refugees – learned that many communities have been “moving every year to keep pace with the lake’s shrinking”. The earliest movement that Tower learned of was recorded in 1973, she tells Carbon Brief.

This example shows that people have been moving in response to human-caused climate change for decades. However, official monitoring of climate-driven displacement and migration is more recent.

In the second working group of its sixth assessment report (AR6), the IPCC states with “high confidence” that “climate hazards are a growing driver of involuntary migration and displacement”.

The report emphasises the “diversity” in climate-related migration “outcomes”, explaining that “specific climate events and conditions may cause migration to increase, decrease or flow in new directions”.

It adds:

“Climate-related migration originates most often in rural areas in low- and middle-income countries, with migrant destinations usually being other rural areas or urban centres within their home countries”.

Every story of human movement is different. However, these stories can be divided into categories based on why people leave their homes, how quickly they make the decision to leave, and whether or not they plan to return.

“Displacement” is the term used when people are forced to flee their homes – often suddenly – for example when faced with an extreme flood or storm. Conversely, “migration” describes a decision to move in search of a better quality of life, often after years of deteriorating quality of life.

The International Organization for Migration – a UN body that promotes “humane and orderly migration” – defines climate migration as:

“The movement of a person or groups of persons who, predominantly for reasons of sudden or progressive change in the environment due to climate change, are obliged to leave their habitual place of residence, or choose to do so, either temporarily or permanently, within a state or across an international border.”

The graphic below shows different categories of mobility and immobility due to climate change.

Different categories of human mobility and immobility due to climate change. Source: Groundswell report (2021).

Displacement due to extreme weather events is usually temporary and people often try to move back home as soon as it is safe. As such, they do not travel far, only crossing international borders when they are nearby and convenient.

For example, in the summer of 2023, Canada experienced its most severe wildfire season in recorded history. Officials ordered thousands of homes to evacuate and more than 100,000 people fled their homes, including some 25,000 members of Indigenous communities.

Climate change doubled the likelihood of “extreme fire weather” in eastern Canada preceding and during the blaze. Authorities monitored the flow of evacuees, providing support and guidance as the wildfires progressed. As the fires subsided, officials and insurance companies began rebuilding the damaged areas and moving residents back in.

The Internal Displacement Monitoring Centre (IDMC) finds that disasters – including floods, droughts and storms – displace millions of people every year.

The graphic below shows the number of internal climate-related displacements recorded every year over 2008-22 due to floods, drought, storms, wildfires and extreme temperatures.

Drivers of internal climate-related displacement over 2008-22. Data source: Internal Displacement Monitoring Centre.

Most climate-linked internal displacement is due to floods and storms. More than 32 million climate-linked internal displacements were recorded in 2022 – mostly in Asia and the Pacific.

One-quarter of disaster displacements in 2022 were due to flooding in Pakistan, which was the world’s largest disaster displacement event in a decade. The rainfall, which was made more intense by climate change, affected more than 33 million people – around 15% of the country’s population – and triggered a nationwide humanitarian crisis.

Around 70% of internally displaced people did not have adequate shelter for weeks, instead seeking refuge at roadsides or on embankments, and thousands of families were still homeless and without livelihoods by February 2023.

The map below shows internal climate-linked displacements in 2022. Larger circles indicate higher numbers of displaced people. The five countries that reported the highest numbers of displaced people in 2022 are shown at the top of the map.

Number of internal displacements – forced movements of people within the borders of their country – recorded during 2022 due to weather-related disasters. Adapted from the 2023 Global Report on Internal Displacement by the Internal Displacement Monitoring Centre.

This IDMC collects data from sources including national governments, the UN, research institutions and the private sector to track internal displacement.

Prof Jane McAdam is a professor of law and the director of the Kaldor Centre for International Refugee Law at the University of South Wales. She tells Carbon Brief the proxy indicators are often used – such as housing loss and the number of people moving in from home – which many countries do not compile well.

Yet she stresses that the IDMC provide “the best numbers we’ve got”, noting that it is difficult to collect data about peoples’ movement, and adding that there are no numbers at all for cross-border climate-related movement

Extreme weather events are typically “rapid onset” disasters. They unfold quickly, destroying important infrastructure and forcing people to flee suddenly. However, climate change also causes slow-onset disasters, which can unfold over months or even years.

When people migrate, they generally move the shortest distance possible, according to Prof Mathew Hauer – an associate professor of sociology at Florida State University. “You can think of this like friction,” he tells Carbon Brief. This means that most climate-related migration is internal.

“It’s not uncommon to be internally displaced within your own country multiple times or over multiple years before wanting to cross an international boundary,” Tower tells Carbon Brief.

She adds:

“When people do cross an international boundary on their first instance, it is generally something extremely sudden, extremely forceful, extremely violent, and their nearest border is a foreign country rather than the internal city within their country.”

“In many cultures, migrants are most often able-bodied, young men”, the IPCC says. It explains that, often, “women wait longer to migrate because of higher social costs and risks and barriers such as social structures, cultural practices, lack of education and reproductive roles”.

Hauer tells Carbon Brief that young adults are the most likely to migrate, because they are generally less “embedded into the community” than their older counterparts who often have children, houses or land.

When people do travel internationally, it is most often between two countries with shared borders, with few documented examples of long-distance, climate-linked migration, according to the IPCC.

In some instances, rather than moving individually or as a family, an entire community may decide to resettle elsewhere. Managed retreat and community relocations involve the strategic relocation of assets and people away from areas at risk, often allowing those areas to be restored to their natural state.

Over the past three decades, around 1.3 million people have been relocated through managed retreat in response to natural hazards including tropical storms, flooding, erosion, earthquakes and tsunamis.

However, the decision to migrate is complex and is rarely driven by climate change alone.

How does climate change interact with other drivers of migration?

More than 11 million people live in a strip of land across El Salvador, Guatemala, Honduras and Nicaragua known as the “dry corridor”. Around 73% of them live in poverty.

More than half of the area’s inhabitants work in agriculture. As droughts intensify and crop yields decline, more families are being pushed into famine. Today, the dry corridor is one of the most food insecure in the world. The area also has a long history of conflict and political uncertainty.

Hundreds of thousands of people from the dry corridor have attempted to cross into the US in recent years to seek a better quality of life. Reporting by the New York Times says that migration from the dry corridor is driven by a range of interacting factors which make the community more vulnerable and less resilient over time.

Climate change is “the ultimate ‘threat multiplier’, aggravating already fragile situations and potentially contributing to further social tensions and upheaval”, according to the UN Environment Programme.

For example, one study finds that “extreme displacement levels are more likely in contexts marked by low national income levels, nondemocratic political systems, high local economic activity, and prevalence of armed conflict”.

“It is impossible ever to say climate change alone causes movement,” McAdam tells Carbon Brief. Instead, she says that climate change amplifies and intersects with “existing drivers of movement”.

These drivers can be divided into “push” and “pull” factors. Poverty and conflict are examples of push factors which can drive people from homes. Conversely, pull factors such as political security and better-paid jobs draw people towards their destination.

Climate change disproportionately impacts poor and marginalised communities, as communities without much disposable income are generally less able to adapt to changes in the climate and take longer to recover after they are hit by extreme weather events.

Climate change has the strongest impact on migration in agriculturally dependent countries, where people tend to be less wealthy, more dependent on consistent weather patterns and more vulnerable to the impacts of climate change.

Prof Ayesha Siddiqi – an assistant professor in human geography at the University of Cambridge – tells Carbon Brief that poorer people often live in more “risky” and “vulnerable” places where wealthier people do not want to live, making them more vulnerable to climate impacts.

The main pull factor behind migration is economic, so people typically move from poorer to wealthier areas. Many migrants send sums of money, or “remittances”, back to their friends or family.

Half of all remittance money is sent to poorer, rural regions, where “it is helping to keep millions of people out of poverty”, the UN says. About one in nine people globally are supported by remittances. For most poor countries, personal remittances far exceed official development assistance.

There were around 281 million international migrants in 2020, accounting for 3.6% of the global population. Around 60% of these people moved for work, and they collectively sent $702bn in international remittances back home. Low- and middle-income countries received $540bn, with India, China, Mexico, the Philippines and Egypt ranking as the top five recipients.

Human development factors, such as access to better healthcare and education services, are also a pull factor for migration.

Social networks can influence migration patterns, Hauer tells Carbon Brief. He explains that every person who moves changes the likelihood that other people will move – a phenomenon known as “cumulative causation”.

For example, if someone moves to a new city, their family members may be more likely to follow them there. Conversely, if the population of someone’s hometown drops significantly, they may be more likely to leave to seek out a city with more people and opportunities.

“It turns out that that second-order effect is humongous,” Hauer tells Carbon Brief. He led a study which finds that in the US, for every person who moves as a direct result of sea level rise, a further 10 other people move due to the knock-on effects.

This means that climate change could become a trigger for more people to move along migration routes that already exist, he says.

Journalist Gaia Vince, who has written a book about climate-driven migration, tells Carbon Brief that in many countries, wealthy people are already moving away from dangerous areas, meaning that the people and economy left behind gets “poorer and weaker”. She explains that “this movement is not just of people – it’s also of capital, of industry and of resources”.

Meanwhile, conflict and violence are among the biggest push factors driving migration. The internal displacement monitoring centre estimates that more than 28 million people were displaced by violence and conflict in 2022.

Central and eastern Africa are consistent hotspots of conflict-induced migration. The IDMC ranks the countries with the most internally displaced people from both conflict and climate disasters as of 31 December 2022. Sudan, Nigeria, the Democratic Republic of Congo, Ethiopia and Afghanistan all rank in the top 10 on both lists.

(It is important to note the difference between internally displaced persons and internal displacements. The former is a snapshot of all the people living in internal displacement at the end of the year, while the latter refers to the total number of forced movements of people within the borders of their country recorded during the year.)

There is a large body of academic literature exploring the links between climate change and conflict – and there is ongoing debate on the extent to which the two can be linked. Some studies find that climate change and conflict are clearly linked, while others find that other factors are more important.

When synthesising all available evidence, the IPCC says:

“There continues to be little observed evidence that climatic variability or change cause violent inter-state conflict. In intra-state settings, climate change has been associated with the onset of conflict, civil unrest or riots in urban settings.”

The IPCC notes that rising food prices due to reduced agricultural production and global food price shocks “are associated with conflict risk and represent a key pathway linking climate variability and conflict”.

However, it adds that while the climate has affected armed conflict within countries, “their influence has been small compared to socioeconomic, political and cultural factors”.

Meanwhile, many people who want to migrate are unable to do so – a situation known as “immobility”.

This may be because they cannot find or afford the resources they need – such as food or transportation – or because they are not healthy enough to move. It may also be because they do not have the social network they require to make such a big change.

These people may be trapped in increasingly uninhabitable locations without any viable path to safety.

Can models estimate climate-driven migration?

Academics have been trying to estimate the potential scale of climate-driven migration for decades.

Prof Norman Myers – an honorary visiting fellow from the University of Oxford was one of the first to produce a definitive number, claiming in the 1990s and early 2000s that climate change could create 200 million climate migrants by 2050.

This number was circulated widely, finding its way into the UK government’s Stern Review on the economics of climate change in 2006 and a speech by then-UN secretary general Ban Ki-Moon at the UN general assembly in 2008, among others.

However, many academics doubted the validity of the method Myers used. Speaking to the BBC in 2011, Prof Stephen Castles – then from Oxford University’s International Migration Institute – said:

“He simply took a map of the world, worked out what areas would be inundated if the sea rose, say by 50cm, and then simply assumed that all the people affected by this sea level rise would have to migrate - and that a lot of them would migrate to developed countries. Really there was no basis for it.”

“His methodology was very crude…I don’t think he ever dreamt for a moment that it would become the definitive estimate,” McAdam tells Carbon Brief.

Migration modelling has come a long way since Myers’ estimate. The Groundswell report on internal migration, commissioned by the World Bank, was the first to project climate-linked migration across dozens of individual countries using a standardised method.

The Groundswell team began with a “gravity model”. This model assumes that people are most likely to move to wealthy areas with a high population. It also finds that the closer two locations are, the more likely people are to move between them.

They “calibrated” the model on a country-by-country basis using historical data on human movement in response to changes in the climate. The report focuses on three key driving forces – water availability, crop productivity and sea level rise.

The team then uses projections from the inter-sectoral impact model intercomparison project to simulate population movement until the year 2050 under three different emissions and socioeconomic pathways:

1. “Pessimistic”: SSP4, RCP8.5
2. “More inclusive development”: SSP2, RCP8.5
3. “More climate friendly”: SSP4, RCP2.6

Scenario one assumes very high emissions in a world of ever-increasing inequality. This scenario projects the highest number of migrants.

Scenario two assumes the same high emissions level, but in a “middle-of-the-road” socioeconomic development scenario in which global population growth is moderate and levels off in the second half of the century.

Scenario three assumes the “middle-of-the-road” socioeconomic scenario, but low warming, and projects the lowest number of migrants.

The model does not include displacement due to extreme weather events, such as those counted by the IDMC. It also does not look at high-income nations or small island states.

The original report, published in 2018, estimated the number of internal migrants due to the slow-onset changes in climate in sub-Saharan Africa, south Asia and Latin America. It was updated in 2021 to include the Middle East and north Africa, east Asia and the Pacific, and eastern Europe and central Asia.

The main findings of the report are shown in the graphic below, where yellow shows the pessimistic scenario, dark green shows the more inclusive development pathway and light green shows the more climate-friendly pathway.

Key findings from the Groundswell report on internal climate-linked migration (2021).

The report concludes that hundreds of millions of people could be forced to migrate due to climate change by 2050.

Prof Bryan Jones is an assistant professor of sustainability at the Marxe School of Public and International Affairs and worked on the models used in the Groundswell report.

He tells Carbon Brief that sub-Saharan Africa is projected to have the largest number of internal climate migrants for two main reasons.

First, the region is highly vulnerable to climate impacts, he says. Second, he explains that the largest populations of many west African countries are currently under 18. This means that they will be “coming into their prime migratory years as the climate crisis is worsening”.

However, Jones cautions against taking the numbers too literally, highlighting the uncertainty in the models.To make the results “consistent and comparable” across the countries analysed, the authors only use data that could be collected across all of these countries, he explains. He notes that for many lower-income countries, this data is quite limiting.

Dr Alexander de Sherbinin – a senior research scientist and co-chair of the Columbia Climate Schools’ climate mobility network – is another author on the report. He tells Carbon Brief that some nuance can be lost when looking over large areas.

For example, the Groundswell report assumes that increasing rainfall and crop production will give people more security, making them less likely to leave their homes. However, de Sherbinin notes that often people want to leave their homes, but do not have the money to do so. In these instances, increased crop production could give farmers the money they need to move.

The report also finds that “hotspots” of inward and outward migration will emerge as early as 2030.

Jones tells Carbon Brief that sub-national hotspot mapping is the most important output of the report, because regardless of the scenarios used in the modelling, the relative “attractiveness” of different regions compared to one another was fairly constant, allowing the authors to identify the regions most at risk.

So many climate hotspots showed up in Africa – and, in particular, around Lake Victoria, which is surrounded by Kenya, Tanzania and Uganda – that the Africa Climate Mobility Initiative was set up to investigate further, Jones says.

New methods are also being explored to track human movement, providing further data to feed into models.

For example, agent-based models can characterise how individual decision processes lead to changes at the population level. These are becoming increasingly popular – in part because they capture social interaction and the social networks that result from it.

Other examples include a study using mobile phone data to track the movement of people before and during Cyclone Mahasen, which struck Bangladesh in 2013. And Hauer’s work modelling migration patterns in the US using data on taxes from the Internal Revenue Service.

Is migration an appropriate climate adaptation strategy?

Climate adaptation refers to measures that an individual or community can take to adapt to the present and future impacts of climate change. Building sea walls, installing air conditioning or planting drought-resilient crops are all examples of climate adaptation measures.

However, it is becoming economically infeasible for some communities to continue implementing in-situ adaptation methods and migration is increasingly being discussed as an adaptation strategy.

If managed well, migration can reduce vulnerability and increase resilience. The IPCC outlines four main categories for climate-linked human movement:

1. Adaptive migration, where migration is an outcome of individual or household choice.
2. Involuntary migration and displacement, where people have few or no options except to move.
3. Organised relocation of populations from sites highly exposed to climatic hazards.
4. Immobility, when people are unable or unwilling to move from areas of high exposure for cultural, economic or social reasons.

Seasonal migration is one example of adaptive migration that is already taking place and which some communities have already been practising for decades.

The 2024 Africa migration report says:

“Across Africa, seasonal mobility has long been used as an adaptation mechanism to deal with climate variability as well as a risk management strategy to manage in unpredictable and extreme environments.”

This type of migration is already an important aspect of rural livelihood strategies in the face of slow-onset climate change impacts, such as desertification, soil degradation, variable rainfall patterns and temperature changes.

(See “How does climate change interact with other drivers of migration?” for more detail on seasonal migration as an economic strategy.)

Dr Chandni Singh is a senior researcher at the Indian Institute for Human Settlements and a Carbon Brief contributing editor.

Singh tells Carbon Brief that classifying migration as a binary – either an adaptation strategy or a failure to adapt – does not reflect the situation on the ground. She explains that there are also equity and ethical considerations in calling migration an “adaptation strategy”.

For example, many small island developing states reject the idea that migration and planned relocation are adaptation measures for them, saying instead that it is a forced response, Singh says.

Alex Randall – a programme lead at the Climate and Migration Coalition – tells Carbon Brief that there is “a lot of merit” in the idea of migration as an adaptation strategy.

However, he highlights concerns raised by the Women in Migration Network that “if we talk about ‘migration as adaptation’ as a sort of panacea, it normalises all forms of human movement in the context of climate change – and some of them obviously not adaptive”.

There are many examples of “maladaptive” migration decisions, which make people more vulnerable to climate change, rather than less.

For example, most residents in the poverty-stricken Indian city of Kolar work in agriculture and other types of farming. However, as the climate warms, Kolar drying out, with devastating impacts on crop yields.

A cattle grazing on dry land at Vemagallu village of Kolar on 21 April 2017. Credit: Sipa US / Alamy Stock Photo.

Singh conducted research on water availability in Kolar. She tells Carbon Brief that many farmers from Kolar – mainly men – have started to commute to nearby cities such as Bangalore in search of work. They send money back home to their families, who invest it in digging borehole wells to extract water from the ground.

However, as more people dig wells and droughts stretch on, the water tables in Kolar are dropping. “In the four years that I was doing fieldwork, the wells kept going deeper and deeper,” Singh tells Carbon Brief. She adds that wells have a high “failure rate”, often drying up after only a year.

She says this type of migration is maladaptive, because the city spends large amounts of money without producing “anything new”, such as schools or long-lived infrastructure. In fact, her study finds that attempting to finance the wells often leaves people in debt.

Many experts tell Carbon Brief how important it is for communities to have agency in migration outcomes, but lament that this often does not happen.

Robin Bronen is a human rights attorney and executive director of the Alaska Institute for Justice. She tells Carbon Brief about the importance of the “right to self determination”.

She explains “most countries in the world have no governance structure to help communities relocate because of the climate crisis”. There are many examples of people who were “forcibly relocated” by their governments, with “horrific consequences”, she says.

“Disasters create opportunities for particular kinds of capitalism to thrive,” Siddiqi tells Carbon Brief. She notes in some instances, forced displacements can be very lucrative for land developers carrying out land grabs:

“When a big land developer decides that they might want access to land, they might use reasons like ‘this is a real flood risk and so we’re going to move this entire community and we’re going to place them somewhere else’.

“So that’s a particular kind of forced displacement that’s taking place all over the global South, in all kinds of big cities.”

Relocations can also leave out the most vulnerable members of society. For example, Siddiqi tells Carbon Brief that in the Philippines, hundreds of people at risk from typhoons are being forcibly relocated. She explains that people with paperwork and signed land titles were able to claim a new house in the relocated site.

However, she says “the poorest people whose paperwork was not in order, who didn’t have legal claims to their land, who were too physically unwell, too old, or too young to be able to afford the cost of the move…got stuck behind”

Workers build houses for typhoon survivors at a Government relocation site in the outskirts of Tacloban city, Leyte province in central Philippines, 2014. Credit: Associated Press / Alamy Stock Photo.

Singh adds that relocations can be very “patronising” to the affected communities, giving them little or no choice about what housing they are moved into and how their new communities are structured. Paying attention to what communities want and the livelihoods they engage in is critical, she says.

In a Carbon Brief guest post, Dr Miyuki Hino – then-doctoral student at Stanford University – says that relocation is “controversial and challenging”. She adds:

“Managed retreat is not a low-regrets option, nor is it easily reversed. There are social and psychological difficulties in moving people from their homes – particularly if it involves loss of cultural heritage or moving a family from their ancestral lands.”

The existence of involuntary “immobile” or “trapped” populations can also be maladaptive. Singh tells Carbon Brief that immobility is a particular problem for women:

“A lot of women I’ve spoken to over many years of fieldwork would like to move and meet their personal aspirations, but social norms around women’s work restrict them from moving out of their villages.”

Older people are also less likely to move. As a result, Hauer tells Carbon Brief, older people often end up being left behind in “very precarious places” after younger and more mobile people leave.

Mariam Traore Chazalnoel is a senior policy officer at the UN organisation for migration. She tells Carbon Brief that many of the “invisible costs” of migration, such as mental health impacts, cultural losses and changing traditions, have not been assessed yet.

In the coming years, it will be important to evaluate the impacts of the migration policies that have already been implemented, Chazalnoel says.

What rights do people displaced by climate change have?

In the aftermath of the second world war, millions of people fled their homes due to fear of persecution. Governments created the 1951 Refugee Convention to provide a legal status for “refugees”.

This international agreement defines a refugee as someone who was forced to flee their home country due to a well-founded fear of persecution due to race, religion, nationality, membership of a particular social group or political opinion, and has crossed an international border to find safety in another country.

Individuals seeking refugee status must apply for asylum once they reach their destination country. Those whose applications are accepted are granted refugee status. This often gives them the option to work, find housing and eventually get citizenship in their destination country.

If their application is declined, they are usually obliged to leave the country.

The 1951 Refugee Convention is the key international treaty on refugees, but it does not mention climate change. McAdam tells Carbon Brief that although the term “climate refugee” is not recognised by law, “there are certainly refugees who are impacted by climate change”.

Some individuals have suggested that a special climate refugee status should be created. However, Dina Ionesco – the head of the migration, environment and climate change division at the UN migration agency – warns that this may lead to people being excluded.

For example, she notes that most climate-linked movement is internal, while the refugee convention deals only with international displacement. She also says that many people impacted by climate change – especially the poorest – move due to a mix of factors and “would not be able to prove the link to climate and environmental factors”.

Bronen adds that the term “refugee” indicates a “failure of national governments to protect the people within their jurisdiction”. However, she says this is not the case in many of the countries worst affected by climate change – many of whom are “begging [countries in] the northern hemisphere to stop producing greenhouse gas emissions because they are doing their best to protect the people within their country”.

Meanwhile, there is no legal definition of a migrant. However, there are still international agreements about how migrants should be treated. International human rights law provides a possible legal route for people fleeing the impacts of climate change.

Under international refugee law and human rights law, there is a principle called “non-refoulement” – a French term meaning “non-removal” or “non-return”. McAdam explains that this principle “prevents people from being sent to a place where they face a real risk of being persecuted or arbitrarily deprived of life, or a real risk of being subjected to torture or cruel, inhuman or degrading treatment”.

This principle was used in the landmark case of Ioane Teitiota v New Zealand 2020.

In 2007, Ioane Teitiota and his wife, Angua Erika moved from the small island state of Kiribati to New Zealand on a three-year work permit. When the couple inadvertently overstayed their visa, Teitiota’s lawyer decided that his best chance of staying in the country was to apply for refugee status in New Zealand, on the grounds that he faced indirect persecution from human-caused global warming.

After a series of rejections and court appeals, Teitiota was deported to Kiribati in September 2015, and his wife and children followed the next week. Teitiota lodged a complaint against New Zealand with the human rights committee in 2016, saying that his deportation had been unlawful. He argued that sea level rise limited the amount of habitable space in Kiribati, leading to violent land disputes, and highlighted the environmental degradation including saltwater contamination of the freshwater supply.

Ultimately, the committee decided that Teitiota’s deportation had not been unlawful because he did not face “a real, personal and reasonably foreseeable risk of a threat to his right to life”. However, the committee recognised that “without robust national and international efforts”, the effects of climate change may expose people to life-threatening risks or cruel, inhuman, or degrading treatment, “thereby triggering the non-refoulement obligations of sending states”.

This decision was hailed as a landmark ruling. The United Nations human rights office published a press release on the decision under the headline “Historic UN Human Rights case opens door to climate change asylum claims”.

McAdam tells Carbon Brief that while the case was the first of its kind, the ruling reiterates the existing principle of non-refoulement under human rights law.

Meanwhile, some countries are considering the idea of new climate visas, which could allow people to enter the country due to the impacts of climate change in their home country.

However, McAdam tells Carbon Brief that climate visas are not strictly necessary. Instead, she emphasises the importance of opening safe and legal “migration pathways” that allow people to move for a range of reasons, including education or work. “It’s just opening up other opportunities for people who want to move to do so,” she says.

For example, Australia’s Pacific engagement visa allows up to 3,000 workers and their families from the Pacific and Timor-Leste to migrate permanently to Australia each year.

And in November 2023, the Australia-Tuvalu falepili union treaty was announced, which will allow up to 280 residents from the island of Tuvalu to migrate to Australia each year. Under the treaty, Tuvaluans will be able to access key services in Australia, such as education, healthcare and the right to earn money, on arrival.

The agreement has been widely praised as “groundbreaking”, “landmark” and “sweeping”. In an article in the Conversation published later that week, McAdam wrote:

“[The treaty] is groundbreaking. Under this deal, Australia will provide migration pathways for people from Tuvalu facing the existential threat of climate change. It is the world’s first bilateral agreement on climate mobility…

“Historically, most Pacific visa programs in Australia (and the region) have been tied to labour mobility. And none has specifically referenced climate change as a driving rationale. In contrast, the measures announced this week are deliberately framed in the context of climate change and – furthermore – are not tied purely to work.”

McAdam led the initial drafting of the Pacific Regional Framework on Climate Mobility (pdf), which was adopted by Pacific Leaders in November 2023. It provides a coordinated approach to climate-related human mobility in the Pacific region.

She tells Carbon Brief that the Pacific is “one of the most mobile regions in the world”, noting that many Pacific islanders travel to other parts of the Pacific for work, including Australia and New Zealand, or work as seafarers travelling the world.

For example, in mid-2022, 34,400 Pacific islanders worked in Australia and New Zealand on temporary worker programmes. And about one-fifth of Tuvalu’s population of 12,000 have already left the island permanently. Many travelled to New Zealand after winning a ballot that grants up to 1,300 citizens of various Pacific island nations permanent residence in the country every year.

McAdam tells Carbon Brief that she thinks a planned “en-masse relocation” of Pacific islanders is unlikely – and not what they want, either. Instead, she thinks that individuals will move gradually, clustering in diaspora communities, including in Australia and New Zealand. For example, she says there is a large community of Tuvaluans living in Auckland in New Zealand.

Nathan Akehurst is a writer specialising in migration, control borders and climate. He tells Carbon Brief that without clear safeguards, climate visas are not the best solution.

Akehurst tells Carbon Brief that visas risk being “very small and limited”, letting in only a few hundred people, while allowing governments to call themselves “progressive” and keep the rest of their migration policy the same.

The EU has the potential to showcase the benefits of flexibility of free movement – for example its rapid protection response for refugees fleeing Russia’s invasion of Ukraine, Akehurst tells Carbon Brief. However, he adds that “sadly its overall approach to people seeking protection, including from climate-affected areas, is increased militarisation and criminalisation”.

The European Union is a good example of the benefits of flexibility and free movement, Akehurst tells Carbon Brief. For example, he notes that free movement throughout the European Union was scaled up rapidly to allow refugees from Ukraine to quickly move throughout Europe when Russia invaded in 2022.

How is the international community responding to climate-driven migration?

The IPCC was the first international body to link climate change and migration.

The organisation has been publishing the world’s most authoritative summaries of the state of climate science since its formation in 1988.

Its first report, published in 1991, states that “the gravest effects of climate change may be those on human migration as millions are displaced”. Since then, reports from the IPCC have given increasing attention to climate-driven migration.

IPCC first assessment report WG2 (1990).

However, it took decades for discussions about climate-driven migration to reach the UN Framework on Convention Climate Change (UNFCCC) through their annual conference of the parties summits.

The International Organization for Migration says migrants were “invisible in the climate agenda” until climate-driven migration was briefly mentioned in the Cancun Agreement on adaptation and the Doha Agreement on loss and damage – adopted at COP16 in 2010 and COP18 in 2012, respectively.

The Warsaw International Mechanism on Loss and Damage was established at COP19 in 2013 to address loss and damage – a term used to describe the serious and, in many cases, irreversible impacts that climate change is already causing around the world.

This mechanism was the result of years of demands from small island nations and less developed countries. One of its nine sections focuses on “human mobility, including migration, displacement and planned relocation”.

Section six of the Warsaw International Mechanism on Loss and Damage, which focuses on “human mobility, including migration, displacement and planned relocation”. Source: UNFCCC.

COP21 in Paris was “a turning point” in the climate migration discussion, Chazalnoel tells Carbon Brief. She says the Paris Agreement includes a “small but mighty reference to migration”.

Reference to “migrants” in the Paris Agreement, (2021).

At COP21, countries also agreed to create a taskforce on displacement. The taskforce sits under the Warsaw Mechanism and aims to “develop recommendations for integrated approaches to avert, minimise and address displacement related to the adverse impacts of climate change”.

Leaders from small island states have also used COPs as a chance to raise the alarm about people from their nations who will soon be forced to leave.

For example, in 2021, Tuvalu’s foreign minister Simon Kofe recorded a speech for leaders at COP26 in Glasgow standing waist-deep in the ocean. He called climate change an “existential threat” and said that “climate mobility must come to the forefront” of discussions.

At COP27 in Sharm el-Sheikh 2022, Mia Mottley – the prime minister of Barbados – gave a speech warning that without a “different approach” to climate finance, “we are going to see an increase in climate refugees”.

Chazalnoel tells Carbon Brief that awareness of climate-driven migration in UNFCCC discussions has increased in the past decade. A decade ago, “you had to convince countries that [climate-driven migration] was an important topic”, but nowadays there is no “pushback”, she says.

The last decade has also seen important developments in international migration policy, separate from the UNFCCC process.

For example, the Nansen initiative on disaster-induced cross-border migration was created in 2012. This was then followed by the Platform on Disaster Displacement, which McAdam says is “arguably the key body in this field today”.

The Sendai framework for disaster risk reduction was adopted by UN member states in March 2015 to “reduce, prevent and respond to disaster risks across the globe”.

However, the Global compact for safe, orderly and regular migration, agreed in December 2018, was arguably the most important milestone.

Chazalnoel followed these negotiations closely and tells Carbon Brief that this agreement marks the first time that the UN has agreed on “guiding principles on how to manage international migration”.

She adds that the text of the agreement is “heavy on looking at the climate and environmental dimensions”.

The global compact lists 23 objectives for better managing migration at local, national, regional and global levels.

These include the need to reduce involuntary climate-related migration and displacement, increase the adaptive capacity and resilience of vulnerable populations through greater international cooperation, and develop strategies for managing climate-related migration in ways that respect human rights and address humanitarian needs.

The document is not legally binding. It commits signatories to improving co-operation on international migration, but allows countries to remain in charge of their own migration policies.

When it was signed, the compact was controversial, sparking protests across Europe. “Supporters of the agreement say it will foster co-operation and improve the handling of millions of migrants, but critics fear it will encourage more illegal migration,” BBC News reported at the time.

However, many experts have told Carbon Brief more action is needed to help climate migrants – especially in lower income countries. “There is a culture of acceptance, that migration and displacement is okay for the poor – for the brown, for the black, for the marginalised indigenous communities,” Tower tells Carbon Brief.

Instead of creating legal routes for migrants and refugees, many nations are putting up barriers to entry.

For example, seven of the world’s biggest emitters – responsible for almost half of the world’s historic greenhouse gas emissions – collectively spent more than $33bn (£26bn) on border and immigration enforcement over 2013-18.

This is more than twice as much as they spent on climate finance in this period, according to a report from the Transnational Institute – an international research and advocacy institute – called “The Climate Wall”.

The report adds:

“This militarisation of borders is partly rooted in national climate security strategies that since the early 2000s have overwhelmingly painted migrants as ‘threats’ rather than victims of injustice. The border security industry has helped promote this process through well-oiled political lobbying, leading to ever more contracts for the border industry and increasingly hostile environments for refugees and migrants.”

The border security industry “is already profiting from the increased spending on border and immigration enforcement and expects even more profits from anticipated instability due to climate change”, the report says.

The report also highlights the “synergy” between fossil fuel companies and top border security contractors, noting that executives from each sector sit on each other’s boards. It concludes:

“This nexus of power, wealth and collusion between fossil fuel firms and the border security industry shows how climate inaction and militarised responses to its consequences increasingly work hand in hand.”

This is despite the benefits that migrants can bring to societies. Smoothing the path for immigrants to integrate into destination countries could add between $800bn and $1tn to the global economy annually, according to the MckInsey Global Institute – a US multinational strategy and management consulting firm.

There is an abundance of research showing the economic benefits of immigration – both for the origin and destination countries, for immigrants and native people. For example, one study concludes:

“The gains to eliminating migration barriers amount to large fractions of world GDP – one or two orders of magnitude larger than the gains from dropping all remaining restrictions on international flows of goods and capital. When it comes to policies that restrict emigration, there appear to be trillion-dollar bills on the sidewalk.”

Ravishaan Rahel Muthiah is the communications director at the Joint Council for the Welfare of Immigrants. He says developed nations have a moral obligation to welcome climate-driven migrants:

“We want to support people in their right to stay in their countries of origin. But if they choose to move because of the circumstances of climate breakdown, which is caused by the global north, colonialism, and multinational fossil fuel corporations from the global north, then they should be welcomed to our countries.”

How is climate-linked migration discussed in the media?

In February 2023, UN secretary general Antonio Guterres said that climate change could cause a “mass exodus of entire populations on a biblical scale”.

Newspapers across the world picked up on this phrase, including the Guardian, Daily Mail, Washington Post, Japan Times and Times of Israel, bringing global attention to the issue of climate-driven migration.

However, many people are wary about such striking language.

Using dramatic language is about “weaponising people’s fear about migration in order to drive some kind of climate action,” Akehurst tells Carbon Brief. He adds:

“Well-intentioned actors raise the ‘threat’ of climate linked migration to encourage climate action but all this does is risk bolstering support for migration control not climate action.”

Instead of pushing climate action, this fear often leads to hardening borders to prevent migrants from entering the country, he says.

(See “How is the international community responding to climate-driven migration?” for more detail on border militarisation.)

The not-for-profit Climate Refugees published a blog post saying that although Guterres’ comments were “well-meaning”, they may have “unfortunate consequences” for people impacted by climate change, given the “era of growing hostility towards migrants”.

Media coverage of complex topics such as climate-driven migration can play a big role in framing how they are perceived by the general public. Many negative stereotypes and assumptions about refugees have been projected onto climate migrants.

Rahel Muthiah says it is easy to use migration as a “scapegoat for all of society’s ills”:

“There has been a series of myths on migration that have been embedded over decades that now create the perfect storm for climate migration to also be used as a fear mongering tactic.”

Although most climate-driven migration is internal, media stories around climate-driven migration often focus on cross-border migration because this is “more disruptive and has all sorts of geopolitical consequences”, Jones tells Carbon Brief.

Randall tells Carbon Brief that climate-driven migration posed a “paradox” for the right-leaning media in the past, but says this has shifted as the science of climate change has become more widely accepted:

“In the past, climate-driven migration was always a dilemma for the right-leaning media, because on the one hand, they were broadly climate sceptic. And on the other hand, they were also always looking for a new immigration scare story…I imagine that in their newsrooms, they were thinking, ‘We can’t really do much on this because it would involve accepting the facts of climate change.’

“One of the consequences behind the acceptance of climate change is that it opened up the possibility of [the right-leaning media] running stories about climate migration and tapping into some of those apocalyptic narratives, or creating stories that fit with the refugee discourse that they already had.”

A report on the representation of climate-linked migration in UK media finds that the media focuses most on Pacific islanders, who are described almost exclusively as victims, and Syrian refugees who were labelled a “threat to European security” and “driver of conflict and terrorism”.

Right-leaning papers have a history of publishing inflammatory language on refugees and migrants from public figures – including Italy’s prime minister Georgia Meloni and the UK’s former home secretary Suella Braverman.

“The dominant migration narrative we’ve heard has been centred on the threat of foreigners overwhelming us,” author Gaia Vince writes in her book “Nomad Century”. She tells Carbon Brief that it is “ridiculous” that “we’ve allowed the entire narrative around immigration to be set by right-wing populists and nationalists”.

Singh adds that the narrative of millions of climate refugees moving from the global south to the global north is “alarmist and downright incorrect”, as many more people move within country borders than internationally.

The imagery used to show climate migrants can also be misleading. One analysis on images in newspapers and websites finds that “the climate migrant/refugee appears as a racialised figure, a passive and helpless victim of global warming”.

But even for the well-intentioned, it can be difficult to get the framing around climate-driven migration right.

Newspapers often report on large numbers from modelling studies when discussing climate-driven migration. These stories provide attention-grabbing headlines, breaking through the saturated media landscape and bring public attention to climate-driven migration.

The Groundswell report produced by the World Bank finds that by 2050, around 50-200 million people could be internally displaced due to climate change.

(See: “Can we model climate-driven migration?” for more information on how the model was produced)

Numbers from the top-end of the pessimistic scenario – the highest numbers generated by the models – were presented as the key findings of the report.

“The World Bank was very keen to get the top level numbers out there,” Jones tells Carbon Brief. He says the numbers are good for generating media attention, as the media “tends to latch on” to big numbers. Most importantly, he says, the big numbers generate investment from important policymakers.

The media quickly picked up on this, reporting that across the six regions studied, 216 million people could be internally displaced due to climate change by 2050.

Randall calls the use of big numbers “well intentioned, but misguided”. He adds:

“There’s a desire to quantify this issue and show that it’s important, and people feel that they can do that by putting a very large number on it… But how those numbers end up being used in the wild may not be how people intended them to be read.”

For example, Rahel Muthiah tells Carbon Brief that on the “far-right”, big numbers can be used as a “scare tactic” to encourage a hardening of borders – especially in countries in the global north:

“[Big numbers] evoke these images of millions of people standing on the border waiting to come in. And when you’ve had this constant barrage of negativity from the government, then you get this hysteria, this false fear instinct that comes into play across the country.”

Randall says that quantifying the number of people who may move as a result of climate change is important, but thinks that “using them as cornerstone of advocacy and campaigning on the issue is maybe misguided”. He adds:

“What we’re aiming for are policies grounded in inequity and justice. There have been lots of movements that have achieved those things in the past, on other issues, without using huge numbers.”

McAdam tells Carbon Brief that the use of big numbers can be “frightening”, and make people feel as if there is no solution. She adds the numbers do not reflect the fact that people will not move all at once, and many will move within their own countries, not across borders.

Akehust says using big numbers can dehumanise people. And Tower tells Carbon Brief that big numbers can be “very unreliable”, noting that they do “nothing to unpack and contextualise” the situations around migration and “tend to excite border security rather than human security”.

Jones says that when the Groundswell report was being finalised, some of the researchers and model developers were “pushing back” on use of the top-level numbers as the main findings for these reasons.

“In a positive way, I think it brought attention to climate migration,” Singh tells Carbon Brief when asked about the Groundswell report. She says the report was a “significant milestone” and its findings became well known, but warns that “everyone’s been quoting those numbers without looking at the methodology”.

Singh was a lead author on the IPCC AR6 on the impacts of climate change, and worked on how climate-driven migration is assessed in the report.

She says that quantifying how many people move due to climate change is “ridden with challenges” because of uncertainties in models. The IPCC team decided to cite numbers from climate migration models in the report, but added “a whole lot of caveats” to signal that instead of a narrow focus on numbers of climate migrants. She adds:

“The more exciting question is how can we enable safe and inclusive movement of people in a changing climate”.

Other groups have conducted separate studies and come up with their own numbers, which have been quoted widely in the media. The largest of these was calculated by the Institute for Economics and Peace, which found that 1.2 billion people could be displaced by 2050.

Vince tells Carbon Brief that beginning to talk about climate-driven migration immediately, and in a constructive way, could bring huge benefits to both developed and developing countries.

In her book, Vince explains why many arguments against migration are wrong, such as that migrants steal jobs from natives or that they increase violence and crime. Both of these are categorically untrue, she shows.

She tells Carbon Brief that “human movement is normal and natural and not a bad thing”, adding:

“By putting up barriers to immigration, governments in rich countries are not only forcibly preventing the world’s poorest from helping themselves, they are also hampering their own national productivity.”

“The economy isn’t a zero sum game”, Vince emphasises. She explains that investment is crucial to integrate immigrants into society, and it would be “more than repaid”, she says.

However, Rahel Muthiah cautions against leaning too heavily on an economic argument. He asks: “What about the people that can’t work?”

He tells Carbon Brief that even people who cannot work still “contribute to our communities” and help to “build our societies”, adding that this should be a focus of messaging around climate-driven migration.

And Randall tells Carbon Brief that he thinks the focus should be on telling stories. “People relate to stories about other people,” he says.