Escalation of displacement estimates in climate change literature

This timeline shows how the IPCC AR6 claim of 700 million climate-displaced Africans by 2030 came into being. The story started almost twenty years ago as two completely independent estimates – one global (645 million displaced by construction projects by 2050) and one concerning Africa (increased water stress for 239 million by the 2020s). The former estimate seems to be especially widely miscited as people displaced by climate change, e.g. in the 2018 IPBES report and by the WMO. Emphases added.

2004 –


Every year, some 15 million people are forced out of their homes to make way for dams, mines, factories, roads and other infrastructure, tree plantations and wildlife conservation parks, according to the world’s foremost expert on development displacement, former World Bank resettlement specialist Professor Michael Cernea.


We estimate that over the years between now and 2050 … 645 million people displaced by development projects such as dams and mines (at the current rate of 15 million a year)

Christian Aid, ”Human tide: the real migration crisis”, 2007

If the absolute numbers of people living in water-stressed watersheds was taken as the indicator of water resources stress, then climate change would appear to reduce global water resources pressures because more watersheds move out of the stressed class than move into it.

[But in Africa, 92-239 million people would experience increased, 11-175 million decreased water stress, based on tables 11 and 12].

Nigel W. Arnell: Climate change and global water resources: SRES emissions and socio-economic scenarios, 2004

2007 – 2009

How many people will be uprooted by environmental change?

Estimates of the numbers of migrants and projections of future numbers are divergent and controversial, ranging from 25 to 50 million by the year 2010 to almost 700 million by 2050 [citing Christian Aid]

Warner et al.: In Search of Shelter, Mapping the Effects of Climate Change on Human Migration and Displacement

In some assessments, the population at risk of increased water stress in Africa, for the full range of SRES scenarios, is projected to be 75-250 million and 350-600 million people by the 2020s and 2050s, respectively (Arnell, 2004).

IPCC AR4, wg2, Chapter 9

In Africa alone by 2020, 75-250 million people may be exposed to increased water stress due to climate change [citing the IPCC].


Christian Aid released a report in 2007 estimating that up to 685 million people were forced to move because of environmental factors, including development projects such as dams that inundated large areas of inhabited land.


Estimates of potential environmentally displaced people range from 24 million to almost 700 million who could be displaced by water-related factors, including development projects designed to relieve future water availability stresses [citing Christian Aid].

The United Nations World Water Development Report 3, ”Water in a Changing World”, 2009


With the existing climate change scenario, almost half the world’s population will be living in areas of high water stress by 2030, including between 75 million and 250 million people in Africa. In addition, water scarcity in some arid and semi-arid places will displace between 24 million and 700 million people. [Apparently summarizing the UN World Water Development Report]

UN website, International Decade for Action, Water for Life


Moreover, with the existing climate change scenario, between 75 million and 250 million people in Africa will be living in areas of high water stress by 2030, with water scarcity in some arid and semi-arid places likely to displace between 24 million and 700 million people.

Conference ”Water Scarcity in Africa – Issues and Challenges”, École Polytechnique


According to findings presented at a 2012 conference, Water Scarcity in Africa: Issues and Challenges, it is estimated that by 2030 up to 250 million people in Africa will be living in areas of high water stress, which is likely to displace up to 700 million people as conditions become increasingly unliveable …

Naik, 2017


Some estimates have suggested that by 2050, the combined effect of land degradation and climate change will have resulted in 50 to 700 million people having migrated (Warner et al., 2009).

The assessment report on land degradation and restoration, IPBES, 2018


By 2030, about 250 million people may experience high water stress in Africa, with up to 700 million people displaced as water stress becomes locally impossible to cope with (Groth et al., 2020; Mpandeli et al., 2020; Naik, 2017).

Leal Filho et al., 2022

By 2030, about 250 million people may experience high water stress in Africa, with up to 700 million people displaced as a result.

IPCC AR6 wg2, Chapter 9

Origins of the 700 million

The most drastic number, 700 million, begins in 2007 rather innocuously when Christian Aid calculates that if 15 million people are displaced annually by construction projects such as dams, tree plantations and wildlife conservation parks, then that would make a total of 645 million in 2050 (15 million x 43 years). The estimate is not related to climate change – the report describes several categories of ”forced migration”, development projects as one of them. Lacking bigger numbers, the UN and CARE (Warner et al.) later refer to this number as people migrating due to ”water-related” or ”environmental” factors.

The 645 million becomes 685 million (typo?), ”almost 700 million”, ”up to 700 million” (IPCC 2022), and ”at least 700 million” in some sources.

The lower bound of about 25 million is dropped, leaving only the 30-fold upper bound being repeated in the literature afterwards. This lowest estimate is apparently Norman Myers’s number for supposedly already existing ”environmental refugees” in 1990s (cited by e.g. CARE and the UN water report).

Origins of the 250 million

The 250 million water-stressed Africans originates from a 2004 modelling study by Nigel Arnell. The number doesn’t appear as such in the paper. The IPCC in their AR4 Africa chapter seem to have summed up the numbers for the most extreme scenario and model in table 11 of the study, ignored the substantial number of people supposedly experiencing less water stress, and rounded it upwards.

Synthesis of the IPCC claim

Some sources, apparently starting with the UN website, subsequently mention these separate estimations together. It seems that Naik (2017) misreads them as referring to the same thing, leading to the seemingly illogical notion that water stress in Africa leads to displacement of almost triple amount of people. The error is then cited by Leal Filho et al. 2022 whose sentence appears in the IPCC AR6 verbatim (up to the 21st word, but the study isn’t in the reference list).

As the years go by, constructing dams, planting trees, establishing wildlife conservation parks and regional ”risk of increased water stress” morphs into ”high water stress”, ”increasingly unliveable”, and ”impossible to cope with”.

With politicians and activists the story will of course evolve even further – Dr Charlie Garner of Extinction Rebellion Scientists endorses the IPCC claim and adds that there will be ”unimaginable levels of suffering and death and war” involved (at about 24:30 in the video).

The fact that climate models serving as the basis for the claim actually projected globally decreasing water stress is never mentioned with these estimates.

The estimated time of arrival keeps changing between the year 2020, the 2020s, the year 2030, and 2050.

The IPCC said already over 30 years ago (FAR wg2, 1990) that forced migration and resettlement would be the most severe effects of climate change in the short term. In today’s discussion the idea is still very much alive. For example the ”global warming as a security threat” narrative is largely based on this. There has obviously been a great pressure to produce evidence of the phenomenon. The fact that even the IPCC still relies on old, basically made-up numbers suggests the biggest climate threat has been baseless at least so far.

As with many other AGW impacts, the magnitude, sign, and existence of the effect seems to be highly uncertain. A similar problem applies to climate policy; if we believe the numbers in Arnell’s modelling exercise cited by IPCC AR4, then emission cuts would rather increase than decrease global water stress and any resulting displacement, death and suffering.

The legend of 700 million ”climate refugees” is probably a good example of Climate migration myths (Boas et al., 2019).

See also

Assessing an IPCC assessment by Netherlands Environmental Assessment Agency confirms the way IPCC AR4 calculated the ”250 million” as described here.

The one billion ’climate refugees’ that never was: INGOs and the human rights perspective to climate change-induced displacement, Oxford Monitor of Forced Migration. Confirms that the 645 supposedly development-displaced people in the Christian Aid report have been often misread as ”climate refugees”.

IPCC AR6 wg2 corrigenda to the final draft rev2 – 84 pages of corrections. The claim is deleted and replaced with new numbers and time range pushed to 2050.

Rapid evidence assessment on the impacts of climate change on migration patterns from the UK Foreign, Commonwealth & Development Office (2021) looks at 273 studies and finds there is no upward trend in weather shock related migration. There is strong evidence that narratives of ”climate crisis” do increase migration.


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