Hans Joachim "John" Schellnhuber | PAS Academician & Kira Vinke

Uninhabitability, the Limits to Resilience, and a Passport to Safety

Flooding events in the Pakistani Sindh province killed more than 1700 people over the summer of 2022, following extreme spring heatwaves. With 15% of the country’s entire population affected by the water masses, several millions were displaced. Even those people well-adapted to the cycles of the monsoon had no options left to guard themselves from relentless rains and rising waters. The floods eventually subside, yet livestock losses and the vast destruction of fertile land will curtail economic development for years to come.

The situation in the South Asian country is no longer solely a tragic abnormality. As global warming is accelerating, high air temperatures can translate into unleashed precipitation. Overall, extreme events around the world are becoming more frequent and more intense, posing grave human security risks and requiring ever larger infrastructural adaptation.

Worst affected are the bottom billions of the human population – the globally deprived, whose active and institutional exclusion from growth and prosperity leave them without protection against the vagaries and hardships of the contemporary climate crisis. Intersecting vulnerabilities such as the marginalization of people of colour or the exclusion of women from decision-making bodies aggravate these inequalities and intentionally fortify group-specific limits to human resilience.

While current impacts at 1.2°C warming lead to loss of life and tremendous suffering, even more disastrous changes could be on the horizon. The scientific evidence indicates that further warming cannot be confined to below 1.5°C, while many recent studies conclude that greater dangers await human civilization beyond that lower guardrail of the Paris Agreement. Climate change can have truly catastrophic effects, such as a shut-down of the Gulf Stream System, which has already significantly weakened,[1] or the melting of the Greenland Ice Sheet, possibly rendered irreversible by powerful feedback loops.[2],[3] Worst-case scenarios accounting for interacting tipping dynamics have hardly been explored,[4] so there is clearly a need for an appropriate research agenda. In fact, a Special Report by the IPCC would be a major step forward in this context. Yet, the Earth System crisis is not only deepening due to climate impacts. Several planetary boundaries have been crossed already and many will be transgressed in the decades to come.[5],[6],[7] These include unprecedented biodiversity loss and disruptions of the nitrogen cycle.

The crises triangle of global warming and large-scale ecosystems collapse, the Covid-19 pandemic, and the Russian war of aggression against Ukraine are overstretching even the management capacities of prosperous societies. Climate impacts will most likely exacerbate the pressures on societal systems, thereby triggering cascading risks that range from food shortages to resource conflicts and forced migration.[8] Over the past decade, the annual new displacements due to “natural” disasters were consistently higher than those triggered by violence and conflict.[9] Disaster-related displacement is not fully attributable to climate change. But population growth in areas highly exposed to environmental disruption will undoubtedly lead to increasingly devastating humanitarian crises. Higher warming scenarios suggest that within the next 50 years, up to three billion people could be living outside the human climate niche, the temperature realm that enabled our civilization to flourish.[10] Because there are physiological and technological limits to the resilience of humans and their respective cultures, such extreme – albeit not implausible – scenarios need to be urgently prevented. We will elaborate on this below.

The international community is now tasked with avoiding the unmanageable, such as run-away global heating, and managing the unavoidable, i.e., the challenges arising from current and locked-in warming. The triad response to avert the most severe outcomes of the climate crisis therefore is: mitigation, adaptation, migration.


Climate change is a negative externality of economic and social systems that results from reckless over-use of natural resources and sinks. This grave imbalance in humanity’s relationship with its environment is finally revealing its detrimental world-wide effects. The burning of fossil gas, coal and oil by middle- and upper-income groups, largely concentrated in industrialized countries, is eroding the livelihood base of lower-income groups, such as smallholder farmers in Pakistan, a country in which average per-capita emissions are approximately 1tCO2/year. Since several decades it is clear that fossil-fuel use needs to be cut. But after a slump in global emissions due to the pandemic-related restraints in 2020, fossil business is reaching new highs as industrial activities return to their old normal.

Moreover, in the expectation of national economic setbacks in the context of the Russian war against Ukraine, wealthy countries like Germany seek to stabilize their energy supply by the short-term ramping up of coal-fired power plants. Other sectors, such as the emissions-intensive construction or shipping industries have barely seen any change towards bending their greenhouse-gas curves. In order to stay on the Paris pathway, global emissions would, however, need to be halved each decade, following the logic of a “carbon law”.[11] The current shocks to the international order and the economic make-up are watersheds for either deepening crises or the rebalancing of natural and social systems. Stimulus packages, which often seek to cement the status quo, rather need to be designed to improve or overcome locked-in economic models that rest on unsustainable practices. The latter have not only wrecked ecosystems around the world, but also imposed structural violence upon disadvantaged groups on all continents.


Intensifying climate impacts require adaptation measures applied to infrastructures, institutions and societies. Without adequate funding mechanisms, those already disadvantaged by industrial globalization will have to pay the highest price. Wealthy countries have agreed to provide 100 billion USD per annum in climate finance from 2020 to 2025 to developing nations. But even this minimum promise has not been held in the first years.[12] Also, most of the spending went into necessary, but largely profit-oriented mitigation measures, whilst adaptation finance fell short, as a rule.

Yet only through adaptive interventions can the most vulnerable be guarded from even moderate warming dynamics. Many smallholder farmers and fisherfolk have sustained their livelihoods in barren environments. But the disturbances of climate change render the upkeep of traditional practices in many places impossible for growing populations. Investments into insurance systems against extreme weather events or nature-based solutions such as Farmer Managed Natural Regeneration (FMNR),[13],[14] which carries large co-benefits for mitigation, are tested ways forward to more resilient ecosystems-based livelihoods.


The latest report of the Intergovernmental Panel on Climate Change (IPCC) outlines the tremendous levels of risks some regions will have to face even at warming levels below 2°C.[15] Some areas may become too dangerous to live in, others may not sustain the same amount of people that are residing there today. Pessimistic scenarios of the World Bank estimate 200 million people moving internally until the middle of the century due to the anthropogenic changes in climate.[16]

At this point, let us address a question, which most of us did not dare to ask for a long time, but which is becoming more and more pertinent as climate change progresses and precious time is lost by the nations of our world: What magnitude of global warming would exceed humanity’s ability to adapt to or recover from the resulting impacts?

There is a robust expert consensus that a sustained increase of global mean surface temperature by more than 4°C could not be managed in any conceivable way. This conclusion is epitomized by Fig. 1, which summarizes the latest findings on tipping elements in the Earth’s climate system.

Fig 1:[17] The location of climate tipping elements in the cryosphere (blue), biosphere (green), and ocean/atmosphere (orange), and global warming levels at which their tipping points will likely be triggered. Pins are colored according to our central global warming threshold estimate being below 2°C, i.e., within the Paris Agreement range (light orange, circles); between 2 and 4°C, i.e., accessible with current policies (orange, diamonds); and 4°C and above (red, triangles).

The basic story told by this cartoon is that the Holocene environment, which has fostered the rise of human civilization, would be almost entirely destroyed in such a hot-house climate. In our view, the 3-4°C range is the diabolical zone: While breaching the 4°C-line can probably still be avoided by sub-optimal climate policies and measures, there are many realistic scenarios that could push our planet towards the 3°C-line or even beyond.[18] Just think of a world disunited by military conflicts such as the current Russian war of aggression against Ukraine or by increasing hostility between leading economies. Given the past failures to implement international agreements and rising international tensions can we safely assume that all countries will cooperate on limiting global warming? Therefore, a planetary temperature rise “well above” 2°C in the Anthropocene is not a far-fetched dystopia. Sea-level rise, water scarcity in the wake of alpine-glaciers melting, unbearable humid heat, or the expansion of climatic areas supporting tropical diseases could unfold in unprecedented ways for human civilization.

This is not the full story, however. Before the world population is supposed to peak at around 10 billion after 2050, roughly two billion human beings would be added by the demographic make-up around the world. To be specific, this population growth will mainly happen in the Global South, and most of these additional 2 billion humans will be born into a life of poverty. This means that they will join and expand the present-day “bottom billions” who are specifically vulnerable to climate change for mainly two reasons:

First, many are forced to settle in locations – flood-prone areas, unstable hill slopes, storm-exposed corridors, agricultural bad-lands, peri-urban areas without essential infrastructures, etc. – which are disproportionally exposed to extreme climate-related events. Second, they do not have sufficient capacities for resilience, i.e., they do not have the income or insurances which would allow them to recover after a disastrous event (such as a tropical storm or a long-lasting drought).

As a consequence, global warming in the 3-4°C range could deprive several billion people (!) of a safe place to live and prosper in the course of the 21st century. This mind-boggling finding is somewhat captured by Fig. 2, which is borrowed from a recent paper on the “climate endgame”.

Fig. 2:[19] Overlap between future population distribution and extreme heat. CMIP6 model data [from nine GCM models available from the WorldClim database][20] were used to calculate MAT under SSP3-7.0 during around 2070 (2060-2080) alongside Shared SSP3 demographic projections to ∼2070.[21] The shaded areas depict regions where MAT exceeds 29°C, while the colored topography details the spread of population density.

What would become of all these people? They would either stay where they are, trapped by social and natural forces, and many would be destined to perish. Or they would decide to move for survival – the majority along thousands of exhausting, pernicious, illegal, and often fatal roads. The mistreatment and human rights violations against refugees happening at quasi-impenetrable borders in various parts of the world already today would likely multiply into chaos on a hot-house planet.

We bluntly conclude that a 3-degree warmer world would become unmanageable and could not sustain a human(e) civilisation as we know it.

Therefore, the global community of nations needs to do everything to keep us as far away as possible from that hard limit to adaptation and resilience. Yet even in a, say, 1.8°C or 2.2°C warmer world, migration challenges of unprecedented dimensions must be met, so conventional approaches will not suffice. Most importantly, significant population redistributions shall occur peacefully, even within and between densely populated countries.

We propose to consider, among other novel approaches, a scheme that has a historical analogue, invented for a different purpose and implemented under different conditions though: At present, international migration is strongly regulated through often forceful border regimes. Suffering climate change impacts confers no eligibility for asylum under the cornerstone of refugee protection, the Geneva Convention. If no legal pathways for migration are created for those severely affected by climate change, loss of life and human rights violations, as they are already taking place in the Mediterranean, the Sahara, the US-Mexican frontier, the India-Bangladesh border and elsewhere, will become rampant.

For this reason, we suggest as one of many necessary instruments to pre-emptively address the looming catastrophe the creation of a climate passport for people living in areas that are becoming uninhabitable due to anthropogenic global warming. This idea is inspired by the Nansen passport, a legal document that enabled people displaced by the First World War to legally reside and work in their host countries. It was initiated by the Nobel peace laureate and renowned polar explorer Fridtjof Nansen (1861-1930) and was eventually recognized by more than 50 states. The instrument of a climate passport intends to offer those whose agency has been curtailed by the extreme effects of global warming the freedom to choose where to continue their lives if their homelands have been destroyed.[22]

We close this article with a climate parable:

Imagine a certain species of fish (say, cod) is driven out of its traditional marine habitat (say, the North Sea) by multiple impacts of anthropogenic interference with the climate system, such as thermal stress, ocean acidification, and depletion of oxygen and nutrients. As a consequence, instinctively and erratically, swarms of that species try to migrate to alternative domains (say, the Barents Sea), where they have a better chance of survival. Imagine also that those animals are stopped and sent back by naval border police at one of the lines separating national exclusive economic zones (say, the respective divide between Norway and Russia). The rejection is justified by the authorities by “the absence of asylum eligibility in line with the criteria of the Geneva Convention”. Apart from its impracticability, such a scenario appears utterly cruel. Yet, many decision makers seem to be prepared to realize that very scenario, if instead of fish (crossing the Barents Sea) human beings were trying to migrate (crossing the Mediterranean on ramshackle vessels, for instance).

The preconditions for resilience under growing climatic pressures are mitigation, adaptation and the possibility of migration in the face of danger. Science confirmed what has long been known: the protection of nature goes hand in hand with the protection of our own kind. Only by addressing parallel crises holistically with a focus on prevention can Planet Earth continue to serve as our common home.

[1] Caesar, L., McCarthy, G.D., Thornalley, D.J.R. et al. Current Atlantic Meridional Overturning Circulation weakest in last millennium. Nat. Geosci. 14, 118-120 (2021). https://doi.org/10.1038/s41561-021-00699-z

[2] Boers, N., & Rypdal, M. (2021). Critical slowing down suggests that the western Greenland Ice Sheet is close to a tipping point. Proceedings of the National Academy of Sciences, 118(21), e2024192118. https://doi.org/10.1073/pnas.2024192118

[3] Zeitz, M., Haacker, J.M., Donges, J.F., Albrecht, T., & Winkelmann, R. (2022). Dynamic regimes of the Greenland Ice Sheet emerging from interacting melt – elevation and glacial isostatic adjustment feedbacks. Earth System Dynamics, 13(3), 1077-1096. https://doi.org/10.5194/esd-13-1077-2022

[4] Kemp, L., Xu, C., Depledge, J., Ebi, K.L., Gibbins, G., Kohler, T.A., ... & Lenton, T.M. (2022). Climate Endgame: Exploring catastrophic climate change scenarios. Proceedings of the National Academy of Sciences, 119(34), e2108146119. https://doi.org/10.1073/pnas.2108146119

[5] Rockström, J., Steffen, W., Noone, K. et al. A safe operating space for humanity. Nature 461, 472-475 (2009). https://doi.org/10.1038/461472a

[6] Persson, L., Carney Almroth, B.M., Collins, C.D., Cornell, S., de Wit, C.A., Diamond, M.L., ... & Hauschild, M. Z. (2022). Outside the safe operating space of the planetary boundary for novel entities. Environmental science & technology, 56(3), 1510-1521. https://doi.org/10.1021/acs.est.1c04158

[7] Wang-Erlandsson, L., Tobian, A., van der Ent, R.J. et al. A planetary boundary for green water. Nat Rev Earth Environ 3, 380-392 (2022). https://doi.org/10.1038/s43017-022-00287-8

[8] Vinke, K., Schellnhuber, H.J., Laplante, B. et al. (2017). A Region at Risk – The Human Dimensions of Climate Change in Asia and the Pacific. A Report by the Asian Development Bank and the Potsdam Institute for Climate Impact Research.

[9] IDMC (2022) GRID https://www.internal-displacement.org/global-report/grid2022/

[10] Xu, C., Kohler, T.A., Lenton, T.M., Svenning, J.C., & Scheffer, M. (2020). Future of the human climate niche. Proceedings of the National Academy of Sciences, 117(21), 11350-11355.

[11] Rockström, J. et al. (2017). A roadmap for rapid decarbonization. Science 355, 1269-1271.

[12] Timperley, J. (2021). The broken $100-billion promise of climate finance – and how to fix it. Nature 598, 400-402 doi: https://doi.org/10.1038/d41586-021-02846-3

[13] Rinaudo, T. (2007). The development of farmer managed natural regeneration. LEISA-LEUSDEN, 23(2), 32.

[14] Haglund, E., Ndjeunga, J., Snook, L., & Pasternak, D. (2011). Dry land tree management for improved household livelihoods: farmer managed natural regeneration in Niger. Journal of environmental management, 92(7), 1696-1705. https://doi.org/10.1016/j.jenvman.2011.01.027

[15] Pörtner, H.O., Roberts, D.C., Adams, H., Adler, C., Aldunce, P., Ali, E., ... & Birkmann, J. (2022). Climate change 2022: Impacts, adaptation and vulnerability. IPCC Sixth Assessment Report.

[16] Clement, V., Rigaud, K.K., de Sherbinin, A., Jones, B., Adamo, S., Schewe, J., ... & Shabahat, E. (2021). Groundswell part 2: Acting on internal climate migration. World Bank. https://openknowledge.worldbank.org/handle/10986/36248 License: CC BY 3.0 IGO.

[17] Abstract Figure in Armstrong McKay, D.I., Staal, A., Abrams, J.F., Winkelmann, R., Sakschewski, B., Loriani, S., ... & Lenton, T. M. (2022). Exceeding 1.5° C global warming could trigger multiple climate tipping points. Science, 377(6611), eabn7950. https://doi.org/10.1126/science.abn7950

[18] United Nations Environment Programme (2022). Emissions Gap Report 2022: The Closing Window – Climate crisis calls for rapid transformation of societies. Nairobi. https://www.unep.org/emissions-gap-report-2022

[19] Figure 1 in Kemp, L., Xu, C., Depledge, J., Ebi, K.L., Gibbins, G., Kohler, T.A., ... & Lenton, T.M. (2022). Climate Endgame: Exploring catastrophic climate change scenarios. Proceedings of the National Academy of Sciences, 119(34), e2108146119. https://doi.org/10.1073/pnas.2108146119

[20] WorldClim, WorldClim-Global Climate Data: Free climate data for ecological modeling and GIS. Accessed 17 December 2020. https://www.worldclim.com/node/1

[21] International Institute for Applied Systems Analysis, SSP Database (shared socioeconomic pathways) (Version 2.0). Accessed 17 December 2020. https://tntcat.iiasa.ac.at/SspDb/dsd?Action=htmlpage&page=about

[22] WBGU – German Advisory Council on Global Change (2018). Just & In-Time Climate Policy. Four Initiatives for a Fair Transformation. Policy Paper 9. Berlin: WBGU.