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A study published in Nature Sustainability attempts to quantify the human cost of global warming.
This Roundup accompanied an SMC Briefing.
Dr Richard J.T. Klein, Team Leader: International Climate Risk and Adaptation, Senior Research Fellow, Stockholm Environment Institute, Sweden, said:
“The idea of niche is an innovative approach to assessing the direct impacts of climate change on humans. While the article answers some relevant questions, it raises many more. In particular, it adds an extra dimension to discussions about climate justice.”
“At first glance, the statistical analysis based on the combination of climate and demographic data looks robust. The study confirms that warming will affect very large groups of people, especially those already living close to the limits of the human climate niche. It also confirms that greater warming affects many more people, and that therefore efforts to limit warming can greatly reduce human suffering.”
“The way in which the authors defined the human climate niche means that there are a number of factors that are not considered. For example, drought and desertification may already happen within the climate niche, making agriculture all but impossible and therefore inhabitable. The same goes for low-lying areas threatened by floods and sea-level rise. In other words, there are regions within the human climate niche that could become uninhabitable for other reasons.”
Regarding the question to what extent the metric used in the study is appropriate to represent the impacts of climate change and what misunderstandings might arise from their use:
“I think part of my answer above also responds to this question. A possible misunderstanding would be that the observed population distribution in the niche reflects some kind of optimal temperature, but the reason many people live in the 13C and 27C zones is also because of biogeographical circumstances, not only climatic (e.g. a number of large river deltas are in these zones, which have historically attracted many people to settle).”
“What this study shows very well though is the direct human suffering that climate change could cause. The authors don’t use this word (they refer to human cost) but living outside the niche means suffering due to an unbearably hot and possibly humid climate.“
Regarding the question to what extent adaptation to life outside the climatic is possible:
“Technically, adaptation is almost always possible. People can spend most of their lives in air-conditioned buildings and import their food from elsewhere, provided they have the means to do so. For many of the people and countries affected, however, this is not an option. The question then is what these people will do. Move to cooler places? Which places are they, and what opportunities will they have there? Might it lead to conflicts over scarce resources?”
Regarding the question what the findings of the current study mean for the issue of climate change-related migration:
“As already indicated above. Migration is a complex process that is triggered much more by loss of livelihoods and by conflict than by temperature. Yet, as temperatures increase, the potential for these triggers increases as well, which means we might be seeing larger numbers of climate refugees. But we should not forget that by far the largest number of climate refugees have moved within their country or to neighbouring countries. This paper should therefore not lead to scare stories about more refugees coming to Europe. But it does show the increasing importance of supporting people locally, as well as urgently limiting further warming.”
Dr Christian Franzke, Associate Professor and Research Group Leader at the IBS Center for Climate Physics, Institute for Basic Science, Pusan National University, South Korea, said:
“This study uses a new measure to illustrate the impacts of climate change: the ‚human climate niche’. Previous studies have focused either on economic costs of climate change or on mortality. The current study uses demographic projections that assume a growing population primarily in already warm areas. People may adapt or migrate to cooler areas. People in rich countries especially can do that; poor ones have fewer opportunities to do so, and it’s those countries that will fall out of the ‘human climate niche.’”
Regarding the question to what extent the metric used in the study is appropriate to represent the impacts of climate change:
“The ‚human climate niche’ is of course a simplification of the complexity of the problem, but it is illustrative and shows the impacts for poor countries, which will have lower damages in economic measures because they are poor. That’s the advantage of this approach.”
Regarding the question to what extent adaptation to life outside the climatic is possible:
“Adaptation is possible, but it will cost money that poor countries and poor people don’t have. For example, not everyone can afford air conditioning. In developed countries – like Germany – most work takes place in buildings that can be cooled. In many developing countries, most work takes place outside, for example in the fields. There, you could change working hours and introduce a siesta at noon, like in Spain, but that probably won’t maintain all labor productivity.”
Regarding the question what the findings of the current study mean for the issue of climate change-related migration:
“One would naturally expect that this will increase climate change-related migration; especially in countries that are already poor now. A forward-looking policy would start now to create legal migration routes and prepare for increasing migration, for example, to Europe and Germany; for example, planning the reception facilities and infrastructure that will then be needed.”
Prof Lisa Schipper, Professor of Development Geography, Department of Geography, University of Bonn, Germany, said:
Regarding the question to what extent the metric used in the study is appropriate to represent the impacts of climate change:
“No metric is going to reflect reality accurately however the concept underpinning the Human Climate Niche is extremely useful to think about outside the numbers. The notion that a decreasing number of people are going to be able to live decent lives directly echoes the IPCC’s warning that there is a closing window of opportunity to secure sustainable and liveable lives for all. Even at 1.5C as Lenton et al show, this is unlikely to be possible.“
Regarding the question to what extent adaptation to life outside the climatic is possible:
“The IPCC already established in its past two assessment cycles that there are limits to adaptation – and these are increasing as adaptation loses effectiveness above 1.5C. Lenton et al’s study suggests that for many people adaptation is hardly going to have any impact, especially in the context of extreme events – many of which we are not able to adapt to because of their timing and magnitude. This may not be the case for all 600 Million people outside the Human Climate Niche, but most of those people are already living in extremely difficult circumstances – due to climate change or other factors that make them vulnerability to climate change.“
Regarding the question what the findings of the current study mean for the issue of climate change-related migration:
“The study results should not be interpreted as climate change triggering mass exodus in places where most or all people are living outside the Human Climate Niche. Yet they should also not be understood as meaning that everyone outside this Niche can adapt – because our ability to adapt is significantly limited as global warming increases. The study puts numbers to how many people will suffer and where. These are places where it looks nearly impossible to live a decent life and it may be likely that those people – if they have the means – will try to relocate. International climate and development policy should support this process, but should not stop providing funding to the places that fall outside the Human Climate Niche. This study should therefore not be used as an argument for not providing funding for loss and damage or other development activities.“
Prof Tom Oliver, Research Dean for Environment, University of Reading, said:
“This study extends previous work using the latest science on likely post and future climate scenarios. This kind of research is essential to furnish public dialogue around our response to the global climate crisis. It confirms we are sitting on an ‘ethical time-bomb’. We need to critically discuss the morality of staunchly defending national borders when large swathes of the planet are becoming uninhabitable. The fact that more vulnerable populations, who are also less responsible for global warming emissions, will suffer the most adds a further moral blow. The results of this study reinforce that climate does not respect national borders. We are one interconnected human population affected by climate impacts and this work prompts us to think about how we might respond as global citizens.”
Dr Laurence Wainwright of the Smith School of Enterprise and the Environment, University of Oxford, said:
“The findings are sobering and a stark reminder as to why we fight tooth and nail to keep global warming to the lowest levels possible. The impact of the difference between 2.7c – what we are currently on track for – and 1.5c – what many countries agreed to at the COP climate conference in Paris in 2015 – cannot be overstated: this research indicates that 2.7c will likely result in a five-fold increase in the number of people globally being exposed to unprecedented heat.”
“While focusing on health in general, the study adds to a growing body of literature illustrating the moderate-to-significant impact that climate change is having, and will continue to have, on human mental health. We know that extreme weather – especially heatwaves – pose a range of serious challenges for both those with underlying psychiatric conditions, as well as the mental health of the general population.”
“In the study the authors use rigorous statistical modelling to make a series of past calculations and future projections as to the impacts of temperature changes by caused climate change on populations in different geographical locations. The findings are sobering and a stark reminder as to why we fight tooth and nail to keep global warming to the lowest levels possible. The impact of the difference between 2.7c – what we are currently on track for – and 1.5c – what many countries agreed to at the COP climate conference in Paris in 2015 – cannot be overstated: this research indicates that 2.7c will likely result in a five-fold increase in the number of people globally being exposed to unprecedented heat.
“Humans have gotten used to living in particular areas at certain temperatures through a range of socio-cultural and even physical adaptations. When things change – especially in terms of higher average monthly temperatures and exposure to unusually long and high periods of heat – serious problems arise, whether in terms of physical health, mental health, crime and social unrest.
While focusing on health in general, the study adds to a growing body of literature illustrating the moderate-to-significant impact that climate change is having, and will continue to have, on human mental health. We know that extreme weather – especially heatwaves – pose a range of serious challenges for both those with underlying psychiatric conditions, as well as the mental health of the general population. In showing the uneven and disproportionate impacts of global warming on particular populations in certain geographical areas, this research shows that we must act in terms of not just reducing emissions, but also in building fairer and more resilient healthcare systems and infrastructure that can be proactive rather than reactive to the mental health impacts of climatic change.”
‘Quantifying the human cost of global warming’ by Timothy M. Lenton et al. was published in Nature Sustainability at 4pm Monday 22 May 2023.
DOI: https://doi.org/10.1038/s41893-023-01132-6
Declared interests
Prof Tom Oliver ‘is seconded with the UK Government Office for Science on a project building national resilience to long-term chronic risks. He was previously seconded with Defra to set up an environmental systems research programme. His work is also helping to inform the development of a UN Foundation project, which is a platform for ‘Accelerating Systemic Risk Assessment’. Tom is author of a popular science book on human interconnectedness, published by Weidenfeld and Nicholson.’
Dr Laurence Wainwright: No conflicts of interest to declare.
For all other experts, no reply to our request for DOIs was received.