What do we mean when we talk about climate adaptation?

An interview by Francesca Menna with Mario Tozzi in Corriere, published last week, merits some comment and further analysis, starting with the question that forms its title, which opens with this query: “Can the human species adapt to sweltering summers?” 

When it is claimed that the human species will be able to adapt to climate change, the first thing to do is to establish what ‘adaptation’ means, because this word is used to refer to profoundly different processes and, above all, because in everyday language it often ends up taking on a reassuring meaning that it does not possess in biology.

In biology, the adaptation of a species refers to the change in the population comprising it in response to environmental pressure; however, as Darwin taught us, this does not occur because individuals somehow equip themselves to tolerate certain biotic or abiotic factors, but rather through selection. Essentially, a large proportion of a population dies off, and if natural selection has favoured certain individuals by endowing them with traits capable of withstanding such pressures, the descendants of those bearing these traits will increase in number, so that the resulting population will change in composition. As we can see, it is a process that we might describe as bloody and deadly: adaptation, within the mechanism of natural selection, means that few survive and many perish, and the population, or species, survives because the descendants of those few survivors re-establish a lineage that will carry the traits of resistance.

No individual effort can alter individuals to make them fit: one either perishes or survives in the lottery of evolutionary genetics.

Returning, then, to the question with which the interview with Tozzi begins, we might well ask ourselves what the tolerance of our naked bodies – given our current average physiology – would be when subjected to heatwaves and the scorching climate that awaits us, were we to have no other means of adaptation than the ‘natural’ one. The human body can, within certain limits, modify its response to environmental conditions: repeated exposure to heat alters the efficiency of sweating, blood flow distribution, plasma volume and various behavioural aspects that contribute to the maintenance of body temperature. Even populations that have lived for many generations in different environments exhibit physiological characteristics derived from their evolutionary history. All this broadens the range of tolerable conditions, but does not eliminate the physical constraints of an endothermic mammal. The heat produced by metabolism must be dissipated into the environment and, when temperature and humidity render this dissipation insufficient, the body’s compensatory capacity reaches its limit. There are therefore conditions in which human physiology, even after acclimatisation, is simply overwhelmed; moreover, we Europeans are among the least well-equipped, and we reach this lethal limit before other populations.

This point is essential when discussing the future of our species. To say that Homo sapiens could adapt to radically different climatic conditions is by no means the same as saying that humans as they exist today – their numbers, their geographical distribution or the forms of society in which they live – will be preserved. A species may prove to be perfectly adapted following a drastic reduction in numbers, the disappearance of entire populations or intense differential selection amongst individuals. From an evolutionary perspective, the persistence of a species is a very different outcome from the preservation of the living conditions of its members.

In our case, however, the picture is made unique by a characteristic that has accompanied much of the history of Homo sapiens: a huge proportion of our adaptive capacity lies outside the body. We live in environments where our physiology alone would not suffice, thanks to clothing, housing, heating and cooling systems, the controlled supply of water, food production, energy networks, medicine and the entire technical and social infrastructure that creates, around each individual, an environment distinct from the immediate physical surroundings.

What we call technological adaptation can therefore be regarded, in a broad functional sense, as a highly developed component of our extended phenotype. A human being living at forty degrees, with access to water, air conditioning, a continuous supply of energy and suitable accommodation, faces a biologically different environment from that faced by a person with an almost identical physiology who lives at the same temperature but without access to those resources. The external climate is the same; the overall set of conditions affecting the individual is profoundly different.

The extended human phenotype also possesses a crucial property: a considerable part of it can be passed down through generations. This transmission does not require a genetic change. Economic capital can be passed on to children and, with it, access to better housing, technology, education, safer neighbourhoods, the ability to move around, and the social networks through which resources and protection are obtained. An advantageous position within the environment can therefore be inherited through economic and institutional means.

Natural selection continues to act on individuals, but it now encounters individuals whose phenotype includes a significant external component. Some of the differences in fitness resulting from climate change may depend on the ability to maintain this extended phenotype and to pass on at least part of it to offspring. In a situation where extreme heat increases mortality, for example, the selectively relevant difference may lie far less in the physiology of two people than in the fact that one is able to live in a cooled environment whilst the other is not. If this capacity for protection is associated with wealth and is passed on to children, an economically heritable component of the phenotype contributes to the intergenerational persistence of the advantage.

It is within this context that our reliance on technology as a general solution to climate change must be viewed. Technology truly represents the most powerful expansion of our species’ adaptive capabilities and is likely to continue to do so. We can cool buildings, desalinate seawater, modify crops, build defences against certain extreme events and rapidly transfer resources between regions that are very far apart. A considerable proportion of the effects of future global warming can certainly be mitigated in this way.

However, this observation does not imply that technology can protect everyone and preserve the existing order indefinitely. The technology that constitutes our extended phenotype exists within complex material and social systems on which it is constantly dependent. An air-conditioner requires energy and an electricity grid capable of supplying it precisely during a heatwave, when millions of other air-conditioners are simultaneously increasing demand. A desalination plant requires large amounts of energy and infrastructure to transport the produced water to where it is needed. Technologically advanced agricultural production depends on machinery, fertilisers, irrigation systems, credit and international trade. Equipment must be manufactured and repaired, whilst raw materials and components must continue to circulate.

Technological protection is therefore a property of the system within which that technology operates. The mere fact that humanity knows how to build something does not guarantee that every human being will have access to it, nor does it guarantee that those who have access to it today will necessarily continue to have access to it under very different environmental conditions.

Here, a second aspect of adaptation emerges that is easily overlooked. A beneficial phenotype always depends on the environment, and a change in the environment can radically alter the value of traits that had previously led to success. This principle applies to an anatomical trait and also to a property of the extended phenotype.

In today’s societies, substantial financial resources are probably one of the most powerful means of individual protection against almost any climate-related risk. Those with a great deal of money can live in better homes, afford energy even when it becomes expensive, secure water and food, access healthcare, insure themselves against certain risks, and relocate if a particular region becomes less habitable. Wealth enables one to rapidly acquire almost all the other components of the extended phenotype.

This advantage, however, depends on a condition that is generally left unstated: money must continue to be worth something and must remain convertible into the resources one needs. Financial wealth provides protection as long as there are markets in which to buy what is needed, institutions that guarantee contracts, functioning monetary systems and the physical availability of the required goods. Money constitutes a right of access to resources, not the resource itself.

The same issue applies to ownership. Owning a house is an advantage as long as that house remains habitable; owning agricultural land is an advantage as long as that land continues to produce or retains an exchange value; owning technological infrastructure is useful as long as there is energy and the capacity for maintenance. The adaptive value of the current extended phenotype therefore depends on an economic and institutional environment that is usually assumed to be stable.

Climate change, however, can alter that very environment. It can render unproductive areas that currently generate wealth, alter water availability, displace populations, change the strategic value of regions and resources, and contribute to the formation of new geopolitical balances. Some states may benefit from new trade routes or a relatively improved availability of certain resources, whilst others may lose economic, productive or political capacity. The consequences of climate change can therefore extend far beyond temperature and go so far as to alter the very structures upon which the maintenance of the extended phenotype we use to protect ourselves from the climate itself depends.

The vulnerability thus becomes recursive. We rely on technology to shield ourselves from an ever-increasing proportion of environmental conditions; that technology depends on energy, resources and economic organisation; these, in turn, depend on political and geopolitical relationships that may be altered by environmental change. Our primary adaptive solution therefore belongs to the very same system that is being disrupted.

In a world where these structures continue to function well, it is reasonable to expect that wealth, technological expertise and the ability to control infrastructure will continue to represent a significant advantage. A more profound change, however, could create a selective landscape very different from the current one.

Under certain circumstances, direct access to resources may matter more than the financial capacity to purchase them. Those who control water, food production or energy sources may find themselves in a better position than those with nominally greater wealth but who depend on markets that can no longer supply those resources. In the event of a severe breakdown of the political order, the ability to directly defend one’s possessions or to exercise coercive force could also become important. The availability of weapons – which is currently of secondary importance compared to the advantages afforded by money and institutions in many developed societies – could take on a completely different significance in an environment where public authorities are no longer able to effectively guarantee access to essential resources.

We cannot know whether such a scenario will come to pass, nor is there any evolutionary necessity for it to do so. However, it is precisely this inability to predict the new selective landscape that prevents us from treating current conditions of security as a guarantee for the future. The mistake lies in taking what currently results in optimal adaptation and projecting it unchanged into a profoundly transformed environment. Evolutionary history shows precisely the opposite: when selective pressure changes, what constitutes an advantage may change – and the extended phenotype, like any phenotype, can undergo a profound shift in value as environmental conditions vary.

Inequality also plays a part in this process. When the resources necessary for survival are abundant, enormous differences in wealth can be maintained within a system in which even those with little retain sufficient access to essential goods. If a resource becomes severely scarce, that same inequality gives rise to a different situation. The advantage enjoyed by those who control that resource grows, whilst at the same time the pressure exerted by those excluded from it increases.

A very large disparity in the availability of water, food, energy or habitable land can therefore directly intensify competition. The owner of an essential resource possesses something that is increasingly valuable; those who risk not surviving without that resource have an ever-greater incentive to obtain it. In extreme conditions, the legal structures that determine who is entitled to possess it are also subjected to the pressure generated by scarcity.

Legal safeguards are, in fact, part of the extended phenotype and the social environment that attributes value to it. Ownership exists materially as control over a thing, but the exclusive right to that thing depends on institutions capable of enforcing it. As long as the state possesses sufficient administrative and coercive capacity, a title of ownership allows its holder to control a resource without having to defend it personally. If that capacity diminishes, the practical significance of the title can change rapidly.

From this perspective, even the security of those who currently find themselves in the privileged segment of the distribution cannot be considered independent of the stability of the entire system. Great financial wealth offers extraordinary protection as long as there is an order that allows it to be converted into real assets; ownership of resources offers an advantage as long as that order allows one to retain control over them; technology provides protection as long as the production and energy system that underpins it continues to function. The extended phenotype of the wealthiest individual therefore remains linked to a collective environment over which they do not have complete control.

It is here that hope in technological developments reveals its ambiguity. Usually, this implies that humanity’s technical capabilities will enable the species to continue to survive on the planet even under very harsh climatic conditions. This possibility is entirely reasonable. However, if it is also meant that technological innovation will prevent severe natural selection amongst individuals, preserve current societies and guarantee the existing population the continuity of their living conditions, this requires much stronger assumptions – and ones that are almost always poorly justified.

Technology can, in fact, reduce one form of selective pressure whilst simultaneously creating or amplifying another. If survival in hot climates increasingly depends on air conditioning, reliable access to energy becomes the key factor. If water requires desalination or large-scale transfer projects, access to the infrastructure that produces it becomes crucial. If food production becomes more dependent on sophisticated technical systems, the value of the ability to maintain them increases. Rather than disappearing, natural selection simply alters the set of characteristics through which it acts, with the same effect as ever: the preservation of well-adapted individuals, and the death of most others.

The same innovation may also accentuate the difference between those who have access to the necessary extended phenotype and those who cannot afford it. A society may possess the technology capable of keeping a person alive under certain conditions without having the capacity – or choosing – to make it available to everyone. From the perspective of the species, the technical solution exists; from the perspective of the individual who is excluded from it, that solution is irrelevant.

This allows us to see more clearly what adaptation really means in our case. Homo sapiens possess a body with certain physiological limits, an extraordinary capacity to modify their environment through an extended phenotype, and economic, cultural and institutional transmission systems that enable a considerable part of that phenotype to be inherited. Climate change affects the entire system. It can exceed the physiological limits of some individuals, alter the value of the technologies and resources that protect them, change the economic conditions through which those resources are distributed, and transform the political balances that ensure control over them.

The resulting adaptation may therefore take forms very different from that implied by the reassuring assertion that ‘we’ll manage thanks to technology’. It may certainly involve new technology and societies capable of using it effectively, but it may also involve a significant differential mortality rate between those who possess and those who do not possess the necessary extended phenotype, migrations that redistribute populations, a loss of value in previously advantageous forms of wealth, new hierarchies determined by control over resources, and transformations of institutions under competitive pressure.

In evolutionary terms, none of these outcomes would be incompatible with the assertion that the species has ‘adapted’. Precisely for this reason, that word, used on its own, should frighten us rather than reassure us. What matters, in fact, is who will manage to adapt, through which characteristics and within which social order. We must ask ourselves what value the extended phenotype – which we currently regard as a form of protection – will have then, and whether it will be possible to pass it on to the next generation, taking into account the capacity of technological, economic and institutional structures to continue reproducing the conditions upon which their very functioning depends.

The security we currently enjoy does not provide an answer to these questions, and this should be particularly relevant to the West and the fortunate inhabitants of the most favourable regions of the planet. It describes the position of an individual or a population within the current selective landscape. If the climate contributes to changing this landscape profoundly, the characteristics through which the ability to survive is acquired, maintained and passed on will also change.

Finally, there remains an even more fundamental problem, because the argument that a new technology will eventually protect us presupposes that it will have time to arrive. In nature, a population subjected to rapidly increasing environmental pressure may disappear when change proceeds faster than the emergence, spread and fixation of the traits that would enable survival under the new conditions. It is not enough for a suitable phenotype to be biologically possible: it must emerge soon enough, be present in the right individuals and spread before selective pressure has reduced the population below a threshold from which it can no longer recover.

A very similar problem exists in the context of technological adaptation, although the mechanism of transmission is different and the timescales can be much shorter than those of genetic evolution. A technical solution must be designed, tested, scaled up for industrial production, manufactured in the necessary quantities, integrated into infrastructure and finally distributed to the populations that need it. Each of these steps takes time. If climatic pressure alters living conditions more rapidly than the technical system can produce and disseminate an effective response, natural selection takes effect before the solution becomes available. A technology that would have been sufficient ten or twenty years later may be irrelevant to a population that, in the meantime, has lost the ability to sustain itself.

The extraordinary pace of human innovation does not, therefore, eliminate the problem of relative timescales. The statement "we will find a solution" implicitly contains a prediction regarding the relationship between at least two rates: the rate at which environmental pressures grow or shift, and the rate at which we are able to generate, develop and distribute the new, expanded phenotype required to address them. The fact that the latter has at times outpaced the former in our history does not constitute a law that must continue to hold true for any intensity or pace of future change.

There is also an even more insidious difference compared with the normal evolutionary problem. The ability to rapidly produce new technological phenotypes is not an invariant property of the species. Modern science and advanced technology require societies that are sufficiently wealthy and stable to sustain universities, laboratories, costly infrastructure, long-term education systems, reliable energy networks, specialised industries and large international networks through which people, tools, data and ideas circulate. The capacity for innovation that we today tend to project onto the future is itself the product of specific historical conditions.

A society under severe climate pressure may find itself forced to allocate an increasing proportion of its resources to managing the current emergency, diverting them from the investments on which future solutions depend. Rebuilding destroyed infrastructure, ensuring food and energy supplies, managing migration, supporting strained healthcare systems or funding security apparatus may become politically more urgent than maintaining research programmes whose results will only materialise many years later. In this way, the very pressure that makes innovation necessary can simultaneously reduce the capacity to produce it.

The same dynamics can play out through geopolitics. Contemporary scientific innovation relies heavily on international cooperation, the mobility of researchers and production chains spread across many countries. Conflicts, political isolation and the fragmentation of international relations can disrupt these networks and reduce scientific capacity at precisely the moment when it is most needed. There is no need to imagine extreme future scenarios to recognise the system’s vulnerability: in the United States, there are already major disruptions to the funding and organisation of federal research, whilst the Russia-Ukraine conflict has led to the migration of researchers, a loss of scientific capacity and the breakdown of international collaborations. These phenomena are not caused by climate change, but they demonstrate just how rapidly political decisions and geopolitical crises can undermine some of the conditions on which the capacity for innovation is based.

The climate crisis can interact precisely with this kind of dynamic. Changes in agricultural production, water availability, migration and shifts in the strategic value of territories can increase internal and international tensions, encourage protectionist policies and divert resources from cooperation to competition. If this happens, the scientific and technological system on which we rely for adaptation may become less efficient precisely because of the indirect consequences of the pressure to which it is supposed to respond. Research thrives more readily in conditions of stability, resource availability and cooperation; conflict and isolation, on the other hand, can fragment the networks on which it relies.

This creates another potentially dangerous feedback loop. Climate change increases the need for innovation; its economic and geopolitical consequences may reduce the conditions conducive to innovation; a reduced capacity for innovation leaves a larger proportion of the population exposed to climate-related pressures; this increased exposure may further exacerbate instability and competition. Technology cannot, therefore, be treated as an external variable that automatically grows in line with the increasing need for it.

This is precisely where the limitation of techno-optimism lies. It assumes simultaneously that we will know which technology will be needed, that we will be able to develop it soon enough, that we will maintain the economic and scientific conditions necessary to produce it, that we will maintain the infrastructure necessary to use it, and that we will be able to distribute it widely enough to prevent selective pressure from taking its course. Any one of these conditions may occur; none is guaranteed by the current existence of a technologically advanced civilisation.

The analogy with natural adaptation is therefore once again particularly instructive. A population may, in principle, possess an evolutionary pathway towards a phenotype compatible with the new environment and yet become extinct because the environment changes more rapidly than its ability to adapt to it. A civilisation may, in principle, possess the knowledge to construct a new, expanded phenotype and yet fail to do so in time, or lose, during the crisis, the economic, scientific and political conditions necessary to complete its construction.

The likelihood of Homo sapiens continuing to exist is very different from the likelihood of technology protecting all human beings from the consequences of rapid climate change. Between the two lies natural selection: that which operates directly through our physiological limitations and that which operates through the varying availability of an extended phenotype capable of protecting us. If the technological response arrives too late, remains confined to a section of the population, or becomes more difficult to produce just as environmental pressure is mounting, the species may still adapt, but it may do so in the ordinary way that adaptation occurs in nature: through the survival of some and the loss of others.

However, compared with natural mechanisms of adaptation – including those linked to our extended phenotype – our species possesses certain characteristics and current resources that can go a long way towards preventing the most harmful aspects of the next phase of selection.

We will discuss this further in the following section.