Experimental Studies

First, note that creating valid experimental designs to study aggression and violence is inherently complicated. This is something that has been noted in much of our research team’s media violence work, where we must design creative paradigms that mimic aggression and violence without allowing participants to seriously harm one another. However, researchers have carefully constructed ways to measure these constructs in the laboratory, and the results from these studies have an incredible impact because experimental studies (sometimes called randomized control studies) allow strong causal inference.

When a person perceives another as behaving inappropriately aggressively towards them, they are more likely to retaliate aggressively (Reference Anderson and BushmanAnderson & Bushman, 2002; Reference Anderson, Buckley and CarnageyAnderson et al., 2008). This basic fact makes it easy to look at how heat impacts one’s perceptions of another person. If heat stress increases such aggressive perceptions, thoughts, and/or feelings, it is likely that heat stress will also increase aggressive behavior. Multiple studies have shown such effects. One study had participants view four video clips of adult couples having conversations. After each clip, participants rated how aggressive or hostile they perceived those recorded conversations to be. Participants had been randomly assigned to do the video clip task in either an uncomfortably warm/hot room or in a room at a comfortable temperature (Reference Anderson, Anderson, Dorr, DeNeve and FlanaganAnderson et al., 2000). Uncomfortably warm participants were not only more likely to be hostile themselves than comfortable participants (thereby replicating similar effects found in Reference Anderson, Anderson and DeuserAnderson et al., 1996) but also perceived the video clip interactions as containing more hostility and aggression. This effect works not only when participants are hot themselves, but also when they are only primed with the idea of heat (e.g., Reference Wilkowski, Meier, Robinson, Carter and FeltmanWilkowski et al., 2009). They found that participants who were exposed to images related to heat were more likely to judge neutral facial expressions as aggressive and were more likely to have aggressive thoughts than control condition participants.

Early experiments of heat effects on actual aggressive behavior were plagued by methodological problems and yielded mixed results (Reference Anderson, Anderson, Dorr, DeNeve and FlanaganAnderson et al., 2000). However, that same review article reported a series of new experiments that clearly demonstrated heat stress effects on immediate retaliatory aggression.

Another interesting experiment examined the effects of heat stress in a police firearms training program (Reference Vrij, van der Steen and KoppelaarVrij, van der Steen, & Koppelaar, 1994). This system presented police officer participants with a video-based burglary scenario in which a person suddenly appears with a crowbar in hand. Participants had to quickly decide whether to draw their weapon (a laser gun) and, if drawn, whether to shoot the suspect. Those who had been randomly assigned to complete this scenario in a hot room reported more aggressive and threatening impressions of the suspect and were more likely to draw and fire their weapon than those assigned to complete the training in a room set to a comfortable temperature.

Although this latter study isn’t a clear example of actual aggression (i.e., behavior intended to harm a real person who wishes to avoid it), overall, these and other experimental studies indicate that heat stress can cause increased aggression-related judgments, perceptions, thoughts, feelings, and aggressive behaviors at the individual level. The evidence from studies like these shows that as people get hotter, they become impulsive, more likely to perceive others as aggressive and hostile, and are more likely to behave aggressively themselves.

Overall, the experimental data paints a clear causal picture of how the direct heat effect works on individuals. This allows consideration of group-level data with a good understanding of how individual-level mechanisms can explain group-level heat effects.

Comparing Geographic Regions

One type of group-level data involves comparing rates of violent crime across geographical regions that have different climates. For example, Reference Mares and MoffettMares and Moffett (2015) analyzed violent behavior in sixty different countries from across the globe and found a positive link between heat and violence. Each Celsius degree increase in temperature was associated with a 6 percent increase in the homicide rate. This effect was magnified in countries that were also mired in some sort of conflict and/or instability.

Ideally, geographic region studies are done across regions that are similar in other key violence risk factors or with datasets that allow such alternative risk factors to be statistically controlled. This allows tests of the plausibility of many alternative explanations (e.g., poverty, culture).

Such similar-region and statically controlled studies have been done; they consistently find that hotter regions (such as cities across the United States) have higher rates of violent crime, even when controlling for as many as fourteen other risk factors (e.g., poverty, age distribution, racial composition, Southern honor culture, and unemployment; Reference AndersonAnderson, 1989; Reference Anderson and AndersonAnderson & Anderson, 1996). Interestingly, some of these geographical region studies have also assessed nonviolent crime rates; they generally find weaker or no heat effect on nonviolent crimes, as expected by the heat hypothesis.

An additional interesting finding is that, although nontemperature risk factors have their own independent effects on violent crime, some data suggests that such nontemperature risk factors can “amplify” the heat effect on violent crime (Reference Harries and StadlerHarries & Stadler, 1983; Reference Van de VliertVan de Vliert, 2009).

Of course, there are significant interpretation issues in comparing geographic region studies. Although researchers have controlled for many potential risk factors that could potentially operate as confounds in detecting this effect (socioeconomic status (SES), poverty, etc.), such correlational studies always leave room for doubt about causality; perhaps there are other unmeasured differences between the regions.

The next type of group data allows tests of the heat hypothesis that are free of region-based alternative explanations. Specifically, behavioral scientists have examined the heat hypothesis within the same region but over different periods of time that differ in temperature.

Comparing Violence Over Time

Numerous studies have used various time periods, including three-hour time blocks, days, months, seasons, even years to look at differences in violence in a specific geographic area. The logic of such studies is that one can assume that the cultural and demographic variables in a given location remain largely unchanged, barring any kind of extreme event or shift (e.g., large seasonal shifts in population). For areas that remain stable over the time period assessed, examining the association between temperature and violent crime rates over time provides a third way to test the heat hypothesis.

In studies such as these, the picture is clear: hotter periods of time yield higher rates of violence (for reviews, see Reference AndersonAnderson, 1989, Reference Anderson2001; Reference Anderson, Anderson, Geen and DonnersteinAnderson & Anderson, 1998; Reference Anderson, Anderson, Dorr, DeNeve and FlanaganAnderson et al., 2000; Reference Anderson, DeLisi, Forgas, Kruglanski and WilliamsAnderson & Delisi, 2011). These results are stable and are found using various time blocks, including years, seasons, days, or even hours (Reference Anderson, Bushman and GroomAnderson, Bushman, & Groom, 1997; Reference Bushman, Wang and AndersonBushman et al., 2005a, Reference Bushman, Wang and Anderson2005b). For example, Reference Anderson, Anderson, Dorr, DeNeve and FlanaganAnderson et al. (2000) reported that there are about 2.6 percent more assaults and murders in the United States during the summer than in other seasons of the year. They also found that hotter summers yield a bigger increase in violence than cooler summers. Furthermore, violence rates are higher in hotter years than in cooler years, even after key statistical controls are applied.

Other time-period studies provide additional and consistent results. Aggression rates – as measures by murder, rape, and assault rates (e.g., Reference Anderson and AndersonAnderson & Anderson, 1984), spontaneous riots (Reference Carlsmith and AndersonCarlsmith & Anderson, 1979), domestic violence (e.g., Reference Auliciems and DiBartoloAuliciems & DiBartolo, 1995; Reference Rotton and FreyRotton & Frey, 1985), assaults on bus drivers (Reference YasaykoYasayko, 2010), aggressive honking at other drivers (Reference Kenrick and MacFarlaneKenrick & MacFarlane, 1986), and even the rate of batters being hit by pitched baseballs (Reference Reifman, Larrick and FeinReifman et al., 1991) – are higher during hotter days, months, seasons, and years. Such findings have occurred with data from cities as varied in climate as Brisbane, Australia, Vancouver, Canada, and the US cities of Chicago, Minneapolis, Dallas, and Houston.

Additional analyses on the US city data give a more concrete idea of the magnitude of heat on annual “serious & deadly assault” rates (Reference Anderson, DeLisi, Forgas, Kruglanski and WilliamsAnderson & DeLisi, 2011). A 1.1 C° increase in annual temperature is associated with up to 25,000 more cases of serious and deadly assault per year in the United States.

Mechanisms Underlying Direct Temperature–Aggression Effects

So, what exactly are the mechanisms behind why heat causes increased violence and aggression? There are a handful of theoretical rationales behind the link between heat and aggression, and often scholars automatically pit these theories against one another. However, we challenge this automatic tendency and demonstrate how many of these theories are compatible. Additionally, when synergized, these theories help create a holistic understanding of the relationship between heat and aggression, as different theories help explain different aspects of the relationship in different contexts.

First, consider strictly physiological mechanisms. As described earlier, we know that the brain is responsible for thermoregulation and has a variety of mechanisms designed to keep us cool and functioning. However, the part of the brain that is responsible for thermoregulation is the same part of the brain that is responsible for emotion regulation (Reference AndersonAnderson, 1989; Reference BoyanowskyBoyanowsky, 1999, Reference Boyanowsky2008; Reference Boyanowsky, Calvert-Boyanowsky, Young and BrideauBoyanowsky et al., 1981). As noted before, the brain has finite resources that can be devoted to functioning. When the part of the brain needed to regulate emotion is already activated in trying to cool ourselves down physiologically, we must either offload those resources elsewhere in the brain or suffer performance issues. Additionally, the body has other reactions to the heat, such as producing more adrenaline (Reference Simister and CooperSimister & Cooper, 2005), which can lead to more reactive and therefore aggressive behavior in certain conditions (such as when provoked). This research demonstrates what we have called the “hardwired” aspect of heat’s impact on aggression (Reference AndersonAnderson 1989; Reference Miles-Novelo and AndersonMiles-Novelo & Anderson, 2019).

Now, consider some basic psychological findings that also underpin the heat/aggression relation. The first comes from embodied cognition research, which suggests that humans are incredibly responsive and susceptible to the stimuli in their environment, which ultimately influences how we think and feel (Reference Wilkowski, Meier, Robinson, Carter and FeltmanWilkowski et al., 2009). Research shows that hot temperatures produce discomfort and irritability, and then we can clearly see how being in an uncomfortably hot environment can yield biases in aggression-related precursors such as hostile perceptions, hostile feelings, and aggressive inclinations.

At first, there may be confusion as to how the basic physiological functions interact with these psychological findings. However, we contend that these findings are, in fact, fully compatible. Although there may be an independent physiological effect, more social psychological factors (irritability, biases in social perceptions) can be a direct consequence of these physiological effects of heat on emotion regulation. There are some effects that we often lump together as “irritability” (see Reference Miles-Novelo and AndersonMiles-Novelo & Anderson, 2019), as there may not be a way (currently) to piece apart the physiological impacts from the psychological ones. That is, heat stress may simultaneously cause both physiological and psychological effects that increase the likelihood of an aggressive (or violent) act emerging.

Another important theory to consider at this juncture is called “routine activity theory” (RAT; Reference Cohen and FelsonCohen & Felson, 1979). Routine activity theory simply states that as our environment changes (e.g., church, school, bar, time of day, day of week), so does the repertoire of likely thoughts, feelings, and behaviors. Thus, some portions of observed differences in aggression during hot/cool weather might be caused by changes in routine activities. That is, when it’s warmer outside (but not exceptionally hot), people tend to engage with more people outside and engage in behaviors that are more social, increasing the opportunity for aggression towards others. For example, during a heatwave, those lacking access to air conditioning may spend more time outside or may go to an air-conditioned bar and drink more beer. Being outside increases encounters with others, and we all know too well the impact alcohol can have on aggressive behaviors and cognitions. This is just one specific example, but a good one to show how the weather impacts our behaviors and how we structure social interactions around it. RAT has quite a lot of data that suggests that it holds merit, such as studies showing that weekends tend to yield higher rates of violent crime than weekdays (Reference Anderson and AndersonAnderson & Anderson, 1984; Reference Anderson, Anderson, Dorr, DeNeve and FlanaganAnderson et al., 2000). However, many of the studies reviewed earlier show that RAT cannot fully explain the heat–aggression findings. Instead, it is but one piece of the puzzle.

There also are culture-based theories of aggression, such as the distinction between honor and dignity cultures (e.g., Reference Uskul and CrossUskul & Cross, 2020). For example, Reference Cohen and NisbettCohen and Nisbett’s (1994 theory about the development of the Southern culture of honor in the U.S. has been used to claim that the heat/aggression effect in U.S. cities is totally spurious because Southern cities have both relatively high temperatures and residents who have adopted a relatively violent culture. Subsequent studies that directly tested this potentially confounding hypothesis have still yielded clear support for the heat hypothesis independent of such cultural variables (Reference Anderson and AndersonAnderson & Anderson, 1996). To reiterate, we view cultural effects on violence rates as a real phenomenon that works in tandem with the heat hypothesis.

A recent theoretical model, known as CLASH (Climate, Aggression, and Self-Control in Humans), seeks to rectify some of these issues. CLASH posits those cooler climates put more of a cultural emphasis on the future rather than the present, more value in self-control, and have a “slower life history strategy” than cultures in warmer climates (Reference Van Lange, Rinderu and BushmanVan Lange, Rinderu, & Bushman, 2017). Although more research is needed to test the CLASH model, note that both CLASH and RAT can help explain that although the direct heat/aggression effect is real, certain moderators can mitigate or exaggerate this effect, whether that be by changing patterns of behaviors and environments, or because of cultural norms.

But Some Data Shows that Crime Rates Are Decreasing?

This is a very important question that comes up when talking about the research mentioned, and in general, when thinking about how rapid climate change is going to impact violence and aggression across the globe. We (the authors) don’t doubt the observable data that, in general, crime statistics in some countries are going down. In fact, a recent article published by the Pew Research Center conglomerated crime data from both the United States FBI and Bureau of Justice Statistics (BJS) and noted that the BJS reported that violent crime rates had fallen somewhere around 74 percent from 1993–2019 (Reference GramlichGramlich, 2020). Similarly, the FBI has reported drops of around 68 percent in the number of robberies, 47 percent in murder/nonmanslaughter cases, and 43 percent in aggravated assaults in that same timeframe.

However, this does not invalidate or contradict the general hypothesis that heat increases aggression and violence. In fact, much of the evidence collected has found that increases in violent crime still occur over hotter periods of time or in hotter geographic regions, independent of the fact that overall crime statistics are decreasing. What we see is that even though overall crime has reduced over time, there are predictably more reports of crime (notably, violent crime) when the temperature is hotter. The same is true when looking at reports of aggression and violence across varying geographic regions, with hotter regions still reporting higher rates of crime. However, more research needs to be done to model how the relationship between heat and crime exists as we continue to see overall decreased rates of crime.

Additionally, as mentioned before, predicting violence and aggression means considering numerous risk factors, of which heat is only one. Simple crime rate statistics that don’t consider other key risk factors that change over time are largely irrelevant. For example, during the same time period in which violent crime rates have declined, there have been massive changes in the population’s age distribution (e.g., declines in high-risk age demographics and increases in low-risk ages), declines in childhood lead exposure by high-risk ages, and massive diminution of the drug wars.

Consider our model of how rapid global warming can increase aggression and violence. Many of the global warming-related risk factors are indirect; the consequences haven’t fully begun to emerge. Some of them will take eighteen years or so to emerge (i.e., those that create violence-prone adults). Resource scarcity, mass migration, droughts, famines, more severe and frequent natural disasters, will all have global-level impacts that increase the risk factors people are exposed to. Although it is clear that heat itself has a direct impact on our behavior, much of the direct effect can be mitigated by reducing these other risk factors (access to resources, political and governmental stability, inclusive environments, income distribution, etc.). However, the much more impactful and frightening result of climate change will be how it undermines these other factors, making it much more likely for violence and conflict to occur.

However, these direct heat effects and their underlying mechanics are not the only paths by which rapid global warming will increase aggression and violence. Additionally, this pathway is perhaps the most “uninteresting,” offers the least amount in terms of potential interventions, and is the least preventable. Rather, the focus of society’s energy and attention should be directed at the more subtle impacts climate change will have on violence, aggression, and conflict. These two indirect pathways offer the most opportunity for policy and social intervention. There is little we can do about the direct heat effects (other than changing behaviors worldwide to curb greenhouse gases). However, there is much we humans can do to short-circuit the operation of these indirect effects (Routes 2 and 3). These indirect effects are discussed in our next two major sections.

Increased Prevalence of General Developmental Risk Factors

Human development is one of the most studied areas of psychology. The ambient physical, social, and cultural environments are integral to the human development process, and we know that climate change is already drastically altering those environments. It’s easy to see the devastating changes that are occurring because of climate change; floods caused by increasing sea levels and more intense storms, increased droughts that lead to devastating wildfires, more volatile and severe natural disasters, increased civil conflicts because of economic and political instability are all caused by the rapidly changing planet (Reference Miles-Novelo and AndersonMiles-Novelo & Anderson, 2019). These sorts of event are drastic enough to potentially harm the surrounding environments that can be vital for human development. People are greatly affected by their living situations, where more positive and loving environments often lead to more positive developmental outcomes than seen in comparatively negative environments. In this section, we briefly summarize some of these negative environmental risk factors and how they become more common and more severe as a result of rapid global warming.

When thinking about risk factors, note that they do not occur randomly across populations. Rather, human developmental risk factors tend to be comorbid; some people (from conception through adulthood) tend to have many risk factors, while others have few (Reference Sandstrom and HuertaSandstrom & Huerta, 2013). Additionally, it is through factors such as family income and socioeconomic status that many adverse developmental outcomes operate. In their excellent review of developmental factors affected by instability, Reference Sandstrom and HuertaSandstrom and Huerta (2013) refer to this as a “domino effect” and point out how low-income or even middle-income families can struggle to have saving assets to handle transitional periods. One can easily imagine the many ways in which climate change could negatively influence a family with low resources, such as making emergency transitions a much more frequent occurrence for middle- and low-income families around the world.

Here, we focus on how some of these changes and instabilities influence individual development. Note that we don’t claim universality of what defines “normal” or “stable”; different families in different places around the world have different cultural expectations and norms. The risk factors that we discuss are those that are somewhat generalizable across differing cultures (for a more comprehensive understanding of how cultural differences in development could be affected by climate change, see Reference Kuwabara and SmithKuwabara & Smith, 2012; Reference OgbuOgbu, 1988).

One particularly strong impact on individual development is family stability. This can manifest in a variety of forms, and for many families, multiple stability-decreasing factors occur simultaneously. This can include economic stressors (low or inadequate family income), unstable housing situations, parental job instability, and lack of parental presence. About one in three children in the United States experiences major family structure change by age six, whether that was from parental death, divorce, separation, or some form of new cohabitation (such as a new adult becoming present in their living situation; Pew Research Center, 2015). Some projections forecast that the percentage of children growing up in single-parent homes, at least temporarily, could become as high as 50 percent globally, in part, due to the environmental challenges presented by rapid global warming (Reference Sandstrom and HuertaSandstrom & Huerta, 2013). We already see a pattern more broadly in immigration, especially when relocation is caused by sudden devastating events, such natural disasters. These kinds of events often serve as a basis for the displacement of families and often also can result in the permanent fragmentation of them (Reference RabinRabin, 2018). This can be because of direct immigration policies or because of the causal event itself, whether it be war, famine, or a natural disaster. Because of the direct consequences of rapid climate change on our environment, we know that billions of people are at risk of displacement, and therefore, at higher risk of family separation. Although these changes are not always negative (divorce or separation could reduce parental conflict), Reference Sandstrom and HuertaSandstrom and Huerta (2013) do note that most experts consider a change in parental dynamics or family structure as a cause of severe anxiety and stress, which can lead to emotional instability in both the caregivers and the children.

Growing up in a home where parents who were living together when the child was born but are separated by the age of five leads to poorer vocabulary skills for that child, poorer prereading skills, and increased aggressive behaviors (Reference Craigie, Brooks-Gunn and WaldfogelCraigie et al., 2012). Similarly, rates of obesity and asthma are higher in these circumstances (Reference Craigie, Brooks-Gunn and WaldfogelCraigie et al., 2012; Reference Sandstrom and HuertaSandstrom & Huerta, 2013). In addition to its well-known effects on heart disease, arthritis, and other medical conditions, obesity has been found to negatively affect brain plasticity, making it harder for people to learn and retain how to do new tasks (Reference Sui, Ridding and HordacreSui et al., 2020). Moving from a single-parent home into an unmarried, unstable cohabitation with a new partner can also lead to decreased academic performance and engagement (Reference Sandstrom and HuertaSandstrom & Huerta, 2013). Such family instability predicts several adverse long-term outcomes, such as failure to complete high school (Reference Sandstrom and HuertaSandstrom & Huerta, 2013). In a world that is increasingly plagued by the impacts of rapid climate change (e.g., natural disasters, mass migration, war), impacts that are known to be devastating to healthy family structures and stability, it seems obvious that the impact on developing children will be especially harmful.

Naturally, this extends to economic and housing stability. Research finds that the parents having unstable employment is associated with adverse academic outcomes, such as more frequent grade repetition (grade retention), lower educational attainment, and internalizing and externalizing behaviors (Reference Sandstrom and HuertaSandstrom & Huerta, 2013). Children whose parents have frequent involuntary job instability often have worse health outcomes, even more so than children whose parents have voluntary job fluidity, work a stable but low-wage job or have inconsistent work hours. Often these effects are not necessarily a reflection on the parent or parents themselves, but are, rather, a product of the situation. When families face such major life stressors, oftentimes the parents must devote more time, energy, and resources to addressing external concerns rather than being able to adequately handle important internal family responsibilities. Therefore, much of the developmental literature has for decades strongly urged societies to strengthen social safety nets and improve access to monetary resources for struggling families. It should come as no surprise that such actions are needed in all nations to combat the impacts of climate change (which are discussed in the last section of this Element).

For families who experience this instability across countries, these disadvantages are even more pronounced. When a family immigrates or migrates, the effects on children (both those who moved and those who were born after the relocation but before successful integration) are potentially very harmful, especially if their new permanent location lacks support for the families that arrive there. Reference Coll, Patton, Marks, Masten, Liebkind and HernandezColl et al. (2012) notes that these children must learn to adapt and grow in not only a potentially completely different environment than where they are from (or that they experience at home) but often that adjustment comes with little guidance from parents and other older family members, as they presumably are adjusting to their new environments as well. Parents struggling to learn a new language, for instance, often have difficulty finding and keeping adequate jobs, engendering economic and income instability. Additionally, migration often impairs language acquisition in children. We know that language acquisition is easier for children who are younger than it is for adolescents, young, and older adults. Thus, acquiring the new country’s dominant language is differentially difficult depending on the child’s age and on the parents’ facility for the new language (Reference Coll, Patton, Marks, Masten, Liebkind and HernandezColl et al., 2012).

Migrating families also must deal with being seen as a potential “outgroup” in their new community and oftentimes face additional stress and anxiety due to perceived and actual stereotyping, prejudice, discrimination, rejection, and lack of community support. Later, we discuss more how climate change increases negative perceptions of “outgroups” (and, subsequently, increased tensions along the lines of race, ethnicity, religion, and socioeconomic class), but for now, just note that having these experiences leads to a host of long-term adverse outcomes for children and adolescents.

One way to think about this is the concept of “adverse childhood experiences” (ACEs; McCoy, Tibbs, DeKraai, & Hansen 2021). The impact of ACEs has been shown to be predictive of many adverse and risky behaviors, such as likeliness to engage in drug and alcohol use, increased chances of early death, and increased likelihood of aggressive and violent behavior in adolescence and adulthood. In some circumstances, having multiple ACEs increases susceptibility to extremist ideologies and results in the engagement of terrorist activities.

ACEs not only affect development at behavioral and emotional levels, they also have neurological and cognitive consequences (McCoy, Tibbs, DeKraai, & Hansen, 2021), including deficits in executive functioning, attention, abstract thinking, memory, and language (Reference De BellisDe Bellis, 2005; Reference Eigsti and CicchettiEigsti & Cicchetti, 2004; Reference Eisen, Goodman, Qin, Davis and CraytonEisen, Goodman, Qin, Davis, & Crayton, 2007; Reference Wilson, Hansen and LiWilson, Hansen, & Li, 2011). Many of these adverse outcomes are directly linked to the likelihood of later violent criminality (e.g., Reference Vazsonyi, Flannery and DeLisiVazsonyi, Flannery, & DeLisi, 2018).

Rapid climate change is already reducing access to a wide range of resources by increasingly large segments of the world’s population, such as education, safe water, and proper nutrition. For example, rapid global warming is causing prolonged droughts, which leads, in turn, to water scarcity and failed crops. This means fewer necessary nutritional resources are available from the date of conception throughout development, and also that those fewer resources are mostly going to places that can afford to buy them. There are a host of developmental consequences for those who lack access to these resources. For example, cognitive performance in children can drop significantly if their diets severely lack protein (Reference ScrimshawScrimshaw, 1998). We also know iron deficiency is the most common manifestation of malnourishment, and that can impact the development of brain enzymes that are essential to the development of cognitive skills, as well as in the development of behavior, and that prenatal and infant iron deficiencies can lead to adverse development that is irreversible (Reference ScrimshawScrimshaw, 1998). We have already discussed the impacts of dehydration on the brain, but it is important to note that those effects are even more harmful and impactful on developing brains.

Rapid climate change increases the frequency of ACEs in yet another way, through pandemics. This is especially true for families with low incomes, much like how adverse outcomes (both directly in who experiences the worst sickness from the virus, as well as the downstream economic and societal level impacts) during the COVID-19 pandemic have disproportionately hurt poorer families (Reference McClure, Vasudevan, Bailey, Patel and RobinsonMcClure et al., 2020). Such families worldwide are much more likely to get the disease (COVID-19 and future pandemics), because of several factors, including lack of resources and education about the disease, being much more likely to live in overcrowded communities, representing much more of the designated “essential” workforce not able to quarantine or work from home, not being able to house children and needing to still send them to school, lack of access to outdoor space, lack of access to testing and treatment, as well as disproportionately meaning that contracting the pandemic disease will be both more likely and more severe (Reference McClure, Vasudevan, Bailey, Patel and RobinsonMcClure et al., 2020).

To make matters worse, scientists have noted that scenarios like the COVID-19 pandemic are going to become more common as rapid climate change continues. On the page for Harvard’s T.H. Chan School of Public Health, Aaron Bernstein speaks on several of these issues, demonstrating how the COVID-19 pandemic serves as a case study for future pandemics that will be caused by climate change and how rapid climate change facilitates the increase in exposure to more harmful pathogens. One of the main mechanisms is that as the more rapidly climate heats up, the more species will migrate to cooler climates. This forces species that normally have minimal or no contact at all to suddenly be in close proximity. This creates more opportunities for diseases to spread or be curated. Additionally, as species continue to die off (both plants and animals), it will force those that survive to consume food from untraditional places, again offering a mechanism for pathogens to spread to new areas, across species, and also for new pathogens to evolve (Reference HarvardHarvard T.H. Chan School of Public Health, 2020).

Increased Prevalence of Developmental Risk Factors For Violence-Prone Behavior

As implied in the previous section, rapid climate change exposes a developing human – from prior to conception (i.e., via epigenetic effects on the mother) through young adulthood – to causal risk factors known to increase the likelihood of that person becoming a violence-prone adult. As the climate continues to change rapidly and create global instability, a greater proportion of children will be exposed to many major risk factors if there are not societal-level interventions to mitigate the potential damage. Delineations of many aggression/violence risk factors can be found in Reference Anderson, Carnagey and MillerAnderson and Carnagey (2004), Reference Plante and AndersonPlante, Anderson, and Delisi (2017), and Reference Vazsonyi, Flannery and DeLisiVazsonyi, Flannery, and DeLisi (2018).

Basically, the major direct effects of rapid global warming on the earth’s physical systems (e.g., more severe and frequent droughts, tropical storms, local storms, sea-level rise, floods, water shortages, and access to food) indirectly increase exposure to known risk factors that can influence the development of violence-prone individuals. These include (among others) poverty, dysfunctional parenting, disrupted families, exposure to neighborhood and community violence, exposure to war and civil conflicts, poor prenatal and childhood nutrition, poor maternal nutrition, and poor living conditions (Reference Anderson, DeLisi, Forgas, Kruglanski and WilliamsAnderson & DeLisi, 2011; Reference Vazsonyi, Flannery and DeLisiVazsonyi, Flannery, & DeLisi, 2018).

One recent study reviewed twenty-eight extreme weather events across continents. The research team found that half of these weather events were either caused by human-induced climate change or were at least exacerbated by it (Reference Herring, Hoerling, Kossin, Peterson and StottHerring et al., 2015). And, of course, each event increased exposure to risk factors for creating violence-prone people.

Some research has shown that genetic factors interact with social, environmental factors in creating violence-prone adults. One study examined a specific interaction between monoamine oxidase A (MAOA: an enzymatic degrader that moderates neurotransmitters) and childhood maltreatment in relation to later antisocial behavior and outcomes. In very simple terms, this enzyme has an impact on the production and release of amines such as dopamine and serotonin, and the researchers wanted to know whether exposure to childhood maltreatment could impact the development of this enzyme, thus impacting other brain functions and potentially causing behavioral disorders (Reference Caspi, McClay and MoffittCaspi et al., 2002). What they found (and has been replicated) was that the relationship between child maltreatment and antisocial behavior was conditional on a person’s MAOA genotype. In one sample, only 12 percent had had both risk factors but accounted for 44 percent of the violent crime convictions by the total sample. Similarly, 85 percent of people who had both risk factors developed some form of antisocial behavior. But, in the absence of maltreatment, the genetic risk factor did not show up in violent criminality or broader indicators of antisocial behavior.

In this and subsequent paragraphs, we focus on four other key factors: food/water insecurity, economic deprivation, susceptibility to terrorism, and preferential ingroup treatment.

Even in the United States, before the COVID-19 pandemic, 10.5 percent of households faced food insecurity (US Department of Agriculture, 2020). Subsequently, that number increased to estimates as high as 25 percent (Reference Schanzenbach and PittsSchanzenbach & Pitts, 2020). Global figures for food insecurity are generally much worse. Scientists from several domains generally find that food insecurity, poor prenatal nutrition, and poor postnatal nutrition can lead to increases in aggressive and antisocial behavior in children. One classic example is a study on Mauritanian children, which looked at their nutritional intake and its relationship to behavioral disorders. What the researchers found was that malnourishment at three years old increased the likelihood of hyperactivity and aggression when they were eight years old and of behavioral conduct issues and disorder at age eleven (Reference Liu, Raine, Venables and MednickLiu et al., 2004). All four of these childhood behavior problems are major risk factors for antisocial and violent behavior in adulthood (Reference Anderson, Carnagey and MillerAnderson & Carnagey, 2004; Reference DeLisiDeLisi, 2005; Reference Warburton, Anderson, Zeigler-Hill and ShackelfordWarburton & Anderson, 2018).

Another relevant well-known finding comes from a study conducted by looking at 100,000 Dutchmen born shortly before and after World War II (Reference Neugebauer, Hoek and SusserNeugebauer, Hock, & Susser, 1999). What makes this cohort interesting is that, from October 1944 until May 1945, there was a German blockade that split the Netherlands. This had a major effect on food supplies to different parts of the country, as resources were held up on account of the blockade. The researchers used this historical event to create two comparison groups, those whose mothers experienced malnourishment during the first and second trimesters of pregnancy and those whose mothers had not. Men whose mothers had experienced malnourishment during fetal development were 250 percent more likely to develop antisocial personality disorder than were the well-nourished ones.

This relationship between malnourishment and antisocial aggression is well established (e.g., Reference DeLisiDeLisi, 2005; Reference Huston and BentleyHuston & Bentley, 2009; Reference Plante, Allen, Anderson and OglesbyPlante, Allen, & Anderson, 2017). For example, malnourishment has a large impact on the release of cortisol in the mother during her pregnancy, leading to numerous adverse developmental outcomes in the fetus (Reference Chen, Cohen and MillerChen, Cohen, & Miller, 2010).

Other studies have specifically focused on climate change’s effect on violence. For example, one study found that each standard deviation increase in rainfall and warmer temperatures was associated with a 4 percent increase in interpersonal violence and a 14 percent increase in intergroup violenceFootnote ² (Reference Hsiang, Burke and MiguelHsiang, Burke, & Miguel, 2013).

The Intergovernmental Panel on Climate Change has issued numerous warnings about the damage rapid climate change will have (and already is having) on agricultural production, greatly diminishing food supply (Reference Parry, Canziani, Paultikof, van der Linden and HansonIPCC, 2007, Reference Parry, Canziani, Paultikof, van der Linden and Hanson2013). Knowing how malnutrition affects development is key to creating effective mitigation and prevention strategies for those most at risk. Specifically, the IPCC has reported that global warming will cause a drop in crop yields, decrease the amount of grazeable land for livestock, and the outright loss of farmable land because of droughts, wildfires, increased humidity, and flooding (Reference Parry, Canziani, Paultikof, van der Linden and HansonIPCC, 2007, Reference Parry, Canziani, Paultikof, van der Linden and Hanson2013).

The effects of poverty and malnutrition on human development are inherently linked; thus, it is also important to understand related poverty-linked violence risk factors. Poverty leads to increased exposure to numerous risk factors, such as decreased life satisfaction, increased resentment, and dissent (Reference Doherty and ClaytonDoherty & Clayton, 2011). Not only does material inequality increase these risk factors, but so does the perception of inequality. Perceived inequality of any kind (race, gender, class, etc.) has been found to be a potential motivation for enacting violent revenge at both the individual level (Route 2) and group level (Route 3) (Reference Archibald and RichardsArchibald & Richards, 2002; Reference CramerCramer, 2003; Reference HageHage, 2003). This effect is exacerbated when the perception of inequality increases rapidly and when that perception leads to anxiety about one’s future (Reference GoodhandGoodhand, 2003; Reference Nafziger and AuvinenNafziger & Auvinen, 2002). It is important to note, however, that poverty itself does not create violence. The conditions often surrounding impoverished communities and families (that is, the systems that create poverty and that encourage inequality) are what create violent outrage (Reference Barnett and AdgerBarnett & Adger, 2007). This discussion leads to the third route through which rapid global warming increases violence.

Ecomigration and Intergroup Conflict

One relatively new term illustrates the magnitude of the effects of rapid climate change on intergroup conflicts: ecomigration. Ecomigration refers to group migration in response to environmental, economic, or political instability brought on them by an ecological disaster (e.g., Reference Plante and AndersonPlante & Anderson, 2017). Some ecological disasters are largely unrelated to global warming, such as volcanoes, earthquakes, and tsunamis.Footnote ³ However, many other types of severe disaster are already increasing in frequency and/or severity as a direct result of human-caused global warming, such as hurricanes, tornados, coastal flooding, droughts, and wildfires.

Ecomigration does not inevitably lead to major intergroup conflicts. Rather, there often are additional associated risk factors that, when combined with ecomigration, almost guarantee major conflicts. For example, economic instability frequently characterizes both the region from which the ecomigrants are fleeing and the area to which the ecomigrants move. That means that these two groups are competing for the same scarce resources, which usually leads to conflict. Indeed, this competition over scarce resources is a major motivation for group conflict (regardless of whether those resources are actually scarce, or simply are perceived to be). Early research on the theory of realistic group conflict showed that previously unacquainted boys assigned to one of two groups at a summer camp would develop hostile attitudes and stereotypes towards members of the “other” group when they compete over scarce resources (Sherif et al., 1954/1961). This theory posits that much intergroup aggression can be explained by competition for scarce resources (Reference KrahéKrahé, 2020). Even moral superiority and religious salvation can be framed as scarce resources that can belong only to one group (Reference AvalosAvalos, 2005).

A key component that influences the outcome of intergroup contact is the “functional relationship” between two groups competing for resources (Reference KrahéKrahé, 2020). If the relationships are positive and cooperative, then feelings about working with an outgroup to achieve a shared goal (or to acquire a shared resource) are positive. However, if the relationship is competitive, then negative stigmas, stereotypes, and prejudice about the outgroup form and the relationship can become confrontational and potentially violent (Reference Barlow, Paolini and PedersenBarlow et al., 2012; Reference PettigrewPettigrew, 2021). If the receiving governments and dominant religious, racial/ethnic groups do not want the migrants for whatever reasons (e.g., perceptions of competition over resources, loss of economic opportunity, existing hatreds, and stereotypes), then intergroup conflict becomes inevitable. In short, it is easy to see how the massive ecomigrations triggered by rapid climate change will lead to increased group conflict.

Several closely related theories (and hundreds of supporting empirical studies) further address how intergroup contact can increase hostility and violence between the groups. Relative deprivation theory (Reference Smith, Pettigrew, Pippin and BialosiewiczSmith, Pettigrew, Pippin, & Bialosiewicz, 2012) asserts that intergroup tensions arise from the perception that one group is given unfair resources over the other group. Group identity shapes attitudes and perceptions of ingroup and outgroup members, whether fairly or unfairly. Importantly, it is the perceptions of the other group that creates hostility, not necessarily the actual material conditions themselves.

Intergroup threat theory (Reference Stephan, Ybarra, Rios Morrison and NelsonStephan, Ybarra, & Rios Morrison, 2009) and social identity theory (Reference IslamIslam, 2014; Reference TajfelTajfel, 1981) note that contact with an outgroup can create a sense of threat that then leads to hostile attitudes and beliefs about the outgroup and extend the “threats” well beyond material resources. One’s social identity (and sense of well-being) is closely linked to one’s ingroups, including religious, political, and racial/ethnic identities. For example, if ecomigrants have a different religion than that of the receiving country, many citizens (and politicians) of that country will perceive that difference as a threat to the basic fabric of the country, regardless of whether the ecomigrants are a burden or bonus to the material well-being of the country. Hostility and prejudice towards an outgroup, such as ecomigrants, can arise merely because of preferential treatment of (and positive feelings towards) members of one’s ingroups. People who strongly identify with one or more of their ingroups (that is, people whose self-worth is tied to the success of their ingroups), are especially threatened by migrants who differ on key self-identities such as nationality, race, gender, politics, and religion. Such self-identities are constantly in operation, with some more salient at some times than others.

It is easy to see how these group dynamics come into play because of rapid climate change and ecomigration. Several examples illustrate the interplay of these normal intergroup processes.

One concerns the ongoing civil war in Syria. This conflict began with an (at the time) unprecedented drought in the region (Reference GleickGleick, 2014). Essentially (and this is a slight oversimplification of the mechanisms at play), this drought caused a large portion of the rural population to relocate into more urban cities in search of jobs, water, and food. Attempts at government intervention were few, ineffective, and poorly received, as the already unstable government failed to provide adequate housing, resources, and jobs for this large group of migrants. This led to increased political and civil unrest, which combined with other pre-existing conditions to help spark the eventual outbreak of civil war.

Interestingly, this conflict then led to a mass movement of Syrian groups to other countries, especially to Europe, which helped trigger tensions and anxieties about immigration.Footnote ⁴ This, in turn, fueled politically conservative anti-immigrant movements in Europe, such as Brexit (Reference EinbinderEinbinder, 2018; Reference GarretGarret, 2019; Reference KrahéKrahé, 2020). Although there has been debate on whether the violence in Syria is directly related to climate change, this remains a perfect case study of how environmental disasters can spark eventual mass migration that has global geopolitical consequences. For example, a similar “immigrant crisis” in the United States has been exploited by alt-right political groups, helping contribute to President Donald Trump’s election in 2016 and subsequent anti-immigrant attitudes, stereotypes, and harsh anti-immigrant laws and policies (Reference Donovan and RedlawskDonovan & Redlawsk, 2018; Reference Hesson and KahnHesson & Kahn, 2020). In general, anti-immigrant rhetoric and policy stem mostly from an increase in support for far-right movements (Reference Dennison and GeddesDennison & Geddes, 2018; Reference EinbinderEinbinder, 2018). This increased anxiety about immigration, the dialogue surrounding it, and policies that harm immigrants, yield a very dangerous picture for our future.

Terrorism, Terrorists, and Terrorist Groups

These same Route 3 factors play a substantial role in the development and expansion of terrorism, often interacting with Route 2 (creating violence-prone adults). The creation and expansion of terrorist groups and terrorist activities are based on rather complex relationships between humans and their environmental, economic, and social conditions (Reference Kruglanski, Chen, Deschesne, Fishman and OrehekKruglanski et al., 2009). The rapid and dramatic loss of one’s family, culture, or livelihood combined with perceptions of inequality that disproportionally harms a distinct ethnic, religious, or social group provide motivation for and success at recruitment and enlistment in terrorist groups (Reference GoodhandGoodhand, 2003; Reference OhlssonOhlsson, 2000. This is especially true when the people that are affected believe that there is no chance at significant or substantial material improvement. Research into people joining militia groups across the globe found these factors to be the major motivations for potential recruits (Reference Archibald and RichardsArchibald et al., 2002; Reference HageHage, 2003; Reference Maclure and SoteloMaclure & Sotelo, 2004). Additionally, research on terrorism and the motivations for joining violent groups has found that not only are there material, environmental, and motivating political motives, but that individual psychological motivations – such as regaining a sense of belonging, status, power, control, and sense of meaningfulness – are major contributors as well (Reference GoodhandGoodhand, 2003; Reference HageHage, 2003; Reference Maclure and SoteloMaclure & Sotelo, 2004).

Committing acts of terror is a result of numerous societal, ideological, and personal causes (Reference Kruglanski, Orehek, Forgas, Kruglanski and WilliamsKruglanski & Orehek, 2011). Rapid climate change has immediate and devastating effects on the most basic resources needed for global stability, and thus, increasingly large parts of the world will experience these risk factors, and, subsequently, the formation of and support for violent extremist groups will increase, especially in the most disadvantaged, unstable, and disproportionally affected countries and cultures.

Basic Psychological Processes at Work

As mentioned earlier, one way to make a target audience feel threatened by and fearful of some outgroup is to blame “them” for the ingroup’s failures, difficulties, and hardships. This is particularly effective if a solution is offered, one that targets one or more outgroups as the cause of the ingroup’s difficulties. Of course, the threat does not have to be factually true. But oftentimes, highly salient events do trigger major changes in large swaths of a country’s population. For example, the Islamic terrorist attack in Madrid in 2004 led to a sharp increase anti-Arab attitudes (Reference EchabeEchebarria-Echabe & Fernández-Guede, 2006). It also led to increases in authoritarianism and anti-Semitism. Similarly, the terrorist attack of September 11, 2001, on several US targets led to more positive attitudes towards war among US college students, an increase that lasted at least a full year (Reference Carnagey and AndersonCarnagey & Anderson, 2007).

The increasing hostility towards outgroups in response to the threat of climate change was being demonstrated as long as a decade ago (Reference Fritsche, Cohrs, Kessler and BauerFritsche, Cohrs, Kessler, & Bauer, 2012). These researchers found that merely reminding people of the adverse consequences that climate change may have for their country increased general authoritarian attitudes (which are hostile to outsiders) and derogation of outgroups.

Several common but seemingly different social-psychological effects – such as the foot-in-the-door phenomenon, conformity, compliance, and attitude change effects – help explain how rapid climate change can create and intensify outgroup hostility and aggression through a combination of Routes 2 and 3 processes. Techniques to induce specific attitudes, beliefs, and behavioral tendencies and to change these have been studied by both basic science and applied science researchers. These include hundreds of studies on stereotypes, prejudice, and racism, some dating back to World War II. Many studies have specifically focused on how humans are led to believe extreme ideologies (such as terrorist ideologies).

Early studies of mass violence focused on understanding the “authoritarian personality,” hypothesized to underlie the success of Nazi ideology and of similar right-wing movements. But how do such extreme constellations of hostile attitudes, stereotypes, and behavioral inclinations develop and persist? It cannot be the case that all or even most citizens of 1930s’ and early 1940s’ Germany had this personality type. This belief system had to develop over time.

The compliance literature discovered that normal people could be induced to do violent behaviors (such as delivering potentially fatal electric shocks) against another person by first pressuring them to perform very mildly aggressive actions (e.g., a barely noticeable shock) for a “good” cause, and then gradually increasing the severity of the demanded action (e.g., Reference MilgramMilgram, 1963). Similarly, the foot-in-the-door behavior change technique involves using social norms to induce a person to first agree to a small request, followed by subsequently larger and more intense ones (Reference CialdiniCialdini, 2021).

The conformity literature has shown (among other things) that people will conform to even incorrect judgments and opinions of others, especially when those judgments are public and are somewhat ambiguous. Over time, repeated conformity to others’ judgments can become internalized.

In general, the attitude change literature shows that one effective way to change attitudes is to first identify the target’s “latitude of acceptance” and “latitude of rejection” on the specific attitude topic. Then, one directs persuasive communications to the target person (or group) that are in the direction of intended change but that still fall within their latitude of acceptance. Over time and repeated persuasive communications of this type, the overall attitude and the latitude of acceptance move in the targeted direction (Reference Petty and CacioppoPetty & Cacioppo, 2012).

In all cases, these techniques are commonly used to manipulate people into eventually engaging in behaviors they normally would not have engaged in, including engagement in terrorism, war, and genocide. In Nazi Germany (and other countries complicit in the Holocaust), Hitler’s Reich Minister for Propaganda and Public Enlightenment, Josef Goebbels, was reasonably successful in using mass media to increase existing suspicion and hatred of Jews.

Over time, repeated use of these techniques, each of which induces small changes to existing attitudes, stereotypes, and behavioral inclinations, can eventually yield extreme beliefs, attitudes, and behaviors in the targeted population. That is, “normal” people can be changed into people (and groups) willing to join extremist groups and commit atrocities. In other words, the extremist view becomes normalized.

The process starts most often as a small concession. For instance, let us say you are frustrated with your government’s perceived poor ability to distribute resources. You see that some resources are being distributed to asylum seekers, climate refugees, and immigrants, but, for some reason, not to you or your favored ingroups. The extreme ideology would start by telling you that since there is a finite number of resources, that outsiders are taking the resources you should have. That creates frustration at the immigration process and with the system that distributes those resources. Over time, you may slowly start to be convinced that rather than a lack of equitable distribution being a fault of the systems at play, the issue stems from the group of people you see as a threat to your well-being and identity. This can happen both on an individual level as well as a group level, much like we are seeing with the rise of far-right ideologies containing anti-immigration rhetoric.

Collective animosity toward outgroups manifests in other ways as well, such as in harmful representations of outgroups in news and entertainment media. This, in turn, can create feedback loops for these hostile attitudes and increase them. Frequently, hostile beliefs about and attitudes towards outgroups are not based on real-life experiences with outgroup members but rather are formed from media presentations of different groups (Reference Nisbet, Ostman, Shanahan and SinnoNisbet, Ostman, & Shanahan, 2009; Reference Saleem, Prot, Anderson and LemieuxSaleem et al., 2017).

Political and Social Unrest

The crisis in Syria illustrates how rapid climate change can cause political and social unrest, but it is not the only country that has faced severe climate-related disasters that resulted in civil unrest and instability. A similar drought in Uganda created a situation in which food prices rose drastically, forcing mass migration within the country. Similar events have taken place in Kenya, Sudan, and Ethiopia, all with a clear pattern of eventually turning into a severe conflict (Reference Plante and AndersonPlante & Anderson, 2017).

Ecological disasters directly related to climate change are not the only type that has a major impact on ecomigration and intergroup violence. In fact, there are political and social actions that can lead to these outcomes as well. One example is the recent increasing tension between Egypt, the Sudan, and Ethiopia over the potential damming of the Nile River. Ethiopia is currently constructing a dam known as the “Great Ethiopian Renaissance Dam,” an attempt to provide a substantial amount of Ethiopia’s growing population with more electricity (Reference AsalaAsala, 2021). However, both Sudan and Egypt have major concerns over the dam, with Egypt’s main concern being the irrigation and agricultural impacts of slowing the Nile’s water flow will have on their country, and Sudan’s concern about what effect the Ethiopian dam could have on its own damming infrastructure. This conflict has seen numerous attempts at peaceful resolution and could yet see a successful negotiated outcome. However, as of the time of writing, Egypt’s president has mentioned that “all options are open” if Ethiopia continues to pursue the project without resolution (Reuters, 2021). Rapid climate change will require other similar major infrastructure projects in the future; this recent tension provides a good case study for how such projects can inadvertently become sources of new intergroup conflicts.

Another example has been the recent migration of 10 million people from Bangladesh into India. While this was occurring, public sentiment in India was that the migrants were responsible for stealing farmland, which led to conflict in which nearly 2,000 migrants were killed (Reference Plante and AndersonPlante & Anderson, 2017). In the United States, Hurricane Katrina led directly to the relocation of thousands of Americans, most moving to neighboring states seeking refuge. In cities that accepted refugees (technically, internally displaced persons), homicide rates started to rise, creating tension between long-time residents and the refugees, in spite of the fact that there was no evidence that the increase in homicides was being committed by the new arrivals.

As noted, countries that already suffer from instability and conflict are the most vulnerable to these kinds of events. For example, it has been found that densely populated countries that are also struggling with land, crop, water, or livestock loss have been found to be even more susceptible and at risk to increased aggression and violence resulting from rapid climate change (Reference Hallegatte, Rogelj and AllenHallegatte et al., 2016; Reference Mares and MoffettMares et al., 2015; Reference Van de VliertVan de Vliert, 2013).

However, this is not only true at the country level, it can also be seen within local neighborhoods. One study examined crime data in the United States city of St. Louis and found that within disadvantaged neighborhoods in the city, hot temperatures yielded a disproportional rise in crime (Reference MaresMares, 2013).

The data from St. Louis shows us that even in parts of the world that are seen as more economically stable, it is those in disadvantaged communities that will experience disproportionate amounts of harm from rapid climate change (Reference Plante, Allen, Anderson and OglesbyPlante et al., 2017). Furthermore, even though wealthy/stable countries have many significant protective factors, as climate change progresses, children in these countries will be exposed to more risk factors for becoming violence-prone adults (Reference Van de VliertVan de Vliert, 2013). In short, all countries will face the consequences of rapid climate change on their own citizens. Our global infrastructure must begin to implement climate change mitigation policies, and must do so in an equitable way so as to not to continue to disproportionally harm disadvantaged communities and countries.

Housing, Climate “Gentrification,” and Environmental Racism

Worldwide the most economically disadvantaged groups tend to be concentrated in the most dangerous situations (e.g., jobs, neighborhoods), where they are most likely to be immediately harmed by the effects of rapid climate change. Examining how natural disasters most often play out, it becomes clear that it is disadvantaged populations (usually racial/ethnic minorities) that suffer the most material damage, their neighborhoods suffer the most infrastructure loss, and their families are most likely to lose homes and belongings. This has been described as “environmental racism,” as it looks and feels like other processes that are based on racism, such as redlining.

A strict definition of environmental racism is hard to come by, but an article by geographer Ryan Reference HolifieldHolifield (2001) used a definition we find uniquely apt. It comes from a 1982 speech by activist Benjamin Chavis:

Environmental racism is racial discrimination in environmental policy-making and enforcement of regulations and laws, the deliberate targeting of communities of color for toxic waste facilities, the official sanctioning of the presence of life-threatening [sic] poisons and pollutants for communities of color, and the history of excluding people of color from leadership of the environmental movement (Reference Chavis and BullardChavis, 1994, p. xii)

This definition doesn’t quite capture the full extent of the discrimination one can see in environmental policies, as well as how these policies and societal structures materially impact and harm people. One exemple that highlights how some of this works is the destruction that occurred in New Orleans with Hurricane Katrina. Estimates suggest that roughly 150,000–200,000 occupied homes were destroyed or damaged when the hurricane struck (Reference GibbGibb, 2016). This affected approximately 500,000–600,000 residents, displacing them from their homes anywhere from a short period of time to permanently. The adverse outcomes of this devastation have been found to have disproportionally affected communities of color and low-income homes. Survey sampling from Gallup, CNN, and others in 2005 found, that among respondents, those who identified as black were much more likely to have gone without food for at least a day (53 percent of black respondents as opposed to 24 percent for white respondents), to have been separated from their family for at least a day or more (55 percent against 45 percent), had their vehicle damaged (47 percent/ 31 percent), went without water for a day (45 percent/21 percent), and were more likely to have to spend at least one night in an emergency shelter (34 percent/13 percent). Similar discrepancies were found amongst respondents on the lines of income, with those making less than $20,000 a year also much more likely to have faced these same adversities.

In the aftermath of the hurricane, it became clear that those who were of diverse backgrounds or were already struggling economically were those most in need of assistance and were the most harmed by the hurricane. However, in the months and years following Katrina’s landfall, it became apparent that those harmed communities and individuals did not receive the assistance they needed (which led to the infamous quote on live TV by rapper Kanye West, who stated that “George Bush doesn’t care about black people,” when participating in a fundraiser for relief funds). Even more alarming is that data from 2016 show there were roughly 96,000 fewer black individuals living in New Orleans than there were before the hurricane (Reference RivlinRivlin, 2016). Additionally, the economic assistance that was offered and delivered, and the areas of the city that were subsequently rebuilt, were not those that saw the greatest levels of damage and relocation; rather, it was the wealthier areas who received these resources.

Low-income minority communities, such as Seventh Ward, saw minimal reconstruction and development in the aftermath of Katrina (Reference RivlinRivlin, 2016). A full decade after the hurricane, only 60 percent of the neighborhood was rebuilt. The Lower Ninth Ward (another low-income community) was about half of its previous population size in 2016. Discriminatory housing practices can be directly linked to findings such as black homeowners being three times more likely to experience flooding (Reference RivlinRivlin, 2015). In 2015 and 2016 articles, Rivlin delved into how some of these practices materialized and were implemented, explaining that because of these policies, “the high-ground was taken by the time banks (who [sic]) started loaning money to African Americans who wanted to buy a home” (Reference RivlinRivlin, 2016).

Other discriminatory actions were openly brazen. Rivlin noted in a Wall Street Journal interview that a prominent New Orleans businessman stated that the city should focus on recovery and growth in a way that would change the demographics and geopolitics of the city, or else wealthy (and mostly white) businessmen would likely abandon it. This was on top of policies implemented after the hurricane that some politicians described as “ethnic cleansing by inaction” (Mosendz, 2015; Reference RivlinRivlin, 2016). Rivlin’s work tells more of what took place in the aftermath of the hurricane:

Now, New Orleans no longer has a public hospital, though prior to Katrina, it was home to the nation’s oldest one. Before the storm, the city was home to thousands of units of affordable housing in a quartet of housing projects locals now call the “Big Four.” Large portions of the Big Four had escaped with little or no water damage. Yet elected officials chose to bulldoze all four anyway. The largest housing recovery program in U.S. history, “Road Home,” was created in the months after Katrina. But money was disbursed based on the appraised value of a home rather than the cost of rebuilding, even though a home in a white community was typically appraised at a far higher price than the same house in a black community. Five years after the storm, a federal judge sided with black homeowners in a racial discrimination suit against the program. But by then, officials had already spent more than 98 percent of the $13 billion that the federal government had committed to Road Home. (Reference RivlinRivlin, 2016)

These actions and inactions following the hurricane greatly harmed already disadvantaged groups, making the city more difficult for them to live in. Although the extent to which the severity of Katrina can be attributed to climate change is hard to estimate, it provides a useful example that increases understanding of how many communities around the world around have been constructed and who is most immediately in harm’s way from the rapid global warming. Coastal cities tend to be more urban, host more ethnic and racial diversity, and are most vulnerable to the joint effects of sea-level rise, increased storm frequency, and increased storm intensity. Previous political practices, such as those in New Orleans, set a dangerous precedent for how cities and countries respond to natural disasters, who gets the most harmed by them, and then who receives assistance and support following them. We see this manifest today in areas that have been ravaged by more recent natural disasters, such as in Puerto Rico, where many civilians still lack power years after Hurricane Maria destroyed large chunks of the island.

The recent California wildfires also provide similar insights when we see that communities of color are much more susceptible to damage from the fires and are more severely affected by the pollution that the fires cause (Reference Davies, Haugo, Robertson and LevinDavies, Haugo, Robertson, & Levin, 2018). Pair these findings with what we have discussed already about the increases in negative rhetoric towards outgroups, and we begin to see a rather bleak picture of how “climate gentrification” operates and who will suffer the most in the wake of climate change. Failing to take care of the most vulnerable communities is itself a form of violence and forcing large populations to move increases the likelihood of additional intergroup conflict, as described in earlier sections.

Step 1

The first step to take is straightforward, albeit not simple: Climate scientists, politicians, and media industries must change the rhetoric surrounding climate change. A key action is to continue to fight the battle of whether climate change is real. Climate scientists have been hard at work at this, but the combination of politicians making false claims and media leaders failing to properly identify such lies have prevented the truth from being understood and accepted by huge proportions of citizens in many countries. We are most familiar with the American situation, so our thoughts might be too focused on our own country. Nonetheless, America has contributed more to global warming (per capita) than any other country. Therefore, it is especially worrying that American politics – especially during the Trump years – has directly attacked the truth about climate change and has directly acted to thwart attempts to reign in the production of greenhouse gases. Indeed, the US pullout from the Paris accords is only a symbol of how successful they have been in hoodwinking the public. Fortunately, at the time of writing, we have a new President (Biden) and Congress who (by the barest of majorities) are trying to redirect efforts to massively reduce America’s carbon footprint. Still, the outcome of the proposed legislation is very much in doubt because of continuing resistance by a sizable conservative minority of federal legislators (especially in the US Senate).

American media leaders also have failed to weed out blatant lies about climate change, giving science denialists “equal time” in news reports and in social media (e.g., Facebook, Twitter). Changes (legal ones, of course) are needed for meaningful progress to ever be made. For example, in 2018, the British Broadcasting Corporation (BBC) released a memo stating that it would no longer give airtime to climate change deniers because giving time to a clearly scientifically false position is not giving “balanced coverage.”

The memo stated that: “To achieve impartiality, you do not need to include outright deniers of climate change in BBC coverage, in the same way, you would not have someone denying that Manchester United won 2–0 last Saturday. The referee has spoken” (Reference WebsterWebster, 2018). Although we believe that responsible scientists, other citizens with relevant expertise, and politicians should push back against climate science deniers, when necessary, we also believe that another (better?) approach would be like that of the BBC. Ignore the denialists and treat climate change as the problem that it is. Focus on valid science and discuss the many ways in which climate change can be reduced. That act alone by social media leaders will help guide most of the public’s opinion towards accurate beliefs on the topic.

One reason for this is the assumption that to get whole societies to take significant action, people must be convinced of the scientific truths, that rapid climate change is real, is human caused, and that dramatic action will mitigate the harmful consequences. Decades of research on attitude and belief change have revealed that it is very difficult to change entrenched beliefs and attitudes. This is especially true when disinformation – such as claims that the evidence and arguments supporting the factual science are fraudulent – is constantly presented by highly visible authority figures. Humans strongly desire to protect their worldviews because changing them is psychologically costly. When their worldview is threatened, people often ignore the disconfirming evidence and arguments, downplay them, or try to dismiss them as outright lies. The psychological pressure to preserve a current worldview is dramatically increased when the new worldview is personally more threatening than the old. Not only is it hard to accept the fact that global warming presents a clear and present danger to human civilization, it is also hard to accept the fact that this impending threat is almost wholly a result of our own action and inaction. Indeed, it also may be that people simply do not perceive climate change as a major casual instigator to the material threats that they face in their daily lives. For instance, in a study conducted in Kenya, it was found that most people did not regard climate change as an immediate threat, instead focusing on other issues such as poverty, unemployment, and crime (Reference Shisanya and KhayesiShisanya & Khayesi, 2007). A major challenge is getting people to understand the causal linkage between rapid global warming and these more material issues.

Step 2

The second needed step is to reframe the climate change issue, not just away from the “debate” surrounding its validity, but toward an emphasis on what both individual and societal actions are needed to mitigate harmful consequences to the planet and to human populations. Part of the hesitancy of accepting the full scope of dangers that climate change represents is that so far, much rhetoric around solutions to climate change is framed in terms of individual action. Common suggestions usually focus on using more public transit, eating less meat, recycling more, using less plastic, buying more efficient vehicles, and so on. Such appeals are useful, but when this individual framework is the primary one, other well-known psychological phenomena such as diffusion of responsibility and social loafing effects reduce the likelihood of major behavioral action. Indeed, such an exclusive focus on individual action is also personally threatening and somewhat overwhelming. The daily lives of most humans across the globe are filled with personal stressors and complex situations that demand their immediate attention, leaving many people unwilling or unable to take on the responsibility of saving the planet. The natural inclination is to assume that climate change cannot be that bad. Otherwise, we are doomed. Increasing public discourse on ways that governments can and should address rapid climate change will have two important consequences: (1) it relieves some of the pressure to resist changing one’s old worldview to a new one that accepts the scientific truths about climate change, thereby increasing public support for taking decisive action; (2) it provides a simple action that individuals can do to address this existential threat of climate change, namely, voting for politicians who strongly advocate government actions to combat the problem, and voting against politicians who deny the need for change and/or who oppose government action.

Step 3

Successfully changing people’s worldview to a more accurate one that includes the need for individual action is a major step in the right direction. But an additional step is needed. The need arises from the perception that either the crisis is not as severe as it truly is or that the actions being proposed cannot possibly be sufficient enough to deal with it. The third needed step begins with the observations that most of the harmful greenhouse gases put into the atmosphere by humans come from global corporations and a super minority of individuals. In 2017, the Carbon Majors Database published a report that detailed how just 100 corporations contribute 71 percent of the global emissions. Therefore, it seems that a much more efficient and effective way to start the global reform to reach net-zero emissions needs to be set at this higher level, not exclusively at an individual level. If legislators, journalists, and the public discourse turned its attention on policies addressed to combat the emissions caused by industry, then the crisis suddenly feels (and is) manageable.

The third step, then, is to focus public discourse more on major and tangible sources of greenhouse gas emissions and on tangible governmental/societal changes that drastically reduce the emissions from these sources. Rather than focusing the blame and responsibility for change on the shoulders of individuals, this approach identifies a tangible entity with material ways to adopt sweeping change.

Note that we do not advocate “blaming” the corporate sources of greenhouse gases. Doing so would trigger defensive actions (psychological, political, and legal) by people who run these corporations and those whose livelihood depends on them. Instead, public discourse should focus on encouraging businesses (especially, but not exclusively, the top 100 emitters) and governments to work cooperatively in reducing the net emissions of greenhouse gases. In short, the goal is to create a new ingroup that includes businesses, government, and individuals to create effective climate change reforms. In short, taking effective action must become more holistic.

Step 4

Steps 1–3 focused on addressing rapid climate change itself. That is certainly a top priority. However, we cannot help but be alarmed at the lack of public discourse addressing the secondary effects of climate change, namely, the harmful effects it will have on humans, as exemplified by the direct and indirect effects displayed in Figure 1. The main points of Steps 1–3 apply equally to these human issues.

Our research team first attempted to draw attention to these issues in 1998 (Anderson & Bushman) and has continued to do so in periodic articles, chapters, and encyclopedia entries (Reference AndersonAnderson, 2001, Reference Anderson and Christie2012; Reference Anderson, DeLisi, Forgas, Kruglanski and WilliamsAnderson & DeLisi, 2011; Reference Miles-Novelo and AndersonMiles-Novelo & Anderson, 2019; Reference Plante, Allen, Anderson and OglesbyPlante, Allen, & Anderson, 2017; Reference Plante and AndersonPlante & Anderson, 2017). These efforts may have influenced the thinking of some academics, but they have had little (or no) impact on public discourse. A primary goal in writing this Element is to educate a much broader audience on the dire need to address both the climate change problem and the associated human issues, using advances in the behavioral sciences.