Clinical Psychology is a discipline that is involved in the research, assessment, diagnosis, and treatment of mental ill-health [e.g., (10)]. At the core of Clinical Psychology lies the motivation to understand the complex nature of the etiology of mental ill-health, as well as the determination to optimally diagnose psychopathology. The overarching aim is to develop new, further improve existing, and supply efficient and evidence-based treatment options. The Diagnostic and Statistical Manual of Mental Disorders, in its fifth edition [DSM-5, (11)], as well as the 10th (and soon 11th) Revision of the International Statistical Classification of Diseases and Related Health Problems [ICD-10, (12)], assist clinical psychologists and others in the diagnosis of mental health disorders for research and practice. Clinical Psychology can thus offer the expertise and knowhow to investigate, assess, describe, and diagnose potentially psychopathological responses to the current climate and environmental crisis. To better understand the impact of the climate and environmental crisis on mental health, we can therefore draw from models in Clinical Psychology.

A central model in Clinical Psychology is the vulnerability-stress model (13, 14), according to which mental health disorders develop as a result of an interaction between the presence of stress and an individual's vulnerability (or sensitivity) to stress. This vulnerability results from the interplay of biological, psychological, and social dimensions. The biological dimension encompasses aspects related to physical health and physiological functioning, including genetic, hormonal, and immunological makeup; but also (mal)nutrition, (non-)communicable diseases, and injuries. The psychological dimension includes emotional, cognitive, and behavioral aspects, such as dysfunctional emotion regulation strategies or negative cognitive schemata. The social dimension includes aspects such as interpersonal conflicts or loneliness. Depending on the interplay of these factors, vulnerability is formed that renders an individual more or less susceptible to stress and the subsequent development of mental ill-health (13, 14).

Existing findings on the mental health implications of various climate and environmental stressors support the notion that these stressors can exert a meaningful impact on mental health via biological, psychological, and social pathways. Furthermore, these pathways do not act in isolation, but rather interact with each other, as can be shown in a study with Inuit in Canada (15): It was found that climate change-related alterations to the natural environment (e.g., ice instability) profoundly interfered with their traditional, land-based lifestyle, i.e., how they work, travel, and gather food (behavioral pathway). This in turn negatively affected diet and activity patterns (biological pathway), cultural identity, connection to the land, sense of place, and self-worth (cognitive pathway). This was further linked to despair, sadness, or hopelessness (emotional pathway); and can also impact social behavior (social pathway) [see also (16)]. The Inuit situation is a very good living example, which impressively shows the diversity of the impact of a changing natural environment, and the interwovenness of the underlying pathways. Through the application of the vulnerability-stress model (13, 14), this example demonstrates how Clinical Psychology can offer a useful explanatory model that can be applied in the understanding of the development of mental ill-health in response to the current climate and environmental crisis.

Current directions in Clinical Psychology include, but are not limited to, the combination of clinical psychological research with collected knowledge from clinical experience and practice, the development of evidence-based treatment guidelines, cross-cultural considerations in the diagnosis of psychopathology and culturally responsive care, the facilitation of low-threshold accesses for the treatment of mental health problems (e.g., using e-mental health interventions), the increased attention to (the treatment of) mental (ill-)health in adults of advanced age, and the adopting of a multisystem perspective on resilience [e.g., (17–19)]. These current directions in Clinical Psychology align with the demands posed by the climate and environmental crisis. It is therefore important not to miss the opportunity to apply the expertise of the large and influential field of Clinical Psychology to the current and constantly evolving climate and environmental crisis. In fact, the field of Clinical Psychology is becoming increasingly aware of the mental health impacts of the crisis [e.g., (20)]. For example, this increasing awareness was reflected in the organization of the first International Summit on Psychology and Global Health in 2019, held in Portugal, which was attended by leaders of multiple psychological associations from over 40 nations (21). At this gathering, the leaders declared an agreement to employ psychological research to fight climate change.

However, despite the readiness of Clinical Psychology to address the climate and environmental crisis, certain barriers exist that may also hinder an in-depth dedication to this emerging research field. Such barriers include, but are not limited to: (a) the vast complexity of the anthropogenic climate and environmental crisis, and the resulting difficulty to attribute a causal link between the climate and environmental crisis and mental ill-health (22); (b) the multiple possible direct and indirect impacts on various biopsychosocial life-domains, which are challenging to assess; (c) the general complexity of the etiology of mental health disorders; (d) the potential personal reluctance to deal with this topic due to a lack of knowledge (e.g., regarding the human-nature relationship), personal fears, or potential denial of the climate and environmental crisis; and finally, (e) clinical psychologists working in research or clinical practice may have to focus on more immediate or urgent priorities. For instance, while the Covid-19 crisis has shed light on the importance of mental health [e.g., (23)], it has also undeniably upstaged the ongoing climate and environmental crisis. Targeting such barriers can help facilitate the effective integration of Clinical Psychology in addressing the climate and environmental crisis.

Ecopsychology has “…a healthy diversity in conceptions” [see for instance, (24), p. 2], which can make it difficult to provide an all-encompassing, commonly-accepted definition of Ecopsychology. Broadly, Ecopsychology can be described as the research field dedicated to the study of the connection between human-caused changes to and destruction of the natural world “…and the spiritual or psychological crises resulting from our increasing experience of separation from the more-than-human world. Ecopsychology looks for the roots of environmental problems in human psychology and society and for the roots of some personal and social problems in our dysfunctional relationship to the natural world.” [(25), p. 68]. “Ecopsychology explores humans' psychological interdependence with the rest of nature and the implications for identity, health and well-being. Ecopsychology topics include emotional responses to nature; the impacts of environmental issues such as natural disasters and global climate change; and the transpersonal dimensions of environmental identity and concern” [(26), Ecopsychology section, para. 1].

Ecopsychology is one of six core sub-fields of Environmental Psychology, in addition to “Behavior and the Built Environment,” “Conservation Psychology,” “Psychology on the Population Level,” “Teaching Psychology for Sustainability,” and “Using Film to Demonstrate Environment and Behavior” [(27), Interest Areas section]. According to Scull (25), in addition to its connection to Environmental Psychology, the field of Ecopsychology is related to several other larger fields, such as Psychotherapy, Spirituality, and Philosophy. Ecopsychology itself is comprised of multiple sub-disciplines, which include (but are not restricted to) sub-categories, such as Nature, Spirituality, Transpersonal Psychology, Environmental Activism, Experiential Environmental Education, Human Ecology, and Ecotherapy and Nature Connection (25). As such, Ecopsychology can be understood as a multi-faceted field comprised of numerous sub-disciplines that are all dedicated to the various aspects of the human-nature interrelationship.

The therapeutic focus of Ecopsychology has been explicitly stated (24), and is a core component of this field [e.g., (28)]. This relates to the assumption of Ecopsychology that human beings are closely attached to nature. This close emotional and spiritual bond and connection to nature is proposed to be due to the phylogenetic development of the modern human, which lasted hundreds of thousands of years and involved surviving in close interconnection with the natural world [e.g., (29, 30)]. Given this evolutionary “up-bringing” in nature, living in equilibrium with nature is thought to be a crucial prerequisite for humans' physical and mental health and well-being (31). While Ecopsychology and Clinical Psychology both have their place in understanding the mental health impacts of the climate and environmental crisis, a distinct research area drawing on the most relevant elements of each field can help advance this research topic further.

Clinical Ecopsychology seeks to systematically examine the direct and indirect mental health impacts of the progressing climate change, pollution, environmental degradation, and/or destruction of the air, soil, water, and ecosystems. More specifically, Clinical Ecopsychology sets out to examine underlying pathways of how the climate and environmental crisis can lead to the development of mental ill-health, which entails the study of specific risk and vulnerability factors. Clinical Ecopsychology also investigates potential protective and resilience factors that may aid individuals in their adaptation and that may foster the maintenance of mental health in the face of the ongoing crisis. Clinical Ecopsychology further aims to thoroughly examine the beneficial mental-health impact of contact with the natural world. Taken together, Clinical Ecopsychology sets out to examine underlying pathways that lead to the development of mental ill-health in the face of ecological adversity. This involves the study of risk, vulnerability, and protective factors to understand interindividual differences in the response and adaptation to ecological adversity, and the promotion of (the creation of) efficient treatment options for mental health disorders linked to the climate and environmental crisis.

It must be noted that Clinical Ecopsychology is not a new research field. Both Clinical Psychology, but in particular Ecopsychology (in addition to Environmental and Conservation Psychology), have previously made extremely valuable contributions to the understanding of these topics [see for instance (32–37)]. As such, Clinical Ecopsychology may also be described as a respective sub-category of these fields: Clinical Ecopsychology is a sub-field of Clinical Psychology in its focus on climate and environmental stressors and its consideration of the beneficial impact of nature/natural stimuli, which is an existing, although still vastly neglected and marginal topic within Clinical Psychology. Clinical Ecopsychology is equally a sub-field of Ecopsychology, as it shares many, though not all, interests of Ecopsychology. For instance, Clinical Ecopsychology may not (or only to a very limited extent) deal with topics such as Nature Spirituality, Transpersonal Psychology, or Environmental Activism, which are sub-disciplines of Ecopsychology (25). Clinical Ecopsychology may also draw on more “clinical” language than Ecopsychology, such as when describing therapeutic processes and outcomes (e.g., to “treat” rather than to “heal”). However, while Clinical Ecopsychology may be most optimally placed between Clinical Psychology and Ecopsychology (i.e., through their shared overlap), this should not mask the fact that Clinical Ecopsychology is in itself a multi-disciplinary research field. In fact, an impressive and rich variety of disciplines (e.g., Psychiatry, Psychology, Medical Sciences, Sociology, Public Health, and Biology) have already contributed to the increasing understanding of the mental health impacts of the climate and environmental crisis. The multiple disciplines from which it is possible to examine the mental-health impact of the climate and environmental crisis mirrors the multi-dimensionality of (the development of) mental ill-health.

As stated above, Clinical Ecopsychology not only focuses on the development of mental ill-health in response to the climate and environmental crisis; but also aims to foster a better understanding of how mental health can be upheld in the face of the ongoing crisis, and how mental health disorders linked to ecological adversity can be most optimally treated. Potentially useful therapeutic approaches include the validation and management of emotional responses, verbalization of (complex) emotions, fostering active hope, finding a balance between pessimism and optimism, stimulating self-efficacy, promoting social connectedness, and training adaptive emotion regulation strategies [e.g., (38)]. Cognitive strategies can also be used to foster functional cognitive coping mechanisms, such as cognitive reframing, problem solving, reflection of responsibility and own contribution, putting negative thoughts into perspective, and radical acceptance [e.g., (39, 40)]. Depending on the needs of the individual, single or group settings should be offered, and low-threshold options should be made available, such as informal meetings with like-minded individuals. These informal meetings may be particularly important, as previous research has shown that becoming active through collective group engagement is linked to hope, a key protective factor in dealing with eco-anxiety: “Hope can help them confront the problem and bear the burden of taking on climate change without becoming overwhelmed” [(41), p. 13]. Furthermore, given the positive impact of natural stimuli, contact with nature and natural elements should be integrated whenever possible into psychotherapeutic work on the topics of Clinical Ecopsychology [for an overview see (42)]. For instance, research on a form of nature therapy called Shinrin-yoku, in which individuals spend time in the forest, has shown reductions in mental fatigue through decreased prefrontal cortex activity, reduced cortisol concentrations, and increased feelings of comfort and calm (43). The deep-rooted psychophysiological connection to nature may help individuals to (sub-)consciously resonate with the natural environment and to respond positively to its restorative influence (44–47).

In conclusion, it is the aim of Clinical Ecopsychology to combine existing multi-disciplinary forces in order to create, share, and promote the necessary knowledge required for: (a) raising awareness of the increasing psychopathology stemming from anxiety, frustration, and despair associated with the climate and environmental crisis; (b) the maintenance of mental health in the face of ecological adversity; (c) the efficient treatment of mental health disorders linked to ecological adversity; (d) increasing access to mental health care across the globe, particularly in those regions most affected by the crisis; (e) the planning and implementation of intervention measures; and (f) the provision of additional research-based arguments for the urgently needed global action on the current and worsening climate and environmental crisis.

Given the wide-ranging, and diverse multidisciplinary literature on the mental health impact of the climate and environmental crisis, a systematic literature search was not considered feasible nor the goal of this report. Instead, this synergy of literature aims to extend existing research by providing a current overview of the core and most recent lines of research by summarizing the existing literature from the perspective of Clinical Psychology. The online databases PsychINFO, Web of Science, PubMed, and Scopus were used for the literature search. Furthermore, reference lists of appropriate articles were also screened for additional studies. Search terms related to the following domains were applied: mental health (e.g., mental health disorders, psychopathology), climate change (e.g., climate crisis, global warming), and environmental crisis (e.g., destruction of nature, pollution). Only peer-reviewed articles written in English and published by the end of September 2020 were considered for the synergy of literature.

This article is structured as follows: climate and environmental stressors are first described, followed by an in-depth examination of the mental health impacts of the various ecological stressors. Potential underlying processes are then summarized, encompassing biological and social pathways, as well as the previously neglected emotional, cognitive, and behavioral pathways. The way in which the climate and environmental crisis can amplify an individual's biopsychosocial vulnerability is then outlined. This is followed by a description of risk and vulnerability factors, including vulnerable populations, and the potential for increased adaptation to ecological stressors. This synergy of literature concludes with a discussion of methodological considerations and future directions.

Extreme weather events (e.g., floods), and natural disasters (e.g., wildfires) have been previously linked to a broad range of adverse mental health outcomes (22, 61–66). The most commonly reported mental health disorders in the aftermath of extreme weather events and natural disasters are posttraumatic stress disorder (PTSD) and depression, as well as anxiety, suicide, and substance abuse disorders (22, 67, 68).

Large differences in prevalence rates are found in studies on the impact of extreme weather events and natural disasters on mental health [i.e., PTSD, 0.7–52.6%, anxiety disorders, −0.4 to 84%, and depression, 0.9–81%, (65)]. This may be due to multiple factors, such as differences in socio-demographics (e.g., age, sex), disasters (e.g., type, severity), magnitude of exposure, or applied methodological differences (e.g., study design, psychometric instruments) (65). In particular, assessment time plays a critical role, as psychopathological burden varies as a function of time (8). Burden appears to be higher in the short-term, reaching the highest levels within the 1st year post-disaster and attenuates thereafter, with variations in peak and trajectory depending on severity of symptomatology (22, 69). Nevertheless, despite these prevalence differences, PTSD is repeatedly observed to be the most frequently examined mental health disorder following extreme weather events and natural disasters (70). Given the particular characteristics of these events, such as the suddenness, the destructive potential, and likelihood for severe sequelae (e.g., injury, death); it is unsurprising that such ecological stressors can trigger the development of stress-related mental health disorders.

There is a lack of longitudinal studies on PTSD following extreme weather events and natural disasters, with some notable exceptions. For instance, McLaughlin et al. (62) examined the impact of Hurricane Katrina on PTSD over time. From the affected individuals, 17.1% were estimated to have PTSD at 7–19 months (baseline) and 29.2% at 24–27 months (follow-up) post-disaster. Around 40% with PTSD at baseline had recovered by the follow-up. More than 40% with PTSD at follow-up showed a delayed onset, i.e., onset later than 6 months after the hurricane (62). It should be noted that this study did not obtain pre-disaster data on psychological functioning, which prevented statements about the change in mental health in response to the disaster. However, a set of studies (63, 64, 66) was able to longitudinally compare psychopathological burden from pre- to post-Hurricane Katrina in a high-risk sample of low-income parents. At around 11 months post-disaster, Rhodes et al. (66) found that serious mental illnesses were twice as high post-disaster (13.8%) compared to pre-disaster (6.9%), with almost half the sample (47.7%) showing probable PTSD. Follow-ups were conducted with the same sample at 5 years (63), and 12 years after the hurricane (64). Probable PTSD declined from 33 to 16.7%, suggesting a slow recovery over time. Similarly, non-specific psychological distress also showed an elevation from baseline (24.0%) to the first follow-up (35.2%), with a slow decline thereafter (second follow-up: 30.1%; third follow-up: 28.5%), but remaining above baseline values (64). These studies show that more than a decade after an “acute” natural disaster, adverse mental health effects can still be detected in some survivors.

Increasing temperatures are resulting in a higher frequency of extreme heat events, such as heat waves (48). The occurrence of these extreme heat events is a major public health problem as they have been linked to a vast array of mental health consequences, including aggressive and criminal behavior, wake and sleep disorders (e.g., insomnia, obstructive sleep apnea), depression, and suicide (71–73). For example, Burke et al. (74) observed an increase in suicide rates in the US and Mexico (0.7 and 2.1%, respectively) between 1990 and 2010, in response to a 1°C increase in average monthly temperature (74). In addition, a recent study provided large-scale evidence for the climate change—mental ill-health relationship, by combining meteorological data (between 2002 and 2012) with mental health data from almost two million US residents (75). Results showed that worse mental health was related to short-term exposure to extreme weather events, multiyear warming, and exposure to tropical cyclones (75).

Increasing temperatures have also been linked to higher admission rates to emergency departments and psychiatric hospitals in individuals with pre-existing mental health conditions. For example, in the study by Shiloh et al. (73), a significant association was found between the maximum environmental temperature and psychiatric hospital admission rates of patients with an acute psychotic exacerbation of schizophrenia. This suggests that psychotic symptomatology, such as hallucinations or delusions, can vary as a function of (higher persistent) temperatures, with disturbed sleep as a result of the higher temperatures potentially playing a role (73). These studies show the adverse impact that “chronic” events (i.e., rising temperature) can have on mental health.

Related to the increasing temperatures, climate change can also increase the likelihood of droughts and precipitation deficits in some world regions (48). Droughts have previously been linked to an increase in general mental distress. For instance, a study examined the mental health impact of a long-lasting drought in Australia and found that in response to the 7-year drought, distress increased in rural (but not urban) habitants by 6.22% (76). Another Australian study including 8,000 individuals found “…that if the population in rural and regional areas of Australia were not exposed to drought the incidence of mental health problems in these areas would be 10.5% lower” [(77), p. 187]. An increase in suicide rates during drought periods has repeatedly been reported, but with inconsistent findings across studies [e.g., (71)]. This research demonstrates the adverse effects of “sub-acute” events on mental health.

Rising temperatures that cause the retreat of glaciers, along with climate-change related variations in precipitation patterns, are leading to a reduction in fresh water resources and in agricultural yield. These changes affect the water and food security of millions of people worldwide, particularly those heavily dependent on rivers and precipitation (78). The impact of climate change on water and food supplies is complex and co-influenced by political, social, and environmental factors (79). Two-thirds of the world population are confronted with severe water scarcity for a minimum of 1 month per year (80); and up to 800 million people are affected by food insecurity (81). These high numbers show that water and food insecurity are large-scale risk factors for health and well-being [e.g., (82)].

Water scarcity has been linked to psychological distress, suicidality, anxiety, hopelessness, and depression [for a review see (83)]. Insecure or scarce access to water can induce worries about material deprivation, shame and stigma for failing social roles or norms (e.g., begging for water, unable to clean oneself), as well as persistent concerns about threats to physical health, such as contaminated water (83). Similarly, food insecurity, and the resulting malnutrition, has not only been linked to physical health conditions (e.g., anemia, adverse physical development), but also mental ill-health (81). A recent systematic review and meta-analysis on food insecurity and mental health found an increased risk for depression and stress (84). The association between food insecurity and depression followed a dose-response pattern, with more food insecurity associated with a higher risk for depression, with a higher risk observed for men and older adults (above 65 years) (84). These studies illustrate the negative impact that “sub-acute” events (i.e., water and food insecurity) can have on mental health.

Several studies have examined the impact of air pollution on mental health [for an overview see (85)]. Exposure to (ultra)fine particulate matter has been linked to depressive symptomatology in both cross-sectional (86) and longitudinal (87) research. In the exploratory longitudinal study by Roberts et al. (87), results showed that exposure to concentrations of air pollution at 12 years of age was associated with the development of depressive symptoms and a higher risk of being diagnosed with depression by the age of 18 (87). A recent systematic review and meta-analysis also revealed that ambient particulate matter (with an aerodynamic diameter smaller than 2.5 μm) was strongly associated with an elevated risk of depression and marginally related to a higher risk of suicide (88). Findings further suggest an accumulative detrimental impact over time, with longer exposure to particulate matter associated with greater risk of depression (88). Furthermore, studies on air pollution and suicide have shown increases in the rate of suicides of 1–2% per day of poor-quality air (71).

In addition, exposure to air pollution has also been linked to cognitive impairment, as well as to diseases affecting the central nervous system (CNS), such as Alzheimer's disease (88–90). For example, a population-based cohort study in Canada found that individuals living in proximity to major roadways with high levels of air and noise pollution had a higher risk of developing dementia (91). Up to 11% of the dementia incidence within the 11-year observation period could be attributed to the heavy traffic exposure and the related air pollution (91). These studies show the adverse impact that air pollution, a “sub-acute” event, can have on psychological and cognitive health and well-being.

Profound changes to the natural environment and landscape, either by human-created destruction (e.g., open mining), destruction through natural forces (e.g., wildfire), or as a consequence of climate change (e.g., melting glaciers), can evoke grief, sadness, and feelings of loss in (place-based) solace. These emotions have previously been examined under the terms ecological grief (16) and solastalgia (92). Ecological grief is defined as “…the grief felt in relation to experienced or anticipated ecological losses, including the loss of species, ecosystems, and meaningful landscapes due to acute or chronic environmental change” [(16), p. 275]. Similarly, solastalgia refers to “…the pain or distress caused by the loss of, or inability to derive solace connected to the negatively perceived state of one's home environment” [(92), p. 96]. Ecological grief and solastalgia have been observed in various populations across the world, such as in the form of undermined notions of place-based, cultural, and self-identity; cumulative and chronic place-based distress; amplified mental health stressors; and heightened perceived risk of depression and suicide [e.g., (15, 93)]. In particular, individuals who live in close connection with nature, such as Indigenous people or farmers, have been found to be more vulnerable to the development of ecological grief and solastalgia (16, 92, 94). These studies highlight the adverse mental health impact of “chronic” ecological events in the form of profound environmental changes.

A recent survey of over 27,000 participants from 26 countries revealed that climate change was perceived as a major international threat for half of the participating nations (95). This indicates an increase in the perception of the threat posed by climate change: while a median of 56% reported climate change to be a top threat in 2013, this number increased to 63% in 2017, and 67% in 2018 (95). This perceived threat illustrates an indirect effect of climate change on mental health. For instance, a qualitative study with young urban children (10–12 years old) found that 82% reported feelings of sadness, fear, and anger in relation to environmental issues and 72% expressed pessimistic, negative, or apocalyptic views about the future (96). Furthermore, a poll conducted with 2,107 U.S. adults on the topic of climate change found that 56% identified climate change to be the most important problem of today's society, with 68% reporting having experienced at least a little eco-anxiety (97). Younger participants (18–34 years) were more affected, with almost half reporting climate change-related stress to have an impact on their daily lives (97).

Thus, far, vast differences exist in the definition of eco-anxiety, or climate (change) anxiety [e.g., (39, 98–100)]. This may be due to the fact that eco-anxiety can be understood quite differently from the varied perspectives of the respective disciplines (e.g., Sociology, Philosophy, or Depth-Psychology). Nowadays, some describe it as “…a specific form of anxiety relating to stress or distress caused by environmental changes and our knowledge of them” [(40), p. 1,233], while others use it to describe a range of negative climate emotions [e.g., (94)]. From the perspective of Clinical Psychology, eco-anxiety is understood as a syndrome, i.e., a set of psychological symptoms related to the broader spectrum of anxiety or fear that are triggered by (thoughts about) the climate and environmental crisis, which can cause subjective suffering and lead to functional impairments. The APA defines eco-anxiety as “…any anxiety or worry about climate change and its effects” [(97), para. 6]. From a clinical perspective, a defined set of criteria/symptoms for eco-/climate (change) anxiety do not yet exist. Instead, various symptoms have been linked to this particular anxiety, such as fear, distress, worry, sadness, or rumination (98). Currently, climate change anxiety can be assessed with a recently developed and validated measure by Clayton and Karazsia (99). It must be noted that responding to this unprecedented climate and environmental crisis with intense negative emotions is not a pathological reaction, but rather can be regarded as a normative, adequate, and justifiable response to a real existential threat [e.g., (16)]. However, if the eco-/climate (change) anxiety becomes maladaptive and so intense that it significantly impacts psychosocial functioning (i.e., interferes with everyday life functioning, causes profound suffering, or is perceived as uncontrollable), ecological syndromes such as eco-anxiety may become a clinically relevant concern warranting clinical attention (98).

Regarding this clinically relevant concern of the climate and environmental crisis, it is correct to state that the current diagnostic manuals, i.e., the DSM-5 (11), and the ICD-10 (12), do not include disorders such as eco-anxiety, climate-change phobia, prolonged eco-guilt disorder, or climate-change depression. However, it is a common misconception that is not possible to diagnose mental health disorders triggered by the climate and environmental crisis. In fact, the stressors associated with this crisis can theoretically cause a multitude of different mental health disorders, depending on the individual biopsychosocial-vulnerability constellation of the affected person (13, 14). For instance, having constant worries about the state of the climate, the continuing deforestation of rainforests, the bee mortality, or the future perspectives of one's offspring, could provide the basis for the development of a Generalized Anxiety Disorder (DSM-5: 300.02; ICD-10: F41.1), if the symptomatology were to cause meaningful distress or significantly impact the psychosocial functioning. Furthermore, Adjustment Disorder (DSM-5: 309.9; ICD-10: F43.20) is defined as “…a maladaptive reaction to an identifiable psychosocial stressor or multiple stressors that usually emerges within a month after the onset of the stressor” [(101), p. S3]. This is a suitable and useful mental health diagnosis that can be used to describe a symptomatology of distress triggered by climate and environmental stressors. However, even if individuals did not meet the diagnostic criteria for an existing mental health disorder, the suffering caused by a sub-clinical/threshold symptomatology can also diminish quality of life and may warrant clinical attention.

Further evidence of the indirect effects of climate change on mental health can be seen in the rapidly ongoing trend toward urbanization, as more and more people lose contact with the natural world. The current discrepancy between the modern (urbanized) lifestyle and our psychophysiological development is thought to impact mental health. For example, the increased amygdala activity observed in city dwellers, compared to country or small-town dwellers, may be an indicator of the higher stress of city living (102). Furthermore, higher levels of urbanization have also been linked to increased psychopathology, such as psychosis and depression [e.g., (103)], and higher suicide rates (104). In addition, a recent large-scale cohort study investigated the relationship between environmental greenness and schizophrenia, using data from almost 870,000 individuals over a 10 years period (105). Results found that higher environmental greenness was associated with a lower schizophrenia incidence, suggesting that a lack of greenness may be one factor explaining why urban areas are linked to lower mental health (105).

In the following two sub-sections, the various physical health impacts are presented, followed by an in-depth description of psycho-pathophysiological processes induced by environmental toxins.

The (topic of) climate change, pollution, and the destruction of the natural environment can impact mental health by evoking intensely negative emotions (98). This potential to induce negative emotional responses is detailed in the following sections, followed by a description of an underlying process through which triggered emotional responses can detrimentally impact mental health.

Climate and environmental stressors can impact mental health through their potential to influence key self-concepts and to induce non-adaptive cognitive defense mechanisms and coping strategies. These components of the cognitive pathway are detailed in the following sections.

Climate and environmental stressors can also impact mental health via health-related behaviors. Health-damaging behaviors are often maladaptive responses to facilitate coping with (overwhelming) negative emotions and affective states (e.g., anger, fear), or unfavorable or harmful circumstances and environments [e.g., (150)]. An example of one health-damaging behavior is lack of physical activity, which has been associated with food insecurity (84), air pollution (86), and lower exposure to greenspace (151). In contrast, being surrounded by greenness has been shown to foster physical activity, which may positively impact weight and health [e.g., (152, 153)]. Surrounding greenspace has also been found to facilitate social cohesion (154). Both (outdoor) physical activities and positive social interactions and social cohesion have repeatedly been linked to beneficial impacts on mental health [e.g., (155–158)].

Another health-related behavior that is affected by climate change is sleep behavior (i.e., sleep time and quality), which can be impacted by heat (72, 159). Given the importance of a healthy sleep pattern for good mental health [e.g., (160)], this is an important pathway to consider in the understanding of how an ecological stressor (i.e., heat) can translate into poorer mental health.

Criminal activity and violence is a further set of behaviors that has previously been linked to changes and shifts in climate and weather and that has potential to affect physical and mental health. A study conducted in California that investigated the impact of drought on state-level rates of crime over an extended period of time found a meaningful increase in property (but not violent) crimes (161). A recently published study that analyzed survey data encompassing information from 80,000 women living in sub-Saharan Africa found that drought was linked to intimate partner violence, particularly in female adolescents and jobless women (162).

Given the impact of the climate and environmental crisis on multiple aspects of social life and socio-economic factors, combined with the fact that social determinants are meaningfully related to mental health (163), the social pathway is a key translator of climate and environmental stressors into mental health effects [e.g., (5)].

The climate and environmental crisis further increases existing inequalities by disproportionally affecting marginalized groups that are inherently vulnerable, for example, due to their development status (e.g., children), socio-economic disadvantage, or having mental health issues [e.g., (8)]. Such vulnerabilities do not act in isolation, but rather interact with each other. For instance, Indigenous people often live in geographical regions prone to extreme weather events, and typically have lower socio-economic resources and social power (7). Such economic, social, and gender inequalities are also risk factors for the development of psychopathology, and the added impact of climate and environmental stressors can lead to worse mental health (38, 132, 163).

There is a repeatedly observed, yet insufficiently understood heterogeneity in how individuals respond and adapt to adversity. While it is essential to consider risk and vulnerability factors in explaining this heterogeneity, protective factors are equally as important in understanding interindividual differences in adapting to the climate and environmental crisis and the impact on mental health. This positive adaptation and potential protective factors will be outlined in the following sections.

Given the vast complexities of the two factors involved (i.e., anthropogenic climate change and mental health), attributing a causal link is difficult and poses multiple methodological challenges (22). While an increasing number of studies have examined the adverse mental health effects of the climate and environmental crisis, much of the available data is based on (retrospective) cross-sectional research, or qualitative, case-study and ethnographic designs. These studies lack information on trajectories and long-term effects and prohibit the establishment of causal connections (83). Baseline data (i.e., pre-disaster mental functioning) is often lacking [valuable exceptions are (63, 64, 66)]. This hinders statements about change in psychopathology in response to the event, as well as the examination of predictors related to interindividual variability in adaptation (199). The mental health impact of acute, isolated events (e.g., hurricanes) can be more easily assessed, such as by examining the change in mental functioning prior- (if available) to post-disaster. However, the attribution of (all) these extreme weather events to climate change is problematic; as while their increased frequency or power may vary as a function of the changing climate, their occurrence may not (8, 131). Attributing the mental health impact of sub-acute and chronic phenomena is also challenging, as they often do not have a defined beginning or ending and their impact is often experienced indirectly due to the subtle, gradually-evolving, and accumulating nature of these types of events (8).

With regard to mental health, the majority of studies assessed mental health disorders with self-report screening instruments, which are prone to subjective bias, are less precise than structured clinical interviews, and limit conclusions to probable/estimated mental health disorders. In addition, many studies did not include control groups, or neglected to control for relevant confounding influences (67, 85). It should also be taken into consideration that mental health disorders can vary as a function of norms and cultural contexts and their etiology depends on multiple biopsychosocial factors (11). Furthermore, the assessment of adverse mental health effects in post-disaster populations is often affected by sample biases. For example, those who are most marginalized, those affected most by (post)disaster-related stressors, and those with the highest psychopathological burden are less likely to participate in studies, which bears the potential for underestimation of mental health effects (62, 170). Mental health disorders are also stigmatized in many cultures, which can impact disclosure and assessment (200).

In addition to addressing these methodological limitations identified in previous studies, some specific recommendations should also be considered for future research. A stronger focus should be placed on underlying processes, particularly emotional, cognitive, and behavioral processes that have previously been neglected. Future studies should also examine potential positive changes that can occur as a result of the climate and environmental crisis, such as post-disaster psychological growth; increased sense of meaning, social engagement, and social cohesion compassion; or increased engagement with mitigation activities (8, 38, 198).

Going forward, mixed-methods approaches are recommended, as they combine qualitative and quantitative methods that are suitable to assess complex relationships, such as the adverse mental health impact of sub-acute weather events (166). Mixed-methods also allow for a person-centered approach and an in-depth analyses and understanding of rich data, as well as the quantification of the mental health burden (67). There is also a need to move beyond the current focus of conventional epidemiology, which “…focuses too much on the individual, on direct or proximate causes, on the past and present, and on current states of being; and too little on whole populations, indirect and distal influences, the life course and the future, and the dynamics of health across contexts” [(131), p. 283]. Future research could apply a systems approach (i.e., combining various perspectives from multiple academic disciplines and perspectives) to better foster an understanding of the intertwined factors and processes underpinning climate change and mental health [see (131)]. With regard to data assessment analysis methods, large-scale, longitudinal, population health studies and experimental epidemiological studies could best fit this approach, using network- and data-driven analyses, as well as agent-based and dynamic models (131).