World Day for Safety and Health at Work – The Impact of Climate Change on Workers’ Safety and Health

Wednesday, April 24, 2024

Written by Senior Researcher, Cristina Ruscitto

How climate change can increase fatigue in the workplace and what we can do to manage emerging risks

With global warming, at 1° Celsius above pre-industrial levels, and likely to reach 1.5° Celsius between 2030 and 2052, the weather is becoming more extreme. This is resulting in more frequent and longer lasting heat waves, cold snaps and rising sea levels, increasing the risk of flooding.(1) These emerging hazards can have a significant impact on occupational safety and health through exposure to high temperature, humidity, poor air quality, changing work conditions and work patterns leading to increased fatigue levels. 

Exposure to increased levels of fatigue is of particular concern in safety critical environments, including transportation and healthcare. Due to operating round-the-clock, the main risk factors for fatigue in such industries are disrupted sleep and circadian rhythms, extended time awake and workload.(2) Fatigue compromises safety by increasing the risk of errors, incidents and accidents through reduced attention, reaction time, memory, poor decision making and poor mental health. 

A key risk is heat stress due to rising daytime temperatures. Outdoor, disadvantaged and vulnerable workers are impacted the most                     
High temperatures make work conditions fatiguing by exposing workers to heat strain, ranging from discomfort to heat exhaustion depending on location, type of work and availability of air conditioning. The combination of hot and humid environments represents a greater risk for safety and health as high humidity can make it harder for the body to cool down through sweating, leading to increased discomfort, physical exertion and fatigue for workers.  Research with young, healthy participants has determined that a 'wet-bulb temperature' of 31°C, occurring in environments with over 50% relative humidity or reaching 38°C at 60% humidity, represents the upper safety threshold. Beyond this point, the body faces difficulty in maintaining a stable core temperature.(3) In the worst-case scenario, prolonged exposure can lead to heat stroke which requires medical treatment. The limits are likely to be much lower for older populations and those with chronic disease.

Workers at increased risk of fatigue induced by heat stress include those who work outdoors and have to wear PPE, in non-air-conditioned factories, do moderate and heavy workload and work long hours. Vulnerable populations include, women, child labourers and those with chronic disease, and workers in low and middle-income jobs, in tropical and subtropical countries.(4)

Too hot to sleep
Sleep is fundamental for our physical and mental health, but climate change poses a risk for sleep globally, increasing the prevalence of insufficient sleep, e.g. obtaining less than 7 hours per night.(5,6) Night-time warming can make it more difficult to fall asleep and stay asleep, affecting both sleep duration and sleep quality.  The National Sleep Foundation suggest that the ideal ambient temperature for sleep is between 15.6 and 20° Celsius.(7) Thermoregulation during sleep is a key factor to sleep quality, as sleep ideally occurs when body temperature naturally drops, reaching a low at around 4 am. Night-time temperatures have risen considerably in the last 150 years at a faster rate than daytime temperatures. Globally, cities are particularly affected due to the urban heat island phenomenon, whereby daytime heat absorbed by concrete is released at night leading to more hot nights than days compared to rural areas. Night-time minimum temperatures greater than 25° Celsius (meteorological data) increase the probability of getting less than 7 hours of sleep by 3.5 percentage points compared with the temperature baseline of 5-10° Celsius.(6)

Although there is little research that examines the direct link between fatigue, sleep and climate change, evidence shows that the relationship between self-reported fatigue (physical and mental) and higher night-time ambient temperature is stronger in individuals with poor sleep, compared to those who sleep well, regardless of whether they used air conditioning.(8) This indicates that workers affected by ongoing sleep disturbance, e.g. insomnia, are potentially more vulnerable to fatigue induced by climate change.

Other climate change risks for sleep include poor air quality, which is also associated with sleep related breathing problems such as Obstructive Sleep Apnea.     

Climate change and poor mental health
The impact that climate change has on fatigue is also through physical and psychological stress associated with climate-related events. Stress can disrupt sleep patterns and lead to insomnia and other sleep disturbances. In turn sleep disturbance is a risk factor for anxiety and depression. In this respect the effects on sleep and mental health are similar to those observed during the Covid-19 pandemic.(9)  Both pandemics and climate change involve significant uncertainty about the future. People may experience anxiety about what lies ahead, including concerns about the duration and severity of the crisis, the effectiveness of response efforts, and the long-term impacts on health, livelihoods, and the environment. 

Increased exposure to fatigue through change in working patterns
One way in which fatigue associated with heat strain can be managed is by shifting work hours to an earlier or later time to avoid peak heat during heat waves, a strategy already used in the hot regions such as the Middle East. However, this mitigation needs to be assessed against the risk of increasing exposure to shift work. Shift work, working outside typical work hours usually 0800-1700, is common in modern societies. It is estimated that 1 in 5 people are employed as shift workers in Europe and the United States.(10) With global warming, it is likely that more workers will be required to work non-standard hours to avoid the daytime heat during the summer, particularly when work is carried out outdoors. This in turn could increase fatigue by causing disruption to sleep and circadian health. At physiological level, optimal alertness and health require circadian rhythms such as the sleep-wake cycle, and hormonal profiles, to be in sync with each other and the light dark cycle. Shift work causes circadian disruption by altering exposure to light, sleep and eating patterns. As well as a safety risk for safety critical industries, shift work is also linked to poor mental health, which in turn affects performance. Compared to non-shift workers, shift-workers have a 30% increase of poor mental health and depression. Women are at greater risk with a 70% higher risk of depression compared to women working day shifts. Poor mental health is associated with reduced productivity, quality of life and places an increased burden to the health care system.(10) 

How can Fatigue Risk Management (FRM) help manage the risk of fatigue induced by climate change?   
At an organisational level, FRM can help understand how climate change contributes to fatigue, by identifying and managing key safety and health risks that are likely to differ across organisations. Depending on geographical location, the proportion of workers vulnerable to fatigue changes due to work patterns and conditions, socio economic background and previous exposure to fatigue.   

Better understanding is likely to require closer collaboration within the organisation and between different industries to benefit from lessons learnt, and further research into the impact of climate change on safety and health. Fatigue does not just affect front-line staff but also those who support operations like managers, supervisors and key external stakeholders who indirectly affect safety at work. The relationship between different climate change hazards needs to be considered, like the potential effect of climate change on transport, food shortages, displacement of communities and staff shortages, all of which contribute to increased fatigue risk. Workers will have to adapt their behaviours to ensure their sleep is protected from the threat of climate change. Much of behaviour change is dependent on cues from the context for its success. As the context may be more changeable due to extreme weather conditions such as cold spells alternating to hot spells, it will be more challenging to form sustainable habits that protect sleep in the long term.    

Science suggests that there is a limit to the extent to which we can adapt to warmer temperatures to mitigate the health and safety risks.(6) Efforts to reduce global warming are key to managing safety and health risks in the workplace and require the commitment from governments around the world to cut greenhouse gas emissions. 

For information on how to improve sleep, and on Fatigue Risk Management, view some more of our papers here


1. Masson-Delmotte, V., Zhai, P., Pörtner, H. O., Roberts, D., Skea, J., & Shukla, P. R. (2022). Global Warming of 1.5 C: IPCC special report on impacts of global warming of 1.5 C above pre-industrial levels in context of strengthening response to climate change, sustainable development, and efforts to eradicate poverty. Cambridge University Press.

2. ICAO (2022), Definition of fatigue: ‘A physiological state of reduced mental or physical performance capability resulting from sleep loss, extended wakefulness, circadian phase, and/or workload (mental and/or physical activity) that can impair a crew member’s alertness and ability to safely operate an aircraft or perform safety related duties.’ In Annex 6—Operation of Aircraft, Part I—International Commercial Air Transport – Aeroplanes, 12th ed. (Original Annex published 2011).

3. Vecellio, D. J., Wolf, S. T., Cottle, R. M., & Kenney, W. L. (2022). Evaluating the 35 C wet-bulb temperature adaptability threshold for young, healthy subjects (PSU HEAT Project). Journal of Applied Physiology, 132(2), 340-345.

4. Habibi, P., Moradi, G., Dehghan, H., Moradi, A., & Heydari, A. (2021). The impacts of climate change on occupational heat strain in outdoor workers: A systematic review. Urban Climate, 36, 100770.

5. Obradovich, N., Migliorini, R., Mednick, S. C., & Fowler, J. H. (2017). Nighttime temperature and human sleep loss in a changing climate. Science Advances, 3(5), e1601555.

6. Minor, K., Bjerre-Nielsen, A., Jonasdottir, S. S., Lehmann, S., & Obradovich, N. (2022). Rising temperatures erode human sleep globally. One Earth, 5(5), 534-549. 

7. National Sleep Foundation (2024). Best Temperature for Sleep.
8. Fujii, H., Fukuda, S., Narumi, D., Ihara, T., & Watanabe, Y. (2015). Fatigue and sleep under large summer temperature differences. Environmental Research, 138, 17-21.
9. Alimoradi, Z., Broström, A., Tsang, H. W., Griffiths, M. D., Haghayegh, S., Ohayon, M. M., ... & Pakpour, A. H. (2021). Sleep problems during COVID-19 pandemic and its’ association to psychological distress: A systematic review and meta-analysis. EClinicalMedicine, 36.

10. Torquati, Luciana, Gregore I. Mielke, Wendy J. Brown, Nicola W. Burton, and Tracy L. Kolbe-Alexander. "Shift work and poor mental health: a meta-analysis of longitudinal studies." American Journal of Public Health 109, no. 11 (2019): e13-e20.