To the Editor — In recent months, there has been an amplified interest in human disease and wellbeing, as well as increased awareness of the vast global disparities in both health risk and care. Despite the ongoing impacts of COVID-19, in general, many developed countries have undergone an epidemiological transition, resulting in a shift in the major types of disease1: the disease pattern has changed to a low burden of communicable and nutrition-deficit diseases and a relatively higher burden of non-communicable diseases (NCDs) and injuries. However, low- and middle-income countries (LMICs) are still in a state of transition, and the burden of communicable diseases in these countries remains considerably high. While ongoing economic growth in LMICs has led to some decreases in these communicable diseases, it has simultaneously increased the burden of NCDs and injuries, giving LMICs a ‘triple burden of disease’2. Using the country of Nepal as an example (Box 1), we highlight how climate change can further intensify this triple burden of communicable disease, NCDs and injuries, adding to the disproportionate economic costs of climate change for LMICs.

The environmental determinants of health, such as clean air, safe drinking water and sanitation, are affected by climate change, which can increase communicable diseases and infections, NCDs and injuries. In Nepal, while previously prevalent infectious diseases such as helminth infection, cholera, acute gastroenteritis, tetanus, respiratory infections and tuberculosis have decreased with economic development, emerging and re-emerging infectious diseases such as dengue, chikungunya, influenza (H5N1 and H1N1), scrub typhus, leptospirosis, cryptosporidiosis and malaria have increased3. Climate change can lead to geographic expansion of infectious diseases4, and has already been implicated in the spread of malaria to hilly and mountainous regions of Nepal3. Moreover, communicable diarrheal diseases and vector-borne diseases such as malaria and dengue are predicted to increase under climate change5, and it is estimated that between 2030 and 2050, climate change will cause 250,000 additional deaths globally per year from communicable and nutritional diseases. Most of these deaths will occur in developing countries6. The situation is worsened by the occurrence of disasters such as floods and landslides, which lead to more clustered disease outbreaks and, under climate change, may occur more frequently and less predictably in space and time7. For example, in Nepal, floods and landslides are normally expected in the lowland Terai and hilly regions of Nepal but have also increased in the Himalayan region8. Such events are responsible for unexpected direct morbidity and mortality in these ill-equipped regions but can also compound water, sanitation and hygiene (WASH)-related health issues9. While economic development has improved facilities for agriculture, tourism and transportation, specific changes in LMICs linked to this development — such as rapid urbanization, agricultural expansion and increased transportation — are also responsible for disease spread across different geographical regions7.

In addition to communicable diseases, the interplay of demographic and lifestyle factors in many LMICs has led to an increase in NCDs such as cardiovascular diseases, cancer, chronic respiratory diseases and diabetes1. In Nepal, NCDs are responsible for nearly two-thirds of total deaths, and it is projected that by 2040, about 80% of total deaths in Nepal will be due to NCDs10. Climate change further increases the burden of NCDs through both direct and indirect effects11, with changing climatic conditions and increasing temperature linked to acute and chronic respiratory illnesses and cardiovascular diseases12, as well as to diseases such as cancer13. Climate change significantly affects global food systems and, by decreasing the yield, quality and affordability of food in many LMICs, leads to food insecurity and malnutrition, which is in turn linked to chronic disease14. Furthermore, beyond direct impacts, many NCDs may be caused by long-term impacts of infectious diseases, the former of which are expected to increase under climate change.

Climate change may also increase the likelihood of injuries that occur due to hydrometeorological and climatological hazards, such as floods, landslides, avalanches, cyclones and wildfires15. These types of extreme event produce massive morbidity and mortality, especially in LMICs, as these countries do not have proper preparedness and disaster management plans16. In Nepal, between 1971 and 2016, over 26,000 natural disasters were reported, which claimed the lives of over 43,000 Nepalese and left over 83,000 people injured17. The trend of disaster occurrence has drastically increased since 2000, probably as a consequence of increasing hazards due to climate change17. Furthermore, economic development with increased transportation in LMICs has led to an increase in road traffic accidents, contributing to injury-related morbidity and mortality10.

Many LMICs are based on an agrarian economy, with mild-to-moderate support from industry and tourism, and all of these are vulnerable to the effects of climate change. These effects are thus predicted to cause future instability and massive economic losses in these countries. The additive impact of climate on this state of the triple burden of disease in LMICs is often overlooked, yet it will present a challenge to the development and stability in these countries that must be addressed with concrete, effective, practicable and proactive health and climate policy.