An analysis of data from the China Health and Retirement Longitudinal Study combined with weather and air pollution information showed that exposure to heatwaves, air pollution, and lack of access to blue spaces are all associated with an increased risk of depression. The increase in depression risk was even higher in individuals simultaneously exposed to these factors. The paper was published in the Journal of Environmental Psychology.
Climate change refers to long-term alterations in global temperatures, weather patterns, and ecosystems. It is understood that currently observed climate changes are mainly driven by human activities such as burning fossil fuels, industrial emissions, and deforestation. These processes release large amounts of greenhouse gases like carbon dioxide and methane, trapping heat in the atmosphere and disrupting natural climate systems. As a result, the planet experiences more frequent heat waves, droughts, floods, and wildfires.
Air pollution, which often comes from the same sources that cause climate change, adds another layer of harm by degrading air quality and contributing to respiratory and cardiovascular diseases. Fine particulate matter and toxic pollutants can adversely affect brain health as well. Extreme weather events linked to climate change can create massive devastation, triggering physical and psychological trauma, post-traumatic stress disorder, and long-lasting psychological distress for those affected.
Chronic exposure to uncertainty about the environment fuels eco-anxiety, a growing concern especially among young people. Communities facing displacement or loss of livelihoods due to environmental degradation may suffer from grief and helplessness. The psychological burden is particularly heavy on farmers, children, and low-income populations with limited access to healthcare.
The study’s authors, Weiqi Wang and his colleagues, wanted to investigate the individual and joint impacts of heatwaves, air pollutants, and access to blue and green spaces on depressive symptoms in middle-aged and older Chinese populations.
They analyzed data from the China Health and Retirement Longitudinal Study (CHARLS). CHARLS is a national survey in China focused on the issue of population aging, encompassing data from individuals aged 45 and older. It was started with a survey in 2011 and included four additional surveys conducted up to 2020. In each of these follow-up surveys, the study recruited a small number of additional participants.
The data analyzed in this study came from 12,316 participants across 124 cities in 28 of 31 provinces of China. The number of participants per city ranged between 51 and 211. Participants’ average age was approximately 58 years. About 53% were men, and 58% lived in rural areas.
This study used data on depressive symptoms from the CHARLS dataset (assessed using the Center for Epidemiologic Studies Depression Scale), and air pollution data (concentrations of ground-level pollutants CO, SO2, PM2.5, and PM10 derived from the China High Air Pollutants (CHAP) dataset), data on heatwave exposure (based on maximum daily temperature data during the warm season from monitoring stations across China, provided by the United States Air Force Weather Agency), and exposure to green and blue spaces (based on the degree of vegetation cover and the proportion of open water bodies in a city).
Green spaces are areas of land covered with vegetation such as parks, gardens, forests, and grasslands that provide natural environments within urban or rural settings. Blue spaces are natural or artificial water environments like rivers, lakes, seas, and fountains.
Results indicated that exposure to heatwaves was associated with a 4-14% increase in the odds of depression. Likewise, exposure to air pollution was also associated with depression risk. The authors reported that for every 10 μg/m3 increase in ambient concentrations of PM2.5 particles, the odds of depression increased by 25%. The increase was 13% per the same unit increase in PM10 particle concentrations, 1% for CO, while the odds increased 55% for every 10 μg/m3 increase in SO2 concentrations.
The risk of depression was also heightened in areas where access to blue spaces was lower. The study found a synergistic effect: individuals simultaneously exposed to both heatwaves and high air pollution, or to heatwaves combined with a lack of green and blue spaces, had a significantly higher increase in depression risk than would be expected from adding the individual risks together.
“The findings indicate that heatwaves, air pollution, and lack of blue spaces each independently have a detrimental impact on depressive symptoms. Furthermore, the interactive effects of air contaminants, insufficient blue and green spaces, and heatwaves exposure significantly affect depressive symptoms, both on multiplicative and additive scales. Our results emphasize the necessity of developing public health strategies to curb air pollution, and preserve blue and green spaces, especially during periods of heatwaves,” study authors concluded.
The study contributes to the scientific understanding of the links between climate and mental health. However, it should be noted that the design of this study does not allow any definitive causal inferences to be derived from the results.
The paper, “Individual and combined effects of heatwaves, air pollution, green spaces, and blue spaces on depressive symptoms incidence,” was authored by Weiqi Wang, Yuqing Hao, Meiyu Peng, Jin Yan, Longzhu Xu, Haiyang Yu, Zhugen Yang, and Fanyu Meng.