June 11, 2024
SINGAPORE – Between 1980 and 2020, air pollution was linked to 135 million premature deaths globally, with the death toll spiking when unhealthy air coincided with climate events, a study led by Nanyang Technological University (NTU) has found.
There was a 14 per cent rise in such deaths – or 7,000 more fatalities each year – in the years when climatic events such as El Nino, the Indian Ocean Dipole and the North Atlantic Oscillation happened.
The main killer is the PM2.5 pollutant – microparticles that come from haze, burning from power plants, and wildfires – that gets lodged deep in the lungs and enters the bloodstream. This can cause breathing difficulties and heart and lung disease, among other issues.
Premature deaths refer to fatalities that occur earlier than expected, based on average life expectancy, due to preventable diseases and environmental factors.
More than 360 major air pollution events occurred worldwide in the 40 years studied. And of the 135 million premature fatalities in that timeframe, Asia had the highest death toll, led by 49 million mortalities in China and 26.1 million in India.
The NTU-led study found that a third of premature deaths during that time were associated with stroke, another third with heart disease, while lung disease and cancer made up the rest.
Higher temperatures, wind pattern changes and reduced precipitation can lead to stagnant air conditions and the accumulation of pollutants in the atmosphere, according to the study’s findings, published in the Environmental International journal in April. These result in higher concentrations of PM2.5 particles that are particularly harmful to human health.
Of the natural climate phenomena, the Indian Ocean Dipole was found to have had the largest impact on the number of deaths, followed by the North Atlantic Oscillation, and then El Nino.
A positive Indian Ocean Dipole causes warmer sea surface temperatures in the western Indian Ocean near Africa, leading to hotter weather in South-east Asia and Australia. El Nino also brings hotter, drier weather in both regions.
During the 2015 South-east Asian haze crisis – when Singapore’s 24-hour Pollutant Standards Index surpassed 300, reaching the hazardous range, and forced schools to close for a day – El Nino had coincided with a positive Indian Ocean Dipole.
On the other side of the world, pressure patterns in the atmosphere over Iceland and the Azores Islands in the Atlantic Ocean result in the North Atlantic Oscillation. During a negative Oscillation, eastern United States and northern Europe get colder, while southern Europe gets warmer.
The researchers looked at historical Nasa satellite data to track the levels of PM2.5 in the atmosphere. They also analysed data on the incidence and mortality of diseases linked to pollution from the US-based Institute for Health Metrics and Evaluation.
South-east Asia is the only region to be impacted by all three climate events, and becomes the most vulnerable when all three weather patterns coincide, said Associate Professor Steve Yim, who led the study.
This was seen in 1994, 1997, 2002 and 2015 – when the region faced 3,100 more deaths annually in those years from pollution, the study found.
There is therefore a need for targeted interventions to prevent pollution during such weather conditions, said Prof Yim, who is from NTU’s Asian School of the Environment and Lee Kong Chian School of Medicine (LKCMedicine), and a principal investigator at NTU’s Earth Observatory of Singapore.
Dr Ajay Nagpure, an urban systems scientist at Princeton University who was not part of the study, compared the effects of PM2.5 pollution to that of a pandemic, which disproportionately affects individuals of low-income backgrounds.
He said: “These populations are severely affected by this threat due to various factors such as higher exposure levels and limited access to healthcare facilities.”
Professor Joseph Sung, the study’s co-author and senior vice-president of health and life sciences at NTU, said healthcare systems need to allocate more resources to address the immediate and long-term health impacts of air pollution.
To prevent short-term impacts such as a spike in patients with breathlessness and respiratory issues, the authorities should have early warnings in place so that residents will have N95 masks at hand and limit outdoor activities when a smog arrives.
“On the hospitals’ side, we should prepare for increased capacity. Of course, this will not be easy because hospitals, particularly public hospitals, are always 110 per cent full,” said Prof Sung, who is also dean of LKCMedicine.
On the long-term front, changes to urban planning and traffic, and the switch to non-pollutive energy sources must be ramped up to prevent man-made air pollution, he added.
Prof Sung also observed that increasingly more women and non-smokers have been developing a type of respiratory cancer called lung adenocarcinoma, adding that this could be linked to climate and air pollution.
Both El Nino and the Indian Ocean Dipole happened in 2019 and 2015, when the haze situations were much worse. A Harvard University study estimated that the 2015 crisis caused 100,000 premature deaths across Indonesia, Malaysia and Singapore.
Singapore had a brief episode of haze on Oct 6 and 7 in 2023, when the PSI crossed into the unhealthy range. But Prof Yim noted how early warning, firefighting and enforcement efforts in Indonesia helped to dampen transboundary haze in the region that year, a year when both phenomena also coincided.
Prof Yim said the impact of the North Atlantic Oscillation on South-east Asia is still uncertain. This is one area that the team will be following up on.
The researchers are also currently tracking Singapore’s air quality over the past decades to have a finer understanding of local air pollution patterns.