While climate change is expected to have disastrous consequences worldwide, it can bring some small benefits, too. A recent study by researchers based at IIT Delhi and University of California, Berkeley suggests that climate change could reduce levels of the highly toxic fine particulate matter of size smaller than 2.5 microns (PM2.5) in the air above the Indian landmass. As a result, premature deaths in India due to ailments such as ischemic heart disease, stroke, chronic obstructive pulmonary disease, lung cancer, and acute lower respiratory infection, which are linked to air pollution, are likely to go down.
A likely consequence of climate change over the Indian subcontinent over the next 80 years is an increase in the average rainfall the country receives, the researchers have said. Reduction in PM2.5 levels will follow the increased precipitation, because rain helps fine particulate matter to settle.
The study, published in the journal Nature Communications, projects that under certain climate change scenarios, the number of premature deaths due to air pollution could go down by as much as 12,000 per year (see box). “If you know the exposure and how people are exposed, you can estimate the (premature mortality) burden,” Sagnik Dey, Associate Professor at the Centre for Atmospheric Sciences at IIT Delhi, and a co-author of the study, said.
The study attempted to assess the change in particulate matter levels with climate change till the year 2100, and its effects on people’s health. In best case scenarios, the reduction in PM2.5 levels (averaged over the entire country) by 2100 could be as high as 80% of the average levels during 2001-05, the baseline period for the study.
The researchers calculated the reduction in PM2.5 levels under different RCP (Representative Concentration Pathways) scenarios used by scientists to project future climate change impacts. The four RCP scenarios (RCP 2.6, RCP 4.5, RCP 6 and RCP 8.5) are a measure of the concentration of carbon dioxide in the atmosphere in the year 2100 as compared to pre-industrial times. For example, RCP 2.6 corresponds to an average increase of 2.6 watts per square metre in the energy of the Earth’s atmosphere due to increased concentration of greenhouse gases compared to pre-industrial times.
RCP scenarios are developed by making assumptions about global population, economic development, land use changes, and policy interventions by governments to fight climate change. An RCP 8.5 scenario assumes no policy interventions to contain climate change.
Using multiple sources, the study established that the average PM2.5 exposure level in 2001 to 2005 was 34 micro g/m3. It projected that “Ambient PM2.5 exposure in India is projected to drop below the baseline period exposure only after 2050 under RCP4.5 and after 2090 under the RCP8.5 scenario.”
In the RCP4.5 scenario, however, a marked decline in PM2.5 levels will be visible from 2030 itself. “The changing climate will lead to increased precipitation, greater wind speeds and larger mixed layer depth. This will lead to a fall in PM2.5 concentration,” study co-author Sourangsu Chowdhury said.
To translate the reductions into a fall in premature deaths, the researchers relied on another set of models called Shared Socioeconomic Pathways (SSPs). These plot the country’s general development using demographics such as age, sex, education, and economic development, represented by GDP. Population distribution data from these models allows for an assessment of the impact of climate scenarios using complex calculations.
Most models suggest that under the most favourable climate scenario, population and premature deaths will see a slide. “Improved health conditions due to economic growth are expected to compensate for the impact of changes in population and age distribution, leading to a reduction in per capita health burden from PM2.5 for all scenarios,” the study notes.
No solution to pollution
The researchers, however, warn against interpreting the study as a solution to air pollution. “We only looked into (rainfall) data averaged at decadal scale. The results should not be interpreted to mean that air pollution problem would go away in future. The (premature death) burden is projected to reduce compared to present day, but the reduction is not enough to take India to a safe zone,” Dr Dey said. A report published in The Lancet last year said India saw 2.51 million premature deaths in 2015 due to diseases linked to pollution. Air pollution-linked disease alone accounted for 1.8 million deaths.
Reviewing the current paper, Professor Michael Brauer of the School of Population and Public Health, University of British Columbia, who had also analysed The Lancet study, told The Indian Express by email: “I certainly agree with the main conclusion of the paper (improving health conditions due to improving economy is expected to lead to a reduction in per capita health burden from PM2.5). However, the analysis is making predictions of health up to the year 2100 which is highly uncertain and even estimates beyond 2050 should be viewed very cautiously.”