The Lancet and Air Pollution

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By Paul Homewood

We’ve pretty much covered the topic of air pollution and premature deaths already this week.

But this latest study has just been published by The Lancet.

No doubt, it will be used to press for more, wonderful renewable energy, and less fossil fuels.

These are the findings, (my bold):

Ambient PM_2·5 was the fifth-ranking mortality risk factor in 2015. Exposure to PM_2·5 caused 4·2 million (95% uncertainty interval [UI] 3·7 million to 4·8 million) deaths and 103·1 million (90·8 million 115·1 million) disability-adjusted life-years (DALYs) in 2015, representing 7·6% of total global deaths and 4·2% of global DALYs, 59% of these in east and south Asia. Deaths attributable to ambient PM_2·5 increased from 3·5 million (95% UI 3·0 million to 4·0 million) in 1990 to 4·2 million (3·7 million to 4·8 million) in 2015. Exposure to ozone caused an additional 254 000 (95% UI 97 000–422 000) deaths and a loss of 4·1 million (1·6 million to 6·8 million) DALYs from chronic obstructive pulmonary disease in 2015.

The study seems to share the same methodology as previous studies, and is based around statistical models. The paper describes its methods:

Attributing deaths and disability-adjusted life-years (DALYs) to ambient air pollution requires spatially and temporally resolved estimates of population-weighted exposure, specification of a theoretical minimum risk exposure level (TMREL), estimation of relative risks across the exposure distribution, and estimates of the deaths and DALYs for diseases linked causally to air pollution. We combined estimates of exposure and relative risk to estimate the population-attributable fraction (PAF), the proportion of deaths and DALYs attributable to exposure above the TMREL. The numbers of deaths and DALYs for specific diseases were multiplied by the PAF to estimate the burden attributable to exposure.

In short, they have to guess the exposure to PMs in different regions across the world since 1990, guess the “safe exposure level”, guess the relative risks for various exposures, and guess the number of deaths that might have arisen from all of this.

In other words, the results depend on the assumptions you feed the model. Change these, and you could easily get ten times the number of deaths, or a tenth.

There are some parts of the study that are worth noting though.

First the geographic distribution. The table below lists the data for the ten most populous countries:

We find that the the Asian countries (excl Japan and Russia) listed account for 2.5 million of the world total of 4.2 million.

At the other end of the scale, death rates in the US and Japan are way below rest. Clearly this is a problem for the developing world, and much less so for the US and Europe.

It is of course no secret that air pollution is a very real problem in much of Asia, and part of this arises from household fuels.

The second thing to note is the role that population ageing plays:

In the US, for instance, there has been less exposure to pollution since 1990, and consequently less deaths as a result.

However, this has been partly offset by an ageing population. As I commented the other day, we all have to die of something sooner or later. An, sadly, when we get to 80, we are much more likely to succumb to respiratory disease. Particularly when we may have been exposed to polluted air for many decades previously.

Indeed, this ageing factor is apparent across every country except Nigeria.

In reality, the increase in deaths estimated by the study since 1990 simply reflects the fact that people have not died from other causes first.

Increased population also accounts for more deaths.

Taking this issue of age into account, the study reckons that deaths from air pollution in the UK has nearly halved since 1990, from 44.0 to 22.8 deaths per 100,000.

How many of these are due to exposure in the past is open to question.

It does not take a genius to work out that countries like China desperately need the sort of air pollution controls that the we in the west have had for decades.

They also badly need access to reliable, cheap energy so they don’t have to rely on burning wood and coal at home.

Provision of modern, clean power stations will achieve all of this in a way that renewable energy never will.

As for us in the west, we must not be afraid to acknowledge just how much things have improved in the last few decades. Without doubt death rates will continue to plummet.

But we must be very careful we don’t throw the baby out with the bath water.