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Topic 34: The Great Dirty Diesel Scare

Updated  October 2015
File Ref. The Great Dirty Diesel Scare 03g

PARTICULATES

The Media headline, that man-made air pollution causes “29,000 premature deaths” in the UK is from a report, dated 2010, by the Committee on the Medical Effects of Air Pollutants, COMEAP.  The snazzy title is The Mortality Effects of Long-Term Exposure to Particulate Air Pollution in the United Kingdom.  The report runs to 98 pages.

Paragraph 2 of the Executive summary provides:

  • At sub-para (a): “The current (2008) burden of anthropogenic particulate matter air pollution is, with some simplifying assumptions, an effect on mortality in 2008 equivalent to nearly 29,000 deaths in the UK at typical ages and an associated loss of total population life of 340,000 life-years. The burden can also be represented as a loss of life expectancy from birth of approximately six months”.
  • At sub-para (d): “The uncertainties in these estimates need to be recognised: they could vary from about a sixth to double the figures shown”.

However:

  1. The range cited represents “75% plausibility limits”.  Had the more usual 95% limits been used they would have embraced zero, meaning that, in statistical terms, the forecast shortening in life expectance due to particulates is no different from zero
  2. The saving may be achieved only if all man-made particulates are eliminated
  3. Only about one tenth of man-made particulates are from road traffic. Separately from the report, COMEAP say that removing all particles attributable to local traffic may increase average life-expectancy by approximately 16 days for England and Wales and approximately 41 days in Inner London.

Furthermore, the computation and assumptions underlying the data are opaque.  The report refers to an earlier report with the title, “Long-Term Exposure to Air Pollution: Effect on Mortality”, published in 2009, 186 pages.  That report refers to “Relative Risk” coefficients derived from the “American Cancer Society (ACS) study (Pope et al, 1995, 2002)”.  COMEAP uses those coefficients, together with other sources, to compute the changes in life expectancy.  However, the complexity and opacity of the whole undermines confidence.  Indeed common sense suggests that it may be nigh on impossible to isolate the effects of particulates from the other factors.

Additionally, many of the estimates and error ranges depend on “eliciting” from “experts” their views.  That process, known as elicitation, is heavily criticised by Professor P K Hopke in the earlier COMEAP report, Long-term Exposure to Air Pollution: Effect on Mortality, cited above

There is also a critique of the ACS paper by Joel Schwartz, Adjunct Scholar of the Competitive Enterprise Institute.  The executive summary, available here, makes compelling reading.  It suggests that the ACS paper is deeply flawed and that, probably, particulates have no effect whatsoever on lifespan.  That conclusion is consistent with the COMEAP findings, where, at section 3.1.3, risk coefficients range from unity to 1.15.  A value of unity implies that particulates have no effect.

Conclude:

The data from COMEAP suggests trivial average life expectancy gains from banning all diesel vehicles.  The plausibility limits on those gains are extraordinarily wide. The basis for the numbers is opaque.  Probably the American ACS study, upon which the whole depends, is junk science. In truth these particulates may very well have no effect on lifespan whatsoever. 

For those reasons it seems that the present attack on the diesel vehicle has no solid basis.

NITROUS OXIDES NOx

The COMEAP paper with the title ‘Considering the evidence for the effects of Nitrogen dioxide on health’, dated June 2014, is extraordinarily cautious.  For example at paragraph 38 we have:

“In 2008, the EPA considered the evidence suggestive but not sufficient to infer presence or absence of an association between short term exposure to NO2 and mortality. Now the evidence has increased and the EPA considered that there is likely to be a causal relationship”. 

The report as a whole suggests great uncertainty.  One senses that the Committee is being pushed to find evidence when none is available or where whatever is available is very weak.

We have not researched the whole in detail, but the impression formed from this report is that, although it would be extraordinary if pollutants had no effect on health and life span, the affects may be slight at the levels found in the UK, Europe or the United States, suggesting that, in those areas, the costs of reducing either particulates or NOx may far outweigh the benefits.



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