This forum is about wrong numbers in science, politics and the media. It respects good science and good English.
Following on from last year's forum thread "Diesel deaths", I noticed this BBC webpage called "Reality Check: Does pollution cut short 40,000 lives a year?". It looks like it was part of a week of promoting awareness of air pollution in the UK that the BBC decided to carry out on the UK public's behalf in March 2017.
BBC Reality Check
"The claim: Air pollution cuts short 40,000 lives a year in the UK.
Reality Check verdict: The 40,000 figure for the UK stems from extensive research over decades in the US. It's a statistical construct not a count of actual deaths. There is no question that air pollution is a serious health problem but it's difficult to assess its precise impact."
I think the idea that air pollution today is a serious health problem can be questioned simply by studying measured air pollution levels in the UK from 1970, as shown in this graph provided via Paul Homewood's blog:
UK air pollution graph
From the graph it is evident that pollution levels for PM2.5 and nitrogen dioxide have come down substantially from previous decades. The only pollutant that does not seem to be under some sort of successful control since 1970 appears to be ammonia. So if air pollution is a serious health problem today, then it was an even bigger problem a few decades ago, but strangely nobody flagged it up as being a problem at the time. You would only regard today's air pollution as being unquestionably a serious health problem if you were in collusion with Big Green.
One of the issues I pointed out in the "Diesel deaths" thread last year was that the prematureness of the premature deaths tends not to be quantified in any articles that get written about air pollution. This statistic would be the most important one that you would need to know in order to make a decision about whether this is a significant problem or not, and whether to take any action. The BBC Reality Check team does quantify the prematureness of the deaths in this extract from the webpage:
"Also, the 29,000 early deaths [the 29000 relates to PM2.5] figure was based on an average shortening of life of 11.5 years. If you're considering how many people actually had their lives shortened at all in a particular year (the report was looking at 200 then the number of people affected would be much higher.
The authors of the report actually prefer to say that air pollution causes 340,000 years of lost life in the UK, but they are concerned that people will not understand that as well, so they translate that figure into damage equivalent to 29,000 deaths, an average of 11.5 years early instead."
So the Reality Check team come up with 11.5 years as the relevant shortening of life figure for UK air pollution, based on dividing 340000 by 29000. Now that sounds pretty significant - many people would want action taken regarding something that could knock slightly more than a decade off their lifespan. But if we look at a COMEAP report:
This report quotes in its Executive Summary for items 18 and 21:
"18 As a central estimate we conclude that anthropogenic PM2.5 at 2008 levels (8.97 µg/m3 in the UK) is associated with an effect on mortality equivalent to nearly 29,000 deaths at typical ages of death in 2008 in the UK and an associated loss of total population survival of 340,000 years and an average loss of between three and four months of life expectancy in Scotland and Northern Ireland and between six and seven months in England and Wales, reflecting differences in the levels of anthropogenic PM2.5 to which these populations are exposed."
"21 It is not known how this population-wide burden is spread across individuals in the population, but we can speculate between various possibilities. Our results are consistent with an average loss of life ranging at one extreme from 11½ years if air pollution was solely responsible for 29,000 deaths to, at the other extreme, six months if the timing of all deaths was influenced by air pollution. We believe both of these
extremes to be extremely unlikely. Given that much of the impact of air pollution on mortality is linked with cardiovascular deaths, it is more reasonable to consider that air pollution may have made some contribution to the earlier deaths of up to 200,000 people in 2008, with an average loss of life of about two years per death affected, though that actual amount would vary between individuals. However, this assumption remains speculative."
So the COMEAP report indicates that the BBC Reality Check team's 11.5 years figure is an extreme upper bound. COMEAP themselves are only quoting months for the reduction in lifespan, but they are also speculating that it could be as high as two years.
I also looked for what the reduction in lifespan for pollution was in London, which would be expected to be a bit higher than the rest of the UK to reflect the city's higher pollution levels. According to this 2015 report "Understanding the Health Impacts of Air Pollution in London For: Transport for London and the Greater London Authority" Table E.2 page 10, the average loss of life expectancy for people born in 2010 and then exposed to 2010 pollution levels for their whole lifetime is 9.5 months for man-made PM2.5 and up to 17 months for nitrogen dioxide, with slightly lower values for females than males.
London pollution report
To give some idea how daft the BBC Reality Check team's claim is that man-made PM2.5 air pollution in the UK is shortening lives by 11.5 years, compare it with the lifetime reductions that are quoted for smoking (this is active smoking, not passive smoking). There was a long-term study carried out in the Netherlands called "the Zutphen Study".
In this study, the average lifetime reduction was found to be 6.8 years for cigarette smoking in general, 8.8 years for heavy cigarette smoking (heavy smoking seems to be defined as smoking over 30 cigarettes per day in the paper), and 4.7 years for pipe or cigar smoking. So the BBC is claiming that breathing in modern day PM2.5 air pollution in the UK is more dangerous than smoking.
As noted in the previous post, academics tend to quote the lifetime reduction for man-made PM2.5 air pollution in months, that is 3 to 4 months for Scotland and Northern Ireland, 6 to 7 months for England and Wales, and 9.5 months for the London area. But even these figures, that are in the order of months, could be regarded as over the top, if you consider an argument put forward by Junkscience.com's Steven Milloy:
Milloy's argument is that a smoker inhales substantially more PM2.5 from cigarettes than a non-smoker breathing in polluted outdoor air. But cigarette smokers are advised by health authorities that if they give up smoking, they will recover most, if not all, of their 'lost lifetime' that they would have incurred if they had carried on smoking. Otherwise there is little point in advising people to give up smoking. But a person who has quit smoking may have taken in a much higher accumulated 'dose' of man-made PM2.5 in their years of smoking than the non-smoker will pick up from air pollution in a lifetime.
I noticed this news story about the UK Liberal Democrat party proposing in their manifesto for the forthcoming General Election in a few weeks time to introduce a ban on the sale of diesel cars and small vans. Also mentioned in the article is that they propose to legalise cannabis and use it as a new tax revenue stream.
At first sight that doesn't look particularly inconsistent, cracking down on pollution and a relaxed attitude to cannabis use are long-established left-liberal hobbyhorses. However the intention behind banning diesel cars is in large part a desire to protect the public from exposure to PM2.5 fine particulate matter. The legalisation of cannabis by a government would mean that it effectively approves of the idea of exposing a section of the public to far greater amounts of PM2.5 than they would experience from air pollution. According to Steven Milloy, smoking a marijuana joint could result in 18,000 times as much exposure to PM2.5 as a person breathing outdoor air for an hour: