London fog: a century of pollution and mortality, 1866-1965

by Walker Hanlon (UCLA)

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Photogravure by Donald Macleish from Wonderful London by St John Adcock, 1927. Available at <https://www.flickr.com/photos/norfolkodyssey/23695833473&gt;

For more than a century, London struggled with some of the worst air pollution on earth. But how much did air pollution affect health in London? How did these effects change as the city developed? Can London’s long experience teach us lessons that are relevant for modern cities, from Beijing to New Delhi, that are currently struggling with their own air pollution problems?

To answer these questions, I study the effects of air pollution in London across a full century from 1866 to 1965. Using new data, I show that air pollution was a major contributor to mortality in London during this century – accounting for at least one out of every 200 deaths during this century.

As London developed, the impact of air pollution changed. In the nineteenth century, Londoners suffered from a range of infectious diseases, including respiratory diseases like measles and tuberculosis. I show that being exposed to high levels of air pollution made these diseases deadlier, while the presence of these diseases made air pollution more harmful. As a result, when public health and medical improvements reduced the prevalence of these infectious diseases, they also lowered the mortality cost of pollution exposure.

This finding has implications for modern developing countries. It tells us that air pollution is likely to be more deadly in the developing world, but also that investments that improve health in other ways can lower the health costs of pollution exposure.

An important challenge in studying air pollution in the past is that direct pollution measures were not collected in a consistent way until the mid-twentieth century. To overcome this challenge, this study takes advantage of London’s famous fog events, which trapped pollution in the city and substantially increased exposure levels.

While some famous fog events are well known – such as the Great Fog of 1952 or the Cattle Show Fog of 1873, which killed the Queen’s prize bull – London experienced hundreds of lesser-known events over the century I study. By reading weather reports from the Greenwich Observatory covering over 26,000 days, we identified every day in which heavy fog occurred.

To study how these fog events affected health, I collected detailed new mortality data describing deaths in London at the weekly level. Digitised from original sources, and covering over 350,000 observations, this new data set opens the door to a more detailed analysis of London’s mortality experience than has previously been possible.

These new mortality data allow me to analyse the effects of air pollution from a variety of different angles. I provide new evidence on how the effects of air pollution varied across age groups, how the effect on different age groups evolved over time, how pollution interacted with infectious diseases and other causes of death, etc. This enriches our understanding of London’s history while opening up a range of new possibilities for studying the impact of air pollution over the long run.

THE IMPACT OF MALARIA ON EARLY AFRICAN DEVELOPMENT: Evidence from the sickle cell trait

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poster “Keep out malaria mosquitoes repair your torn screens”. U.S. Public Health Service, 1941–45

While malaria historically claimed millions of African lives, it did not hold back the continent’s economic development. That is one of the findings of new research by Emilio Depetris-Chauvin (Pontificia Universidad Católica de Chile) and David Weil (Brown University), published in the Economic Journal.

Their study uses data on the prevalence of the gene that causes sickle cell disease to estimate death rates from malaria for the period before the Second World War. They find that in parts of Africa with high malaria transmission, one in ten children died from malaria or sickle cell disease before reaching adulthood – a death rate more than twice the current burden of malaria in these regions.

 

According to the World Health Organization, the malaria mortality rate declined by 29% between 2010 and 2015. This was a major public health accomplishment, although with 429,000 annual deaths, the disease remains a terrible scourge.

Countries where malaria is endemic are also, on average, very poor. This correlation has led economists to speculate about whether malaria is a driver of poverty. But addressing that issue is difficult because of a lack of data. Poverty in the tropics has long historical roots, and while there are good data on malaria prevalence in the period since the Second World War, there is no World Malaria Report for 1900, 1800 or 1700.

Biologists only came to understand the nature of malaria in the late nineteenth century. Even today, trained medical personnel have trouble distinguishing between malaria and other diseases without the use of microscopy or diagnostic tests. Accounts from travellers and other historical records provide some evidence of the impact of malaria going back millennia, but these are hardly sufficient to draw firm conclusions. Akyeampong (2006), Mabogunje and Richards (1985)

This study addresses the lack of information on malaria’s impact historically by using genetic data. In the worst afflicted areas, malaria left an imprint on the human genome that can be read today.

Specifically, the researchers look at the prevalence of the gene that causes sickle cell disease. Carrying one copy of this gene provided individuals with a significant level of protection against malaria, but people who carried two copies of the gene died before reaching reproductive age.

Thus, the degree of selective pressure exerted by malaria determined the equilibrium prevalence of the gene in the population. By measuring the prevalence of the gene in modern populations, it is possible to back out estimates of the severity of malaria historically.

In areas of high malaria transmission, 20% of the population carries the sickle cell trait. The researchers’ estimate is that this implies that historically 10-11% of children died from malaria or sickle cell disease before reaching adulthood. Such a death rate is more than twice the current burden of malaria in these regions.

Comparing the most affected areas with those least affected, malaria may have been responsible for a ten percentage point difference in the probability of surviving to adulthood. In areas of high malaria transmission, the researchers’ estimate that life expectancy at birth was reduced by approximately five years.

Having established the magnitude of malaria’s mortality burden, the researchers then turn to its economic effects. Surprisingly, they find little reason to believe that malaria held back development. A simple life cycle model suggests that the disease was not very important, primarily because the vast majority of deaths that it caused were among the very young, in whom society had invested few resources.

This model-based finding is corroborated by the findings of a statistical examination. Within Africa, areas with higher malaria burden, as evidenced by the prevalence of the sickle cell trait, do not show lower levels of economic development or population density in the colonial era data examined in this study.

 

To contact the authors:  David Weil, david_weil@brown.edu

EFFECTS OF COAL-BASED AIR POLLUTION ON MORTALITY RATES: New evidence from nineteenth century Britain

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Samuel Griffiths (1873) The Black Country in the 1870s. In Griffiths’ Guide to the iron trade of Great Britain.

Industrialised cities in mid-nineteenth century Britain probably suffered from similar levels of air pollution as urban centres in China and India do today. What’s more, the damage to health caused by the burning of coal was very high, reducing life expectancy by more than 5% in the most polluted cities like Manchester, Sheffield and Birmingham. It was also responsible for a significant proportion of the higher mortality rates in British cities compared with rural parts of the country.

 These are among the findings of new research by Brian Beach (College of William & Mary) and Walker Hanlon (NYU Stern School of Business), which is published in the Economic Journal. Their study shows the potential value of history for providing insights into the long-run consequences of air pollution.

From Beijing to Delhi and Mexico City to Jakarta, cities across the world struggle with high levels of air pollution. To what extent does severe air pollution affect health and broader economic development for these cities? While future academics will almost surely debate this question, assessing the long-run consequences of air pollution for modern cities will not be possible for decades.

But severe air pollution is not a new phenomenon; Britain’s industrial cities of the nineteenth century, for example, also faced very high levels of air pollution. Because of this, researchers argue that history has the potential to provide valuable insights into the long-run consequences of air pollution.

One challenge in studying historical air pollution is that direct pollution measures are largely unavailable before the mid-twentieth century. This study shows how historical pollution levels in England and Wales can be inferred by combining data on the industrial composition of employment in local areas in 1851 with information on the amount of coal used per worker in each industry.

This makes it possible to estimate the amount of coal used in over 581 districts covering all of England and Wales. Because coal was by far the most important pollutant in Britain in the nineteenth century (as well as much of the twentieth century), this provides a way of approximating local industrial pollution emission levels.

The results are consistent with what historical sources suggest: the researchers find high levels of coal use in a broad swath of towns stretching from Lancashire and the West Riding down into Staffordshire, as well as in the areas around Newcastle, Cardiff and Birmingham.

By comparing measures of local coal-based pollution to mortality data, the study shows that air pollution was a major contributor to mortality in Britain in the mid-nineteenth century. In the most polluted locations – places like Manchester, Sheffield and Birmingham – the results show that air pollution resulting from industrial coal use reduced life expectancy by more than 5%.

One potential concern is that locations with more industrial coal use could have had higher mortality rates for other reasons. For example, people living in these industrial areas could have been poorer, infectious disease may have been more common or jobs may have been more dangerous.

The researchers deal with this concern by looking at how coal use in some parts of the country affected mortality in other areas that were, given the predominant wind direction, typically downwind. They show that locations which were just downwind of major coal-using areas had higher mortality rates than otherwise similar locations which were just upwind of these areas.

These results help to explain why cities in the nineteenth century were much less healthy than more rural areas – the so-called urban mortality penalty. Most existing work argues that the high mortality rates observed in British cities in the nineteenth century were due to the impact of infectious diseases, bad water and unclean food.

The new results show that in fact about one third of the higher mortality rate in cities in the nineteenth century was due to exposure to high levels of air pollution due to the burning of coal by industry.

In addition to assessing the effects of coal use on mortality, the researchers use these effects to back out very rough estimates of historical particulate pollution levels. Their estimates indicate that by the mid-nineteenth century, industrialised cities in Britain were probably as polluted as industrial cities in places like China and India are today.

These findings shed new light on the impact of air pollution in nineteenth century Britain and lay the groundwork for further research analysing the long-run effects of air pollution in cities.

 

To contact the authors:  Brian Beach (bbbeach@wm.edu); Walker Hanlon (whanlon@stern.nyu.edu)

EHS 2018 special: London’s mortality decline – lessons for modern water policy

Werner Troeksen (University of Pittsburgh)
Nicola Tynan (Dickinson College)
Yuanxiaoyue (Artemis) Yang (Harvard T.H. Chan School of Public Health)

 

The United Nations Sustainable Development Goals aim to ensure access to water and sanitation for all. This means not just treating water but supplying it reliably. Lives are at stake because epidemiological research shows that a reliable, constant supply of water reduces water-borne illness.

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Available at <https://heartheboatsing.com/2015/08/13/death-on-the-water/&gt;

Nineteenth century London faced the same challenge. Not until 1886 did more than half of London homes have water supplied 24 hours a day, 7 days a week. The move to a constant water supply reduced mortality. For every 5% increase in the number of households with a constant supply, deaths from water-borne illnesses fell 3%.

During Victoria’s reign, eight water companies supplied the metropolis with water: 50% from the river Thames, 25% from the river Lea and 25% from wells and springs. By the 1860s, the companies filtered all surface water and Bazalgette’s intercepting sewer was under construction. Still, more than 80% of people received water intermittently, storing it in cisterns often located outside the house, uncovered or beside the toilet.

Rapid population and housing growth required the expansion of the water network and companies found it easier to introduce constant service in new neighbourhoods. Retrofitting older neighbourhoods proved challenging and risked a substantial waste of scarce water. The Metropolis Water Act of 1871 finally gave water companies the power to require waste-limiting fixtures. After 1871, new housing estates received a constant supply of water immediately, while old neighbourhoods transitioned slowly.

As constant water supply reached more people, mortality from diarrhoea, dysentery, typhoid and cholera combined fell. With 24-hour supply, water was regularly available for everyone without risk of contamination. Unsurprisingly, poorer, crowded districts had higher mortality from water-borne diseases.

Even though treated, piped water was available to all by the mid-nineteenth century, everyone benefitted from the move to constant service. By the time the Metropolitan Water Board acquired London’s water infrastructure, 95% of houses in the city received their water directly from the mains.

According to Sergio Campus, water and sanitation head at the Inter-American Development Bank, the current challenge in many places is providing a sustainable and constant supply of water. In line with this, the World Bank’s new Water Supply, Sanitation, and Hygiene (WASH) poverty diagnostic has added frequency of delivery as a measure of water quality, in addition to access, water source and treatment.

Regularity of supply varies substantially across locations. London’s experience during the late Victorian years suggest that increased frequency of water supply has the potential to deliver further reductions in mortality in developing countries beyond the initial gains from improved water sources and treatment.