Death and disease from climate-sensitive diseases and events are small relative to those from all causes, and getting smaller

Indur M. Goklany

Between 1990 and 2017, the cumulative age-standardized death rate (ASDRs) from climate-sensitive diseases and events (CSDEs) dropped from 8.1% of the all-cause ASDR to 5.5%, while the age-standardized burden of disease, measured by disability-adjusted life years lost (DALYs) declined from 12.0% to 8.0% of all-cause age-standardized DALYs. Thus, the burdens of death and disease from CSDEs are small, and getting smaller.

Figure 1: Climate-related deaths are a small proportion of all-cause fatalities (1990–2017). Based on data per IHME (2019).

But readers of the 2019 report of the Lancet Countdown (hereafter ‘the Countdown’), a partnership of 35 academic institutions and UN agencies, established by the prestigious Lancet group of medical journals and supported by the equally-esteemed Wellcome Trust to track progress on the health impacts of climate change, may well be left with the opposite impression, particularly if they do not delve beyond the Executive Summary, the section most likely to be read by busy policymakers or their advisors.

Not once does it mention that cumulative annual rates of death and disease from CSDEs are declining, and declining faster than the corresponding all-cause rates. The Countdown also fails to provide adequate context for the reader to judge the burdens of mortality or disease posed by CSDEs, individually or cumulatively, relative to other public-health threats. In fact, it even suggests that the health effects of climate change are ‘worsening’. But the data do not support that claim. Moreover, an analysis of the text makes it clear that the Countdown conflates estimates of increasing exposure, ‘demographic vulnerability’, and increased ‘suitability’ of disease transmission with actual health effects.

Figure 2: Burden of mortality from CSDEs, 1990–2017. The Forces of Nature group excludes deaths from geophysical causes per EMDAT (2019). Data per IHME (2019).

But readers of the 2019 report of the Lancet Countdown (hereafter ‘the Countdown’), a partnership of 35 academic institutions and UN agencies, established by the prestigious Lancet group of medical journals and supported by the equally-esteemed Wellcome Trust to track progress on the health impacts of climate change, may well be left with the opposite impression, particularly if they do not delve beyond the Executive Summary, the section most likely to be read by busy policymakers or their advisors.

Not once does it mention that cumulative annual rates of death and disease from CSDEs are declining, and declining faster than the corresponding all-cause rates. The Countdown also fails to provide adequate context for the reader to judge the burdens of mortality or disease posed by CSDEs, individually or cumulatively, relative to other public-health threats. In fact, it even suggests that the health effects of climate change are ‘worsening’. But the data do not support that claim. Moreover, an analysis of the text makes it clear that the Countdown conflates estimates of increasing exposure, ‘demographic vulnerability’, and increased ‘suitability’ of disease transmission with actual health effects.  These estimates are used as proxies, but trends in these estimates have not been verified to reflect, and do not track, long-term trends in deaths or death rates.

In addition to overlooking the diminishing overall significance of CSDEs for public health, the Countdown chooses to focus instead on CSDEs that have, contrary to the general trend, become more prevalent. As a case in point, dengue, a mosquito-borne tropical disease, was responsible for 40,000 deaths in 2017. This seems a lot, but it represents only 1.4% of the cumulative 2.8 million deaths from CSDEs or 0.07% of the 55.9 million people who died globally from all causes that year. Yet dengue gets more attention in the Countdown than malaria, another mosquito-borne tropical disease, which was responsible for fifteen times as many (620,000) deaths.

Because of its failure to provide context, the Countdown fails to give the reader or policymakers a balanced account of public-health threats and, therefore, risks distorting public health priorities. Without proper context, a molehill may well be mistaken for a mountain. Context is thus essential to help policymakers keep perspective and focus on larger and more important public health problems.

Regarding context, much of the critique examines trends since 1990. This is because the data from the Institute for Health Metrics and Evaluation (IHME), on which the Countdown primarily relies, commences in that year. However, the declines in death and disease rates from CSDEs since 1990 are only a small proportion of longer-term declines across the globe. In the USA, one of the few places with good long-term data, death rates from dysentery, typhoid, paratyphoid, other gastrointestinal diseases, and malaria – all water-related diseases and therefore, almost by definition, climate-sensitive declined 99–100% between 1900 and 1970.

To summarize, we are solving our problems with CSDEs faster than we are solving our other health problems.

Read the full paper, The Lancet Countdown on Climate Change: The need for context, published by the Global Warming Policy Foundation, here.