Part II: Where does global warming rank among future risks to public health?
Guest essay by Indur M. Goklany
In Part 1, we saw that at present climate change is responsible for less than 0.3% of the global death toll. At least 12 other factors related to food, nutrition and the environment contribute more. All this, despite using the World Health Organization’s scientifically suspect estimates of the present-day death toll “attributable” to climate change,
Here I will examine whether climate change is likely to be the most important global public health problem if not today, at least in the foreseeable future.
This examination draws upon results generated by researchers who are prominent contributors to the IPCC consensus view of climate change. I do this despite the tendency of their analyses to overstate the net negative impacts of climate change as detailed, for instance, here, here and here.
Specifically, I will use estimates of the global impacts of climate change from the British-government sponsored “Fast Track Assessments” (FTAs) which have been published in the peer reviewed literature. Significantly, they share many authors with the IPCC’s latest assessment. For example, the lead author of the FTA’s study on agricultural and hunger impacts is Professor Martin Parry, the Co-Chairman of the IPCC Work Group 2 during the preparation of the IPCC’s latest (2007) assessment. This Work Group was responsible for the volume of the IPCC report that deals with impacts, vulnerability and adaptation.
I will consider “the foreseeable future” to extend to 2085 since the FTAs purport to provide estimates for that date, despite reservations. In fact, a paper commissioned for the Stern Review (p.74) noted that “changes in socioeconomic systems cannot be projected semi-realistically for more than 5-10 years at a time.” [Despite this caution, Stern’s climate change analysis extended to at least 2200.]
In the following figure, using mortality statistics from the WHO, I have converted the FTAs’ estimates of the populations at risk for hunger, malaria, and coastal flooding into annual mortality. Details of the methodology are provided here.
In this figure, the left-most bar shows cumulative global mortality for the three risk categories in 1990 (the baseline year used in the FTAs). The four “stacked” bars on the right provide mortality estimates projected for 2085 for each of the four main IPCC scenarios. These scenarios are arranged from the warmest on the left (for the so-called A1FI scenario which is projected to increase the average global temperature by 4.0°C as indicated by the number below the stacked bar) to the coolest on the right (for the B1 scenario; projected temperature increase of 2.1°C). Each stacked bar gives estimates of the additional global mortality due to climate change on the top, and that due to other non-climate change-related factors on the bottom. The entire bar gives the total global mortality estimate.
To keep the figure simple, I only show estimates for the maximum (upper bound) estimates of the mortality due to climate change for the three risk factors under consideration.
This figure shows that climate change’s maximum estimated contribution to mortality from hunger, malaria and coastal flooding in 2085 will vary from 4%-10%, depending on the scenario.
In the next figure I show the global population at risk (PAR) of water stress for the base year (1990) and 2085 for the four scenarios.
A population is deemed to be at risk if available water supplies fall below 1,000 cubic meters per capita per year.
For 2085, two bars are shown for each scenario. The left bar shows the net change in the population at risk due to climate change alone, while the right bar shows the total population at risk after accounting for both climate change and non-climate-change related factors. The vertical lines, where they exist, indicate the “spread” in projections of the additional PAR due to climate change.
This figure shows that climate change reduces the population at risk of water stress! This is because global warming will decrease rainfall in some areas but serendipitously increase it in other, but more populated, areas.
The figure also suggests that the warmest scenario would result in the greatest reduction in net population at risk.
[Remarkably, both the IPCC’s Summary for Policy Makers and the original source were reticent to explicitly point out that climate change might reduce the net population at risk for water stress. See here and here (pages 12-14 or 1034-1036).]. Thus, through the foreseeable future (very optimistically 2085), other factors will continue to outweigh climate change with respect to human welfare as characterized by (a) mortality for hunger, malaria and coastal flooding, and (b) population at risk for waters stress.
In the next post in this series, I will look at a couple of ecological indicators to determine whether climate change may over the “foreseeable future” be the most important problem from the ecological perspective, if not, as we saw here, from the public health perspective.