Is Climate Change the World’s Most Important Problem? Part 2

Despite using the World Health Organization’s scientifically suspect estimates of the present‐​day death toll “attributable” to climate change, we saw in Part 1 that climate change contributed less than 0.3% of the global death toll. At least 12 other factors related to food, nutrition and the environment contribute more. 


Here I’ll examine whether climate change is likely to be the most important global public health problem if not today, at least in the foreseeable future. 


Once again I’ll rely on analyses done by scientists who are not part of the community of skeptics. Specifically, I’ll 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 Chairman of the IPCC WG 2, responsible for the section of the IPCC report dealing with impacts, vulnerability and adaptation. 


I’ll adopt the FTAs’ estimates for the sake of argument, despite some flaws in their analyses, noted here. 


I’ll also consider “the foreseeable future” to extend to 2085 since the FTAs’ estimates 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.” [Yes, that’s the same Stern that did a climate change analysis extending to 2200, or was it 2300? No matter.] 


In the following figure, using mortality statistics from the WHO, I have converted into annual mortality the FTAs’ estimates for the population at risk (PAR) for hunger, malaria (which is responsible for an estimated 75% of the global burden of disease due to the main vector‐​borne diseases), and coastal flooding. 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 numbers below each 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, the original source was reticent to explicitly point out that climate change might reduce the net population at risk for water stress. See 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’ll 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 from the public health point of view.