On behalf of Anthony Oliver-Smith:
As someone working in the field of disaster research for over 4 decades, I read this blog with interest. Ehrlich is almost always interesting, even though I think this argument is flawed. Of course disasters are not natural, but not because of population numbers or density. Vulnerability to hazard impact is not a function of population, but of the way a population is organized in terms of access to power and wealth that benefits some with environmental security and exposes others to extreme risk. Arguing only on the basis of number and density of population leaves out the role of power and wealth as well as the adaptive capacity of human beings. Population numbers do not construct or constitute vulnerability; society does. Society, not population, takes the naturalness out of “natural disasters.” That his analysis may ring somewhat true today is because of current political economic conditions in the world and so it may have some descriptive traction rather than being analytically correct.

-Anthony Oliver-Smith

On behalf of William Lidicker:

Paul Erhlich’s blog appropriately puts “natural disasters” in the context of population size. Toward the end of his essay he mentions the terms “density dependence” and “density independence” that are still widely used in population ecology. These terms are loaded with ambiguities, and since the 1970’s I have been trying to get these terms rejected and replaced with the clearly descriptive terms: regulating, anti-regulating, and non-regulating. Although there has been some progress, the classic terms remain entrenched.
Paul’s example of the term “density independence” as analyzed by Andrewartha and Birch can serve as an example. He posits that this term can mean that an environmental factor can have “the same power regardless of the size of the population.” He gives as a hypothetical example severe cold weather mortality and the proportion of cold-sensitive individuals in the population. Other possible examples are floods, lava flows the drying up of ponds, and habitat destruction. So this interpretation is possible, but as he points out generally such influences, while not changing themselves in response to changes in some target population, actually have an impact on the subject population that is very much related to its size. So, the first ambiguity is: does density independence mean that the factor itself is uninfluenced by changes in the population, or is it that the impact (power) of the factor does not vary with population density. The same ambiguity applies to so-called “density dependent factors.” A second ambiguity is whether or not the influence (density independent or dependent) has a positive or negative effect on population growth; both are common. Thirdly, even when a factor’s impact does change with density, is this change merely numerical (absolute) or is it proportional, that is, the change is per capita? This last consideration is vital if we are at all concerned with the extent to which environmental influences can actually stimulate or inhibit population growth. If such factors can cause or contribute to causing a population to stop growing as it gets larger and to encourage growth as it gets smaller, this is regulation. Factors which influence growth in the opposite direction are anti-regulating, and those whose impacts are trivial and/or not related to density are non-regulating.
Paul exhorts us to not be fooled by terms like “natural disasters.” To this good advice I would like to add that we not be fooled by ambiguous terms like “density dependent “ and “density independent.”

-William Lidicker

On behalf of William Lidicker:

Anthony Oliver-Smith’s comments on the essay by Ehrlich, dated Dec. 5, are correct in pointing out that human populations will vary in their experiences and vulnerabilities to major disasters. Contributing to this variation are political structures, access to power and wealth, and the “adaptive capacity of human beings.” To this we can add the geographic setting of various human groups. While these variations are real, they are mere ripples on the larger picture of the human predicament. The essential point is that as human numbers increase, both the numbers of serious disasters and the negative impact of those occurrences will increase. Moreover, these increases will be not just incremental but proportional, that is, on a per capita basis. This is unfortunately just an unavoidable consequence of living on a finite planet with finite resources for life support. Wealth, power, ingenuity, and geography can delay and reduce these negative impacts for some of humanity. However, if we focus too much on the “ripples” we will only delay any serious attention to the realities of the “big picture” as summarized by Ehrlich.

Bill Lidicker

On behalf of William Lidicker:

Anthony Oliver-Smith’s comments on the essay by Ehrlich, dated Dec. 5, are correct in pointing out that human populations will vary in their experiences and vulnerabilities to major disasters. Contributing to this variation are political structures, access to power and wealth, and the “adaptive capacity of human beings.” To this we can add the geographic setting of various human groups. While these variations are real, they are mere ripples on the larger picture of the human predicament. The essential point is that as human numbers increase, both the numbers of serious disasters and the negative impact of those occurrences will increase. Moreover, these increases will be not just incremental but proportional, that is, on a per capita basis. This is unfortunately just an unavoidable consequence of living on a finite planet with finite resources for life support. Wealth, power, ingenuity, and geography can delay and reduce these negative impacts for some of humanity. However, if we focus too much on the “ripples” we will only delay any serious attention to the realities of the “big picture” as summarized by Ehrlich.

Bill Lidicker