Environmental Decisionmaking

Problem Set #2:

1) (4 pts) Draw a schematic stock-and-flow diagram for the amount of water in a pond. Imagine that the amount of water flowing into that point is not a function of the amount of water in the pond, but that as the amount of water increases, the amount flowing out increases as well. You don't need to include any numbers, just draw the diagram.

2) (4 pts) Think about an animal population colonizing a new island. At first, there is plenty of food available for the animals, and the population explodes, but eventually they fill the island. Draw a very rough plot of what you expect to happen to population in time on this island, beginning with the time of initial colonization. How would you represent this in a stock-and-flow type diagram?

You might expect something like this:

where the population rises, runs out of food, and then crashes, but you also might draw something that levels off near the carrying capacity, or something that oscillates somewhere below it. Those are actually kind of difficult to get to work in a model, although they are probably more common in the real world. We'll try to figure out why in class, perhaps.

I'd draw a diagram something like this:

3) (6 pts) Lester Brown is far out of the mainstream in the food-supply debate. Most experts believe that genetic engineering and other technological advances will continue to improve the food situation of the world's hungry. Brown's argument, that it is hard to think of a way that we can meet this growing problem, was made in the 70s and turned out to drastically underestimate the human capacity for innovation. And yet, Brown's arguments are compelling. Discuss Brown's "mental model" in relation to more traditional mental models. What can policymakers use to base decisions on in cases like this?

Brown's "mental model" assumes that dramatically new innovations don't just come out of the blue, and that we have to work to produce them. Moreover, sometimes they don't come at all. As it turns out, sometimes they do just come out of the blue, and we have been fairly fortunate this way in the past. The question is, will we continue to be fortunate? How you answer this depends a little on how much you trust markets and innate human ingenuity. Regarding what policymakers can use to base decisions on, I am making the argument here that you can't entirely trust scientists, because they are trained to only believe what they can understand (i.e. if we can't see how we will cure hunger, it isn't going to happen), but at the same time it is naive to have complete faith in continuing miracles. You might want to talk about ideas like the Precautionary Principle (Google it if you don't know what it is), or other ways of making decisions in the face of great uncertainty.

4) (4 pts) What is the basis of the "Population Surprise" (Singer article)? What is it about the mental models that people used that kept people from thinking about the possibility of "depopulation"? Is depopulation something that should be on our minds at this time?

People have generally thought of birth rates and death rates in terms of "above replacement" or "not above replacement". They thus have tended to imagine, in a careless way, that there is a link between birth rates and death rates, or that "replacement" represents some zero state for birth rates. Of course, it doesn't, and there is no reason why birth rates should suddenly stop falling once they reach the magical line of 2.1 births per woman.

Personally, I would like to have a less-full world, and would be happy to support a lot of old people in order to get it! But this isn't a very thoughtful answer. I would say that the point of global depopulation is fairly far in the future, and assumes the continuation of a lot of trends which may or may not actually continue. Falling birth rates have taken a lot of work, and there is no reason to assume that they will continue to fall if we don't continue that work. At this point, it seems to me that the danger and immediacy of continued population growth are greater than those Singer points out for population decline. It seems like a bridge we can cross when we get there. You don't have to agree with me, but that's how I'd answer the question.

5) (2 pts) Gallopin and Raskin present what they consider to be possible future outcomes, with the hope of informing public debate. Does this exercise differ from numerical modeling in a fundamental way (if so, why, if not, why not)?

We talked about this in class. I would say that it doesn't differ in a fundamental way, as even numerical models are just ways of testing where our assumptions lead. One advantage of numerical models is that sometimes they show us that our assumptions lead to a different place than we thought they did, and so we learn something in the process, but this only happens if we think about our results carefully. Anyway, you can answer this how you like, as always.