To many, especially likely visitors of an environmental site such as this one, this page's title question may seem obvious. For those, this entry is entirely optional, it may only reaffirm already deeply held convictions, but I am fairly sure it contains some useful, possibly new, information. Others may have stumbled on this page by chance, but are convinced that there is no reason to go out of your way to achieve any environmental goals, and perhaps that if an environmental problem becomes serious enough, market forces will modify relevant costs so as to discourage people, governments and businesses from further contributing to the problem. If you fall into this category, I encourage you to continue reading, because while this view is entirely logical, there is mounting compelling evidence it does not work in reality, at least not for current environmental matters. At the same time, I can't swear you will end up convinced. Others still may be on the fence, but are open to persuasive, cogent arguments in favor of, or against, voluntary environmental impact minimization actions. If you fall into this latter category, I definitely hope you will keep on reading.

Let's start with an often invoked motivation for impact minimization efforts I find logically uncompelling: pending catastrophic environmental outcomes stemming directly from resource shortages. While well-informed, cogent versions of this argument, e.g., this, this or this, are definitely worth considering, I still find them partially persuasive at best, offering a weak model of reality. But what I mostly argue against below is less nuanced, resource scarcity literalism (see, e.g., this).

The reason that argument has not often carried the day—and I doubt it will very often in the future—is innovation; when availability of a given resource declines appreciably, but well before it becomes materially scarce, market motivated research and technical innovation are focused on improving methods of locating and extracting the resource, or in some cases into identifying abundant alternatives for hard to get resources, restoring the availability-to-demand ratio of the original resource. For example, consider this brilliant example of obviating the need for hard to get, polluting, heavy metals with, well, dirt. Or take natural gas and oil proven global reserves (shown in Figure 1 for 1980-2007); have these reserves declined in recent decades?! Not really, despite rapidly rising cumulative consumption. (But it is true that the rate of supply increase has now leveled off, and will begin declining in the not too distant future.) How is that possible?! Improved extraction technologies (for example, the deep ocean—now a major fossil energy source, as this paragraph's upper right figure makes clear, made popularly infamous by the Deepwater Horizon explosion—was all but closed for oil exploration until a couple of decades ago).

Is this behavior unique? some inexplicable, irreproducible fluke of fossil fuels? No, not really. Take, for instance, global reserves of the three industrially important metals figure 2 addresses. Over roughly four decades starting in the mid-'50s, the ratios of those reserves and their respective global demands have not really changed appreciably, and at times have actually gone up. Figure 2 does not have the telltale appearance of a pending scarcity catastrophe, even though during this time actual cumulative demand of these metals increased dramatically. Clearly, the rate at which we discover new deposits of these metals has roughly kept pace with rising demands.

Are there limitations to this view? Are some resources hitting the immovable wall of resource finality applies? To some extent there are. Take, e.g., the aspects of global agricultural production figure 3 summarizes, portraying a mixed, nuanced picture. Over the shown roughly half century, world arable land as a percent of global land area has expanded steadily, at least through 1990 (figure 3a), but only by about 10% at most. At the same time, world population (b) has more than doubled. As a result of the arable land expansion falling well short of population growth, per capita arable land area (c) declined by 45% (the 2009 value is 55% of 1961's). At the same period, however, per acre productivity of cereals and other crops (3d) has gone way up. We can derive an overall crop production index per capita, by dividing panel 3d's green curve, per acre crop productivity, by population, 3b's blue curve. This scaled index (3e)—arguably the most pertinent measure of food supply adequacy, at least in terms of average food quantity—has increased by more than 40% between 1961 and 2009.

While the significant growth in per capita crop production over the last half century is consistent with my contention that hitting the wall of actual material scarcity is rarely realized, the decline in per capita arable land is not. The apparent self-contradictory duality of the food production example showcases the current food system's main triumph, seemingly inexorably rising supply of food calories, while also implicitly emphasizing (as I demonstrate below) its equally important shortcoming, the large and rising environmental costs the supply increases have exacted. This dualism also highlights what I view as the key failing of the "hitting the scarcity wall" argument:

To appreciate the dilemma, consider the environmental costs the expanding caloric supply has exacted. While this expansion is partially attributable to agricultural land expansion (figure 3a, and see also further down), its central element is rising per acre productivity (figure 3d). In turn, the two key ingredients of rising per acre productivity are irrigation and fertilizer, both with major environmental consequences. Let's examine irrigation withdrawals first. While figure 4a shows a factor of 5 or so rise in Irrigation water withdrawal (IWW, blue), arguably more remarkable is the close tracking of global total and irrigation related consumptive withdrawals (Gwc and IWC, respectively, essentially the net water losses). What this close tracking means is that the lion's share of the rise in global water consumption is attributable to irrigation, which is of course consistent with the (logistic-like) rise in both crop- and pasturelands figure 4b shows. Note that consumptive water use comprises all water uses that directly compete with (and sometimes rob) other uses. For example, consumptive use for irrigation in California's central Valley directly competes with, and undermines, ecological integrity of Western aquatic ecosystems and species. This often amounts to a simple zero-sum choice between agriculture and other uses, such as, e.g., the choice between the water needs of farmers, Native Americans, and wild salmon in Oregon's Klamath Basin or the Columbia. So it is not running out of water—a geophysical virtual impossibility on large scales—we should be concerned with, but the rising environmental costs of exploiting ever more oversubscribed existing supplies.

Another aspect of the expanding irrigation fueling the steadily rising per acre productivity is the need for dams. When irrigation is the deciding factor (figure 4c's green dots), the dams are needed in order to regulate major river flows so as to maximize water extraction capacity when withdrawal (i.e, in many cases, primarily irrigation) needs dictate, not when the rivers naturally crest. Dams, a dominant continental scale global presence (figure 4c), raise many serious environmental issues. This is too broad a topic to address here in any meaningful way (you can read a nice review of dam hydrology here and a discussion of the benefits, as well as a few short-term pitfalls, of dam removal here), but suffice is to say that globally proliferating dams and the reservoirs upstream of them (figure 4d shows a roughly 12-fold increase in global storage capacity upstream of dams) are a key force behind human alteration of landscapes, the hydrological cycle on land, biodiversity declines, and species endangerment, among many other undesirable impacts. Again, it is not running out rivers to dam that is most concerning, but the environmental burdens existing and planned dams exert.

The second element of agriculture's rising per acre output is fertilization. In this issue too, the scope of the problem and the volume of literature documenting nitrogen fertilizer's many adverse environmental impacts far exceed the scope of this modest venue (this, this or this are nice lay-person introductions, while a classic scientific introduction is here). Below I therefore summarize briefly a few key issues. Here again, the point is that the main issue with food supply is not so much running out of land—we can easily double the number of adequately but not overly nourished people globally over a year or two timescale with significant but tractable structural changes to the food production system—but the rising environmental costs of getting more out of existing agricultural land while failing to reconsider priorities, customs, preferences and resource allocation patterns. Graphically, the problem is the logistic nature of many resource extraction histories, such as those shown in figure 4a, b or d: a rapidly (quasi-exponentially, if you want to get technical) rising phase (e.g., 1930-1975 in figure 4a or 1950-1975 in figure 4d), followed by declining rates (during which the curves gradually level off, approaching horizontal lines, e.g., after 1985 in figure 4d). This leveling off indicates that we still need more, but manage to add less and less as time goes on; that's precisely the time for innovation to kick in, to displace demand toward more available resources.

A life saver in some circumstances and a driving force behind the Green Revolution (see this or this), overuse of nitrogen fertilization comes at staggering environmental costs. To begin with, its production uses tremendous amounts of fossil fuels (both for energy and as a raw material, the latter alone accounting for 4% of global natural gas consumption), contributing about 1.2% to global greenhouse gas emissions, and to air pollution. The trick here is that the source of all N used for fertilizer is the atmosphere, which is almost 80% N. But nitrogen in the atmosphere is in the form of molecular nitrogen, N, in which the two participating atoms are bound together with a triple bond (they "share 3 electrones" Wikipedia has a nice entry on N), which is incredibly hard to break, but must be broken in order to render largely biologically inert molecular atmospheric nitrogen biologically active and available. Naturally (mostly be bacteria), about 100 million metric tons (10¹¹ kg) of inert atmospheric nitrogen is converted into biologically active forms ("fixed") per year. In recent years, at least as much—probably about 120%—nitrogen is fixed annually by industrial processes, nearly all for fertilizer production.

By far most troublesome is nitrogen fertilizer's central role in undermining water quality in rivers, ponds and lakes, and the world coastal oceans. In a nutshell, the issue is as follows. Nutrients—elements, primarily nitrogen and phosphorus, needed for basic life functions such as protein synthesis; think about nutrients as "food" plants need—in most natural, undisturbed aquatic systems (e.g., pristine ponds or lakes) are fully or nearly used up by plants (algae), so that the nutrient concentrations in the upper water column are nearly zero. Then, the system "productivity"—how much carbon in the form of atmospheric CO₂ the system transforms, or fixes, into living tissue per unit time—is maximized, and any further productivity enhancement is limited by nutrient availability. If additional nutrients are somehow introduced into the system—by fertilizer rich runoff in most cases—nutrient availability limitations on productivity are at least temporarily removed, and productivity rises. Think about wading into a warm pond in August through a thick, green slimy mat of aquatic vegetation, and you get the picture, or you can go here for breath taking photos. These events are called algal "blooms", and you can see an example below (figure 5).

In coastal oceans and estuaries the world over (see this compelling map of global distribution), algal blooms occur, on a grand scale, typically in summer. Some (e.g., in the cold coastal waters along northern California, Oregon and Washington) are perfectly natural. Many, however, are due to fertilizer rich runoff from agricultural intensive lands (the one in the northern Gulf of Mexico off the mouth of the Mississippi is particularly notorious and well-documented). Figure 6 presents some aspect of dead zone mechanism and fishery consequences.

The coastal ocean typically comprises, in a highly idealized manner, two layers (right). In the top layer (spanning the surface to a depth, highly variable in space and time, ranging from a few, to tens, or even hundreds or more meters below the surface), sea water is typically fairly warm and fresh, and thus light. Below the top layer is a thicker layer containing heavier, colder, often saltier water . Figure 6's schematic shows these two layers, separated by the thick cyan line, the so-called pycnocline (a thin layer, marked "rapid transition" in the upper right figure, in which water density increases rapidly with depth, idealized here as a single line). Because this configuration is stable (lighter water rides over denser water), the two stacked water masses exchange heat and other properties sluggishly (vertical mixing is slow). Near the surface, where in summer water is intensely heated by the sun and is thus warmer and more buoyant, there is plenty of sunlight for algal photosynthesis. Algal growth is thus so ubiquitous, using up nearly all the nutrients in the surrounding water. The importance of the pycnocline is that it prevents replenishing upper layer nutrients by deeper, nutrient rich water, because raising the lower layer's heavier water required energy. Thus under normal conditions, algae growth near the ocean surface is limited by nutrient availability. But if you add a strong flux of nutrient rich water from a river draining a large agricultural province (e.g., the Mississippi), the upper left thick arrow into the figure 6's "ocean", you lift this limitation. The result is an algal bloom near the surface, shown as the greenish upper layer. There, the water is very rich with oxygen both because of the proximity to the atmosphere and because of internally produced O₂ due to the algal photosynthesis. The blooming algae live briefly, and die quickly. Some of this dead organic matter makes its way to the bottom, where it behaves just like that head of lettuce forgotten in the back of your refrigerator; it decomposes, or decays. Organic matter decomposition—the reverse of photosynthesis—requires rather than generates oxygen. The needed O₂ is supplied by the water column, and the result is O₂ depleted water column. The oversubscribed oxygen supplies of the near bottom waters could have been replenished by downward oxygen flux from surface waters that are oxygen saturated because of their intimate contact with the overlaying atmosphere, but this flux is rendered too sluggish by the afore-mentioned stratification—near surface waters less dense, or more buoyant, than deeper, denser, waters—to suffice. This is hypoxia (low dissolved oxygen) or, if it's even more intense, anoxia; either means insufficient levels of dissolved oxygen in the water.

And marine life forms? Well, they need dissolved oxygen, without which they suffocate. Large fishes in small, mild hypoxic regions can swim away. Shellfish and other slow- or non-moving creatures of the sea, on the other hand, die, just like the crab figure 6 depicts, posthumously. Figure 6's lower left inset shows the history of effort required for Gulf of Mexico shrimping; clearly the bottom area that needs to be scoured for a fixed shrimp catch increases with passing years, with every decade's average catch per ha lower than the previous decade's average.

I hope the above synopsis' brevity doesn't obscure the scope, magnitude and seriousness of reactive nitrogen (biologically available nitrogen not locked in the largely inert N₂ molecule) impacts on aquatic environments. Given the severity of the problem, the high environmental costs of fertilization, you probably envision a global trend underway toward ever increasing fertilization efficiency, toward getting more out of less. As figure 7 makes clear, just the reverse is true, with decreasing yields per unit N applied in all continental agroecological systems. For example, in the U.S., grain mass produced per N mass applied declined from roughly 90 in 1960 to about 30 in recent years. Further, the longer a continental agroecological system has been subject to routine, widespread fertilization, the less responsive its yield is too added nitrogen, with western Europe getting the least grain, followed by the U.S., culminated by South America, whose industrial fertilization history is, on average, much shorter. Here again, the issue is not so much running out of land to feed the world, but rather the ostentatiously wasteful way we go about using available land.

As I mentioned earlier, a less impactful, yet very environmentally costly, element of rising agricultural productivity (figure 3e) is expanded agricultural land. While figure 3a quantifies the process globally, figure 8a breaks it down regionally. In the developed world (e.g., North America here; Europe—not shown—behaves similarly until 1990, but features a massive jump following the collapse of the Soviet Union), agricultural lands have either held steady or declined slightly. Conversely, in the developing world (e.g., figure 8a's uppermost three curves), agricultural land extent steadily rises. The important issue here again is the environmental costs of this rise, mostly through tropical deforestation.