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Living on the Edge


by Bill Chameides | September 28th, 2009
posted by Erica Rowell (Editor)

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Is there a limit to how much we can grow and survive?

Are there limits to how much we can grow as a society and survive?

A new paper in Nature argues there are several, and we’re already bumping against some of them.

Malthus’s Population Prediction

Starting in 1798 and extending through 1826, the Reverend Thomas Malthus published six versions of “An Essay of the Principle of Population.” His thesis: human population grows exponentially while access to resources like food grows linearly. Eventually, he argued, population growth will outstrip food production, resulting in mass starvation.

History, of course, proved Malthus wrong. With the industrial revolution and the technological innovations it brought, increasing food production and resource availability came far faster than Malthus predicted. And because of something called the “demographic transition,” we now know that populations do not grow exponentially indefinitely — witness the slow or even negative growth of populations in many developed countries.

Exit Malthus.

Club of Rome’s Limits to Growth

Enter the Club of Rome, an international think tank founded by “a small international group of professionals from the fields of diplomacy, industry, academia and civil society” first meeting in Rome in 1968 “to discuss the dilemma of prevailing short-term thinking in international affairs and, in particular, the concerns regarding unlimited resource consumption in an increasingly interdependent world.”

Shortly after its formation, the club commissioned a report by scientists from the Massachusetts Institute of Technology; the result was “The Limits to Growth” published in 1972. Sounding a Malthusian warning, the authors used a world economic model to show that exponential growth in resource utilization could not be sustained, and that society was approaching critical resource limitations, such as the availability of oil.

But How Close Are We to Resource Limits

While I don’t think anyone disputes that exponential growth is not sustainable indefinitely, there is a good deal of debate over how close we are to reaching resource limitations.

Here again, it is argued that technological innovation is key: as resources become limited (and prices rise), new technologies help meet demand by, say, allowing the extraction of previously unrecoverable resources or finding substitutes for diminishing resources (for example, the use of electricity from renewable energy to power cars previously run on gasoline).

Clearly there must ultimately be some limit to growth in a finite world; Malthus and the Club of Rome got that much right. Where they got into trouble was trying to characterize the rates at which human production and consumption rise.

Planetary Boundaries

Now comes a new variant on their thesis. In a paper in Nature, Johan Rockström of the Stockholm Resilience Centre and 28 co-authors (including climatologist James Hansen and the Nobel Prize-winning chemist Paul Crutzen) argue that there are “planetary boundaries” that for the well-being of humanity we must not cross. What makes this paper unique and intriguing is that it avoids the rates argument and focuses on the limits or boundaries to that growth.

The authors’ thesis starts with the fact that over the past 10,000 years, roughly since the last Ice Age, the Earth’s environment has been remarkably stable. Not coincidentally, they argue, this period, known as the Holocene, has seen the rise of humanity from primitive beginnings to modern civilizations where people live at an unprecedented standard of living.

But, Rockström and his colleagues contend, our very success as a species threatens to upset the Holocene’s benign conditions. Since the industrial revolution, the Holocene has given way to a new epoch, coined the “Anthropocene” by Crutzen and defined by its key feature of humans being the primary driver of change. In Crutzen’s own words:

“It seems … appropriate to emphasize the central role of mankind in geology and ecology by proposing the term ‘anthropocene’ for the current geologic epoch. …  A … date [of] the onset of the ‘anthropocene’ seems somewhat arbitrary, but we propose the latter part of the 18th century.”

In the paper, published in long form here, Rockström and company ask the question “How far can humanity push the system before the natural systems we depend upon begin to collapse?” They identify nine critical boundaries, proposing quantifications for all but the last two on this list:

From Nature Sep. 2009.

  • atmospheric carbon dioxide (CO2) and radiative forcing that cause climate change,
  • extinction rates that cause a loss of biodiversity,
  • the amount of nitrogen and phosphorus used for fertilizers that pollutes ground water and oceans,
  • stratospheric ozone depletion,
  • acidification of the ocean which stresses calcareous marine species,
  • consumption of fresh water,
  • percentage of land used for cropland,
  • loading of atmospheric particles, which cause climate change and threaten human health, and
  • chemical pollution.

The authors then attempt to use historical data and extrapolations from current impacts to estimate where these boundaries exist. They find that we have already crossed three limits:

  • atmospheric CO2 (climate change),
  • extinction rates (biodiversity), and
  • nitrogen usage (water and ocean pollution).

The boundaries for ocean acidification and phosphorus usage are close to being crossed. Land use change and freshwater usage are estimated to being about halfway to their boundaries.

The Boundaries: How Well Do We Know Them?

I find the Rockström boundary hypothesis to be intellectually appealing. We know from experience that major changes and pollution on local and even regional scales can lead to ecological collapse. Why should there not be similar consequences from global-scale perturbations?

However, as the authors themselves acknowledge, some of their boundaries are better characterized than others. Certainly we know enough about climate to conclude that we are, at the very least, very close to passing the boundary. Those scientists who hold 450 parts per million (ppm) of CO2 as being the threshold for dangerous interference in the climate would argue that we are close but not past the boundary. The authors argue that 350 ppm is the threshold and that with CO2 approaching 390 ppm we are well past the boundary.
Other boundaries such as extinction rates and use of cropland are more difficult to quantify, but by the authors’ best reckoning we have yet to cross them.

The authors acknowledge that we can never be sure exactly where the boundaries actually lie — especially when we consider that all of them are being approached at the same time. Since we have never seen a world with the set of perturbations we are imposing upon the global environment, how can we know what the reaction will be? How can we know whether either positive or negative feedbacks will make the boundaries closer or further away from where we are today? We can’t.

My own feeling is that such uncertainties should cause us to err on the side of safety. Many, I suspect, will take a similar viewpoint, but many will take the opposite. We’ve been down this road before.

What About the Human Boundary

And there is another type of boundary that needs to be considered: that established by what is needed to meet the needs of humanity — I’ll call them the “human boundaries.”

For example, the authors conclude that using nitrogen for fertilizer has crossed a planetary boundary producing dead zones in the ocean. But we must bear in mind that there’s a reason for using all that fertilizer — to feed people. Is there a minimum amount of fertilizer we MUST use to nourish our population today? Our population in 2050? Certainly there must be, and that minimum defines a human boundary we must not fall below without dire consequences.

So now we have the crux of the problem alluded to by Rockström et al. As populations grow and standards of living rise, at some point the human boundary will squeeze into the planetary boundary — leaving no space for sustainable society. Now there’s a predicament we would do well to avoid.

filed under: agriculture, carbon dioxide emissions, climate change, faculty, global warming, oceans, pollution, water
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