Shaping Tomorrow's World

By Stephan Lewandowsky
Professor, School of Experimental Psychology and Cabot Institute, University of Bristol
Posted on 6 April 2011
Filed under Integrated Sustainability, Population

Our planet is finite. We have 510,072,000 km2 of surface area to sustain all human economic and social activity.  We have 510,072,000 km2 to support all of life. Nothing will change this physical limit. Our economy is based on growth. A fundamental tenet of capitalism is a continually growing economy that produces more and more goods. Indeed, per capita world economic output (GDP) has increased nearly 20-fold since 1960. During the same period, the world's population has increased from 3 billion to nearly 7 billion.

The figure below shows those two variables together: The explosive growth of wealth (in red) has outpaced the growth of population (in blue), thus permitting us to be wealthier now than our parents and grandparents ever were.

Figure 1

Figure 1

So far so good.

So where is the problem?

The problem is that a widely accepted model of population growth (e.g., Berryman, 1992), the so-called Malthus-Verhulst theory, proposes that populations do not grow indefinitely; instead, population growth typically follows a “logistic” function. This function is illustrated in the figure below, which implements the Malthus-Verhulst model (for a population of 10 animals initially across 700 time steps).

Figure 2

Note the similarity between the left-hand part of this curve (below time step 250) and the growth functions shown in the earlier figure: until such time as resources are beginning to be depleted, animal populations can enjoy increasingly fast growth, much like our economy has been enjoying near-continuous growth for the last century at least.

This gives rise to an obvious question: can we be sure that the world economy and the world population can continue to grow unabated? Do the trajectories in Figure 1 promise ever increasing wealth for ever more people? Or are we riding on the lower end of the type of trajectory shown in Figure 2, which retrospectively appears very promising at any of the first 250 time steps, but which need not hold for the future? And if our world is evolving along the path in Figure 2, how close are we to the inflection point beyond which things slowly grind to a halt?

There is evidence to suggest that we are right at or just past that inflection point, and that the world is facing multiple crises simultaneously that arise from our economic activities or expansion of human population.

Johan Rockström and colleagues recently presented an analysis in Nature (Rockström et al., 2009) that identified what they called a “safe operating space for humanity.” In a nutshell, this team of nearly 30 researchers made a first attempt at estimating boundaries for the biological and physical processes that underpin our welfare as a species. The team considered 8 global environmental parameters: (1) climate change, (2) ocean acidification, (3) stratospheric ozone depletion, (4) freshwater use, (5) biodiversity loss, (6) the nitrogen cycle, (7) the phosphorus cycle, and (8) land-use change.

Those particular parameters were chosen because they map into the principal large-scale systems that determine our global environment; namely, biogeochemical cycles (nitrogen, phosphorus, carbon, and water), the major physical circulation systems (climate, stratosphere, oceans), and biophysical features of Earth that contribute to the resilience of its self-regulatory capacity (biodiversity, land systems).

Their analyses and main conclusions are summarized in their beautiful figure, which I reproduce below:

Figure 3

Each sector in the figure represents one of the 8 indicator variables considered by Rockström and colleagues, plus two others that are highly relevant but which have escaped quantification so far (chemical pollution and aerosol loading). The safe operating space for humanity is represented by the green polygon in the center. Within each individual sector, the dotted black lines represent the measured trajectory since the 1950’s of the relevant driver variable. For example, atmospheric CO2 levels, which drive climate change, have continually increased in an outward trajectory, whereas ozone depletion has recently been reversed owing to global action on replacing CFC’s with other, more benign chemicals. The extent of the red wedge within each sector indicates the estimated current location of the underlying driver variable.

Without going into the specifics of each instance, it is clear that at least three of those crucial variables have exceeded their safe operating value—namely climate change, the rate of biodiversity loss, and the Nitrogen cycle. Given that Rockström and colleagues suggest that crossing even one of these boundaries would risk triggering abrupt or irreversible environmental change, the preceding figure does not present a reassuring pattern. To compound the problem, transgression of one boundary increases the likelihood of another one being breached—as is most readily apparent if one considers the fact that both climate change and ocean acidification are correlated consequences of increases in atmospheric CO2 levels.

Further interesting expert commentary on the article by Rockström and colleagues can be found on the Nature website. For present purposes, I accept that to a first approximation, their analysis is qualitatively correct.

Houston, we have a problem.

Except that there is no Houston that can help us with sage advice: There is only us, and it is upon us alone to rise to the enormous challenge of returning the state of the planet to its safe operating environment.

This, then, is the context for : how do we prepare for, and how do we shape, a healthy and prosperous tomorrow in a finite world?

This requires new and creative thinking at many levels. It requires analysis of physical as well as psychological variables. Most of all, it requires acceptance of the fact that “business as usual” is no longer a safe option.

We look forward to exploring all those issues with you here on


Berryman, A. A. (1992). The origins and evolution of predator-prey theory. Ecology, 74, 1530-1535.

Rockström, J., Steffen, W., Noone, K., Persson, A., Chapin, F. S., Lambin, E. F., Lenton, T. M., Scheffer, M., Folke, C., Schellnhuber, H. J., Nykvist, B., de Wit, C. A., Hughes, T., van der Leeuw, S., Rodhe, H., Sorlin, S., Snyder, P. K., Costanza, R., Svedin, U., Falkenmark, M., Karlberg, L., Corell, R. W., Fabry, V. J., Hansen, J., Walker, B., Liverman, D., Richardson, K., Crutzen, P., & Foley, J. A. (2009). A safe operating space for humanity. Nature, 461, 472-475.

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