Ayers blog chapter 3

John C. Ayers

Steffen W., Richardson K., Rockström J., Cornell S. E., Fetzer I., Bennett E. M., Biggs R., Carpenter S. R., de Vries W., de Wit C. A., Folke C., Gerten D., Heinke J., Mace G. M., Persson L. M., Ramanathan V., Reyers B. and Sörlin S. (2015) Planetary boundaries: Guiding human development on a changing planet. Science (80-. ). 347. Available at: http://www.sciencemag.org/content/347/6223/1259855.abstract.

1. I was familiar with the "planetary boundaries" concept since the first paper by Rockstrom et al. appeared in 2009 in Nature.
2. I now have a better understanding of how the boundaries are defined. Figure 2 shows that, according to the precautionary principle, the "safe limit" is placed at the upper end of the "safe operating space", before the zone of uncertainty is reached. In the figure the control variable is a process controlled by anthropogenic activity that we assign a threshold level to and that affects the response variable of the earth system. For example, the control variable phosphorous loading can cause the system response eutrophication.
3. The paper defines the important environmental measures we need to monitor, both globally and locally, and shows how rapid anthropogenic changes have pushed some of them past safe limits (book chpt. 3). It also discusses risk and resilience (book chpt. 4).
4. The planetary boundaries concept has become very influential because it assigns quantitative values to global planetary limits that can be used for policy-making, and it presents the information in a form that has impact yet is easy to understand (Fig. 3). This paper advances the planetary boundaries concept by better defining some limits and by extending it to the local scale, as illustrated by the maps in Fig. 2.