Thinking about Planetary Constraits

Sachs (2015) writes about the work of Rockstrom et al (2009), which identifies several major areas of constraints to economic and demographic development, described as "planetary boundaries."  One major strategy for working within those constraints is to voluntarily reduce human fertility rates.  Included below is the UN Population Prospects (2015) chart for projected US population growth.  The US forecast predicts the addition of 100 million people by 2100 (using the medium variant).  The next chart shows the decline in US fertility rates, and the estimated convergence of global rates to levels near those of the US.  So, for the US, few changes are expected for fertility rates in the coming century.  Solutions to our constrains will need to come from elsewhere.

One major planetary constraint of concern is the use of fertilizers in industrial agriculture.  Current global nitrogen use is creating irreversible changes to marine ecosystems.  According to the FAO, the US used 67 tonnes of nutrients per Ha, on average, between 2002-2012.  In the future, additional yields need to be obtained with lower nitrogen and phosphorous use, to protect freshwater supplies, as well as freshwater and ocean ecosystem health.

However, for the US, the most urgent constraint that we need to address is the reduction in greenhouse gas emissions into earth's atmosphere.  This will require a complete transformation of our current energy fuel sources, by converting from fossil fuel use to renewable use.  In 2012, the US emitted 16.2 tonnes of carbon dioxide per person (see last chart, source: gapminder.org).  This trend must be reversed for continued survival of the current systems that humans have developed for life on our planet.