The Albatross

Literature embellishes the albatross with near-spiritual endowments. These magnificent wanderers fly near-effortlessly. For example, they completely circumnavigate Earth’s southern polar region without once touching land. Obviously, they must be energy efficient. Using some simple assumptions, we calculate that their lifetime energy consumption is about 3.3e+10Joules per bird. This is a great example of how energy flows through the ecosystem and sustainably supports life on Earth.

We can calculate lifetime energy consumption for people as well. Using assumptions that are similar to those for the albatross, we calculate that a typical, busy human would consume 40e+10Joules in a lifetime. But this is solely our biological energy consumption. Humans have learned to access and utilize energy stored in other forms. Adding these, the total consumption of energy for the lifetime of a person in Switzerland (a randomly chosen reference) becomes 1000e+10 Joules. Or, over a lifetime, a person consumes over 300 times the amount of energy than an albatross.

Let’s take a ‘bigger picture’ view of these calculations. The albatross has found an ecological niche that may enable it to survive for a very long time into the future if its sources of energy, the squid and fish, remain. Humans also have taken an ecological niche. But we are expanding into just about every other niche. “How so?” you ask. Well, we’ve subjected a half of Earth’s arable lands to agriculture. We’ve discovered and utilized many of Earth’s (finite) stores of energy. And our population continues to expand. The number of albatross decreases. Is this sustainable for a long time into the future?
Wangering albatross
By JJ Harrison ( – Own work, CC BY-SA 3.0


Will they fit? How many can you put into one space? These are questions of density. Sometimes the answer is easy to measure such as with determining the number of glass marbles that can fit within a box. Or, we can predict population densities over time with the Lotka Volterra predator-prey model. In all density calculations, it is a defined space that is key to the calculation.

Let’s set the space as the land surface of Earth and the question is, “How many people will fit?” For the record, some believe that at one time there were less than a hundred thousand hominin living on the surface. These easily fit and the density barely registers. Yet we predict the population this century to crest at over 10 billion humans. The resulting density is 83 people per square kilometre. It rises to 117 people per square kilometre when we locate people only on viable land cover, i.e. excluding deserts and such. This will be the average global density.

For comparison, at the end of the last glacial period about 12,000 years ago when humans lived as primitive hunter-gatherers, the estimated population was 2 million or about 0.02 people per square kilometre. Contrarily, in the city of Manila today, there’s a local density of 46,178 people per square kilometre. This increased density speaks to our prolificacy.

Density is important as it relates to the amount of resources humans consume. For instance, to maintain current density, we use a third of all Earth’s land surface for agriculture so as to produce food. What do you expect of the future as the human population continues to increase while the land surface remains constant? How can we use local density values to predict sustainability and future survival?