Discovering an Improved Metric to Assess Human Ecological Footprints: Evaluating the Price of Sunlight

This planet of 8 billion people is bumping into its ecological limits, and researchers are trying to determine the impact of human activity on these limited resources. Some keep records of how much carbon they contribute to the atmosphere, others measure direct and indirect water consumption or keep tabs on how much land our eating habits require.

Each of these “footprints” provides an estimate of the impacts of individuals and institutions on the wider world, and is useful—but flawed, according to geographer Chris Lant, of the Queenie School of Natural Resources, because most footprint metrics only refer to a piece of the whole. Lant and a team of researchers are working on improving a better way to measure the whole system In a recently published research.

Just calculating the disembodied footprint of one aspect of an interlocking system, Lant said, provides an incomplete picture of the cost of any one product.

Think of a taco you might have for lunch today—determining the carbon footprint of a quarter cup of shredded cheddar jack and three ounces of ground beef could explain the methane produced by meat- and milk-producing animals, as well as the fuel consumed by the semi-truck on the trip from Texas or Idaho.

But it won’t take into account the water used to feed the animal or indicate whether the food was produced in fragile bush steppes or resilient grasslands, or calculate the energy cost for the light bulbs, heating and dish water at the restaurant where you bought it, or for the landfill where the wrapper ends up. .

The human food, energy and water system is sinisterly interconnected, Lant said, but most of the links in the network are neither global nor local—the action lies in the daily trade between provinces and nations that depend on each other’s ecosystems.

To get a better picture of human influences in this system, you need a measurement starting at the source — the Sun. An emerging measure, called Human Allocation of Net Primary Production (HANNP), promises to be a more comprehensive way to accurately estimate the effects of human actions on Earth systems, according to Lant and co-authors.

The calculation begins by counting the total biomass that a plot of land can produce in a given period of time, called net primary production (NPP). Through satellite images, researchers can determine how much plant matter is produced through photosynthesis, which provides a bird’s eye estimate of the total plant (and eventually animal) growth that a piece of land contributes to the world. Tall forests or wetlands have a high NPP. Nebraska grasslands or crop fields have an average NPP, while the arid red rock landscapes of southern Utah have a low NPP.

Humans already claim that a significant portion of the total biomass of plants is produced by the sun. The HANPP scale compares total biomass to what humans have appropriated for their own use—corn, soybeans, alfalfa, wood, onions, cotton, pasture plants, apples, coffee, rice, paper products, peanut butter, sugar, quinoa, and more that humans claim from the diet, livestock feed, fiber, and biofuels. (In the US, the lowest of these four categories is direct food at 16%).

People tend to be very good at keeping records of crop yields and agricultural productivity – so although the HANPP calculation is data intensive, it is more of a theoretical calculation. It also has significant advantages over other environmental impacts.

“HANPP is measured in relation to environmental capacity, not just land area,” said Lant. “So it’s easy to see that a square mile of the Gobi Desert is not equivalent to a square mile of the Brazilian rainforest. Also, almost all of the water we consume and the nutrients we use are used to grow the things we harvest. HANPP represents many of the links in the system, particularly between consuming cities and producing commodities in rural lands.”

Cities depend on rural areas for everything from blueberries to biofuels. This link is not always evident in ecological footprint measures. In effect, Lant said, rural lands export water, nutrients and energy to keep cities running. HANPP demonstrates the power of this connection through the line of production and consumption—supply chains—and documents how cities displace environmental impacts to land beyond their borders.

The scale also allows researchers to see how much total NPP humans leave behind for natural systems to function, such as supporting biodiversity, Lant said. In some very intensively harvested places, this number can be close to zero.

“Photosynthesis on the planet produces 55-60 billion tons of carbon each year… That’s a hard total to comprehend, but when human use goes up to half of that total, nature starts to disappear,” said Lant.

Lant said the new research pushes the HANPP scale forward and refines it. The team determined how to calculate HANPP down to the 30-meter level, tracking trends on how biomass is produced and what it is used for, he said.