Science to Live By: Top Heavy


© J. Dirk Nies, Ph.D.

Have you ever wondered how much of the world’s biological productivity humans consume each year? Are we living in harmony with the energy patterns of Nature? Or are we in danger of taking too much honey from the hive, of drawing too much water from the well? To help address these questions, we will begin with an overview of the productivity and energy efficiency of the biosphere.

Spring has arrived in the Northern Hemisphere. The sun now traverses the northern side of the equator. The sleeping continental giants of North America and Eurasia are arousing from winter hibernation. The northern Atlantic and Pacific Ocean waters are stirring again with new life. As air, water and soil temperatures warm and the sun shines longer and more brightly, terrestrial and aquatic plants rev up. We are entering upon the time of year when the biological economy is most productive. Photosynthesis on land and sea is shifting into high gear.

Humans, like all other life forms that cannot make their own food, are utterly dependent upon photosynthetic plants. Plants transform carbon dioxide obtained from the air into the organic building blocks of life from which all our food is derived. Their productivity makes our life possible, providing the energy and nutrients we need to live.

Climate and nutrients determine the productivity of the various ecosystems that comprise the biosphere. Because temperature, precipitation and soil fertility differ widely across the globe, ecosystem productivities also vary widely. For a given surface area, estuaries, swamps, marshes, and tropical and temperate forests are the most productive ecosystems for transforming inorganic carbon dioxide into organic biomass. They typically change 1 to 3 percent of the energy of sunlight falling on them into chemical energy stored in new organic matter. The open ocean, deserts and tundra are among the least productive, capturing and retaining as little as one hundredth to perhaps a few tenths of a percent of available sunlight. Lakes, grasslands and agricultural lands fall in the midrange of productivity.

Oceans are vast, covering most of the surface of the Earth. Their extensive surface area compensates for their relative barrenness. In terms of total quantity, they are the most productive ecosystem. Tropical rain forests also are major producers of organic material. Together, oceans and tropical rain forest account for half of all new biomass made each year. Cultivated lands contribute only about 6 percent to total annual plant growth worldwide.

So at first glance, it might appear that humans do not consume much of the world’s new biological wealth (what ecologists call ‘net primary productivity’) created each year.

Yet, when ecologists add together the crops, wood, animals, fish and other biomass we extract from cultivated lands, grazed lands, forestry lands, and fisheries and combine that total with biological productivity losses caused by urbanization, desertification, and conversion of more productive forests to less productive cultivation and pasture, they find humans are co-opting nearly 40 percent of available terrestrial production, and about 25 percent or more of world production!

In other words, by manipulation of the landscape, we have diminished the natural biological productivity of the earth. And of what is available for consumption, we take the lion’s share. If we set the total value of food and other biomass consumed each year at 10 million dollars, one single species— Homo sapiens—takes between 2 and 3 million dollars for itself. On average, the rest of the non-plant world must fend on a meager dollar or two per species.

In the energy economy of the natural world, this level of gluttony by a single species of omnivore or carnivore is not possible. Fundamental energetic constraints on population size would have intervened. I will explain.

With each step (trophic level) up the food chain, roughly 90 percent of energy is lost as waste heat to the environment. The biomass (energy) of grass is much greater than the biomass (energy) of rabbits and other herbivores. And there are many more rabbits (herbivores) than foxes (carnivores).

Humans, like eagles and wolves, stand atop the food chain energy pyramid. The privilege of being on top comes with the constraint of being greatly restricted in number. There simply isn’t enough energy flowing up from plants through the vast, interconnected and interdependent web of life to support huge populations of omnivores or carnivores.

But unlike eagles and wolves, human population is relentlessly increasing. By a thousand percent, we have made the energy pyramid top heavy.

Scientists have investigated the total weight of large animals (more than 100 pounds) that have lived on earth at any one time during the past 100,000 years. They have discovered that the combined biomass of humans, our domesticated livestock, and large wild animals is 10 times greater now than their combined biomass before the advent of the Industrial Revolution. The manmade imbalance in the energy pyramid began slowly to emerge about 250 years ago. Since the 1950s, the disparity has skyrocketing upward.

How have we accomplished this? By dramatically augmenting natural energy flows with energy generated from fossil and nuclear fuels, hydroelectric, wind and solar power. We draw upon the equivalent of an extra planet’s worth of net primary productivity from these sources each year to support our population of  7 billion. Most humans would starve if we stopped generating energy technologically; there simply isn’t enough natural, biologically generated energy to support this many of us.

I raise this issue in light of the goal to power the world’s economy with renewable energy as expressed in the Paris Agreement negotiated during the 21st Conference of the Parties of the UN Framework Convention on Climate Change. The U.S. Energy Information Agency projects that world energy consumption will grow by 50 percent over the next 30 years. This means that the human-induced energy imbalance will worsen, even if all generated power were to come from renewable sources.

I caution my readers, especially those of you who are younger, to be less sanguine about wholeheartedly pursuing a renewable energy paradigm to power the world economy as it is presently configured. There is much more at stake than climate change. Can we handle power on a planetary scale wisely? Can we employ it in ways that cooperate with the natural world? I urge you to ponder and weigh not only the benefits but also the risks arising from our choosing to deviate so widely from Nature’s established energy patterns. It is an unrepeatable experiment; conducted within and upon the ecosystems that support us.


Please enter your comment!
Please enter your name here