The Sunlight Budget of Earth

Summary

By Sam ClamonsEditor’s Note: This article contains numerical estimates compiled from various research articles. It was reviewed by three climate experts: Casey Handmer, Paul Reginato, and Jonathan Burbaum. Their notes are recorded in the footnotes. Our full dataset and calculations are available for download. We hope this will be a useful starting point for much deeper discussions.Modern biotechnology is powered by sunlight. Light-gobbling algae, both natural and engineered, are harvested and squeezed for biofuels or dried and pressed to make shoes. We use sugarcane and sugar beets — essentially autonomous, self-replicating, solar-powered biofactories — to mass-produce sugar. That sugar, along with hydrolyzed yeast, form the basic media used to grow genetically engineered E. coli, yeast, and other microbes that make various medicines and foods. At some point in the supply chain, nearly every bioengineered product either is a solar-powered plant or derives its energy from one.Sunlight is an exquisite energy source. It’s abundant, renewable, and cheap to access. Its consumption produces no greenhouse gasses or toxic byproducts. However, “renewable and abundant” is not the same as “infinitely abundant.” Wildlife, agriculture, and solar electricity generation all use sunlight, too. In principle, all of these processes compete for photons. A joule absorbed to synthesize plastic precursors in an algae can’t also be used to feed a tree or charge a cell phone.Fortunately, there is a lot of sunlight to go around. While humanity might be forced to make trade-offs between wild plant life and food for humans in the future, it won’t be because we run out of sunlight.To get a sense of where sunlight goes, we can compare the sunlight inputs to our most sunlight-intensive industries — solar power and agriculture — to the sunlight used by wild organisms, while also accounting for the photons that do nothing but heat the ground or bounce right back into space. These numbers are impor...