Albedo is a measure of surface reflectivity. It is the ratio of sunlight reflected by a surface to the amount absorbed.1 Freshly fallen snow, ice, clouds, and deserts are highly reflective surfaces with a high albedo; wine-dark seas, forests, and swamps have a low albedo. Drawn from the Latin term for “whiteness,” Joseph Heinreich Lambert’s concept of albedo has traveled beyond the eighteenth-century measurement of light in optics to the discovery of worlds and world-making in astronomy and planetary sciences.2
Albedo makes distant worlds visible. It allows astronomers to pick out bright objects from the night sky, from exoplanets to comets. Albedo also brings into focus the power of reflectivity to produce worlds. Consider “Daisyworld,” a thought experiment to demonstrate the power of plant life and albedo.3 Cover a computer-simulated Earth surface with white daisies and the temperature drops; seed model Earth with black daisies and the temperature warms. The Earth, in other words, is highly sensitive to changes in albedo.
Albedo’s world-building potential and promise of alternate worlds lend the concept to speculative applications. Speculation joins the optical origins of albedo with the etymology of “speculate”—from the Latin specere “to look at, view,” and specula or “lookout point,” “contemplation, observation”4—into a creative practice of imagining. Borrowing from speculative fiction, albedo as a speculative concept invites people to envision how things could be otherwise: What if the planet did not look like the one we know today? What difference would this make for life and living today?
Harnessing these speculative possibilities, technologists have mobilized albedo as an analytic lens and practical instrument to shift Earth into the state they want—not only inside computers but also in the world where we eat, sleep, live, and die. By ordering the face of the Earth into brighter and darker surfaces, albedo renders up new objects of intervention that can be managed and worked on, from clouds and sea ice, to building rooftops and crop cover.5 Through albedo technologists see global warming as a “solar radiation management” problem. Solutions include injecting sulfate aerosols into the stratosphere to reflect sunlight, aerosolizing seawater to seed more reflective marine clouds, and/or brightening the surface of sea ice with hollow glass microspheres. According to its proponents, such schemes would “buy time” to transition to a zero-carbon world or, even, “restore” Earth to a nostalgic climate of the early twentieth century.6
Uncertainties, however, lurk at the edges of a techno-scientific field of view. Fundamental uncertainties about the planet’s response animate concerns about the social, political, and ethical effects of albedo modification.7 Even if albedo modification cools the face of the planet as a whole, what new climatic features will emerge from recontoured storm tracks to altered cloudiness? Such uncertainties draw attention to the limits of humans’ abilities to foresee things and push thinking beyond scientific calculations into speculative territory. In this endeavor, albedo can help expand one’s imaginative horizons beyond human reference frames. In particular, albedo shows how nonhumans can author alternative worlds of their own, suggesting that speculative world-building is not limited to technologists or humans alone.8
Take Snowball Earth, which scientists hypothesize occurred between 750 and 580 million years ago.9 Unlike the Ice Ages, which involved the expansion of land ice and was bounded by continents, Snowball Earth includes the spread of land and sea ice to encompass the globe. The secret to global glaciation, scientists suspect, lies in planetary albedo; namely, the existence of an ancient supercontinent near the equator that received the most sunlight.10 More reflective than the ocean, this supercontinent and its breakup lowered temperatures, which favored ice formation on land and sea, whose high albedo reflected away yet more light, which further lowered temperatures and unleashed the proliferation of fantastic icy formations. Sea glaciers—or sea ice thickened over millennia to several hundred meters deep by snow from above and freezing water from below—moved under their own weight from the poles to the equator. Life, if it existed, was radically different from today’s.
Albedo shows how the planet can produce other worlds, too. The planet, of course, does not need albedo as a metric to produce one world or another. Albedo is a concept that allows humans to see from a nonhuman perspective. It directs attention to the creativity of nonhumans,11 whose activities are not fully determined by scientific knowledge and, importantly, not resolvable through more accurate representations. Albedo challenges people to expand their imaginative horizons and, insofar as it can produce worlds otherwise, albedo suggests that planets have the capacity to speculate, too. As a speculative concept albedo would be not just a fraction of reflected sunlight, or a climate engineering tool, but a practice that formally acknowledges and includes more-than-human entities as authors in a collective effort at world-building. One that, furthermore, decenters and enlarges human ways of seeing, knowing, and envisioning worlds to come.
Acknowledgments
Thank you to the Living Lexicon editors and two anonymous reviewers for their helpful feedback. I would also like to thank Darcie DeAngelo, Jonathan Wald, Fiona Gedeon Achi, and Adam Fleischmann for helping to grow this piece.
Notes
Studies suggest there were multiple global glaciations. Hoffman and Schrag, “Snowball Earth.”
