We are in black and absolute cold of space, looking down on a circling plane of planets gliding silently in their orbits around the sun. We see below us, at increasing solar distance, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto. All these planets have climates. All these climates confront a common set of physical influences—distance from the sun; shape of orbit around the sun; tilt of axis; atmospheric composition and chemistry; volcanic activity; magnetism and gravity, and the shifting, rising and subsidence of planetary surfaces, which affects the release and absorption of material to their atmospheres.
Yet one of those planets stands out. That one, third from the sun, has something the others don’t—life, and as we will see, when it comes to climate that makes, well, a world of difference.
But let’s first take a quick look at what they share in common, some of the enormous physics at work and the wild range of climatic phenomenon that result, stretching the meaning of the word itself. There is Mercury, close up against the sun and racing around it in 84 days yet spinning so slowly around its axis it takes 178 Earth-days to complete a year. Yes, the days on Mercury are longer than its years. As a result, the sun facing side heats to 800o F during its 178 day-long day. But because it has virtually no atmosphere, all the heat is lost during the 178 day-long night, with temperatures dropping to 300 below zero. It’s a racing ball of extremity. Venus next door, on the other hand, with a dense, heavy atmosphere almost entirely composed of CO2, broils at a steady, lead melting 900o F.
Then there’s Earth, circling the sun in 365 days in what we see is a slightly elliptical orbit, with corresponding temperature effects. We also see the planet tilts on its axis, and if we were to follow its circular voyage around the sun, would notice how the north pole leans away on one side of the sun and leans toward the sun on the other, vice versa for the south. Thus, we perceive the dance of Earth’s seasons, winter minimums and summer maximums with spring and autumn in between. We would also notice that the planet wobbles slightly around its axis in what are called the Milankovitch cycles, resulting in periodic and predictable glaciation.
Mars, just past Earth, has a 24.6 hour revolution around its axis, making it a bit Earth like. Yet its atmosphere, despite being 98% CO2, is so thin it hardly holds a greenhouse, resulting in average temperature of -81 degrees Fahrenheit, dipping to -225 at the poles in winter. Nonetheless, it still features certain atmospheric patterns seen on Earth. For instance, like Earth, Mars has a Hadley Cell, which occurs when air above an equator heats, rises and moves poleward, dropping again at about 30o and flowing back toward the equator. For each planet the physics is the same.
Past Mars, massive Jupiter begins the series of gas giants that follow, blurring the line between planetary surface and atmosphere. With virtually no tilt to its axis, Jupiter has no seasons. Saturn, next in line, spins so fast on its axis, it’s seared by winds as fast as 500 miles per second. Technically, it has a climate, but conceptually it’s hard to imagine. Same with Uranus and Neptune, which are like giant, blue helium slushies, their massive gravitational pull holding on to abundant helium, which evaporated from Earth’s surface early, during its hot formation. Finally, there’s Pluto, which some astronomers no longer recognize as a planet. It’s so far from the sun that an observer there, looking up at high noon, would only detect only a faint dot from their dark and icy outpost.
Looking down on these nine silent orbs as they circle, spin and wobble about the sun, we observe a common cosmic architecture, how they’re all physically strung to the same sun, gliding on vast and eternal laws. A sense of equilibrium abides, atomic and timeless, anchored by the solidity of physical laws obeyed by physical bodies through time.
Yet as we’ve noted, that third one from the sun is different. It moves within the same physical laws as the others, yet its blue sky and swirling white clouds hint at a character completely its own. That character is derived of life, defining not only the planet but it’s climate.
Consider a single beam of sunlight hitting the Earth. Almost everything about its trajectory is influenced by living things and the processes between them. First, the sunbeam must make it through cloud cover, otherwise it is reflected back toward space. And that cloud cover is profoundly effected by vegetation, which not only contributes water vapor, but rain-drop nuclei, both of which assist cloud formation.
If the sunbeam makes it through the clouds, its fate then depends on whether it lands upon a living or non-living surface. If it lands on a non-living surface, such as rock or man-made surface such as concreate or bare, plowed soil (oceans and lakes are left out of this analysis for our purposes here,) it reemerges as long wave radiation, a form which greenhouse gasses such as carbon dioxide and water vapor are able to absorb, what we refer to as a greenhouse blanket. We’re busy thickening that blanket with carbon emissions, but the blanket itself is regulated by life. Without living things running a carbon cycle and a hydrosphere, we’d not have this planetary greenhouse, which was just right before we messed it up.
Should our sunbeam land on vegetation, however, most of its heat is taken up by the plant’s transpiration, a kind of sweating, not by pores in skin but by pores in leaves and needles, by which the plant cools itself and its locale. The sunbeam, having been used to evaporate water, “enters” the vapor as a latent form of heat, only to exit when the vapor condenses again as rain, only higher in the atmosphere and closer to space. In this way, living landscapes act as a heat pump, moving heat from low to high, cooling place and planet as they do so.
And we shouldn’t forget the simple drag on wind provided by trees, shrubs and grasses, what scientists call “surface roughness.” Mars, lacking such living fabric, is covered by a powdery dust, scoured from rock and occasionally blown around the planet. Here’s what it looks like in action.
Photo credit: National Air and Space Museum.
Here’s what a living climate looks like in action:
Photo credit: NICHOLAS_T, FLICKR
Do you see now why I speak of a “climate according to life?” Earth’s climate is no accident of physics, but a thing evolved, arduously, over billions of years, persisting through asteroid strikes and volcanic surges. In fact, our climate, the one we are trying to save, is a very specific climate, the seeming apex of all that evolutionary exertion. Science calls it the Holocene, meaning time of wholeness, a period of stability we are rashly tearing apart. When we speak of saving the climate, it’s really the Holocene climate we are trying to save, and the biological richness holding it up.
And yet, as I’ve written elsewhere, the IPCC, the official global assessor of climate, declares a “physical science basis,” for its assessments. What do they mean by that phrase? From this perspective, knowing that there are two branches of science, physics and biology, it seems odd. Wouldn’t a physical science basis make more sense for the other, purely physical planets, such as Mars where, according to the National Air and Space Museum, “the winds on any given day are often the same as those for the same day during the previous year? Wouldn’t a biological basis make more sense on Earth, where is there is so much living dynamism? And why not combine the two and simply call it a scientific basis, or a biophysical basis, a term being used more and more frequently?
These are complicated questions, best reserved for a future essay, where we’ll look at how the physical science basis came about in the mid 1970’s, what it meant then and what it means now, how it’s useful and how it gets in the way, and why it’s something we ultimately must look beyond if we are to see clearly the peril we’re in, as well as the astounding possibility that still surrounds us.
Meanwhile, we’ve been up here long enough. Time to head back down. As William Shatner, aka Caption Kirk, wrote after his Blue Origin trip, “there was no mystery, no majestic awe to behold . . . all I saw was death.” He had expected in space a “catharsis,” but beheld instead “cold, dark, black emptiness. It was unlike any blackness you can see or feel on Earth. It was deep, enveloping, all-encompassing. I turned back toward the light of home. I could see the curvature of Earth, the beige of the desert, the white of the clouds and the blue of the sky. It was life. Nurturing, sustaining, life.”
