KIMBALL, Neb. – I wrote a bit about nighttime sublimation last week, and in passing I mentioned daytime sublimation as well.
Sublimation is, as I described last week, a material phase transition. In that (and this) case, specifically a phase transition of water. In general, most materials in the universe as we understand it can exist in three different phases – solid, liquid, and gas. For instance, if you put a piece of cold rolled steel in your vice it’s a solid. Apply a cutting torch, however, and the hot bit melts into liquid, and if you watch carefully, some of the liquid flashes into gas. So that’s steel in three material phases.
Water is also a material. Uniquely among most materials, water can exist in all three phases at most atmospheric pressures on our planet. In part, this is due to the unique polar arrangement of the water molecule and the bonds that hold a pair of hydrogen atoms to an oxygen atom, yielding molecular water or H20.
In part because of the geometry of the water molecule, with the hydrogen atoms scrunched over on one side, and in part because of the arrangement of bond charges holding the whole thing together, water molecules are constantly gaining and losing hydrogen atoms, going from H20 (a hydroxide) to H30 (a hydronium) and back again. This characteristic allows water to change phase with less energy input than nearly any other material.
This means that sublimation is common, and water can easily go from ice phase directly to gas phase at a fairly broad range of temperature and atmospheric pressure.
The reverse is also true, which means that water vapor in the air can flash to ice without passing through the liquid phase, resulting in frost being deposited on surfaces. This process is called, unsurprisingly, deposition.
Last week, when my sheets dried on the clothesline overnight, the water they contained first froze in the low air temperature, then sublimed into water vapor as the night’s light breeze added the required energy.
Later in the morning, as I drove out to check cattle, the sun rose above the horizon and rained down even more energy. As warming sunshine added energy to the snow mass covering the ground, the icy snow also began to sublime. In only a few minutes a palpable mist was leaping from the snow into the sky as ice became water vapor. The clear air took on a hazy, milky appearance and I was suddenly surrounded by fog. This was daytime sublimation. It was breathtakingly beautiful.
Early the next morning, when overnight clouds fled the sky and the air temperature fell below freezing, water vapor in the humid air began to deposit as frost on exposed surfaces everywhere. I had to scrape my windshield clear of ice deposition, and this was water acting exactly the reverse of the night before. What a wonder.
Water is an interesting molecule. It’s also a major constituent and requirement for life on our planet.
Which means that water is critical for survival. No water means no life. So how are we doing on our planetary water supply? Are we about to run out?
Well, probably not.
There’s plenty of water on our planet. In fact, there’s far more water on Earth than life will ever need or use. When you add it all up, there’s more than three-hundred million (300,000,000) cubic miles of water on Earth. That’s such a fantastically huge volume that it’s pretty hard to put in context. Placed one cubic mile atop the next, if such a thing were possible, Earth’s water would reach all the way from your front yard to the orbit of Jupiter.
Even more amazing, at least in some sense, is that so very little of that enormous mass of water is available to terrestrial life. Most of the Earth’s water, about 97 percent of the total, resides in the oceans. Another two percent is frozen in ice caps and glaciers. The remaining one percent makes up essentially all the water available to the planet’s land areas. All the water in aquifers, lakes, rivers and streams, rainfall, and soil moisture come from that final one percent. It’s all part of the hydrologic or
That one percent is always in motion. There’s no beginning or end of the cycle, just water constantly moving from one place to another. In simple terms, water is evaporated from one place, is carried through the atmosphere in clouds, then falls to the surface as rain, where it collects or flows until it is evaporated again.
There’s more to the story of course, as we should all recall from elementary school. The water cycle is complex, and you can really drill down into a lot of detail, but complexity and detail do not equate to ‘hard to understand.’ The basic concepts are simple and beautiful. Keeping those concepts in mind can help us all navigate the increasingly sensationalized and disingenuous narrative surrounding the science of our environment. At some point, rational people are going to have to take the present narrative to task, before we squander more precious time and treasure on slick Ponzi schemes.
The more we know and understand, the more effective we can be in defending ourselves. Learning and knowledge is the path to take. Maybe it’s time to shift gears, turn away from being a know-it-all, and become a learn-it-all.