An Invitation to Nature Engineering

The Earth, floating in space, is a star shining with blue and green between white clouds. The white clouds and the blue glow are the colors of the sky and water, forming the beautiful spatial environment of our planet. Upon it shines the green of life, which begins with photosynthesis. And all this brilliance is brought by sunlight. I believe that cherishing these three primary colors of light—“blue” (atmosphere and water), “green” (soil and life), and “red” (the sun)—is what it means to be in harmony with the natural environment.

Science and technology have provided comfortable artificial spaces for many people. Today, however, humanity's greatest challenge is the conservation of the natural environment on a global scale. I wish that science and technology were what I call “Nature Engineering ^* ,” learning from the natural sciences. Instead, it has come to devour fossil fuel resources, destroying the balance of the natural environment and causing significant impacts on ecosystems. To ensure the sustainability of humanity, I believe we need the wisdom to live in harmony with the natural environment. I do not think I am alone in wanting to learn from “the dignified traditional culture of Japan, built on the wisdom of living with nature,” as represented by Japanese dwellings with their ideas of tsuboniwa (small courtyard gardens) and shakkei (borrowed scenery) that incorporate the surrounding nature.

The sun showers the Earth with energy equivalent to about 7,000 times the total energy consumption of humanity. It would be disastrous if all this energy became heat that warmed the atmosphere. Plant leaves, even those of weeds, do not get hot when exposed to sunlight due to transpiration, and they also create shade, preventing the ground surface from warming up. Furthermore, photosynthesis uses sunlight, soil, and water to convert atmospheric carbon dioxide into nutrients. These nutrients become the energy source for all life, simultaneously reducing carbon dioxide in the atmosphere.

In other words, cutting down plants raises surface temperatures, reduces the water cycle into the atmosphere through transpiration, and increases atmospheric carbon dioxide. We can feel that forests are several degrees cooler than their surroundings. On a clear day, a single tree several meters tall transpires tens of kilograms of cool water into the atmosphere in a day. Transpiration returns water that has fallen on land directly to the atmosphere without going through the sea. This water cycle between land and sky also works to reduce the total volume of seawater, preventing sea-level rise. A rough calculation shows that the annual 1.7 mm sea-level rise, said to be an effect of global warming, corresponds to about 0.5% of the annual precipitation on land. It is quite plausible that forests have been cleared to that extent.

Now, I have tried to artificially replicate transpiration using porous ceramics. As shown in the figure, a porous ceramic piece dipped in a cup of water wicks up the water and remains constantly moist. It then naturally cools down by transpiring from the surface that is in contact with the air ^*** . This is the same as plant transpiration.

The water vapor that transpires from the ceramics is cooler than the surrounding air, so it continuously draws heat from its warmer surroundings. Because water vapor is lighter than the components of air, such as oxygen and nitrogen, it creates an updraft. When you climb a mountain, the atmospheric pressure drops and it gets cooler. Similarly, the water vapor in the updraft also cools as it expands due to lower pressure, drawing heat from its surroundings and absorbing thermal radiation as it rises. Only when it reaches a very low temperature high in the atmosphere (for example, about −50°C at an altitude of 10,000 m) does it release its latent heat ^**** to the atmosphere, solidifying (condensing) to become white clouds.

Look up at the sky. Clouds are found in such places (from near the ground to 13,000 m). White clouds reflect sunlight, reducing the amount of light that reaches the Earth's surface. Then, they cool the surface as cold rain or snow. The water cycle between land and sky lowers surface temperatures in both its upward and downward phases, and it also prevents sea-level rise.

Only by compensating for the lack of progress in reducing carbon dioxide emissions with global-scale transpiration, and by striving to harmonize the Earth's “blue,” “green,” and “red”—that is, the water, carbon, and energy cycles—with the original natural environment, can humanity live in peace and safety. I would like to call the wisdom of cherishing these three primary colors “Nature Engineering.”

Let us maintain a healthy global cycle of water and carbon, overcome global environmental problems by building an energy-environment system that utilizes solar energy, and realize a happy life.

^* The term “Nature Engineering” is a neologism. The content of this text is an introduction to the author's interpretation of natural environmental phenomena and his ideas on harmonizing with the natural environment, aiming for an engineering that can coexist with it (such as the development of solar panels that do not get hot and transpiration-based heat exhaust systems).

^** The cup design is based on a catalog photo from the website of Ryohin Keikaku Co., Ltd. (viewed August 7, 2016).

^*** On the ceramic surface, the temperature is determined by the balance between the amount of water entering from the air and the amount leaving through transpiration. When the relative humidity is 100%, the inflow and outflow of water are equal, the energy exchange is balanced, and the ceramics remain at the same temperature. When the humidity is low, more water leaves the ceramics, and energy (latent heat of vaporization) is taken away, making the ceramics cool. It is worth noting that this latent heat of vaporization is not immediately transferred to the air to warm the atmosphere. The water vapor retains it as internal energy. This latent heat is only released to the atmosphere when the water vapor that transpired from the ground becomes a cloud high in the sky and undergoes a phase change into liquid water or ice, which happens at a very low temperature. In contrast, steam from boiling at a high temperature is immediately cooled upon contact with the air, releasing a large amount of latent heat of condensation to the surrounding air, warming it, and returning to liquid water. These liquid water particles are visible as white steam. Transpired water vapor is invisible.

^**** Latent heat ( sennetsu ) is the heat required for a phase change between gas, liquid, and solid states, such as from liquid to gas or from gas to solid. In such processes, the temperature does not change even when heat is added or removed. When the temperature does change as heat is added or removed, it is called sensible heat ( kennetsu ).