Wednesday, May 15, 2013

Heat Balances

Some people may suspect our post title, Heat Balances, suggests a discussion of heavier science than they prefer. The scientific dimension of the earth’s heat balances may not seem interesting in ordinary conversation with our friends. Instead, we may speak about how cool or warm we keep our homes, or cold or hot it has been outdoors lately.

How much effort do we devote to pursuit of personal temperature comfort? What low-end to high-end temperature range would most people claim as their personal comfort level? Without bundling up in a sweater or peeling off clothing back to bare arm conditions, what is the temperature range at which you feel comfortable? When I posed this question to my wife, we agreed that a 6˚F range provides the extreme limits. Beyond this, our indoor comfort level demands either bundling up in a sweater or baring our arms. Outdoors, the range may be greater because of breezes or sunshine. Most would agree that the human body is tolerant of only a few degrees of temperature range, depending on how long we remain in a room and what our activities are.

Our personal body systems have been created with provisions for maintaining a satisfactory heat balance. Apart from the tendency of humans to add or remove clothing, our bodies have the ability to sweat when we become overheated. Animals use a variety of other strategies to maintain a comfortable heat balance. None are known to wear exterior clothing, and perspiring is practically unknown in the world of animals. Humans, in contrast, after removing outer clothing or ramping down their activity level, have only one other natural defense against overheating, apart from retreating to the comfort of human-engineered air conditioning systems. It is called perspiring. Of course, health warnings about drinking fluids and other precautions should be observed.

What is the secret success of sweating for the human? Sweating is a markedly human trait. So is putting on articles of clothing and the desire to remove them. Design and volitional use of clothing is a distinctly intelligence-enabled human trait. Perspiring appears to be a divinely authored adaptation uniquely available to humanity from the beginning. A trait called the latent heat of vaporization is responsible. Quantitatively, 540 cal/g is the heat of vaporization. For each gram of water that vaporizes, 540 calories of heat must be absorbed. An enormous amount of heat is quickly removed from our bodies. More evaporation of perspiration results in more cooling. Our body loses heat; we feel cooler. When our bodies are overheated the inability to lose heat could be hazardous or even fatal.

Taking a giant leap from everyday human comfort to the broad topic of the continual inflow and outflow of heat on our planet, we discover earth’s mechanisms for heat balance are important physical phenomena. The global balance of incoming heat from the sun and the outflowing of heat from earth back to space is of interest to physical scientists. The earth has many systems to distribute the heat it gains in a manner beneficial to life on this planet. Apart from the effects of ocean and atmosphere, earth’s heat balance would be simpler to understand. Life on earth, of course, would be impossible without water and air. Water and air are tremendous storehouses, constantly giving up, absorbing, distributing, and balancing their store of heat.

In the past few decades climatologists have become more aware of changing ocean circulation patterns which affect the global distribution of heat in the atmosphere. These patterns of circulation are termed “oscillations.” They recur periodically, bringing with them a few degrees of change in ocean temperature over large areas of our water-covered globe. Subsequently, earth’s atmosphere is warmed or cooled to some degree. In our recent post entitled “Weather-caused Humility” we discussed the effect of evaporation of liquid water into vapor and its effect on the transfer of atmospheric heat over long distances. Of course, the more obvious transfer occurs when rainfall reaches us from water vapor originating hundreds or thousands of miles away in the ocean.

Climatologists have discovered and explained the ENSO (El Nino Southern Oscillation), the PDO (Pacific Decadal Oscillation), and the AMO (Atlantic Multi-decadal Oscillation). These variations cause significant episodic changes in ocean and air temperature. Atmospheric temperature swings are due not only to contact with warmer or colder water, but also from evaporation rates resulting in warming of the air. The changes result in significant weather variations over a few years, over a few decades, or even longer. One wonders what sort of ocean oscillations triggered the megadroughts across America during the past 1000 years. What caused desert-like conditions to spread across the Great Plains, including the formations of sand dunes still visible in some areas such as Nebraska?

Our awareness of the perspiration phenomenon from the human body may inspire inquiry into more extensive heat balance processes occurring on our earth. If I were to return to the classroom to teach a lesson on heat balance, I would consider introducing the topic with a discussion of--of all things--human perspiration! Many wonders of our daily environment operate within a diverse set of physical laws. Our Creator authored these laws and provided them for our welfare, awareness, and enjoyment.