It's uncanny how many essential functions water serves for living processes. But perhaps the most important function is the regulation of temperature. And the amazing thing is, water acts to regulate temperature simultaneously and independently on multiple levels. On a micro sub-cellular level, a human level, a regional level, and a global level.
Life survives in a narrow temperature range that just happens to correspond with the temperature at which water is a liquid. That's not a coincidence. Life and water are tightly coupled on Earth. All of life's metabolic processes – the things that make a living organism “alive” - happen in water.
The temperature at which water is a liquid is not necessarily the temperature that's ideal for many types of chemical reactions. In some cases heat needs to be added to get a reaction underway, or a chemical reaction can produce a lot of heat in an uncontrollable chain reaction. Either way, the reaction proceeds at a temperature much too hot for life.
All biochemical reactions are catalyzed (made easier) by large convoluted protein molecules called enzymes. The key to an enzyme's function as a catalyzer of chemical reactions is its complex shape. And the key to an enzyme's shape is how the molecule twists and folds in on itself in relation to the water molecules that surround it.
Water is also necessary because it facilitates the flow of dissolved molecules that form the raw materials and the products of enzyme mediated reactions. But that's another story.
The enzymes that catalyze most biological reactions work best within a narrow range of a few degrees centering around 37 Centigrade, normal body temperature. Hotter than this and the enzymes lose their shape and cease to function. Too cold and the chemical reactions slow down too much to sustain metabolic processes.
The human body has several independent systems that work to keep the body's temperature within the narrow range necessary for life. All of these systems involve water in a crucial way and yet each uses water in a unique way.
When we are cold our circulation system shunts blood away from the extremities, where it would be more likely to lose heat to the external environment. This keeps more of the body's water within the better insulated core where it protects the vital organs.
When we are too hot our circulation system shunts more water out to the extremities where heat can be transferred out of the body. Another independent system kicks in to cool the body by secreting water in the form of sweat on the body's outer surface. On a hot sunny day the sweat on our skin evaporates cooling us off.
When we are cold another independent system come into play. We “shiver”. This is a muscular reaction that produces heat to warm the body by increasing metabolic rates and shunting blood to the large muscles of the body. Muscle cells are controlled by nerve cells, and nerve cells cannot tell muscle cells what to do without the medium of water.
So here comes the analogy. Just as water plays the major role in keeping our bodies alive it also plays the major role in keeping life on Earth alive. For it is water in all it's forms that moderates temperature on Earth's surface.
Water has the second highest heat capacity of any liquid. Water retains heat. That's why we use it for radiators. But that's also why it's warmer near the ocean in winter, and cooler in the summer. Large bodies of water moderate climate, because they absorb heat and are slow to give it up.
In places far inland it's colder in the winter and hotter in the summer because these places lack the moderating influence of a large body of water. Note that the majority of the world's population lives within 50 miles of the ocean.
Water also has a huge role to play in temperature regulation via an entirely different system – the weather. Here's how it works: The Sun's radiant energy heats the surface water of the oceans. When this happens some of the surface water evaporates. It changes from it's liquid form to water vapour – a gas. In doing so it absorbs heat and cools the surface water.
Not a big deal in terms of the proportion of water that ends up in the atmosphere .001 % of Earth's total, but it's still enough to make a huge difference to the Earth's surface temperature.
The water vapour rises up into the atmosphere where it gets blown far away by the winds. The higher the water molecules rise the colder the air. Eventually the the molecules condense back to liquid and form water droplets. When this happens the latent heat of evaporation is given off into the atmosphere.
But here's the deal - where the water molecule absorbed the heat and where it gives it back can be thousands of miles apart. Thus the sun's energy powers water's transfer of heat over the Earth's surface through the medium of the winds in the atmosphere.
But that's not all folks. There's another couple of systems involving water in a major role that effect the Earth's surface temperature independently of the one's I just mentioned. Water freezes into ice at 0 C. Ice reflects sunlight and cools the Earth's surface. That's why during an ice age the Earth's surface gets colder.
But there's more. In the atmosphere water vapour molecules have a stronger greenhouse warming effect than carbon dioxide. This is counterbalanced both by the cooling effect of evaporation, and the fact that water molecules do not stay long in the atmosphere before gravity takes over and pulls the water down to the earth in the form of rain.
OK but there's still more. Because water, unlike most other liquids expands when it freezes, ice forms on top of liquid water and because of that ice insulates water and keeps most of it from freezing in the winter.
Used for warming and cooling, multiple independent systems involved, tightly coupled with life itself -That's Water.
