Climate, Magic or Physics? 196

Warning: This is not a three-minute read.

When confronted with weather and climate, if one does not know the science, it seems both are beyond understanding and in the realm of TV meteorologists, gods, or magic.

After all, the weather arrives on a wind, is often invisible, and forms giant white mountains of fury right over our heads. It was not until the mid-1850s when the famous Royal Navy Admiral Fitzroy applied science to forecast weather that we began to understand weather. Due to his diligent work mankind began attributing weather to science phenomena rather than the wrath of God.

Climate science and the resulting extreme weather can seem closer to cruel magic than science. Years ago, I set out to understand it.

What puzzled me was why a mere one degree C rise in global temperatures, that is only 1.8 degrees F rise, could give us so many floods and areas of drought. I had figured out why carbon pollution from burning coal, oil and gas was heating the earth and why the oceans were warming and evaporating faster. This evaporation, the world meteorologists figured, had added 7% more moisture to the earth’s atmosphere. It just seemed to me a 1.8 degrees F rise in the average global temperatures and a 7% increase in global moisture were not large enough to create so much havoc.

I read books on meteorology and wrote to climate scientists. I started to put a few things together. What I discovered is there are two related elements often ignored in the climate discussion. One is the ability of air, as it warms, to hold more water vapor. The other is we lay weather people are not educated in the nature of water vapor itself.

As air warms it can hold more water. If you analyze a meter cubed of air, (roughly a cubic yard), the air will hold only so many grams of water vapor at any given temperature. When it reaches its capacity, its dew point, the vapor will start to condense into liquid water. (clouds, fog, rain, snow, etc). At 0C or 32F the air will hold only 4.8 grams of water vapor. At 20C or 50F the air will hold up to 9.3 grams. And at 30C or 86F the air will hold an amazing 30.1 grams of water vapor.

Notice the temperature blocks I used are the same size, ten-degree (18F) blocks. The first 10C degree increase adds only 4.5 grams. The next increase from 10C to 20C increases the water holding ability 7.9 grams. If we raise the temperature to 30C, adding another 10C, the airs’ ability to hold H2O increases a whopping 12.9 grams.

The point of this exercise is to demonstrate, as we raise the temperature of the atmosphere its ability to hold water increases rapidly. This also means the air must accumulate more water to reach the dew point and when it does there is more rain waiting to drop. Much more.

This is not the end of the discussion revealing nature at work with weather. The next factor is the energy in water vapor called latent heat. Latent means hidden another term leading to a sense of the magical.

Digressing, it may be easier to understand this hidden energy, the energy stored in a storm, by defining a calorie. A calorie is the amount of heat required to raise one gram of liquid water one degree Celsius. Thus, to raise the temperature of water from 0 to 100C takes 100 calories. At that point, the rules change abruptly. Water will not get warmer than 100C (212F) unless a lot more calories of heat are added. It is a whopping 540 calories of additional heat to bring the water to boiling and evaporate. This heat changes water from liquid to vapor. If water did not change state and we added 540 calories its temperature would be 640 degrees!

When water becomes vapor, the vapor has in it all this potential energy. For each gram of water vapor there are 540 calories of hidden heat waiting to be released if and when it reaches the dew point and reverts to the liquid state.

The point here is 7% more moisture in the vapor state due to climate change carries within it 540 calories of latent heat energy for every gram. When the vapor load reaches dew point then the process of releasing this latent energy begins. The heat creates updrafts lifting air and water aloft. As the additional water becomes buoyant and rises it too condenses and adds more energy to the storm. What was invisible, becomes the visible white thunderhead of now visible water held aloft by this energy.

This is the basics of a storm. The more water vapor held by warmer air the greater the potential. Seven percent more water in vapor form is not just seven percent more water but it is seven percent more water and an incredible amount of storm energy. Exactly, 540 calories per gram of vapor.

Today, we have 24/7 weather reports and forecasts which we take for granted. ALL modern forecasts are the product of science. The chance we will be surprised by pop up storms, magically appearing, grows less and less. But before the 1850s, before Admiral Fitzroy dedicated his life to understanding the physics of storms, they were at best magical. At worst, they were the sign of an angry god.

That is the beauty of science. It is like magic, only real. Now we can understand a little more about nature, and spend less time attributing bad weather to, “Acts of God”.

Path to greater understanding: The Senior Climate Scientist at our National Center for Atmospheric Research is Kevin Trenberth. He has many papers on energy and weather. Search his name and NCAR for in-depth explanations.