Skip to comments.It's Not the Heat. It's the Humidity
Posted on 01/20/2013 12:01:46 AM PST by kathsua
Climatologists pay too little attention to the role water plays in earth's energy system, including the way water vapor affects air temperature. Water's potential to affect air temperature is well established in science. As I have noted in previous posts the ability of CO2 to affect temperature is highly questionable. Those who spend much time in greenhouses know that they are often very humid places because water evaporates from plants and from surfaces that get wet when the plants are watered. Meteorologists typically refer to the water vapor content of the air as relative humidity which is how close the air is to holding as much water vapor as it can hold at its current temperature.
Unfortunately many climatologists waste so much time on the nonexistent impact of radiation on air temperature that they don't provide sufficient emphasis to the significant impact of water vapor on air temperature. Those who want to blame climate changes on humans ignore the fact that the combustion of hydrogen containing fossil fuels increases the amount of water vapor in the air. Other human actitivies such as watering yards, washing cars and operating public fountains also add water to the atmosphere.
Water has some special thermal characteristics that can significantly affect atmospheric temperatures. Water heats and cools signicantly slower than other components of the atmosphere. Water vapor needs to absorb over four times more heat energy than the same mass of other air molecules to raise its temperature the same amount.
Thus as the water vapor content of the air increases the atmosphere will heat and cool slower than when the air is drier. This process tends to keep the temperature from rising as high during the day or cooling as much at night, although the increase in the overnight low may lead to an increase in the daytime temperature because the air doesn't have to heat as much to reach a higher temperature. In equatorial areas deserts have higher maximum temperatures and lower minimum temperatures than jungle areas where the humidity is higher.
Water vapor possesses what physicists have traditionally called "latent" heat. Latent heat refers to the heat energy water molecules must absorb to go from a solid to a liquid (heat of fusion 80 calories/gram) or a liquid to a gas(heat of vaporization 540 calories/gram). This energy isn't reflected in the temperature of the water vapor. However, when water vapor condenses back to a liquid, or freezes, the release of this latent heat can raise the temperature of the air. A gram of water vapor releases enough heat energy when it condenses to raise the temperature of 2 kg of air by 1 C.
At approximately 65 F water vapor in the atmosphere holds as much heat energy as the rest of the atmosphere. This condition explains why dew points above 65 F are associated with the strongest thunderstorms.
Physicists define a "calorie" as the amount of heat required to raise the temperature of a gram of water 1 C. 27 C (82 F) is the same temperature as 300 Kelvin [the absolute temperature scale]. At 300 K water vapor has 300 calories of heat from its temperature and 620 calories of latent heat.
The dew point is the temperature at which water vapor will condense on objects or aerosals. The dew point normally is the lowest temperature the air will fall to. As the water vapor content of the air increases the dew point rises and the air doesn't get as cool at night.
The situation is more complex than I am presenting it in this post. I . The important facts to consider are that increases in humidity can raise the low, or minimum temperature, and limit the high, or maximum temperature, each day. In areas where significant snowfall occurs, the increase in low temperature can increase the melting of snow and ice by keeping the temperature above freezing for longer periods of time.
I recently came across a 10 year old study done by David R. Easterling of the National Oceanic and Atmospheric Administration's National Climatic Data Center in Asheville, N.C., indicating that humidy had increased and, as should have been expected, the minimum temperature had been increasing and the difference between the minimum and maximum daily temperatures, diurnal temperature range (DTR), had been declining.
The potential impact of changes in atmospheric water vapor are real science. Water vapor holds a substantial amount of heat energy. The only potential impact climatologists can find for carbon dioxide is the highly questionable claim about absorbing and re-radiating low energy IR. But then, if would be difficult for the politicians behind the global warming scare to make a case for getting rid of water
True. However, given the unbelievably huge amounts of water that evaporate and condense each day, the "human" contribution is so small it literally cannot be measured on a global scale.
It can effect climate in localized areas, for instance where irrigation become widespread in desert areas, but not the global climate.
Right. The minimum temperature will increase and the maximum temperature will decrease. Now if you have a data base of temperatures taken at 3 pm every day, the recorded temperature will be lower if the humidity is higher. Simply because more water vapor molecules increases the density of the atmosphere. A denser atmosphere requires more energy (sunlight) to reach a given temperature. It is probably easier to make sense of the situation by thinking in terms of air density. More dense air (higher humidity) can hold more energy, but will achieve lower peak temperatures for a given amount of solar input. So higher humidity will cause lower peak temperature readings at 3 pm every day and lower humidity will cause higher peak temperature readings. So the temperature delta (change) from day to day in this specific case is responding the exact opposite of energy delta (or change). Higher max temps, lower total energy. Lower max temps higher total energy.
You really are just playing with noise if all you work with are temperatures. Total energy or latent heat is the key. But hey, global warming is not about science. It is all about political science. Now imagine a planet if you will, that is heading into an ice age. Less energy means there should be less water vapor, since energy is required to get water to evaporate (turn into a gas). So a planet is cooling and the air is getting less dense. Temperatures if taken at 3 pm every day, might actually show an increase. Since basically the air is less dense and can warm higher given the same amount of solar input. So by the time you actually see big drops in maximum daily temperatures due to the onset of an ice age, it will probably be too late to prepare. So for any temperature change, must be biased or adjusted with any change in air density (humidity or heat content). Otherwise you might as well be throwing dice in Vegas.
Man that di-hydrogen monoxide is a killer.