Climate Sensitivity and the Madness of Climate Alarmists
INTRODUCTION
If a travel brochure encouraging tourism to planet Earth needed a single catch phrase, it could only be “water world”. Vast oceans cover most or about 71% of the surface. Warm tropical seas rich in nutrients gave rise to life and now contain the greatest number and diversity of all living species. And no less important, it is water vapor, and water vapor alone, that moderates and stabilizes global temperatures.
FORTUITIOUS PROPERTIES OF WATER
If we add energy to water, in most cases its temperature increases accordingly, as for instance when we place a pot of water on a stove. The energy added is called the “sensible heat.” And the temperature we measure is effectively the average speed of its constituent molecules. To be precise, this energy of motion is called the “kinetic energy” which is calculated as the mass times the velocity squared. Basically as the temperature increases, the molecules move faster.
In the liquid state, water molecules are attracted to each other and are continuously bumping into a crowd of neighbors. But in the gaseous state, they are much further apart and travel relatively large distances before coming into contact with anything and to which they do not bond.
In equilibrium, water molecules will have a range of energies about their average value. At a particular temperature even well below the boiling point, a few will have a velocity fast enough to escape the attraction of their neighbors and will leave the surface to enter the vapor state. The remaining liquid will get a little colder but will suck heat out of the environment returning it to the equilibrium temperature. If the air has a low humidity it doesn’t contain many water molecules, so only a few will find their way back to the surface. Eventually all the water will evaporate.
If we increase the water temperature to its boiling point, the liquid and gaseous states will be in equilibrium. The average vibrational energy of molecules in the liquid will be the same as the translational kinetic energy of molecules in the air. But molecules in the liquid will be in an “energy well” due to mutual attraction between neighbors.
At this point, adding more energy will not increase the temperature of either state. Rather we need to break the chemical bonds of all the molecules in the liquid so they can enter the vapor state. This energy is called the “latent heat” of evaporation. Before and after that phase transition, adding energy, i.e. sensible-heat, will again raise the temperature.
CLOUD FORMATION
The air can hold quite a bit of water vapor with warm air able to hold much more than cold air. Humidity varies on Earth from about 1% to 4% of all air molecules with an average of about 2.5%. As water vapor diffuses upward, at some point it will get cold enough so the air holds the maximum amount possible. This is called the “dew point” temperature. Water vapor molecules will then condense to form liquid droplets.
As liquid droplets grow in size, they will attract molecules from the gaseous state. This force will accelerate nearby vapor molecules increasing their kinetic energy until they slam into the liquid surface. This “latent heat” will be returned to the droplet and to the surrounding air heating it up. As a consequence, the air will become less dense and more buoyant. This happens in clouds when it rains and can cause quite violent updrafts.
Indeed, some water vapor molecules caught in this rapidly rising air will have enough momentum to cross the boundary between the lower atmosphere, or troposphere, and the upper atmosphere, or stratosphere, increasing the humidity at high altitude.
FEEDBACK LOOPS
Since water vapor is a strong greenhouse gas, and indeed is the dominant greenhouse gas, extra humidity at high altitude results in a dramatic increase of global warming.
By contrast, CO2 has an extremely weak effect on warming because each molecule only absorbs about 1/8th the energy of a water vapor molecule, is up to 100 times less abundant, because most of the energy it might have absorbed is instead absorbed by water vapor, and because its effect is already “saturated” so adding more has much less of any effect whatsoever.
Indeed the initial global warming effect of adding even large amounts of CO2 is almost too small to measure. But its effect is not zero either and since water evaporation increases exponentially with temperature, a little bit extra heat at the surface might cause a positive feedback by increasing the water vapor content at high altitude.
This catalytic effect is not observed in the real world because the temperature difference between the surface and upper troposphere is reduced with global warming because the troposphere warms faster than the surface. Thus any convective upwelling of humid air associated with rain is also reduced as the world gets warmer.
Satellite measurements confirm this intuition. The upper air humidity is reduced and the feedback is “negative” and not “positive” as hoped for by climate alarmists. But climate models still claim an 3 to 10 or more times multiplication of the initial CO2 warming effect in defiance of the empirical evidence and theoretical considerations.
REAL WORLD MEASUREMENTS
From before 1978 until a little after 2005, NOAA (National Oceanic and Atmospheric Administration) had been measuring the amount of water vapor in the upper troposphere using several satellites. Each of these satellites carried an identical HIRS/2 instrument which provided data at a frequency of 6.7 um to produce a vertical profile of water vapor to high altitude.
Since the 1930’s, balloons have been carrying radiosonde instruments aloft to also measure humidity as a function of altitude. Although reasonably accurate at lower altitudes, they are not considered reliable in the stratosphere.
Computer models on the other hand predict exactly the opposite to what is observed to include a significant increase in humidity at high altitudes during El Nino events which was not observed in the satellite record.
REFERENCES
1. “Trends in middle- and upper-level tropospheric humidity from NCEP reanalysis data” by Garth Paltridge, Albert Arking, and Michael Pook, in Theoretical Applied Climatology 98:351–359 (2009).
“The National Centers for Environmental Prediction (NCEP) reanalysis data on tropospheric humidity are examined for the period 1973 to 2007. … Negative trends in q (i.e. zonal-average annual-average specific humidity) as found in the NCEP data would imply that long-term water vapor feedback is negative—that it would reduce rather than amplify the response of the climate system to external forcing such as that from increasing atmospheric CO2.”
“… Our results call into question previous estimates of surface radiative forcing based on presumed long-term global lower-stratospheric water-vapor increases.”
“The new
merged satellite water‐vapour record extends back to the late 1980s and shows
long‐term decreases in the lower and mid‐stratosphere, in contrast to the Boulder record which is shown not to be globally representative.
Upper-stratospheric water vapour instead shows a long‐term increase. [And what is crucial for global warming, the lower and
mid stratospheric water vapor shows long term declines contrary to computer
models.] The contributions of the two recognized drivers of water-vapour changes – the stratospheric entry values of water vapour and of methane – are quantified and shown not to be sufficient to explain the observed water-vapour trends, particularly the difference in the trends between the upper and lower stratosphere.”