Vincent J. Curtis
12 Dec 2018
One of the prospects of global warming held forth to
frightening people is increasing severity and frequency of storms, particularly
of hurricanes. Superficially, it makes
sense that if there is more heat in the atmosphere there will be more power packed
into weather events like storms. But the
people who offer such prospects reveal gaps in knowledge about how hurricanes
work and how they originate.
Simply put, hurricanes, to take the extreme example, cannot
be more severe or more frequent than they have been. They cannot be more severe because hurricanes
are not driven by the transformation of the heat latent in the permanent gases
of the atmosphere: nitrogen, oxygen, argon, and carbon dioxide. They do not originate on account of the
latent heat of the permanent gases.
Let me explain. A
philosopher would describe a hurricane as a form in the matter of the
atmosphere. A mechanic would describe a
hurricane as an engine that transforms the latent heat of atmospheric moisture
into rain and kinetic energy, i.e. wind.
When water vapor condenses into rain, the latent heat of vaporization is
released, and what this heat does is power the winds of the hurricane. A reason why hurricanes form over tropical
waters is that warm, moist air over the tropical ocean possesses enough
absolute humidity to drive a storm of
hurricane size and power.
There is relative humidity and absolute humidity. Relative humidity refers to the amount of
moisture in the air relative to the saturation point, when condensation in the
form of fog, frost, or clouds occurs.
Absolute humidity refers to the actual amount of water vapor in the air,
and warmer air is able to hold more water as vapor.
When hurricanes pass over land, they rapidly lose strength
because their supply of warm, moist air is cut off. Less moisture, less condensation, less heat
available to drive the winds. Likewise,
if a hurricane diverts northward but remains over the ocean, the Gulf Stream
can sustain it for a while, but as the disturbance encounters cooler air
farther north, there is less absolute humidity, and therefore less latent heat of
condensation available to convert into rain and wind.
The latent heat of the permanent gases of the atmosphere
play no role in this because the heat they contain is not transformed in any
permanent way, as water vapor is converted into rain. But could a change in the ratios of the
permanent atmospheric gases increase the amount of absolute humidity?
The answer is no, for two reasons. The first is that the increase in the amount
of carbon dioxide is infinitesimal. The
second, and more important reason, is that the limit of absolute humidity is
determined by the vapor pressure of water, which is governed by temperature,
not the atmosphere above the liquid.
The intensity of a hurricane is determined by the
atmospheric pressure in the eye of the storm; the lower the pressure, the
higher the wind speed in the eyewall.
Atmospheric pressure is determined by gravity and the mass of the
atmosphere above. The force of gravity on earth isn't going to change on account of carbon dioxide in the atmosphere. Atmospheric mass is
not going to change appreciably by a minute addition of carbon.
Hurricanes originate as “convective instabilities” in the
atmosphere. They are the product of the
effect of the heating of the sun on the tropical waters between West Africa and
the Caribbean Sea. This is a complex phenomenon,
but the heat capacity of the atmosphere over those waters is not going to be
changed significantly by infinitesimal changes in the carbon dioxide content,
and besides that the heat capacity of carbon dioxide is not substantially
different from that of nitrogen, the primary constituent of the atmosphere.
Heat capacity refers to the amount of heat required to raise
an amount of the substance by one degree in temperature. Since the heat from the sun, and the
temperature of the ocean waters will be unchanged, the origin of hurricanes as
convective instabilities will remain robustly the same.
Hence, there is no need to worry about increasing numbers or
intensity of hurricanes particularly, or storms generally. The power of these do not come from the
conversion of the latent heat of carbon dioxide gas.
-30-
Vincent J. Curtis is a research scientist and occasional
free-lance writer.
No comments:
Post a Comment