Strong negative feedback in Climate

  1. A concept for strong negative feedback in Climate?

    I have been following some of the more interesting concepts in climate model theories for a couple years. Svenmark's cosmic ray theory in "The Chilling Stars", Svensmark and Calder, is very interesting. Miskolczi's theory of strong negative feedback causing a fixed optical density for the atmosphere has intrigued me the most. I wish he would write a book to explain his paper and answer some of the questions about it.

    As I understand the history, some important work on radiative transport was done decades ago for stellar atmospheres. The differential equations were solved using infinitely thick atmospheres for the boundary conditions. This worked well as stars have no surface. Unfortunately the same solutions were used for planetary atmospheres. This is OK for the gas giants but not for the Earth, Mars, or Titan. When Milkolczi went back to the original differential equations and solved them using a finite atmosphere with a surface at the bottom, the resulting solution had a negative term in the solution.

    This negative term allows for an equilibrium to be established. According to Milkolczi, the presence of large oceans provides and effective infinite supply of the green house gas, water vapor. Any heating event in the past that caused warming, would have caused water to evaporate resulting in runaway global warming. His point is that this happened as soon as there were oceans and that the atmosphere warmed to an equilibrium temperature has remained at the equilibrium ever since. Note that orbital mechanics, solar changes, or Svensmark's theory are drivers from outside the equilibrium that could cause climate change such as ice ages, little ice age, medieval warming period, and the like.

    Miskolczi's paper considers the atmosphere as a whole and uses some complex thermodynamic arguments to predict an equilibrium optical density for the atmosphere that corresponds remarkably well with actual measurements. He says that as CO2 is added to the atmosphere, a little water will rain out to maintain the equilibrium. He does not present mechanism for how this happens.

    I propose the following mechanism and am looking for useful comments on it.

    The atmosphere consists of several distinct layers, troposphere, stratosphere, mesosphere, and thermosphere. Here I will consider heat transport in the troposphere and the stratosphere.

    Heat transport in the troposphere is dominated by convection. Heat transport by radiation is important but highly variable due to clouds. The clouds are in turn are determined by the convection of water vapor in the troposphere. A very important variable for convection is the rate of decline of the temperature with altitude known as the lapse rate. As a parcel of air rises, it cools due to adiabatic expansion. The cooling is reduced when the temperature drops below the dew point and the latent heat of vaporization of the water is released. If the rising parcel of air is much warmer than the surround air it will ascend rapidly and we get the towering cumulonimbus thunderstorms.

    Convection in the troposphere continues up to the tropopause where the lapse rate in the temperature results in very cold temperatures. The tropopause is at about -70°C, 17km at the equator and -50°C, 8km at the poles. Note that adding heat and water to the atmosphere at the equator increases the height and lowers the temperature of the tropopause. The height of the troposphere changes rapidly at the jet stream at mid latitudes. At the tropopause the dew point is -50° C or lower.

    Above the tropopause is the stratosphere. Temperatures rise with altitude so that convection stops. Heat transport is dominated by radiation. The ozone layer exists from about 20-60 km and absorption of UV causes the temperature to rise in the stratosphere. There is little water in the stratosphere and the dew point is controlled by the dew point at the tropopause. Water simply cannot get above it.

    Now consider adding CO2 to the atmosphere. On average, a rising parcel of air will absorb a little extra IR. The CO2 does not simply absorb IR and readmit in all directions. The time constant for the decay of the excited CO2 molecule is much longer that the mean time be between collisions up to about the mesosphere. The IR energy absorbed by the CO2 is shared with all of the gasses at that level. The entire parcel of air is warmed and the CO2 only admits IR corresponding to the average temperature. The rising parcel of air will not cool quite as quickly so it will go higher before all the water vapor condenses.

    Thus the net effect of adding CO2 is to cause the troposphere to rise a little resulting in a lower dew point throughout the entire stratosphere. The stratosphere becomes more transparent to IR, compensating for increased CO2. Note also that the parcel of air that has reached the tropopause and lost its water to ice and begins to descend in the troposphere, absorbs less IR in the water absorption bands.

    This then provides a mechanism for Miskolczi's constant optical density.

    The lack of convection in the stratosphere can cause a lag in the time for the atmosphere to reestablish an equalibrium. A recent paper by Michael Beenstock1 and Yaniv Reingewertz1, "Polynomial Cointegration Tests of the Anthropogenic Theory of Global Warming" finds that the rates of change of temperature and CO2 do not match and a permanent increase in temperature does not exist in the data. They do find, however, a short term effect where a permanent increase in CO2 is consistent with a short term rise in temperature. The mechanism described here is consistent with this lag due to the time for the slow mixing in the stratosphere to allow the dew point to drop throughout the stratosphere.
  2. jcsd
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  3. Monique

    Monique 4,700
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