Paradoxically the strongest evidence for AGW is based on temperature measurements of the lower stratosphere.
While AGW increases the temperature of the troposphere, the lower stratosphere which is immediately above the troposphere is getting colder.
This was a prediction made in 1967 before AGW was even a fashionable topic and has been confirmed by satellite measurements from 1979 onwards.
While there are other factors that contribute to lower stratospheric cooling such as ozone, stratospheric clouds, convection etc; once these factors are taken into account, the lower stratosphere is still getting colder due to the increasing amounts on greenhouse gasses in the troposphere.
While the maths is complicated a simplified explanation will suffice as to why the troposphere is warming up while the lower stratosphere is cooling as greenhouse gases increase.
Imagine the Earth’s atmosphere is devoid of greenhouse gases.
Solar radiation in the form of UV, visible and IR strikes the surface which warms up.
Longer wave radiation in the form of IR is radiated back into the atmosphere.
This is a simplified blackbody model.
Now lets add a greenhouse gas such as CO₂ to the atmosphere.
The CO₂ forms a layer in the troposphere.
CO₂ like any greenhouse gas molecule has an interesting property where the chemical bonds stretch, bend, vibrate and can absorb IR radiation.
When this occurs the molecule goes from a ground state to an excited state.
On returning to the ground state IR is re-radiated in all directions including back to the surface which forms the mechanism for greenhouse warming.
Increasing the amount of CO₂ is modelled as increasing the number of layers in the troposphere where each layer absorbs and re-radiates in all directions.
Each successive layer receives less IR radiation than the layer immediately below it.
In the lower stratosphere greenhouse gases also exist which contributes to heating but if CO₂ levels are increased in the troposphere, less IR reaches greenhouse gases in the lower stratosphere which results in cooling as more heat is radiated into space then is supplied by IR radiation from the troposphere, despite the temperature increase there.
Since the temperature changes of the troposphere and lower stratosphere are out of phase it eliminates the idea that current climate change is caused by variations in the solar radiation output, sunspots or Milankovitch cycles in which case temperature changes would be in phase.
While AGW increases the temperature of the troposphere, the lower stratosphere which is immediately above the troposphere is getting colder.
This was a prediction made in 1967 before AGW was even a fashionable topic and has been confirmed by satellite measurements from 1979 onwards.
While there are other factors that contribute to lower stratospheric cooling such as ozone, stratospheric clouds, convection etc; once these factors are taken into account, the lower stratosphere is still getting colder due to the increasing amounts on greenhouse gasses in the troposphere.
While the maths is complicated a simplified explanation will suffice as to why the troposphere is warming up while the lower stratosphere is cooling as greenhouse gases increase.
Imagine the Earth’s atmosphere is devoid of greenhouse gases.
Solar radiation in the form of UV, visible and IR strikes the surface which warms up.
Longer wave radiation in the form of IR is radiated back into the atmosphere.
This is a simplified blackbody model.
Now lets add a greenhouse gas such as CO₂ to the atmosphere.
The CO₂ forms a layer in the troposphere.
CO₂ like any greenhouse gas molecule has an interesting property where the chemical bonds stretch, bend, vibrate and can absorb IR radiation.
When this occurs the molecule goes from a ground state to an excited state.
On returning to the ground state IR is re-radiated in all directions including back to the surface which forms the mechanism for greenhouse warming.
Increasing the amount of CO₂ is modelled as increasing the number of layers in the troposphere where each layer absorbs and re-radiates in all directions.
Each successive layer receives less IR radiation than the layer immediately below it.
In the lower stratosphere greenhouse gases also exist which contributes to heating but if CO₂ levels are increased in the troposphere, less IR reaches greenhouse gases in the lower stratosphere which results in cooling as more heat is radiated into space then is supplied by IR radiation from the troposphere, despite the temperature increase there.
Since the temperature changes of the troposphere and lower stratosphere are out of phase it eliminates the idea that current climate change is caused by variations in the solar radiation output, sunspots or Milankovitch cycles in which case temperature changes would be in phase.
Upvote
0