Guest contribution by Jim Steele
Most people are unaware that the greenhouse gases CO2 and H2O are both warm and warm cool our planet. When I mention that CO2 has a cooling effect, I am amazed at the hateful tirades of paranoid people who dismiss scientific truth as “dangerous misinformation”.
However, discussions about temperature inversions have occasionally led to a more respectful debate with critical thinkers. Most people have seen “frost fans” set up in orchards and vineyards and are interested in why they are working. Frost fans disrupt frozen surface air layers, which can develop at night in the spring and damage flowers and fruits. Frost fans simply pull warmer layers of air from top to bottom to the surface, thus increasing the minimum temperatures. But why is there this warmer layer of air?
During the day, the earth’s surface absorbs both solar radiation and the downward infrared heat given off by greenhouse gases. If the energy is absorbed faster than infrared can emit it back into space, the surface will heat up. However, sunlight does not directly heat the lower atmosphere (also called the troposphere). Nitrogen, oxygen and argon make up ~ 99% of our atmosphere and are transparent to the incoming solar energy. In addition, unlike greenhouse gases, these gases do not absorb or emit infrared energy. The troposphere heats up mainly through the generation of energy through collisions with a heated surface of the earth. During the day, the warmest layer of air is closest to the heated surface. Rising warm air causes turbulent mixing and collisions with cooler air above, increasing air temperatures there. However, because the air cools down as it rises due to the decreasing air pressure, the heating is limited.
Without solar heat, the earth’s surface cools by giving off more infrared heat than it absorbs from the recycled heat given off by greenhouse gases, because greenhouse gases do not capture all of the heat given off. “Atmospheric windows” allow around 23% of surface heat to escape directly into space without being recycled. The layer of air closest to the surface then cools down by transferring heat to the colder surface. However, higher layers of air can only sink and collide with the surface if they lose their heat. However, nitrogen, oxygen, and argon can only release this energy by colliding with cooler greenhouse gases, which absorb their energy and release half of it back into space.
Since the majority of our atmosphere only cools down through heat transfer to greenhouse gases, a small percentage of the greenhouse gases create a “cooling choke point”. As a result, the atmosphere releases energy more slowly than the solid earth, which loses energy more quickly through atmospheric windows. This difference in cooling rates creates a warmer layer of air over the cooler surface air and is known as temperature inversion. Now imagine a world without greenhouse gases. Without the greenhouse gases nitrogen, oxygen, oxygen and argon cannot give enough heat back to space and the atmosphere would continue to warm.
Outside the tropics, inversion layers form more easily in winter and spring. The earth’s surface holds less heat during the reduced solar heat in winter. Where people use chimneys to stay warm, the inversion layer is made visible by rising smoke, which suddenly flattens out when it meets the warmer air above. Frost fans pull down warmer layers of air to mix with cooler surface layers, protecting the plants from freezing. Similarly, months of “polar nighttime” cool the inner surfaces of Antarctica down to -89.2 ° C, creating a continent-wide inversion layer. If above-average surface temperatures are regularly reported, this is often the result of strong winds that, like a fan of frost, destroyed the inversion layer of Antarctica.
In the 1990s, climate researchers found that urban warming effects increased minimum temperatures by several degrees, but not maximum temperatures. Such areas did not heat up, but became less cold. This suggests that urbanization has disrupted the local inversion layers. As the land is increasingly covered with heat-storing asphalt and concrete, surface cooling is reduced. Removing vegetation or moisture leads to hotter surfaces that store more heat. Traffic, tall buildings or frost fans disrupt the surface wind and bring warmer air to the surface. All of these dynamics increase the minimum temperatures and thus the average temperature. Various local perturbations of the inversion layers may better explain why some US weather stations are showing warming trends while 36% show long-term cooling.
Our atmosphere also has a global inversion layer. Above the troposphere is the warmer stratosphere, where temperatures rise with altitude due to the absorption of solar UV. Since CO2 emits infrared faster than it absorbs from the troposphere in a warmer stratosphere, more CO2 cools the stratosphere. (For similar reasons, CO2 has a cooling effect in Antarctica.) In addition, storm clouds bring the enormous amounts of heat stored in water vapor into the stratosphere. Again, we can see where the warm inversion begins when the clouds stop rising and develop an anvil shape in the stratosphere. Since the stratosphere is almost anhydrous, the wavelengths of the infrared heat, which is released when water vapor condenses to form liquid and ice, mostly travel freely into space without being returned to earth.
If this dynamic were better understood, people would laugh at climate catastrophe narratives rather than succumb to paranoia.