Humid hazes

2. The formation of warming, dimming and aridifying humid hazes (Walter Jehne)

As the water vapour that has been evaporated and transpired into the air cools, both at night and at higher altitudes it will re-condense on very small aerosol particles to form liquid micro-droplets or hazes, mists and fogs. As it condenses the latent heat used to sustain it as vapour is released. This will warm the surrounding air from which some of it may re-radiate up and back out to space.

When the sun comes out these liquid haze micro-droplets will then directly absorb solar radiation and again evaporate to form humid air masses containing up to 5% water by weight. This cycle of releasing and reabsorbing heat will continue daily while they remain in the air, continually warming that air as well as reducing the solar energy reaching the surface, as evidenced by global dimming.

The increased levels of these persistent humid hazes over many regions often now absorb and retain up to 20% or 60 w/m2, contributing to the abnormal warming of the atmosphere and the planet.


Figure one: Dust clouds in California (Image credit Raymond Gehman, National Geographic)

We have grossly and directly increased the level and warming effects of these hazes via our emission of vast quantities of microscopic aerosols particles into the air to form haze micro-nuclei. While there are many natural sources of haze micro-nuclei such as organic volatiles from algae, trees and fine dusts we now emit many billions of tonnes of extra dust, carbon, particulates, pollutants and polyaromatic hydrocarbon molecules into the air that form warming pollutant humid hazes.

As the haze micro-droplets are far too small to fall out of the air under gravity they persist, creating major humid heat and bronchial health risks but also aridifying the regions below them. By persisting they also ensure that very high relative humidity levels occur daily as soon as they are re-evaporated to water vapour, which is the dominant gas in the greenhouse effect as discussed subsequently.

Walter discusses humid hazes at 54.48 into this video.

More about the science

This 2004 NASA article discusses water vapour in the atmosphere revealing that CO2 “can’t compete with water for heat-trapping power”.

This NASA article Water Cycle quotes the National Research Council’s report on Research Pathways for the Next Decade (NRC, 1999): “Water is at the heart of both the causes and effects of climate change.” 

This Malaysian article raises concerns about the role of atmospheric hazes in advancing climate change.

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