7. The natural nucleation and enhancement of rainfall (Walter Jehne)
These highly hygroscopic bacterial precipitation nuclei can not only coalesce the haze micro-droplets into the larger cloud droplets but also coalesce cloud droplets into raindrops, that are large and stable enough to fall out of the air under gravity. In this way the water that was transpired by plants from the Earth’s soil carbon sponge in #1 can be returned as rain to again recharge that sponge and sustain this natural hydrological cycle and regulation of the Earth’s heat dynamics and cooling.
The extension and reliability of this rainfall and hydrological cycling enabled microbial life, soils, and vegetation to naturally establish across all of the ice-free land on Earth following the last ice age. While we have degraded over 5 billion hectares or 40% of this into man-made desert and wasteland over the past 10,000 years, most of these arid wastelands still have a river of humid air with 2-5% moisture contents continually flowing over them.
Many arid regions are blanketed by persistent humid heat hazes in summer that are often also highly polluted and threaten the health of people living under them from heat stresses. While there is adequate water in the air to regenerate such regions and re-establish their hydrological cycles, by removing the vegetation that naturally produced the hygroscopic bacterial precipitation nuclei we turned these regions into deserts. We can only regenerate them by restoring these nuclei processes.
More seriously and urgent we are currently aridifying large areas of our degraded but still vegetated global landscape via these same processes; resulting in an increase in persistent aridifying and warming humid hazes and the systemic decline in their nucleation to remove them via rainfalls. Vast regions and populations are and will increasingly be threatened by this systemic decline in rainfalls. Options exist to reverse this naturally and in time but only by recognizing these risks and processes.
Rivers in the sky
Figure one: Atmospheric rivers are long, narrow weather systems that carry large amounts of moisture from the tropics into the midlatitudes. This NOAA illustration of a system stretching from the tropics around Hawaii to the U.S. West Coast, with darker blue shades representing greater amounts of precipitable water, depicts an atmospheric river that drenched Northern California in April 2018. Credit: NOAA National Environmental Satellite, Data, and Information Service. From the Earth Magazine website
More on greening deserts
There are projects around the world to regreen deserts and aridified areas. See Greening deserts on this website for more detail.
Here is an example of greening efforts that changes the climate in the region.