Oil refinery and chemical plant, Ashland, Kentucky. Photo: Jeffrey St. Clair.
Like CO2 (carbon dioxide), H2O (water vapor) is a strongly heteropolar molecule — having one end with a positive electrical charge, and another end with a negative electrical charge — and absorbs outgoing Infrared Radiation (IR) from Earth’s surface, thus capturing heat in the atmosphere. Homopolar molecules like N2 (nitrogen) and O2 (oxygen) are transparent to IR. Inelastic molecular collisions redistribute that heat (as kinetic energy) to other atmospheric molecules (N2, O2, mainly) and atoms (Ar, He, trace components).
Most of Earth’s surface heat eventually diffuses into the oceans. Heat flows along the heat gradient in the negative direction from warmer air to colder water. The heat capacity (storage ability) of the oceans is IMMENSE (this is where ‘global warming’ ends up), and their heat content takes centuries to diffuse into a stable stratified distribution, rearranged by thermo-haline currents (a solar forcing effect) and by geometry (oceans as a spherical shell with warm equator and cold poles, so ocean heat diffuses poleward).
The fundamental problem of global warming is the ‘excess’ capture of outgoing IR (infrared radiation), reducing the rejection of Earth heat (originally delivered by incoming LIGHT radiation) into space: causing an imbalance between incoming energy (in the form of light to which atmospheric molecules are almost completely transparent) and outgoing energy (IR, to which heteropolar molecules, like CO2, H2O, CH4, NOx, are all quite opaque — absorbing).
Water vapor is by far the ‘greenhouse gas’ (IR absorber) with the highest concentration in the atmosphere at any time (immensely larger than that of CO2). It has been found by a combination of climate modeling calculations coordinated with field measurements in many global environments, that though the whiteness of clouds reflects sunlight back toward space (a global cooling effect), their IR absorptivity overwhelms that cooling, so that water vapor has a net global warming effect. As the average global temperature increases there is more water vapor in the atmosphere and this mode for global warming grows in magnitude — this is a self-amplifying or positive feedback effect.
CH4 (methane) and NOx are ‘short lived’ because they are eventually oxidized (by O, OH, formed by UV breaking up O2 and H20, and by other chemical reactions), whereas CO2 is very long lived because it is an endpoint product/species of chemical reaction chains that oxidize carbon compounds in oxygen-containing mixtures. CO2 has a low “chemical potential” and is known as a “chemical thermodynamic sink”. CH4 is eventually converted to CO2 and H2O. NOx is eventually converted to HNO3, nitric acid, which attaches itself to water droplets, so it has an aqueous form and rains out.
The long-term ‘chemical sink’ nature of CO2 is why science focuses on it as the leading culprit in the long-term trends of global warming. With greater warming of the ocean surface, more H2O vapor rises and releases its latent heat when it condenses into droplets (liquid) and ice crystals, and that ‘extra’ heat adds power to storms (winds, hurricanes: mass motion), and ultimately that ‘extra’ heat energy finds its way back into the oceans (for the portion of atmospheric heat that does not escape as IR into space).
When analyzing global warming, it all comes back to CO2. I highly recommend the book ‘Thermodynamics’ by Enrico Fermi (available in a budget-priced Dover edition): a slim volume that is a classic on the topic of chemical thermodynamics, and one of the best books on science of any kind that I have ever read.
My highly detailed outline of the chemical thermodynamics of atmospheric global warming can be read here: ‘Closing The Cycle: Energy and Climate Change’.
The process of capturing atmospheric CO2 with rocks on the ground is one of rock weathering. CO2 in the air that brushes against the surface of carbonate and silicate rocks has a finite (and very low) probability of undergoing a chemical reaction with the rock surface, fixing the airborne CO2 onto a solid substrate. This is the longest term natural process of capturing CO2 from the atmosphere (10s to 100s of millennia).
A shorter term process is capture by the surface waters of the oceans, and that aqueous CO2 then combining with water molecules and already existing carbonate ions (CO3-2) in the water to form carbonic acid (H2CO3), which is weakly bound and both acidifies the oceans and scarfs up free floating carbonate ions to both starve mollusks, corals and foraminifera of the easiest chemical species from which to grow their shells (CO3-2), and even dissolving such shells of existing organisms (most being part of the masses of plankton, the base of the oceanic food chain).
The surface (not too deep) load of absorbed acidifying CO2 is then slowly cycled to the ocean floor by the ~1,000 year vertical currents, and at the bottom it dissolves the chalk deposited as the calcium carbonate (CaCO3) remnants of dead sea life, basically bone, shell and foraminifera casing ‘fossils’ — an ocean acidifying effect. So ocean capture of CO2 happens all the time, but the intake rate can saturate as the ocean becomes more acidified; eventually this intake process could shut off, coral reefs being a long lost memory by then.
Loss of “excess” ocean CO2 requires a low CO2 concentration atmosphere that can accept the gaseous release (is not saturated with CO2) of ocean CO2 that slowly diffuses out on mainly kilo-year timescales. A technically accurate description of ‘the carbonate system in seawater’ is given at https://sundoc.bibliothek.uni-halle.de/diss-online/04/04H141/t5.pdf. My more formal article than the discussion here, ‘Global Warming and Ocean Acidification Accelerate,’ is at https://manuelgarciajr.com/2020/07/18/global-warming-and-ocean-acidification-accelerate/.
The next quicker process of fixing atmospheric CO2 is photosynthesis, and this is done both by plants on land and in the oceans, like: seaweed, giant kelp, and many small plankton-sized organisms; ocean based photosynthesis is a huge component. This happens all the time and fixes CO2 at the rate of plant growth. At a high enough CO2 concentration this process saturates, too.
What is not commonly appreciated is that there is an unbelievably gargantuan amount of fungal and bacterial ‘biome’ in the soil worldwide (as well as inside each of us in our intestines and colon) that interconnects plant roots and actually makes possible the fixing of CO2, by breaking down organics and minerals in the soil enabling plant roots to absorb nutrients they need to complete their growth cycles, which result in carbon being fixed into plant cellulose, and into soil carbonates. The TV show ‘Fantastic Fungi’ gives a visually stunning explanation of this, and is available here, https://www.netflix.com/title/81183477, and here https://fantasticfungi.com/. This plant-based natural process of “carbon capture” is disrupted and destroyed by chemical pesticide dependent industrialized monoculture farming.
I know it is a bitter pill to swallow, but the only real way to slow global warming in any noticeable way is to stop anthropogenic CO2 emissions FOREVER. There are no post-facto technological ‘capture’ or ‘remediation’ techniques that exist now or “could be developed” that would actually work as “silver bullets” of salvation; they would only ‘work’ as money making scams with which to gull those despairing of the ‘loss of easy living.’
Our best response to climate change is to change ourselves in every way possible and without ever looking back, like a butterfly emerging from its chrysalis — and to have fun doing so together. This has to be a willed conscious process because we do not have the luxury of a long timescale in a slowly changing world to allow the transformation of humanity to happen naturally through the unconscious genetically paced process of evolution.
But, with the right shared attitude, that much shorter timescale consciously willed personal and societal transformation could be more magical and take us to more wondrous new worlds than any fantasy of intra-galactic space travel at Warp Speed on the Starship Enterprise.