Part 3: The Water Cycle & the Travesty of Bare Soil
In Part 1 of this series we talked about the soil carbon sponge, which is central to what we are going to explore here, through the water cycle. So for a very quick recap: soil with no organic matter is just dusty dirt, which holds very little water and is highly susceptible to desertification. However soil containing organic matter (largely made up of carbon), which gets incorporated into the soil structure by the myriad of organisms present in healthy soil, becomes like a sponge; springy in texture, able to hold vast quantities of water and support endless healthy growth of plants.
Water
The water cycle is rarely part of the climate debate, which is strange because it drives the heat dynamics of our planet. Water itself is the most significant greenhouse gas, so it is essential that we cultivate a holistic perspective here, we can’t simply see things as good or bad; without the greenhouse effect we would not have a habitable planet, and water acts just as much to cool the planet as it does to warm it. Everything is about balance, and our climate, something nature has finely tuned over millions of years, is now out of balance. We are locked into global warming and it is essential we explore how best to naturally cool our planet.
Anthropogenic climate change is not just about the addition of ‘ancient’ carbon to the system, but also about the ways in which management of land affects the water cycle, and therefore the heat dynamics of our planet.
Incidental Radiation
The sun shines and warms the planet (incidental radiation), which absorbs 342 watts per m2 of heat energy a year. Before climate change, the same amount was reflected back and lost into space, but due to our out of balance greenhouse effect, the energy reflected back into space is just 339w/m2, a shortfall of 3w/m2, which is creating global warming.
Latent Heat Flux
When the sun shines onto the earth, the heat causes evaporation of water from the soil and bodies of water, and evapotranspiration from plants and trees. For each gram of water that transpires from plants and trees up to 590 calories of heat energy is removed with it, cooling the earth’s surface in the process. 24% of incidental radiation is sent back into space through this process.
The micro-water droplets created in the latent heat flux rise up to form high albedo clouds. These clouds then reflect about 1/3 of incidental radiation back out into space. It used to be the case that around 50% of the earth was covered by clouds at any one time, but cloud cover is reducing, due to the disruption that land management is causing in the water cycle. If we could increase cloud cover by just 2% then we would mitigate the 3w/m2 heating.
So it is easy to see why geo-engineering and cloud seeding is such a temptation to ‘the powers that be’ in an attempt to halt run-away climate change. But these ‘sticking plaster’ approaches are fraught with problems and don’t address the root-cause of the problem, which could be far more safely and effectively addressed by restoring the earth’s hydrological cycles.
Heat Hazes, Clouds and Rain
Desertification and bare soils mean the amount of dust in the atmosphere is increasing, as are smogs from fossil fuel combustion (especially in Asia), plus the smoke from forest fires around the world. All these particulates are known as aerosols.
Aerosols in the atmosphere attract the micro-water droplets creating a heat haze, raising humidity and heat, but never aggregating into clouds. These heat hazes contribute to higher ground temperatures. The ‘Asian Brown Cloud’ is an example of one of these hazes. It hangs over eastern China and southern Asia each year from November to May, and is associated with a decrease in India’s summer monsoon over the last 100 years.
The reason these hazes persist is because such aerosols cannot seed rain clouds. There are in fact only three natural factors that can aggregate micro-water droplets into clouds and rain. These are: Ice Crystals – which form at colder higher altitudes, Salt Crystals – in water evaporated from the oceans, and Bacteria – which are present in the water transpired from plants and trees. Yes, forests do create their own rain due to these bacteria. In the Amazon five times as much rain falls as leaves via its rivers as a result.
Re-radiation
The focus of climate science is almost exclusively on carbon dioxide, and more recently methane and nitrous oxide. However the re-radiation of heat from the earth surface, and the failure of global water cycles is less talked about. Perhaps because these things are difficult to quantify and therefore model.
Re-radiation is the heat created and then radiated back out, by any surface exposed to the rays of the sun. When sunlight hits plant leaves, as we have already discussed, those leaves transpire water, creating the latent heat flux, which cools the surface of the planet and sends the radiation back into space. With dense leaf cover, the soil beneath the plants rarely rises above 20 degrees centigrade.
However when the sun’s rays hit bare ground, the surface can reach 60+ degrees centigrade, and there is no sustainable, natural function, other than plant transpiration, that can remove that heat energy back to space and cool the surface.
The re-radiation from bare soils therefore, is a massive factor in the warming of our planet, because re-radiation from bare ground is exponential in nature. Temperature to the power of 4, which is temperature x temperature x temperature x temperature. Re-radiation from bare ground therefore, is super-heating the planet.
Bare soils, deserts and desertifying lands end up with heat domes (high-pressure weather systems) parking over them and not shifting. Low pressure cannot displace high pressure, so these places get hotter and hotter. The only thing that can change this situation is the return of plant cover to the land and the rebuilding of the carbon soil sponge, which creates a soil water reservoir, essential to the function of that water cycle.
Bare Soil Agri-culture
Intensive agriculture is largely associated with mono-crop systems, because they are still seen by most farmers as the most efficient way to produce food. But these systems are efficient only under partially calculated costs, and subsidised inputs. With the UN warning that we have less than 60 harvests left if we carry on producing food in this way, then the way we measure efficiency and productivity needs to become more holistic, and include all the collateral costs to the environment and human health.
Such intensive systems not only kill living soils and oxidise carbon into the atmosphere, but also leave bare soils, often for large parts of the year.
Millions of hectares of olive trees throughout Europe for example, are managed with bare soil underneath. Instead, understory meadows could be managed by grazing animals like sheep. This would reestablish living soils and sequester carbon which would benefit the health and productivity of the trees. But perhaps most importantly this plant cover would help cool the planet and halt the desertification of Europe’s mediterranean regions.
Regenerative Grassland Management
There are farmers around the world doing extraordinary things using the principles of regenerative agriculture using livestock, our mobile bio-digesters, to rehabilitate degraded lands. For us this is perhaps the most hope-generating story of our time. The re-greening desertifying areas, the rehydrating of drylands, where rivers once more flow. With no fancy engineering, but simply the use of animals to re-establish living soils and the soil carbon sponge. Below is a short film from Kiss the Ground about this:
Conclusion
In this series on Climate Change and Agriculture we began with the soil carbon sponge and we are ending with it, and rightly so, for it is the key to unlocking us from the multiple crises of climate change, biodiversity loss and extreme weather events. All of these are, at least in part, a symptom of the loss of healthy living soils.
Finally The Soil Carbon Sponge:
- sequesters carbon from the atmosphere.
- requires herbivores, especially in the drylands, to create it.
- is the foundation of living, biodiverse soils, which in turn are the foundation of above-ground biodiversity.
- the mechanism through which soils are able to hold water.
- is central to production of nutrient dense foods.
- if re-established can reverse desertification.
- is critical to mitigate both flood and drought events.
- results in the return of clean healthy rivers, because rapid runoff becomes a thing of the past.
- is the foundational aspect of the water cycle, helping water driving planetary cooling rather than heating.
- makes soil smell good.
References
Walter Jehne on the Soil Carbon Sponge and the Water Cycle (much of this final article is taken from Walter’s inspiring work)
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