Climate Change

How Soil Mismanagement Drives Climate Change

Why having land with vegetative cover is so crucial to mitigate heat creation in our atmosphere.

July 28, 2022

We at Carbon Count spend most of our lunch breaks chatting about the relationship between soil, carbon, and climate change. The following deep dive into this relationship comprises extracts from our CEO Philip Mulvey and his daughter Freya’s book Ground Breaking: Soil Security and Climate Change. The basic tenet in this book underpins all that we seek to achieve at Carbon Count.

How agriculture impacts our climate

As discussed in our previous blog post, climate change is initially and significantly controlled by the small water cycle from continents (see figure 1). 

What’s important to understand is that soil and precipitation, especially the small water cycle, are interconnected aspects of landscape management. Southern and central Australia have experienced a reduction in rainfall up to 30% in the last 50 years, as well as a decrease in rainfall predictability. However, it is not generally recognised that this rainfall loss is partially attributable to degraded soil caused by agricultural practices.

Let’s have a closer look at the relationship between agricultural land management and climate.

Figure 1: The small water cycle. (Source: Ground Breaking: Soil security and Climate Change. P Mulvey and F Mulvey, August 2021)

Our favourite image depicting how agriculture affects climate is the below aerial shot of the Rabbit–Proof Fence in Western Australia (Image 1); a 1166km long pest–exclusion fence constructed between 1901 and 1907 to keep rabbits and other agricultural pests out of Western Australian pastoral areas. 

In 2005 the world’s largest experiment in climate change and desertification began on the two sides of this fence. 

Image 1: Aerial view of clouds forming preferentially over native vegetation. J M Hackere in Eesaul N, Lyons T J, Agricultural and Forest Meteorology 114 (2002) 3–12. Source J M Hacker

The landscape offers striking evidence of the negative impacts of agricultural practices on soil and climate. It became known as ‘the Bunny Fence Experiment,’ the only regional scale, a paired–climate experiment in the world (we dive into more detail in Groundbreaking: Soil Security and Climate Change). 

On the left, the cloud build–up over native vegetation is evident; on the right, there are no clouds over the less vegetated agricultural ground. However, to understand that the climatic events captured in the photograph are not coincidental, we’re going to explain the basic science that underpins the landscape and atmospheric processes at play. 

Understanding how the sun’s radiation impacts earth: Sensible and latent heat explained

It all starts with the sun. Greater than 95% of incoming radiation from the sun is converted to one of two types of heat: latent heat and sensible heat. 

  • Latent heat is used in the phase change of materials from one state to another: solid to liquid and liquid to gas; for example, snow to water and water to clouds. 
  • Sensible heat is simply a temperature change, no change of state occurs.

The difference between latent and sensible heat is best illustrated through an experiment: 

  • Step 1: Put a thermometer calibrated to 600°C in a large pot of water and heat the pot. The water temperature increases to 100°C and then stops and remains at 100°C while there is water in the pot. No matter how high the heating knob is set, while the water is boiling, the water temperature will not exceed 100°C. 
  • Step 2: Place the empty pot on the stove and set the heating knob to medium. The temperature rises rapidly past 100°C, the thermometer will read above 550°C, and the pot's base overheats.

In Step 1, once the water reaches 100°C, the water temperature does not change because the energy is converted to latent heat due to changing the state of the water from liquid to gas.

In Step 2, as energy is added, it is converted to sensible heat and causes a temperature rise far beyond 100°C in the pot. This is because sensible heat increasingly agitates the atoms of a material without changing its state; it just makes it hotter. Furthermore, when the sensible heat source gets weaker (and the material it has been heating cools down), infrared radiation is released by that material as it returns to its former level of rest.

Why is this important to understand? Because the type of heat the sun’s incoming radiation is converted to directly impacts the small water cycle and hence our climate; and the deciding factor is vegetative ground cover.

This experiment demonstrates why having land with vegetative cover is so crucial to mitigate heat creation in our atmosphere. Plants store water and help to trap water in the soil by providing the substrate for organic matter. This is why building organic matter is a key component in mitigating global warming.

The mining of organic matter from the soil by suboptimal agricultural practices has had, and continues to have, a profound impact on the ratio of sensible heat warming up the earth and, via infrared radiation, the atmosphere to latent heat used in evaporation. 

This drastically reduces, if not eliminates, the small water cycle, significantly impacting the Earth's precipitation and temperature regulation, one of the results being loss of cloud coverage, as can be seen has happened in the above image of the Rabbit–Proof Fence.

The associated reduction of precipitation and increase in sensible heat accelerates desertification by not only the obvious impacts of less rain and higher temperatures, but also destroying soil as organic matter diminishes. 

Reducing emissions is an essential part of climate change mitigation, as is removing excess of the principal greenhouse gas, CO2. From this discussion however, we must conclude that changing agricultural practices will be easier, more immediate, and have a greater impact on climate, than reducing GHGs in the atmosphere to zero emissions. 

Immediate action is required to develop sustainable solutions for soil security, not just to moderate but to reverse anthropogenic climate change. 

We at Carbon Count have made it our mission to regenerate landscape, reverse anthropogenic climate change, and reinvigorate agricultural communities through soil carbon farming practices. If you would like to find out more about the power of soil carbon sequestration or would like to understand whether your land is suitable for a soil carbon project, reach out, and someone from our team will be in touch.

A note on measuring climate change by global temperature rise

As discussed in our previous blog post, climate change is initially and significantly controlled by the small water cycle from continents. Because of this, we argue that global temperature rise is an inadequate measurement of climate change.

Our research suggests measurement of precipitation loss predates the agreed measurable global temperature increase by at least 20 to 30 years. 

It is essential to understand that, because of the complexity of the climate system and the limitation of computing power, caution should be exercised in over–reliance on current climatic modelling methods. This is specifically focusing solely on global temperature rise to gauge the intensification of climate change.

Nevertheless, given the critical role of science in shaping how we understand climate change and our policy responses, modelling global temperature rise is necessary to explain the range within which an outcome may occur and evaluate the impacts of proposed solutions. Even so, we stress that climate model projections of precipitation must be carried out that account for soil and vegetation cover as well as season variability, and all associated sensitivity analysis.

Postscript:  A book shop release of Phil’s and Freya’s book, Titled Ground Breaking is due out later this year.

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