Land–Based Climate Change is Real

Philip Mulvey

April 28, 2021

Discussion Paper on Agricultural impacted climate change

Climate during the interglacial period currently occurring, changes due to a number of factors. More recently, impacts by humans has become one of the factors. There has been a strong international focus on the global increase in greenhouse gases but the local factors impacting climate change have been largely ignored. The purpose of the following paper is to stimulate debate and promote change. It is not intended to be an academic paper suitable for publication but has been written with due regard to scientific process and providing support from publications.


While noting CO2 emissions are a significant influence on climate, a number of scientists believe the greatest short term impact on climate change is not CO2 emissions but land use changes, in particular how we practise agriculture (Kravcík M et al 2007) . The need for changes in agricultural practise is clear, essential and urgent. If not the outcome of this process will be progressive desertification as has been demonstrated by the collapse of numerous past civilisations (Lowdermilk, 1956, Hillel, 1992, Montgomery, 2012). In 1986 (El-Baz F and Hassan M, 1986) predicted that desertification was likely to decimate all the bread baskets of the world within the next 50 years. Exploring all alternatives to current systems of commercial agriculture as practiced in the developed world is essential and desperately urgent.

The Role and Factors Influencing Soil Organic Matter

Prior to arrival of white settlers, it appears likely that all of Australian landscape (including fauna and flora) was actively managed by the indigenous people, Australian Aborigines, in a proto agricultural manner (Gammage B, 2011 and Pascoe B 2014). Depending on where you are in Australia and reliance on historic documents organic carbon levels in soil were possibly around 4% C and as high as12% C (Strzelecki 1845) prior to impacts from modern agriculture and introduction of introduced pests. Currently soil organic carbon in the eastern wheat belt is typical below 1% and in the western wheat belt on the sand country as low as 0.2% and in the clay areas around 0.8%.

Excluding desert areas, in Northern America organic carbon levels prior to agriculture were thought to be as high as 15% with typical levels in the mid-west being 8 to 12%. Currently organic carbon levels in the mid-west have stabilised between 2 and 4%. Europe follows a similar trend to USA and similar levels, while southern Africa is similar to Australia.

Overall Europe and USA have rocks, alluvium and glacial till (both depositional and windblown) that are rich in primary rock minerals olivine, pyroxene and biotite mica which weather to high charged clay minerals. These high charged clay minerals bind more carbon to the soil than soil of a lower charge in a similar climate zone (Gray et al, 2015). Lower charged and particular pH-variable charge minerals found in continents of old rocks have very limited ability to bind dissolved organic matter(DOM) released during the initial breakdown phase of organic matter. Without bound DOM soil organic matter (SOM) more rapidly mineralises or washes out of the profile. Though it is well known that SOM is important for many soil functions and as the primary indicator for soil health, it’s function in regional climate is not well known.

Reduced organic carbon reduces aggregation and the rate at which soil heats increasing diurnal temperature variation, substantively reduces infiltration, increases hard setting or disaggregation(via raindrop splash erosion), increases runoff, and finally reduces soil moisture capture and retention. The lower soil moisture (and altered moisture characteristic) reduces evapotranspiration.The lower relative humidity from the soil and increased heat radiating from the soil (sensible heat)increases the moisture in the atmosphere required for rainfall. This in turn increases the size of the raindrop initially needed to reach the soil, cool the soil and infiltrate, such that not only does some rain not form but some rain evaporates before the ground and on the ground before infiltrating.Thus effective rainfall, the amount that infiltrates or runs off, is reduced.

The disaggregation and enamouring at the surface and aquaphobicity of low OM soil, prevents air escaping from more intense events which delays infiltration and promotes runoff. The lack of aggregation and surface litter does not impede or pond water which in turn promotes runoff, reducing the time for infiltration.

Thus loss of vegetative cover and loss of organic matter not only reduces rain formed and effective rainfall but also hugely reduces infiltration. The net effect is soil infiltration inputs potentially have been reduced by as high as 60-80% from pre-agriculture levels.

In agriculture a reduction in soil organic matter is often accompanied by a loss of vegetative cover and vegetative roughness due to clearing for grazing and/or cropping. Cropping in particular often involves sowing single species or mono-cultures which also impacts biodiversity. As explained later the percentage of bare ground and variation in vegetation height have a significant impact on the local water cycle.

Water Cycles

Most people are familiar with the large water cycle. Incoming solar radiation heats the sea, causing water to evaporate, known as latent heat, to form clouds. Thus latent heat is the heat lost in causing evaporation and transpiration, known together as evapotranspiration.

Plate 1: Conceptual Model for the Water Cycles

Image from Kravcik et al, 2007, Water for the recovery of climate

The increased evaporation of water over oceans explains why the temperature of the ocean has less diurnal temperature range than the land as only a small fraction of incoming radiation is not converted to latent heat but is used to heat the ocean. This heating of objects by incoming radiation is known as sensible heat. More solar radiation over land is converted to sensible heat, making the land hotter than the sea, causing wind and moisture laden clouds to blow from the sea to the land.This moisture laden wind rises to clear hills and mountains and in so doing causes precipitation, which then runs off via rivers to return to the sea, thus completing the cycle. Within the LargeWater Cycle are numerous Small Water Cycles.The Small Water Cycle is the result of radiant energy being converted to both latent heat and sensible heat with the latent heat evaporating water from the soil surface and transpiring plants.This increased moisture content when the air is cool results in clouds forming locally and light rain,mist, and fog forming. When the temperature is warm thunderstorms form. Clouds are generated locally and precipitated locally. Thus the magnitude of the small water cycle is dependent on the increased dominance of latent heat over sensible heat.

Plate 2: Relationship between solar radiation, latent heat (evapotranpiration)and sensible heat with land use

Image from Kravcik et al, 2007, Water for the recovery of climate

The small water cycle in non-arid areas makes up between 40% to 67% of rainfall with the lower amounts being in semi-arid areas. Removal of native vegetation and in particular the resultant effect of agriculture on soil carbon disrupts the small water cycle by the two fold effect of reducing latent heat by increasing sensible heat (i.e. heating the ground).

Plate 3: Impact of land use on air temperature as a result of increased sensible heat

Image from Kravcik et al, 2007, Water for the recovery of climate

Most proof of this is generally at continent scale over long time frames and therefore difficult to prove. The exception being the rabbit proof fence in Western Australia, which provides the clearest evidence of the impacts of agriculture on climate.

The Bunny Fence Climate Project

The rabbit proof fence in Australia was installed as 3 separate barriers to prevent the migration of rabbits (unsuccessfully). On the western side of the fence, land has been cleared for agriculture while the eastern side remains as native vegetation. An international study involving researchers from Murdoch University, Flinders University, University of Alabama and FZK, IMK-IFU, Germany has become known as the “Bunny Fence Climate Project”. Between 1950 and 1980 rainfall on the western side of the fence declined by 20% (Lyons 1996), while on the eastern side it is generally considered not to have significantly declined.

Deduced interim outcomes from a preliminary review of those the papers readily available to me on the “Bunny Fence Project” include:

  1. Sensible heat from the earth’s surface provides the heat energy for thunderstorms
  2. There must be a differential in temperature laterally for air to ascend turbulently faster than adjoining air
  3. The convective boundary layer (where thunderstorms form) is influenced by surface heat and soil moisture (assuming transpiration equates to soil moisture) A sharp boundary between agricultural land and non-agricultural land (natural) that has surface heat difference, soil moisture differences, and vegetative height and variability differences will increase temperature differences and turbulence in air masses, promoting cloud formation and in particular turbulent cloud formation which has a greater chance of producing rain.
  4. More rain falls over the natural vegetation than the comparable agricultural areas except during late winter and early spring.
  5. More clouds form over the natural vegetation areas during summer, starting in earlier morning right at the boundary. Thus on a plain a boundary of different height of vegetation can create clouds.
  6. More clouds form over crops in late winter to spring than natural vegetation, due to latent heat. However, a change in boundary layer does not mean more rain will fall over equivalent agricultural areas.
  7. Most if not all the climate change in SW Australia has been initiated and sustained by the large regional change in land use in particular change in surface temperature, soil moisture and land texture (less roughness) caused by agricultural practises and elsewhere urbanisation. In SW Australia this has been accelerated since the 1970s with the widespread use of fertilisers and abandonment of 4-6 year crop rotational system for a wheat, canola, wheat system. This meant that legume or pasture phases were no longer practised. Initially, in the 1970s and 1980s, tillage, leaving bare paddocks, was used to control weeds in summer and autumn. More recently, with the widespread adoption of minimal/no till , spraying of stubble with herbicides is used to prevent loss of soil moisture to summer/autumn weeds. It is these most recent practises that are likely to have accelerated loss of soil carbon and created a more uniform landscape in terms of vegetative height difference.

Aerosols from degraded land include non charged soots and salt particles. I hypothesise that aerosols from fully vegetated land, inclusive of trees include charged organic molecules that are cross-linked by chemically stable water bridges forming larger water aerosols (compared to non charged salt and soot) as nucleation for bigger raindrops.

Plate 4 Aerial view of clouds forming preferentially over native vegetation

From: Esau I N, Lyons T J Agricultural and Forest Meteorology 114 (2002) 3-13

Given the first publication on the evidence from the “Bunny Fence” studies, that I could find, on this was 1993 with the more significant paper in 1996 (both by Professor Tom Lyons of MurdochUniversity), it could be said that the climate change in the wheat belt of WA was known to be significantly impacted if not caused by past and current agricultural practise since 1996. If there was any doubt about this conclusion it was stated in the conference paper by Deepak Rays et al (2001)and inferred by Esau and Lyons (2002). However, it is categorical stated by Nair et al, 2011, who concluded that the increased heat from the agricultural areas results in regional change in precipitation for all of SW Australia and concludes “This study identifies some of the processes through which landscape influences weather and climate. It suggests that the impact of land cover changes on atmospheric processes should be a consideration for land management policies in the regions around the globe where significant land clearing for agriculture purposes is occurring” or has already occurred.

Thus it also appears that ongoing climate change impacts by land use changes since the 1950s (orearlier depending on when the change from traditional crop/animal rotation occurred) will/are having a bigger impact or at least as big as the global climate changes caused by CO2 increases. It also explains why all civilisations ultimately result in increasing frequency of drought, collapse of soil fertility leading to war and lack of resilience in the civilisation prior to collapse of the society(Lowdermilk W C 1953, Hillel D, 1992, Montgomery D, 2012).

Without blaming current and past farmers, who have responded to market, government initiatives and narrowly focused research outcomes, the need to rapidly find a commercial agricultural system(s) that can stabilise and better still reverse this process of desertification should be apparent to everyone in the community. Unfortunately the normalisation of climate affects by CO2 emissions has resulted in the expectation by the public that we can adapt to climate change. Such that most extreme climatic events are now blamed by the media as CO2 caused climate change. The fact that climate change and climate extremes currently experienced is more likely due to our land use (both rural and urban) is not even discussed.

Stalled climatic highs are more likely to relate to excess sensible heat over land than change in heat of the ocean. Good example recently have occurred in Australia, USA and Europe in which the summer heat waves related to increased sensible heat of the land. If this is dominant cause of the heat wave it relates to land clearing/agriculture changes causing increased sensible heat more than effects of increased CO2 (ie increased heat in oceans). The most recent example may be the monsoonal low over Townsville in 2018/19 in Australia which caused massive floods which was stalled by a climatic high parked over continental Australia after a period of below average rainfall.The loss of the small water cycle and soil organic matter is exacerbating global climatic cycles making it difficult to select a single cause for an extreme event. Not coincidently, these changes in climate are also occurring with obvious landscape degradation and concurrent loss of profit (annualised over5 years) by farmers, see Plate 5 and 6, leading to an increasing desire by many in the agricultural community to find a better, less destructive and more profitable way of farming.

The relationship between Carbon Dioxide in the Air and Soil Organic Carbon

Carbon Dioxide is a significant green house gas. Carbon dioxide concentrations are transient and move between different pools. The relationship between the pools is not stable over time resulting in carbon dioxide in the atmosphere varying from as high as 6600 ppm to low as 200 ppm in the last500 million years.

Plate 5: The theoretical relationship between soil organic matter and 5 year annualised profit

Note scale on OM axis depends on cation exchange capacity

There are three major sinks of Carbon Dioxide from air. The first is the ocean both directly (the dissolved phase which is short term) and indirectly via marine organisms to limestone/dolomite/siderite and bacteria to black shale and plankton to oil (which is exceptionally long term). The second sink is vegetation which comprises short term pool stored in vegetative structure and the exceptional long term pool via terrestrial swamps to coal. The third sink is soil which comprises short, and medium term storage pools.

Carbon dioxide exists in the soil as organic matter, carbonates and Black Carbon (soots and chars).Soil carbonates (calcrete) are usually an outcome of evaporation exceeding precipitation for most months of the year and thus are associated with semi-arid to arid conditions in the environment.Char can occur in all soil, however, the greatest rate of production and longevity is associated with temperate and semi-arid grasslands and woodlands. Though these pools can be increased by biogeoengineering the fraction in the soil is low.

The most significant soil carbon dioxide pool is soil organic matter which is approximately 50%carbon dioxide equivalents. Soil is made up of mineral matter, organic matter and living matter.Organic matter occurs in all soil as a result of decaying roots, vegetative litter, and the death of organisms which comprise living matter in the soil. The degradation of vegetative litter, extraction of minerals and growth of roots is almost exclusively dependent on the relationship between bacteria, fungi and the root, with algae, animals, nematodes, beetles, worms etc, having a minor but important role.

Organic matter occurs in a number of phases;

  1. labile or dissolved organic matter (DOM) usually produced as exudates from roots and fungi which only lasts in the soil from hours to days,
  2. particulate organic matter that lasts in the soil from months up to several years; and,
  3. recalcitrant organic matter that last from a year to decades and includes organic matter bound to clay and other charged minerals (sesquioxides and soots).

The conversion of organic matter to microbial biomass and carbon dioxide is called mineralisation.Surprisingly increased retained DOM, even though it only lasts a short time, is indicative of increased fungi in the soil and a slower rate of mineralisation as leaf litter is converted to longer term SOM and entrapped in aggregates by DOM acting as a glue. Increased bacteria over fungi results in less DOM, less aggregation and increased mineralisation of litter bypassing sequestration to SOM. Increased DOM means increased algae which means increased non-rhizobium nitrogen fixation. The type of land use or land practice defines whether organic matter is mined for carbon dioxide (i.e. exported to the air), maintained balanced between the pools or sequestered. Practices that increase effective rainfall, increase vegetative litter and increase pH-variable charge will further increase soil organic matter and in so doing remove carbon dioxide from the air. These practices are known in the farming sector as regenerative.

Changing the Agricultural System

There are several different systems of agriculture that may be regenerative, Conservation Agriculture, Biodynamics and more recently Regenerative/Restorative Agriculture, and these should be explored. Finding quickly the right system appropriate to soil charge, climate and landscape and ensuring its uptake is fast and extensive should be the focus of every government. In rural Australia the success of changing practices on properties to conservation agriculture or more regenerative practise is sometimes observed by surrounding neighbours as “they get more rain than us” or “their farms get more thunderstorms”. This has led to the coining of the terming “square clouds ” where rainfall appears to be influenced by boundary fences.

With our continuous crop clients we use a combination of crop rotation, manure and pulse crops, stubble retention, controlled traffic, strategic tillage, together with a targeted reduction or elimination in the reliance on herbicides and acidic fertilisers (most manufactured fertilisers) to achieve a more diverse and sustainable farming system.

Principles of Conservation Agriculture

Powerpoint slide from “Boogeoengineering– An opportunity for soil scientists to participate on the debate on the future o theEarth” – Philip Mulvey Plenary Talk SoilAustralia Biannual Conference Nov 2018

A widespread uptake of the whole suite of practices has been limited. At issue is that main stream agricultural advice and research tends to address individual aspect of a farm system rather than a whole integrated system (Teague 2017). In addition funding for change can be difficult to justify to financial lenders where there are increasing debt concerns or even within a multi-generational farm family.

Consequently at the same time as evaluating the best system of regenerative practices for different farm regions communicating and transitioning farm practise will require a well thought out communication strategy to governments, researchers, lenders as well as the farm community.

Underpinning all these practises are increased soil organic matter and ensuring there is no bare ground anywhere any time. Measuring soil carbon and the spatial variability of soil carbon across the farm together with incentive to do so via a mechanism to trade sequestered soil carbon as an offset will achieve this. All government should consider mechanisms to achieve this outcome before the prediction of El-Baz F and Hassan M (1986) become true.


Since the introduction of agriculture, the clearing of land for food and fibre production has resulted in increasing bare ground, reducing plant and animal diversity, and the mining of soil organic matter.These factors have combined to increase sensible heat and reduce latent over the land. The loss of vegetation variation in height across the landscape due to agriculture together with the change in latent heat and sensible heat has resulted in a substantive reduction, to a complete loss of the small water cycle. The loss of the small water cycle has had a huge impact on rainfall received and together with the factors mentioned above has significantly reduced available soil moisture in the soil. The loss is so great that without change it has been predicted that all agricultural areas will be largely non-productive within 20 years (El-Baz F and Hassan M, 1986). More so than CO2 influence on regional climate, these change in landscape factors are having the greatest impact on climate change of agricultural land.

If we wish to avoid what has happened to previous civilisations we need to avoid the desertification of our agricultural land. I believe there is a desperate need to stop mining soil organic carbon and to restore the small water cycle. Land managers, of which the most numerous are farm land owners, should be encouraged (i.e. government backed incentives or at the very least remove disincentives)to undertake production practices that return the small water cycle to its former significant role in the landscape water cycle. Land practices that maintain vegetative cover, increase organic matter, increase surface roughage and increase landscape vegetation height variation should be researched and encouraged for the continuation of our civilisation. This is the most important climate management factor for farmers.


El-Baz F and Hassan M, 1986, Physics of Desertification, Dordrecht, Netherlands,: Martinus, Nijhoff

Esau I and Lyons T, 2002, Effect of sharp vegetation boundary on the convective atmospheric boundary layer, Agricultural and Forest Meteorology 114 (2002) 3-13

Gammage B 2012, The Biggest Estate on Earth: How Aborigines Made Australia

Gray J, Bishop T and Wilson B 2015, Factors controlling soil organic carbon stocks with depth inEastern Australia, 2015, Soil Sci. Soc. Am. J. 79:1741-1751, doi:10.2136/sssaj2015.06.0224

Hillel D, 1992 – Out of the Earth, Civilisation and the Life of Soil, University of California Press,

Kravcík M, Pokorný J, Kohutiar J, Kovác M, Tóth E, 2007, Water for the Recovery of the Climate - ANew Water Paradigm, ENKI

Lowdermilk W C 1953, Conquest of the land through seven thousand years, US Government Printing Office

Lyons T, Smith R and Xinmei H, 1996, The impact of clearing for agriculture on the surface energy budget. International Journal of Climatology Vol 16, 551-558

Montgomery D, 2012, - Dirt: the Erosion of Civilisation , University of California PressRay D, Nair U, Welch R, Su W and Kikuchi T, 2001, Influence of landuse on the regional climate of SW Australia

Nair, U. S., Y. Wu, J. Kala, T. J. Lyons, R. A. Pielke Sr., and J. M. Hacker, 2011, The role of land use change on the development and evolution of the west coast trough, convective clouds, and precipitation in southwest Australia, J. Geophys. Res., 116, D07103, doi:10.1029/2010JD014950Pascoe B, 2014 Dark Emu, Black Seeds: Agriculture or Accident?

Pielke Sr. R, 2001, Influence of the spatial distribution of vegetation and soils on the prediction ofCumulus convective rainfall, Review of Geophysics, 39, 2 , May 2001, p151-177

Teague R, 2017 Managing Grazing to restore soil health and Farm Livelihoods. Proceedings 2017Western Canada Conference on Soil Health and Grazing

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