When I visited South Africa in the late 1990’s, I met rangelands scientist Dr Louis du Pisani. He told me how he had discovered the difference between perennial grasses and perennial edible shrubs, in terms of how they storeand utilise energy reserves. He explained that what happens in the roots is different.
His research into the Karoo Bush, which is similar to our perennial saltbushes, showed that when the shrub called on energy reserves, the root volume did not reduce. The energy reserves were in the centre of the roots and not part of the structure. The ability of the Karoo Bush to maintain root volume, after calling on energy reserves, means it can keep sourcing moisture and nutrients below the roots of perennial grasses.
In good years, annuals utilise excess moisture lying between perennial grasses to add to carbon flows, while in dry times, edible shrubs utilise moisture that is below perennial grasses to provide some carbon flows when perennial grasses are dormant. But, it’s critical that both the grass and the shrubs are managed according to their needs.
Like perennial grasses, if the energy reserves become depleted, then edible shrubs become weak and die. What alerted Louis to the different storage process, was that the Karoo Bushes that had died from overgrazing, had the normal root volume, i.e. the roots did not reduce with the depletion of the energy reserves.
ANOTHER LESSON IN TIMING
His other important discovery was that, unlike perennial grasses, which replenish energy reserves before reaching maturity, the shrubs made the main transfer of plant sap out of the leaves and down to the roots, with the onset of a dry season, but little before. We know that in Australia, Old Man Saltbush has the ability to transfer plant sap from leaves to roots.
Because of the timing of the transfer from leaves to roots, the complete defoliation of edible shrubs before the onset of dry times, if allowed to happen regularly and then followed by continuous grazing, can see the death of shrubs through depleted root reserves.
A BLESSING AND A CURSE
It is the ability of shrubs to grow in dry times, that puts them at risk if not managed properly. A shrub producing new growth in a dry time from subsoil moisture, after it has been completely defoliated back to stems, is no different to a perennial grass plant that is starting to grow from rain after being dormant. In both cases, energy reserves will start to run down if animals keep them defoliated as they keep trying to grow.
In a mixed pasture of grass and edible shrubs, poor grass managers transfer grazing pressure onto the shrubs too early in the drought cycle. If animals are only removing some of the leaves on the shrubs, to source trace elements, then there is not a problem.
Appreciating that edible shrubs have a different process to perennial grasses, is important for the management of saltbush plantations. It also explains why established plantations of Old Man Saltbush perform well for some and not others.
Francis Ratcliffe’s novel, “Flying Fox And Drifting Sands”, published in 1938, documented how over grazing early in the twentieth century in South Australia, saw the demise of saltbushes in large sections of the arid areas.
While shrubs have the ability to produce carbon flows in dry times, they do need to be managed differently to grasses.
Could it be that a lot of cattle producers world-wide are being unfairly blamed for progressing climate change because of the methane released by their cattle? Going one step further, this article will suggest that the methane emissions of the Australian sheep and cattle industry are not changing the climate, because they have been stable since the 1970’s.
We have to ask the question, is the current way of comparing methane and carbon dioxide, using the Global Warming Potential (GWP) approach, the best way to assess the outcome of the methane produced by ruminant animals like sheep and cattle? I raise the point, keeping in mind that the debate is about “climate change”. We keep hearing the comment that we have to limit “change” to two degrees.
I am not suggesting that the science the IPCC and the world is relying on is wrong, but maybe it is worth having another look at how we are interpreting it in the area of ruminant animals.
The scientific evidence to support what follows in this weeks’ column, resides in the peer reviewed paper, “Offsetting methane emissions – An alternative to emission equivalence metrics”, which was published in the “International Journal of Greenhouse Gas Control” – (click on “Download PDF” after the link opens, then click on “Article”). The thrust of the published paper is that we should be comparing “ongoing methane emissions (or reductions)” to “one-off emissions (or reductions) of carbon dioxide”. This weeks’ column will focus on the outcome of “ongoing stable methane emissions” from ruminants. The GWP approach focuses on one-off emissions and compares a one-off emission of methane to a one-off emission of carbon dioxide.
ONGOING STABLE METHANE EMISSIONS FROM CATTLE REACH EQUILIBRIUM
The best way to understand the diagram of the cow below is to visualise methane constantly being released by the cow and accumulating above it (in the green circle). While the cow is releasing methane, past emissions will be breaking down in the atmosphere at the same rate. Methane lasts 12 years in the atmosphere (some suggest shorter), before being broken down into CO2 and H2O. It is broken down by a chemical reaction with hydroxyl radicals (OH) that keep forming in the atmosphere. Assuming the methane released by the cow each year is the same, then the methane residing in the atmosphere (green circle) will be in equilibrium, with the additions and subtractions. It is true that cow size and pasture quality determines the amount of methane released, however, the fact the cow changes size and eats a different diet over time is a variable which averages out over time.
In the diagram above, think of the equilibrium amount of methane, as a permanent balloon of methane that follows the cow around every day.When the cow is sent to the meat works and replaced by another cow, the balloon follows the next cow that is put in the paddock. In fact, all the cows that followfor the next 500 years.
The cow and its replacements, will be producing methane permanently, however, at the end of the life cycle of the methane, what is produced in the first year of the new cycle, will only be replacing the first year in the previous cycle, which will now be gone. Methane is not an accumulating gas like carbon dioxide is.
HOW THE ATMOSPHERE FUNCTIONS
I am a very basic person, I like to get back to basics and go from there. So let’s look at the climate change debate from the atmosphere’s perspective, and how it functions.
The atmosphere does not understand the difference between all the different greenhouse gases, nor the comparative figures we put on them with the GWP approach. It only understands the total “radiative forcing” of all the gases combined. A bit like we are only interested in the flood height, not where all the water came from.
The warming effect of each greenhouse gas is known and is referred to as “radiative forcing” and is measured as watts per cubic metre of gas. Stabilising the climate relies on stabilising the total radiative forcing of all the greenhouse gases in the atmosphere. The purpose of the cow diagram was to show that ongoing stable methane emissions from ruminants, do not change the total radiative forcing.
AUSTRALIAN METHANE EMISSIONS
If you talk to the atmosphere, it sees sheep and cattle in Australia as the mouse in the room in terms of the changes it is witnessing. This is because the combined methane emissions of sheep and cattle in Australia peaked in 1970 and have basically remained stable since, with just a slight decline. This is a little known fact. It is interesting to note that the 1970’s was the last time the herd was at 30 million head. S o while it is true that methane from Australian ruminants have always influenced the day to day climate, in recent times, their methane has not been a cause of the ongoing change in the net balance of greenhouse gases, as the diagram below shows.
The bottom line on the graph is the amount of methane released each year by livestock.
The top line on the graph is the net mass of methane attributed to livestock. The net mass is emissions less what has broken down. It is often referred to as the atmospheric burden.
The amount of methane in the atmosphere is still increasing, however this is not due to Australian ruminants.
THE METHODOLOGY BEHIND THE GWP APPROACH
The Global Warming Potential (GWP) approach has been widely adopted as the metric for comparing the climate impact of different greenhouse gases.
For those wanting to know exactly how the GWP methodology came into being, read the paper, “The global warming potential – the need for an interdisciplinary retrial” by Keith P Shine.
The GWP approach was designed for decision makers in government and considers three time horizons, 20/100/500 years.
As Keith Shine explains in his paper, decision makers were presented with modelling showing comparisons over 20 years, 100 years or 500 years, they put their finger on the middle time horizon and ran with it. That is why we have the 100 year rule.
HOW I CAME TO MY CURRENT POSITION
When I went into Idalia National Park in Nov 2009, a year that was very wet in the first half, the photo below is what I saw. There were no sheep or cattle in the park, just kangaroos. It was obvious that the kangaroos had completely shut down the carbon flows in the area between the trees, i.e. carbon that should have been in the paddock was still in the atmosphere.
At the time, it was being suggested by some that sheep and cattle should be replaced with kangaroos because kangaroos emit virtually no methane. It was a perfect example of having a single issue debate and not looking at the big picture (taking a systems approach). I then decided to compare the carbon footprint of kangaroos versus sheep and cattle. If kangaroos reduce carbon flows, then their methane advantage is immediately being eroded. Also, a kangaroo researcher at the University of Sydney had told me that kangaroos are even more selective than sheep in what they choose to eat. This means that when they are present, they are reducing the digestibility of the diet available to cattle, which means the cattle will then produce more methane per kg of production.
As somebody who knew absolutely nothing about how the atmosphere functioned, I started reading and really struggled, as it was so complicated. However, having no formal training in the area, meant I was reading with no preconceived ideas. After I progressed past the stage of total confusion, something did not add up with how the science was being applied in regard to ruminants. If my memory serves me right, it was the three different figures placed on methane that really started me thinking. One thing lead to another and then a group of well respected scientists joined me in thinking outside the square. Hence the paper referred to at the start.
THE PEER REVIEWED PAPER
In the paper “Offsetting methane emissions – An alternative to emission equivalence metrics”, the science is very complicated but the logic is not. The reference to “equivalence metrics” is a reference to the GWP approach.
The paper is part of an emerging body of work on how to do better than the 1990 IPCC approach. As well as our paper, Smith has written one and later Myles Allen has also written a paper. The paper has been cited by another paper.
The way the GWP approach works, is that ONE OFF emissions of methane are compared with ONE OFF emissions of carbon dioxide. Also, the GWP approach comes up with different figures when comparing methane and carbon dioxide, depending on the time frame of the comparison. If we are looking 20 years forward, then they say methane is 72 times worse than carbon dioxide, 21-23 times worse if the time frame is 100 years, 7.6 times worse if the time frame is 500 years.
However, our paper makes a strong case for comparing ONGOING emissions of methane with ONE OFF emissions of carbon dioxide. This approach gives the same comparison between methane and carbon dioxide, regardless of the time horizon chosen.
Experts in the field initially struggle with this approach much more than lay people, because their mindset is fixed on the GWP approach and how it compares methane and carbon dioxide.
APPLYING THE SCIENCE OF THE PAPER IN THE PADDOCK
After suggesting that methane and carbon dioxide should be compared differently, the paper then looks at how much carbon needs to be sequestered in the paddock, to remove the effect of the ongoing stable methane.
The paper proposes that a one-off sequestration of 1t of carbon would offset an ongoing methane emission in the range of 0.90 – 1.05 kg CH4 per year. Provided we keep the carbon from the CO2 in the landscape, then the one off sequestration accounts for the ongoing methane for centuries.
The paper came up with building up the sink over forty years, a bit like paying off an interest-free loan at 2.5% of the balance each year.
Applying the equation published in the paper is like leaving the cows in the paddock as if they were not emitting methane.
Putting it another way, the green circle above the cow in the diagram, is the atmospheric burden produced by the ongoing methane and, this is what has to be offset by bringing down carbon dioxide from the atmosphere and storing it’s carbon in the paddock.
Because of the way the atmosphere functions over time, the paper had to apply the 0.3 factor (about to be discussed) to calculate the figure for carbon. The 0.3 factor increases the figure for carbon because sink efficiency reduces over time.
Committed warming, which was mentioned in the column beside the cow diagram, did not have to be considered in the offsetting calculations, because it applies to both CO2 and CH4.
In a sense, the paper documents how producers can be part of the solution. The equation in the paper is reversing climate change. Even offsetting 5% of ongoing stable methane is reversing climate change.
Realistically, nobody expects cattle producers to be applying the paper’s equation and reversing climate change, when society has chosen to let climate change continue with the ongoing release of carbon dioxide.
However, there are plenty of cattle producers who are good managers of carbon flows, who without even realising it, are applying the paper’s equation. This is because better management of carbon flows increases paddock carbon, especially short term carbon. I deliberately mentioned short term carbon, because the atmosphere doesn’t differentiate between short term carbon and long term carbon. It just knows that the carbon atom is not in the atmosphere.
THE 0.3 FACTOR
Feel welcome to skip this section and the next one. They are a bit heavy going and are included more to answer the questions technical people would be asking.
When the paper calculated how much carbon has to be removed from the atmosphere, and stored in the paddock, to offset the ongoing stable methane emissions, the oceans had to be considered. This is because carbon dioxide moves between the oceans and the atmosphere, as part of rebalancing.
For fossil carbon emissions, this re-balancing of carbon by the oceans works for you, and takes some of the carbon out of the system. For sequestering carbon, the re-balancing of carbon by the oceans works against you.
Atmospheric scientist, Pep Canadell explains that in the short term, in times of growing CO2 emissions, a proportion of 0.4 remains in the atmosphere. This is called the airborne fraction. When one looks at the longer term, this fraction drops to a proportion of 0.3 (the 0.3 factor that we use in the paper). Put simply, if you are talking long term, for every tonne of carbon you remove from the atmosphere, the end result will be a reduction of 0.3 of a tonne in the atmosphere.
The 0.3 is called “the airborne fraction of cumulative emissions”.
The long-term nature of CO2 is what justifies balancing it against the long-term equilibrium CH4 level, in which case, you have to use the actual long-term number for CO2.
Putting all this into a layman’s perspective, you have to sequester three times more than simple logic suggests. The reduction in “sink efficiency” is because of the rebalancing of carbon by the oceans is undermining your efforts on land.
THE ABSTRACT OF THE PAPER
It is widely recognised that defining trade-offs between greenhouse gas emissions using ’emission equilivalence’ based on global warming potentials (GWPs) referenced to carbon dioxide produces anomalous results when applied to methane. The short atmospheric lifetime of methane, compared to the timescales of CO2 uptake, leads to the greenhouse warming depending strongly on the temporal pattern of emission substitution.
We argue that a more appropriate way to consider the relationship between the warming effects of methane and carbon dioxide is to define a ‘mixed metric’ that compares ongoing methane emissions (or reductions) to one-off emissions (or reductions) of carbon dioxide. Quantifying this approach, we propose that a one-off sequestration of 1t of carbon would offset an ongoing methane emission in the range of 0.90 – 1.05 kg CH4 per year.
Our analysis is consistent with other approaches to addressing the criticisms of GWP-based emission equivalence, but provides a simpler and more robust approach while still achieving close equivalence of climate mitigation outcomes ranging over decadal to multi-century timescales.
If you believe in human induced climate change, then it is the long term gas carbon dioxide which will paint us into the corner, not stable methane from ruminants (sheep and cattle).
“Stabilising the climate means cutting all future carbon dioxide emissions and stabilising ongoing methane emissions from ruminant animals. This statement does not apply to fossil methane which is different to ruminant methane as it keeps adding a new carbon atom to the atmosphere.
Sheep and cattle produce less methane per kg of production when carbon flows are managed better. This is because the digestibility of their diet is better. Also, with better management of carbon flows, the extra carbon (including short term carbon) residing in the paddock is offsetting some of the equilibrium methane.
If you are lucky enough to catch those first summer storms, subsequent storms will often follow the same track. The first storm changes the ground cover (carbon levels) relative to surrounding areas, as well as increases soil moisture.
Weather and land are inseparable and interrelate with each other.
My initial interest in this subject was stimulated by a discussion I had with Robert (Bob) Leighton over tea one night. I sought his opinion, as one of Australia’s leading meteorologists, on why storms often follow where previous storms went. Often one property or part of a property would remain dry, while the one next door was having a reasonable season.
It was not his area of expertise, but he started to explain how storms required a certain amount of moisture for it to start raining and, the rain stops when the moisture drops below a certain level. If there is an additional source of moisture, then the storm would proceed instead of petering out. Creeks and rivers were discussed as a source of moisture, which is consistent with storms often performing better near them over time. In the course of conversation, he raised the issue of vegetation cover and its influence on rainfall by contributing moisture. The other issue he raised was the temperature of the landscape due to vegetation cover or lack of it and how this effected the weather.
In a previous trip to America, Bob had been told by US researchers that they had been researching the issue of vegetation and its effect on rainfall. This is the question he asked on my behalf:
I remember when I was visiting AWC over four years ago that there were discussions about the interesting weather experienced in Kansas storms, tornadoes, ice storms etc. And they told me that a major moisture input for tornadoes, storms originated from the vegetation through “tornado valley”. (Of course, I originally thought that most of the moisture would have come from the Gulf of Mexico). I was wondering if you know of any statistics or papers on the subject of moisture availability from vegetation for cloud build-up in your territory that would be available
Response from Steve Corfidi (Kansas):
I don’t think that there is much question that local evapotranspirative fluxes affect patterns of convective initiation. The role of “vegetatively-derived” moisture is, however, a comparatively new one; the importance of the subject has become more widely accepted only in the last 10 years or so. Canadian meteorologists in the prairie provinces are especially interested in the subject, as their short wheat-growing season corresponds to the time of maximum thunderstorm frequency.
Steve included a manuscript received by the Iowa State University, which in part stated;
Vegetation cover was found to promote convection, both by extraction of soil moisture and by shading the soil so that conduction of heat into the soil was reduced (thereby increasing the available energy).
Studies of 30 years of monsoon patterns over India by Purdue University scientists showed that tropical storms are sustained by moist soil, but tend to fizzle over dry ground.
The storm will have more moisture and energy available over wet soil than dry (Associate Professor Niyogi)
GRAZING PRESSURE AND RAIN
In 1998, while in South Africa, one of the groups of scientists I spent time with was at the Range and Forage Institute in Bethlehem. During discussions, it was explained to me by one of the scientists that he was convinced that lack of vegetation cover due to excessive grazing, was responsible for a drop in rainfall on the plateaus that rise up above the plains. He said that these small elevated areas were the most productive sections as they had much higher rainfall than the lower plains area. His theory was that due to greatly reduced vegetation cover (carbon levels), there was much more heat rising up from the soil and dispersing the rain bearing clouds.
DAM CHANGED RAINFALL
The concept of moisture from the landscape promoting thunderstorms, is well supported by a long term change in rainfall near Inglewood on the Qld/NSW border. A long-term producer who had a property beside the Coolmundra dam explained to me that, after the dam was built, the rainfall increased above the-long term average recorded in his family’s records. He explained that the path of the storms was over the dam before getting to his property. This gave the storm clouds an opportunity to increase their moisture level. When questioned on whether others further along the storm path had an increase in rainfall, he assured me they had not. It is likely that the dam activates clouds close to raining and so they part with much of the moisture before getting to others’ properties.
German scientist Wilhelm Ripl talks about preventing large thermal differences in the landscape:
The more evaporation processes at and within the surface and foliage of vegetation per area that takes place, the more even the temperature is distributed and the cooler are vegetation structures, markedly so at times with high-energy flow (midday in summer). Areas that are mostly better cooled show lower atmospheric pressure than the overheated surroundings. It is easy to understand that these small local areas lacking any means for an efficient temperature-regulating system are channelling energy into global weather systems and thus modulating them. Areas with an even cover of vegetation, with sufficient evaporable water, have more predictable weather events than do damaged areas without proper vegetation cover.
AN EXAMPLE OF TEMPERATURE DIFFERENCES
This is a comment by a reader of the column some time ago:
Hi Alan, The carbon flow and the outcomes you describe has some impact and can be impacted by the conditions in the ground, including temperature. I have taken temp readings here on my farm and find that on hot days the variation in temp from bare soil to trash covered soil and then to growing grass covered soil can be 5 degrees c between each, i.e. a full span of 10 degrees c
Resilient landscapes, due to better management of carbon flows over time, have the potential to attract higher rainfall, as they have different energy patterns and often have more moisture to offer weather systems.
Have you ever thought of drought in the context of carbon balances?
Graziers run a carbon business, and they are out of business, when animals consume the last of the carbon residing above ground. A producer’s day job is recycling carbon and then selling carbon based products, be it meat or fibre.
WHO DOES DROUGHT VISIT AND WHEN?
Droughts are the climax of a dry spell, however the arrival of drought is determined by more than just lead up rain. The timing comes down to the ability of paddocks to generate some carbon flows from any isolated small falls of rain to postpone drought. This relies on how well soil is structured to let rain in and the ability of plants to respond. Of course, good operators sometimes postpone the drought phase for long enough to escape it with, what others call, drought-breaking rain.
Thinking cause and effect, drought is the run-down of “short term” carbon above ground, i.e. ground cover.
One strategy for slowing the onset of drought is to increase the percentage of perennials in the pasture. The advantage of perennials is that they can respond to isolated single falls of rain while annuals can’t.
The survival mechanism for perennial grasses to cope with dry times is to go into dormancy. Interestingly, soil microbes have the same strategy. During dry periods, perennial grasses will be going in and out of dormancy, adding a bit to ground cover each time they come out of dormancy.
The survival mechanism for annuals is to avoid dry times. They do this by producing seed so that the next generation can germinate and grow next time there are good conditions. This is why pastures weighted towards annuals are fair weather friends and let you down quickly when the going gets tough.
Because perennials are the only reliable source of carbon flows over time, avoiding drought is all about maintaining the health/resilience of the perennials.
Having paddocks with healthy/resilient soils is the other aspect of slowing the onset of drought. Healthy soils let rain infiltrate quicker, reducing run off. This is very important because there seems to be a pattern lately for rain to be heavier, even in dry years. Soil health relies on carbon flows to feed the soil life needed to keep it well-structured and fertile.
Plants fail first and then the soil starts to fail. This is because carbon flows reduce as plants become unhealthy. So in reverse, with better management, it is the perennials that repair quicker than the soil. Whichever way you look at it, plant management after rain determines your destiny.
INCREASING SHORT TERM CARBON BALANCES IN PERENNIALS POSTPONES DROUGHT
If you want perennial grasses to respond to small falls during dry periods, they have to be resilient.
Resilience relies on good energy reserves needed for coming out of dormancy and, increased root volume to allow them to source more water and nutrients. Because energy reserves and roots are short term carbon, they will disappear quickly without adequate management of carbon flows.
PLANT ROOTS ARE IMPORTANT FOR WATER INFILTRATION
Paddocks are more water efficient and have increased capacity to capture resources when plants are physically present.
Roots, which are 45% carbon, act as “wicks” to take water down through the soil profile, especially important with harder soils.
This is achieved by water travelling down beside roots. Better managed plants, with more extensive root systems, distribute water faster through the soil and to greater depth.
With perennial grasses, the roots grow and die back. This results in cavities where roots have previously been. These cavities are very effective for water infiltration.
This wick effect is especially important if isolated small falls of rain are heavy.
WATER USE EFFICIENCY RELIES ON PLANT HEALTH & SOIL HEALTH
The example that follows demonstrates why some producers achieve higher carbon flows from isolated falls during dry periods and so postpone the arrival of drought. It relates to the combination of better soil structure and the wick effect.
The exercise documented in the box above, was one I carried out in a degraded paddock. It was a harder soil type where both the soil and perennials were unhealthy in a lot of areas. It followed 50 mm (two inches) of rain. I used a piece of high tensile fencing wire many times to establish how far water penetrated depending on the configuration of grass cover and the health of the area being sampled. It is likely that the isolated perennial grass plants, with access to less water, went into dormancy quicker than the ones in the grass clumps. When management of carbon flows changed for the better, following this exercise, the isolated perennial grass plants acted as a catalyst to see small clumps develop, i.e. there was already a source of carbon flows unlike the bare areas.
DROUGHT PREPAREDNESS IS JUST AS IMPORTANT AS FORECASTS
In recent times, there has been a focus on improving long term weather forecasting. This is a step in the right direction provided graziers don’t become too focused on when to destock instead of reducing the impact of drought. Both strategies are risk management, so should be considered together and not seen as separate issues.
Natural droughts are a lack of rain, while man made droughts are a lack of carbon flows from what is actually enough rain to just remain in production.
Perennial grasses are well adapted to drought but not to continuous defoliation, because it runs down their energy reserves.
Those who manage carbon flows better are stressed less by dry times.
Make every drop of water go through a plant. Water must leave via transpiration and not runoff.
The smart operators think about drought when it rains.