Understanding agricultural contributions to climate change

How the earth is warmed

Our earth is warmed by energy coming from the sun in the form of shortwave radiation visible to us as light and infrared radiation that is not visible because it has a long wavelength. Each day, about one-third of this energy is reflected back into space, as light bounces off our atmosphere and reflective surfaces such as snow and ice, while the remaining two-thirds is absorbed into the planet’s oceans and terrestrial surfaces.

Each day and night, this absorbed energy is released back into our atmosphere and space beyond, as infrared non-visible radiation. A good example of this invisible energy release is the heat you feel coming off a west-facing brick wall at the end of a hot summer’s day. Another example is an old-fashioned two-bar radiator: the red glow of the element is radiation in the visible light spectrum, while the heat you feel on your hand, is non-visible infrared radiation.

Image: The Mauna Loa Observatory is situated 3,353 metres above sea level and has been measuring carbon dioxide concentrations in the atmosphere since 1958. Hawaii, 2013. Photo courtesy of Associated Press.

Fortunately for us, our earth’s atmosphere contains water vapour and gases that absorb this infrared radiation which is again radiated both up and down, both day and night. This ‘back radiation’ actually supplies twice as much energy as direct sunlight and without it our planet would be 33^oC cooler. That is: our planet would have an average temperature of -18^oC, rather than 15^oC.

Water vapour and condensed water in the form of clouds are the strongest absorbers and radiators of this infrared energy. You may have noticed that cloudy nights are noticeably warmer than clear nights. This temperature difference that you are feeling is not the insulation of a ‘blanket’ of cloud, but the powerful infrared radiation emanating from water particles.

The process described here is called the greenhouse effect, but it isn’t how a greenhouse works. Greenhouses work by trapping heat energy from sunlight inside a glass box that prevents air convection from blowing the heat away. In contrast, the process of keeping our planet warm, is one of capturing radiation inside molecules that constantly radiate energy back to earth. So perhaps the process would be better thought of as the radiator effect and the gases, thought of as radiator gases, rather than greenhouse gases.

While nitrogen and oxygen make up 99% of our atmosphere, they do not behave as radiators because their simple symmetrical structure does not allow them to absorb radiation in the first place. The three main gases that behave as radiators: carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O), make up only 0.04% of our atmosphere. However, due to their asymmetrical structure, these gases are capable of absorbing and then re-radiating energy in the same way as clouds at night time.

The measurement of radiative power of two of the gases first occurred in 1859, when Irishman, John Tyndall, first measured the radiative values for CO₂ and N₂O. Since that time, the relatively simple laboratory procedures necessary to measure the radiation from gases and particles have been replicated so many times that it is not rational to doubt either the process of radiation, or the amount of radiative power that each molecule of gas will generate.

Why the earth is warming

The Industrial Revolution began in 1781 with the patent of James Watt’s steam engine, which was capable of generating enough power to replace 10 horses that were used to drive a pump for dewatering tin mines. Watt defined the imperial measurement of power, horsepower, and with today’s metric measurement, ‘watts’, named after him. This then began the wholesale or industrial-scale process of converting fossil fuels such as coal, oil and gas, into power.

The measurement of the concentration of CO₂ gas in our atmosphere was instituted by Charles Keeling in 1958, when he commenced measurements at Hawaii’s Mauna Loa Observatory. When plotted on a graph, the sixty years of data obtained from this site form a curve of relentlessly increasing CO₂ concentration known as the Keeling Curve. Following Keeling’s initiative, there is now a global network of monitoring stations able to measure and confirm the concentration of radiator gases in our atmosphere is inexorably rising.

It has been calculated that between the industrial revolution and 2011, mankind emitted about 2,000 billion tonnes of CO₂ (2,000 Giga tonnes (Gt)) to the atmosphere. About 60% of this has been stored in natural sinks such as the forests and oceans, with the balance remaining in the atmosphere. This process cannot however continue forever, since there are limits to the breadth and density of vegetation, while absorption by the oceans has both environmental and physical limits.

Since the onset of the Industrial Revolution, the CO₂ emissions have caused CO₂ concentrations in our atmosphere to increase from 280 parts per million (ppm) to 408 ppm by November 2018. Increases in the concentration of the two other radiator gases, CH₄ and N₂O have also been measured.

Because we know the increase in atmospheric concentration of these gases, it is a relatively simple mathematical task to calculate their total mass (or weight) and multiply it by the known radiation factor for each particular gas. The product of this calculation then tells us accurately how much additional radiation the earth is receiving as a consequence of the known increased radiation-generating capacity of these gases in our atmosphere. For this reason, it is not rational to doubt that a known quantity of gas is radiating a known quantity of additional energy as a consequence of mankind’s industrial revolution.

The result of this mathematical calculation is that the earth is now receiving an additional two watts of energy across every square metre of our planet. The following discussion will give you some sense of the immense power that this additional energy is projecting back at our planet.

In 2017, mankind generated 25.6 trillion kilowatt hours of electricity. To do this, we had to run power generators with a capacity of three trillion watts (or 3 terawatts (TW)). By comparison, the radiator gases that we have installed in our atmosphere since the Industrial Revolution, have a capacity 350 times greater. If the numbers here are too large to grasp, all you have to understand is that the radiator gases we have installed in our atmosphere are 350 times more powerful than the capacity of the power generators we used to produce all of mankind’s electricity in a year! And while our power plants probably have a useful life of about 50 years, the radiator gases are there radiating heat for thousands of years. This is a phenomenal amount of additional energy that is being trapped on a relatively small planet.

Where is the extra heat going?

So far, we have established through some basic measurements, that we have a very large amount of additional radiator gases in the atmosphere and the amount of energy they are producing. Then with some relatively simple mathematics, we have calculated that the earth is receiving a known amount of additional energy. The next step is to prove where the additional heat from this extra energy is going.

Much of the energy is being absorbed by the oceans, a massive body of water that covers 71% of our planet at an average depth of 3,800 metres. Fortunately, water has a high capacity to absorb heat, meaning that it takes only 3.2 metres of our oceans to absorb the same amount of heat as our entire atmosphere. Nevertheless, as the atmosphere absorbed its share of additional energy, there has been a measured increase in global atmospheric temperature at ground level of one degree Celsius (1°C).

While there is an increase in atmospheric heat, most of the energy is being buried in our oceans, waiting to rise again via the oceans’ great currents, that will return it to the atmosphere in future years, as the planet finds a new hotter equilibrium. While ever CO₂ emissions continue to accumulate in our atmosphere, the earth’s oceans will experience a compounding combination of CO₂ and energy absorption, that will buffer us during this accumulation phase and render dividends of increased CO₂ and heat emissions back into the atmosphere for centuries to come, as the oceans seek to spread the load.

Once again, these observations are not theory or conjecture. They are based on long-held scientific knowledge about how energy is absorbed and distributed both within a substance, such as water, and between other substances such as air. Roman baths, and people thinking in them, were pondering these observations at least 2,000 years ago.

Figure 1: The combustion reaction

Managing waste streams

If you have ever struggled to light a fire, you may appreciate the following explanation. The process of burning wood, to generate heat, is a thermo-chemical reaction, which to start with, involves getting the wood warm enough, so that it gives off methane (CH₄). Figure 1 shows how this gas then combines with oxygen, to produce three things: heat, water and CO₂. If you couldn’t get the fire going, it is because you did not generate enough methane to make the thermo-chemical reaction self-sustaining.

This is the same process used for burning coal in our power stations, petrol in our cars and natural gas in our home heating. Figure 1 also shows how inefficient this process is, with 2.75 tonnes of CO₂ produced for every tonne of methane used. This is the reason why we produce so much CO₂ each year.

Every year we Australians generate just over half a tonne of council waste per person. Fortunately, this waste stream is very well managed, with rubbish taken to tips and hazardous waste disposed of in ways designed to prevent the poisoning of our groundwater or the environment generally.

If you are in the habit of cycling or driving on quiet country roads, more than occasionally you will stumble upon sites such as in, a pile of rubbish illegally dumped by the side of a road. This pile of rubbish, probably weighing about half a tonne, generates a sense of outrage on a number of fronts. What sense does the perpetrator have of a civil society? What sort of person would do this, knowing that the community must bear the cost of the clean-up and disposal?

Image: Rubbish dumped illegally on a country road side near Canberra

In 2017, we Australians generated around 22 tonnes of CO₂ equivalent emissions per person¹ – around 40 times greater than our council waste. The symmetrical molecular structure of CO₂ and the other radiator gases, enables visible light to pass through, rendering them non-visible to the human eye. For this reason, it is not possible to take a photo of this massive uncontrolled waste stream and generate the same sense of outrage evoked by the picture of dumped garbage. But invisibility is not a rational reason for leaving this waste stream unmanaged. Managing this waste stream is also how mankind can prevent further planetary warming.

Conclusion

This article has explained the process by which radiation keeps our planet from freezing and how increased concentrations of radiator gases are now causing our planet to get hotter. By properly explaining this process, it is hoped that the readers understanding of climate change is enhanced.

Agriculture's radiator gas

About 14% of Australia’s radiator gas emissions come from our agricultural sector and 70% of this is due to methane emissions from ruminant livestock, primarily beef cattle, dairy cows and sheep. Therefore, 10% of Australia’s radiator gas emissions are coming from these three industries.

Methane gas is emitted primarily through the mouths of these ruminant animals as cellulosic plant matter is fermented and broken down in the foregut, known as the rumen. On average, beef cattle each produce around 2 tonnes of CO₂ equivalent radiator gas each year, while dairy cows produce around 3 tonnes and sheep produce about 0.25 tonnes per head. Globally, there are about 1.5 billion beef and dairy cattle and about 1.75 billion goats and sheep.

Methane is a much more powerful radiator gas than CO₂ but it only resides in the atmosphere for around 10 years, versus thousands of years for CO₂. For this reason, a quick reduction in the methane emissions from livestock would be very effective in reducing the level of radiation emanating from our increasingly crowded atmosphere. This is because a cessation in methane emissions would see the complete removal of anthropogenic methane from the atmosphere within the 10-year residence time of the gas. Moreover, because it is such a potent gas, the reduction in radiation would be material.

For this reason, there have been strident calls for people to move to a vegetarian diet and inflated claims regarding the amount of emissions reductions that can be achieved. Forsaking meat alone would not have much impact because dairy cows produce 50% more methane than beef cattle, while other products, such as wool, leather and eggs, are dependent on livestock industries.

A recent study by Virginia Tech, a US university, modelled the impact of the entire US switching to a plant food diet. The study found that because more crops would need to be grown using synthetic fertiliser, and due to the loss of natural manures from livestock, the actual reduction in gas emissions would be only 2.6%. This ignores the economic phenomenon known as rebound, where people save money eating plant foods, but spend this saving on other things that themselves generate emissions – such as a return economy flight on an airline, that may not serve beef, but emits 5.4 tonnes of CO₂ per passenger, to make a round trip to Europe.

Research is being undertaken by Australia’s livestock industries and the CSIRO, to look for ways to reduce methane emissions from ruminants. Examination of the digestive process of kangaroos, confirms they have rumen-like digestive systems, but emit virtually no methane, because their stomach microbes perform a different type of fermentation. Trials by the CSIRO of seaweed-based feed additives have reduced methane emissions in sheep by 80%.

Timely and successful reduction in methane emissions from livestock will make an important contribution to containing the global temperature increase. For this reason, those working or wishing to prevent further global warming would provide more assistance by campaigning for increased investment in research and development, rather than ruminating on misleading rhetoric.

RFM is engaging with scientists with expertise in the emissions and offsets that can occur in the agriculture sector, with the aim of understanding how the assets and enterprises managed by RFM can reduce or abate emissions of radiator gases.