CO2: Friend or Foe to Agriculture?

To look from a different perspective, today I would like to discuss some of the possible impacts that global warming could impose on the agriculture sector. 

Impacts on Crops

Fig. 1 Effects of climate change on maize and rice yields in 2050 under climate change ad compared with potential 2050 yields in there had no change in climate. Negative in red; Positive in blue.
Source: Based on Ignaciuk and Mason-D’Croz (2014)

• Higher carbon dioxide concentration can affect crop yields. A few studies suggest that higher CO2 levels aids photosynthesis and increase plant growth. However, plant growth is also affected by other factors such as water and nutrient constraints, which could offset the potential increase in yields. 
• Higher frequencies of extreme event affect crop growth. Extreme events such as drought and flooding are thought to harm crop and reduce yields. 
• A variation in food quality. Studies have suggested that nutrient values of most food crops is reduced with higher CO2 concentration. On the other hand, some suggested that a doubling in vitamin C concentration is found in specific fruits.  
• Different areas would experience different effects. According to the latest IPCC report, an improvement in food production in mid to high latitudes over the next decade. Conversely, other parts are thought to experience declining conditions. Overall, productivity levels are expected to be lower than without climate change. 

Impacts on Livestock

• Heat waves can directly threaten livestock. It can increase vulnerability to disease, reduce fertility, and reduce milk production over time. 
• Drought could affect pasture and fodder supply. For livestock that depends on grains could be affected by changes in grain production. 
• A possible increase in the prevalence of parasites and disease. Early springs and warmer winters may allow the survival of them to be more easily. 

Biochar: the Future of Sustainable Agriculture?

Fig 1. Burning Charcoal (Source)

Using biochar as a form of soil amendment technique have been discussed a lot in scientific literature and popular press in recent years. It has been almost been regarded as a silver bullet to solve all problems in agricultural activity. So for today's post, I would like to give a brief overview of biochar regarding it potential implications when it is added to the soil. 

Biochar and its Historical Perspective

Biochar is charcoal added into soils as a form of fertilizer. It can be made from any form of biomass via pyrolysis (heating in the absence of oxygen). The history behind the idea of using charcoal as soil amendment traces back to the discovery of terra preta, an anthropogenic, dark-colored soil created by the indigenous people of the Amazon 2500 years ago. It was said to be created by continuously adding charcoal derived from cooking and/or fresh biomass waste. Terra preta was very versatile and extremely high in organic content. Therefore, people are trying to regenerate similar solid by adding modernly produced biochar. 

Claimed Benefits

The list of potential benefits of the use of biochar is almost endless: 

• Improve fertilizer efficiency and reduce run-off due to improved nutrient retention through cation absorption. 
• Increase yields due to the more available nutrients (Liang et al. 2006). 
• Increase water quality by continuous retention of pollutants such as heavy metals, pesticides, herbicides, etc. 
• Increase soil pH (Lehmann et al., 2003; Van Zwieten et al., 2010a). 
• Increase soil microbial biomass (Liang et al., 2010; Jin, 2010) . 
• Have high climate mitigation potentials through the reduction of greenhouse gas emission (Lehmann et al., 2006; Laird, 2008; Sohi et al., 2010). Biochar's high recalcitrant nature slows the rate of photosynthetically fixed carbon return to the atmosphere. It reduces nitrous oxide (Cayuela et al., 2013) and methane emission (Jeffery et al., 2016). 
• Source of renewable bio-energy, which can improve agricultural productivity. 

Fig 2. Chart showing biochar's benefits (Source: International Biochar Initiative)

Drawbacks

Concerning the potential benefits stated above, some drawbacks were found as well:

• Spokas et al. (2011) found that biochar has no effect whatsoever on crop yield, in some cases, it may actually lead to a reduction in yield due to its water and nutrient sorption ability. 
• The sorption of pesticide and herbicide could reduce their efficacy and could in turn become a source of contaminant. 
• In high pH soils, increasing the pH is not desirable for certain type of crops sensitive to pH. 
• The reduction in methane production is not universal and could even increase methane emission (Wang et al. 2017a). 
• Fine ash of biochar may pose potential risk for respiratory diseases.  

Some Thoughts

Most of the trials and experiments on biochar were conducted in laboratory conditions and most of them are carried out to focus on the benefits. While little was carried out to find any possible shortcomings of using biochar. Moreover, most trials were conducted for a fairly short term of around 2 years. The long-term effect of biochar on our soil, plants and atmosphere is still an open question. Hence, more research is required to determine a more comprehensive understanding before proceeding with the promotion of biochar as a soil improving amendment. 

Currently, my personal opinion is mainly skeptical about its climate mitigation potentials as biochar require burning lots of biomass. Large quantities of biomass would have to be harvested and burned to have any measurable impact on the global atmosphere. Not the mention burning itself would produce lots of pollutants. However, I am not against the small-scale use of waste charcoal by individual farmers to improve agricultural productivity, particularly in low-fertility and degraded soils. 

COP23: Achievements in the Agriculture Sector

Fig 1. COP23 (Source)

The World Climate Conference (COP23) took place a few weeks ago (6-17th November) in Bonn, Germany. The focus was on how to implement the climate change agreement set at the Paris Conference in 2015 (COP21), rather than making new agreements. 

Agricultural emissions have been flagged as a key issue in the climate change talk. A notable outcome of COP23 was a historic agreement was reached by parties on agriculture for the first time in history of climate negotiations. The agreement includes helping countries to develop and implement new strategies for adaption and mitigation in the agriculture sector, and to reduce emission as well as build resilience to climate change effects.  A deadline was set for submission of views on agriculture to UNFCCC in March 31st 2018, which will be taken forward into the COP24 in Poland where the Paris rulebook will finally be agreed upon. 

The following video is recorded by IIED senior fellow Saleemul Huq with his concluding views on COP23.

COP23: Conclusion with Saleemul Huq, 21 November (Source: YouTube) 

Sustainable Livestock Management

Fig.1 Cows wearing backpacks to measure their methane output, at the Ellinbank Dairy Research Centre in Victoria, Australia (Source: ScienceNews)

The name Allen Savory kept coming up during my research into sustainable livestock management, who holds some intriguing claims such as ''livestock is the only hope for a dying planet''; ''only livestock can reverse desertification''. In his TED Talk, ''How to green the world's deserts and reverse climate change'', he challenged the conventional wisdom of regarding livestock as the reason of land degradation from grassland into deserts. 

Savory's hypothesis is based on the holistic management and planned grazing of livestock, which mimics the role of wild herds in nature, which he argues would increase the carbon sequestration in grassland, and counteract the methane production of cattle and even reverse climate change. Savory claimed that his experiments with livestock in Zimbabwe, Mexico, Argentina have successfully reversed degraded dry lands by increasing the stocking density, which is the number of animal grazing at a specific area of land, by as high as 400%. 

Although I am not fully convinced with his statements, I do think his claims are somewhat advisable. It is reasonable to research on a possible more sustainable management of livestock, especially considering that it is a major GHG emission source while a rise in the demand of animal protein is inevitable with the growing world population. Research has shown that the mitigation potential for GHG emission is huge. The new FAO report concluded that the existing livestock production system could cut emission by around 30%. 

Efficiency is key

According to the FAO, reducing GHG emission and improving efficiency measures, especially concerning the use of natural resources, are directly linked. This is based on sustainable intensification, i.e. producing more livestock protein with fewer input of resources, which reduces both the emission and the cost of farmers. Therefore, possible interventions to reduce emissions are largely based on measures to improve production efficiency. 

Enhancing efficiency measures include using better feeds and feeding techniques for ruminants. This can reduce GHGs generated during digestion as well as the released by decomposing manure. First and foremost, we need to feed animal with less human food. 
Livestock consumes about 1/3 or more of the world's cereal grain production, with 40% fed to ruminants, mainly cattle. It is said that cows produce more methane when they eat corn or soy-based feed or over-grown grass as they are harder to digest. A study from the National Trust found that grass-based beef production can reduce the agricultural carbon footprint, considering grassland carbon sequestration potentials. Although some papers hold the opinion of feeding livestock energy-dense feed such as cereal grain to improve production. 

Interventions aiming to improve breeding and animal health that would also help to reduce GHG emission. This can be achieved by adopting measure to improve the genetics of cattle. It would lead to a reduction in herd size, but an increase in production rate which increases the feed availability and productivity of individual animals as well as the total herd. Thus lowering the GHG emissions per unit product. 

Emissions can be reduced by manure management practices that ensure the recovery and recycling of nutrients in manure. For example, by storing manure appropriately to minimise the loss of nitrogen by volatilization and run-off.   

Regeneration of Our Soil: Conservation No-Till Agriculture

Fig.1 Tractor Cultivating Field At Autumn (Source: Shutterstock) 

Agriculture originated in the Fertile Cresent of the Near East, together with it tools to place and cover seeds in soil were produced. Since then, soil preparation through tillage has been an important component of traditional agriculture. However, this practice has come at a cost. It has lead to widespread soil erosion and land degradation. The Dust Bowl is one of the severe incidences happened through human-induced land degradation when more than 75% of the topsoil was blown away by the 1930s. 

The loss of soil can impact strongly on the environment and has high economic costs. It leads to the decline of soil organic carbon (SOC) and precious nutrients, effects water infiltration and storage and the breakdown of soil structure. Therefore, scientists revisited the scientific basis for ploughing as a seedbed preparation and the idea of no-till farming originate in the 1940s with Edward Faulker. However, it was not until after WW2 when researchers and farmers started to try out this idea (Lal et al., 2007). 

What is No-Till and How is it Done 

A No-till (NT) system usually refers to the combination of farming practices such as residue management that seek to use the natural organisms of the soil to obtain the best possible sustainable return from our soils. 

The main principles of a no-till system are as follows:

• no disturbance of the land through tillage
• retain surface residue once harvest
• plant cover crops during winters 
• crop rotation over years 

Fig.2 Cover crop growing in plant residue in a no-till agriculture field
(Source: No-Till Farmer) 

What are the Benefits 

These series of activities have a number of impacts on the physical and biological properties and have shown to improve the soil structure. 

Erosion control and moisture conservation

Research has shown that no-till management improves surface soil physical properties which dictate to the infiltration characteristics and potential of the soil. Shaver et al. (2001) found that no-till systems resulted in the decreased bulk density, increased soil porosity and increased macro-aggregations as crop intensity, crop residue and subsequent SOC production increased in no-till systems. This reduces in overall soil compaction, results in the significant increase of water infiltration into the no-till soil than into ploughed soil at similar water contents. With more water infiltrating and stored in the soil, less of the topsoil along with the precious nutrients would be washed out under the impact of rain and wind. Moreover, the plant residues and cover crops act as a shelter to the underlying soil,  other than slowing down the wind and water speed at ground level which reduces water run-off and soil erosion, it also conserves water moisture by reducing evaporation from the soil. Basche et al. (2016) found that cover crop treatment has increased soil water storage by 10-11%. 

For a more intuitive demonstration please look at the following video, which shows the interaction between rail and soil between conventionally tilled (left) VS. no-till with a cover crop (right). The comparison is stunning. 

Watch what happens when rain interacts with #soil that's been conventionally tilled (left) vs. no-till with a #covercrop (right) #EarthDay pic.twitter.com/2UElhFO8qI

— Indiana Dept of Ag (@ISDAgov) 21 April 2017 

(Source: Indiana Dept of Ag Twitter @ISDAgov)

Land management of reduced/no-till, plant residue retention and cover crop and other supporting practices such as contour farming have been included in policies of the Good Agricultural and Environmental Condition (GAEC) for several decades. It has reduced the soil loss rate by an average of 9.5% in Europe and by 20% for arable lands (Panagos et al. 2015). 

Organic matter content increase 

A good soil carbon management is vital for its role in maintaining soil fertility, physical properties and biological activities required for food production and environmental quality. Conventional farming system mined soils for nutrients and organic matter through repetitive harvesting, resulting in the dramatic decline in soil organic matter and gaseous carbon released to the atmosphere. Reicocksy and Lindstrom (1995) found that there's a major short-term loss of CO2 immediately after tillage which partially explained the long-term carbon loss into the atmosphere. Soil erosion caused by extensive tillage may lose 75-80% of its carbon content and have a consequence release of carbon into the atmosphere (Morgan, 2005). 

Allmaras et al. (2000) showed that conventional tillage system store less SOC than conservation systems. It is shown that surface plant residue results in the accumulation of SOC at the immediate soil surface (Novak et al., 2007), even though some studies report that measured carbon has not necessarily increased below the horizon of tilled soil. If combined with strategies such as adding animal manure to the soil, no-till management has shown to increase organic matter content compared to conventional tillage (Jiao et al., 2006). However, some studies argue that the increase in SOC stock is short-term and continuous resupply of fresh residue is needed. 

Other benefits include economic aspects such as reducing fuel, labour and machinery requirements. 

Some Disadvantages

Although many studies have reported an increase in yield after adopting no-till, numerous studies have shown no changes or a decrease in yield associated with the adoption of NT. 

No-till with residue management significantly increases rain-fed crop's productivity in dry areas, while yield decreases mostly in wet and cool climate conditions.The plant residue layer causes depression on soil temperature which would affect the yield by delaying the planting date 1-2 weeks, according to Gupta (1985). Moreover, Dwyer et al. (2010) suggested a slower crop growth in spring due to less warm soil caused by the surface plant residue layer. Other studies found that no-till cause crops to be more susceptible to disease and weed infestation, which may increase dependence on fungicides and herbicides. 

The Impacts of Agriculture on the Environment: Atmosphere

Last week we talked about the dramatic amount of land and water used for agriculture. However, other than land and water, it also largely affects the atmosphere. People typically attribute greenhouse gas (GHG) emission to energy production, what they do not realize is that agriculture is also one of the biggest emitters of greenhouse gases which make it one of the largest contributors of global warming. 

Agriculture's Contribution to Greenhouse Gas Emission 

The most recent IPCC report (2014) state that agriculture, forestry and land use (AFOLU) was responsible for 24% of direct global GHG emission, which is even more than industry emission of 21% and transportation of 14%. 

The chart below shows the total greenhouse gas emissions by sector. The combined percentage of agriculture, forestry and land use sources shows a similar result to that of the IPCC: collectively they account for 11.8 million GgCO2-eq (=11.8 GtCO2-eq) which is approximately one-quarter of the total anthropogenic emissions of GHGs. 

Fig.1 Global greenhouse gas emissions by sector (Source: OurWorldInData)
Data is based on UN reported figures, sourced from the EDGAR database. 

To be specific (IPCC):

• Carbon dioxide (CO2) accounts for 21-25% if total CO2 emission;
• Methane (CH4) accounts for 55-60% if total CH4 emission;
• Nitrous oxide (N2O) accounts for 65-80% if total N2O emission.

Emission sources and Potential for Control

These emissions are generally linked to the management of agriculture soil, livestock, rice production and biomass burning. 

CO2 emission comes from the direct human-induced impact on forestry and land use, such as deforestation and shifting patterns of cultivation and also fossil fuels used on farms. 
At the same time, land can act as carbon sinks through reforestation, soil improvements and other activities. 

CH4 comes mainly from livestock breeding. Enteric fermentation by ruminant animals such as cattle, sheep and goats, produces CH4 as a by-product as part of their normal digestive processes. As our agriculture reliance in most countries is on these animals, it is one of main anthropogenic methane production sources.  Since this process is not 100% efficient, some of the food energy is lost in form of methane, ranging from 2-12% of gross energy intake. Therefore, mitigating enteric fermentation by decreasing enteric CH4 production without altering animal productivity is a desirable strategy to reduce GHG emission and improving digestive efficiency (Martin et al., 2009). The other major contribution of CH4 emission is from rice cultivation, which is the staple food for more than half the world’s population. The warm, waterlogged soil in paddy fields provide ideal conditions for methane-producing microscopic organisms. On average, the paddy soil is only fully waterlogged for around 4 months each year, so for the rest of time, the methanogenesis is considerately less. Moreover, when the soil dries out, it can be a temporary sink for atmospheric methane.  Therefore, it is considered that any farming method that reduces the period of flooding could reduce methane. 

Nitrogenous fertilizers cultivated soils are the primary source of N2O emissions, including synthetic fertilizers such as urea or anhydrous ammonia, or organic fertilizers such as manure. As most fertilizer nitrogen is mobile, it is hard to contain in soil and susceptible to loss when it is not taken up by plants. It can be lost as nitrates to groundwater or as gases N2O, N2, ammonia to the atmosphere. Cassman et al. (2014) found that typically only half of the applied nitrogen is taken up by crops during the growing season. The management of better targeting the fertilizer application in both time and space can prevent the build-up of nitrogen and significantly reduce N2O emission. 

The Impacts of Agriculture on the Environment: Land and Water Resources

The relationships between agriculture and climate change are complex which involves the interaction between land use, food and the environment. So I would like start by introducing some of the major effects of agriculture onto the environment, including changes in landscape, depletion of water sources and intensive GHG emission into the atmosphere. Today, I will be focusing on the first two. 

Land Degradation

First, I would like to take you on a little journey to our planet from space.

Fig 1. June 19, 1975, Landsat 2 (path/row 249/67) — Rondônia, Brazil (Source: USGS)Deforested land and urban areas appear lavender, healthy vegetation appear green. 

Fig 2. July 16, 1986, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

Fig 3. Aug. 10, 2001, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

  Fig 4. July 5, 2011, Landsat 5 (path/row 232/67) — Rondônia, Brazil (Source: USGS)

Above is a series of Landsat images, showing part of the Amazon basin, in a state called Rondonia located at West of the Brazilian Amazon. In the first image, one thing we would notice is the thin white lines on the right-hand side, they are roads built in the 70s. If we come back to the same place in 1986, what we can immediately see are the expansions of roads and urban areas in a fish-bone pattern. Then this pattern of clearing forest continued through 2001 into 2011, causing the whole place to be dramatically changed, with roads and human facilities occupying the original rainforest like spider webs. Rondonia was once home to 208,000 km^2 of forest, now it has become one of the most deforested parts of Amazon, with an estimate of 67,764 km^2 of rainforest have been cleared until 2003. 

The deforested lands are mostly used for cattle ranching. The cows here would be used to produce beef and exported around the world. Currently, the Amazon is home to approximately 200 million cattle, with most of the beef destined for urban markets. And as the largest exporter to the world, the cattle industry here supplies about 1/4 of leather and other cattle products of the global market. As a consequence, cattle ranching is the leading cause of deforestation in the Amazon rainforest. It attributes close to 70% of deforestation in Brazil. 

Fig.5 Cause of Deforestation in the Amazon based on the median figures for estimate ranges 
(Source: MONGABAY)

Another major driver of deforestation in the Amazon basin is soybean cultivation. 
Soybean seeds contain high protein content, so 80% of Amazon soy is being shipped to Europe and China as livestock feed, especially after the mad cow disease during the 90s. Since animal protein can transmit disease, people feed livestock vegetable protein instead. Today, Brazil has about 24-25,000 km^2 devoted to soy cultivation and is the second large producer of soybean in the world.  

The Amazon is just one of the examples of landscape after landscape that have been cleared and altered for growing food and other crops. At present, according to the World Bank, about 37% of land surface is devoted to agriculture, this is about 60 times larger than all the area we live in. Of course, we have been using the best land, what is left are lands like the Sahara Desert, Siberia or the middle of the rainforest. 

Freshwater Decline

Other than using an enormous amount of land to feed us, we are also using plenty of water. Currently, we have used about 50% of Earth's sustainable fresh water, with about 70% of it go towards irrigation use for agriculture. For a more intuitive illustration, let's look at another group of Landsat images. 

Fig 6. Sep 1, 2, 3, 22, 1977, Landsat 2 (path/row 172–175/27–30) — Aral Sea (Source: USGS)

Fig 7. Sep. 18, 27; Oct. 27, 1998; Aug. 20, 1999, Landsat 5 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

 Fig 8. July, 24; Aug. 2, 11, 2010, Landsat 5 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

Fig. 9 Aug. 20, 29; Sep. 7, 2014, Landsat 8 (path/row 160–162/27–30) — Aral Sea (Source: USGS)

The above images show the drying of the Aral Sea, which is located in the former Soviet Union in between Kazakhstan and Uzbekistan. The Aral Sea was once the world's 4th largest body of inland water, covering about 68,000 km^2. Now it only holds 10% of its original volume of water. The Aral Sea used to have two rivers feeding this basin with snow-melt from large permanent snowfields and glaciers in mountains from the far east. As the precipitation rate over the area is very low, the water level largely depends on the inflow of these two rivers. However, in the 1950s, the Soviet decided to divert this water to irrigate cotton in the desert. The turn-off of water supply caused the Aral Sea to dry out at a high rate. 

The effects of this dramatic change are far-reaching: geographically, environmentally and economically. Fishers and the community that depended on them collapsed. Local freshwater species died off when the water turned increasingly salty. 19 of the unique fish species found only the Aral Sea is now wiped out. The remaining water wad also polluted due to fertilizers, pesticides and metals. These toxic waste collected at the lake bed are becoming air-borne as the sea further dries out, causing public health hazards. The weather pattern has also changed. Without the moderating effect of the water body, winters are colder and summers hotter, which cause a shorter growing season. 

A Brief Overview: The Origin of Agriculture

The history of agriculture dates back thousands of years. The origins of agriculture are scattered in a number places across the globe and interestingly, they rise roughly around the same times. Today, I would like to have a brief introduction to the origin of farming. 

Prehistory: Neolithic Revolution

In the Palaeolithic period, about 200,000 years ago, anatomically modern human has first appeared. Since then into the Neolithic (15,200 BC in the middle east), human were living a nomadic lifestyle, moving constantly with the food supply chain. From around 15,000 to 10,000 years ago, the cultivation of crops seems to have risen independently over the course of millennia in a number of places. There are at least 11 separate regions being regarded as an independent origin. 

The Fertile Crescent

Fig 1. Fertile Crescent Map. Credit: Thing Link

As one of the early recognized area of origin of agriculture, the Fertile Crescent in the Levant region presented some of the evidence of the transition from a nomadic hunter-gatherer society to an agriculture-based one. For example, the Natufians which are recognized as semi-sedentary hunter-gathers before the introduction of agriculture. They build villages that seem to be lived in all year around. There was evidence of summer and winter kills all brought back to the village through the teeth of hunted animals such as gazelles. Also, evidence of house mice, rats and sparrows number accords with a village occupied all year. The houses they live in shows a surprising degree of care in organisation and maintenance (Bar-Yosef, 1998). 

Fig 2. Neolithic grindstone for processing grain

They also seem to be harvesting grains. The settlements of the Natufians occurred in the woodland belt where the underbrush was grass with high frequencies of grain. Archaeologists have found burnt of remaining grains in their fireplace, sickles that were probably used for harvesting and grinding stones for processing grains. More importantly, studies have provided with results of isotope tests of Natufian teeth showing that their diets were rich in grains.

Hypotheses of the Origin of Cultivation

There are several hypotheses trying to discern how crop domestication originate. Some of the theories concern with the global climate variability of the time. Most of the literature assumes either a better climate made agriculture more suitable in comparison to foraging, or that a worse climate that has the same effect.

As the start of the cultivation roughly coincides with the end of small ice age, the Younger Dryas (~1,1000 BC). Rickerson et al. (2001) argued that the end of the ice age brought a warmer, wetter climate which is favorable for the cultivation of plants. However, the empirical problem is there is no evidence of agriculture around the world during the initial warming, only ~2000 years after the start of warming. Other scientists such as Bar-Yosef and Meadow (1995) have proposed that the cold and dry conditions during the Younger Dryas caused the wild grasses to decrease in yield and thus provide motivation for cultivation. The connection between the beginning of agriculture with the end of Younger Dryas Period is still highly debated. 

Other hypotheses that were put forward is related to population growth. Archaeologists such as Cohen (1977) suggest that population pressure is the dominant factor causing the transition into agriculture. However, this is regarded as inconsistency with recent archaeological evidence which is that population growth is extremely slow prior to agriculture and only exploded after the transition. 

Technology change has been considered as one of the driving force of this transition. In this view, farming is invested by a group of pioneers and spread widely as soon as it benefits were recognized. This is opposed by some archaeologists saying that people in hunter and gather society are experts in botany and it's inconceivable that they could not understand how harvesting crops works. 

Overall, since none of the major factors have been shown to be dominant in the transition of agriculture, it can be argued that agriculture arose from a combination of these factors. 

The Early Anthropocene Hypothesis 

The hypothesis has been suggested by William Ruddiman who believes that the Anthropocene started 8000 years ago due to intense farming activities instead of starting in the industrial age of 18th century. He argues that as agriculture became worldwide, along with the deforestation associated with it, caused increased levels of GHGs. He also argues that this forestalled the arrival of the scheduled ice age. This made the Holocene warmer and more stable than it otherwise would have been. And the elevated greenhouse gases is also thought to also contribute significantly to modern global climate change. However, this hypothesis is still highly debatable but it does put forward farming's possible impacts on climate change.