Climate change, a new IPCC report says, is intimately linked to our land use. Changes in land use result in changes to the climate, and vice versa. In other words, what we do to our soil, we do to our climate – and ourselves. The Conversation reported on this issue.
Humans now exploit more than 70% of the Earth’s ice-free surface; more than a quarter of land globally is suffering degradation as a result of human activities. Soil is being lost up to 100 times faster than it is formed; desertification is growing year on year. Damaged soils are further degraded by temperature increases and heavy rains associated with climate breakdown. Unless we stop and reverse this, food supply chains will become unstable; and nutrient levels in foods will decrease. The effects of this will be felt mainly by people living in poverty already; but they will also be felt around the globe.
From soil to oil
We need well-functioning soils to produce food. But, The Conversation writes, the modern farming system is based around oil, not soil. For most of our history, humans could only produce as much food as local ecological and soil conditions could support. Some societies developed complex and sustainable systems: nutrients were returned to the soil in the form of organic waste. Maintaining soils in a good state was the key to survival.
But modern farming mainly relies on fossil fuels. Limited soil fertility was overcome through fertilisation, mainly with synthetic nitrogen – made from natural gas or coal. Consequently, emissions from nitrogen fertilisation are a major source of greenhouse gases; the emissions produced in making that nitrogen are the biggest carbon cost in a loaf of bread. And then, modern agriculture makes use of diesel-powered machinery. Through it, we can cultivate land previously inaccessible. Therefore, more land is brought into cultivation. As a result, deforestation is the biggest source of agriculture-related CO₂ emissions. Compacting of soils by heavy machinery adds to the damage. Organisms such as earthworms and microbes which make soils function are constantly disturbed through ploughing and compaction – leading to soil degradation and exhaustion.
Helping plants grow
We need to acknowledge that soil is the most diverse habitat on the planet. Home to as much as 59% of all life on Earth. This includes insects and spiders, and also soil specialists such as enchytraeidae (resembling mini earthworms), oligochaeta (worms) and nematodes (tiny worms), but relatively few mammals. Plant roots profit from the help of these organisms. And then, there are the microscopic organisms – a mind-blowing 430 million species (or more than 50%) of bacteria and 5.6 million species (or 90%) of fungi.
Small animals, including earthworms and springtails, break down plant material and other forms of organic matter, such as dead insects, and incorporate them into the soil. This process releases the nutrients that most plants rely on to grow. But it’s not the only way that soil organisms help plants gain more nutrition. There are mycorrhizal fungi that embed themselves in the roots of plants where they extract energy-rich compounds. In return, the fungi help plants expand their reach in the soil, allowing them to access a greater amount of nutrients. And there are nitrogen-fixing bacteria, commonly associated with legumes such as beans and clover. These convert nitrogen gas from the atmosphere into compounds that the plants can use. This can otherwise only be done synthetically, using vast amounts of energy. All this soil life helps to produce the food we eat; it also plays a crucial role in holding the soil together and even gives us potential sources for new antibiotics and medicines.
Holding soil together
Organisms that penetrate the soil, like termites, engineer pathways through the soil and contribute to its structure. The incorporation of decomposed plant material into the soil helps to hold the soil together and creates pores that protect it from erosion; it also increases its capacity to store water. Moreover, organic material is being locked away in soils, leading to the storage of carbon. In fact, soils hold three times as much carbon as vegetation and twice as much as the atmosphere.
In many cases, these functions involve a variety of species. Having multiple species perform the same function offers a safety net if conditions change, such as during a drought or a flood. Then, other organisms can step in to fulfil the same functions as those that might have suffered. In this way, soils can withstand and recover from environmental shocks.
Rainfall
One of such environmental shocks is the increased variability of rainfall. This has become much more volatile over the past century. Particularly over Australia, Europe and eastern North America, as new research shows. This means dry periods are drier than in the past, and rainy periods are wetter. This means that the long-term average rainfall doesn’t change much, but extremes occur much more frequently. Alarmingly, the problem will worsen as global warming continues. The increase in variability means that rain is more unevenly distributed over time. It might mean that a year’s worth of rain at a given location now falls in fewer days. It can also mean long, dry periods interspersed by torrential downpours, or drought and flooding in quick succession. This means that we need to adapt to these changing patterns.
Several factors are at work here. Firstly, warm air can contain more moisture. Every degree of global warming creates a 7% increase in the average amount of water vapour. Then, storm winds can get stronger. And higher temperatures will yield larger raindrops. All in all, rainfall will become more variable. Dry periods will more often be alternated with extreme rainfall. The world needs to prepare for such changes.
Tropical forests
More variable rainfall patterns will also affect tropical forests. Often called ‘lungs of the world’, as they remove about 15% of man-made carbon emissions and help to slow climate change. Moreover, they pump water from the soil into the atmosphere. There, it will form clouds which eventually release the water as rain, to be reabsorbed by trees. This cycle is critical to the survival of forests situated far from the ocean. Like the Amazon and Congo river basins, where somewhere between a quarter and a half of all rainfall comes from moisture pumped from the forest itself. This recycling of moisture helps to maintain the large amounts of rainfall tropical forests need.
But cutting down trees stops this transfer of water between the earth and the air. It causes the surrounding area to heat up. Scientists have long assumed that such a mechanism would be at work. But proof has only been provided by satellite measurements. These showed a marked difference in rainfall over forests and areas that have been cleared; in all tropical regions, including the Amazon, Congo and in Southeast Asia. As the area of cleared forest expands, rainfall decreases by a larger amount. Scientists start to fear that we approach a tipping point, where there could not be not enough rain to sustain the remaining forests. And this could have severe consequences, like loss of crop yields. As The Conversation writes, we should conserve tropical forests in order to maintain a cooler and wetter climate.
Heavy farm machinery
Modern combined harvesters weigh so much that they compact the soil beyond repair. Soils are fragile structures. They contain pores and pathways that allow air to circulate and water to reach plant roots and other organisms. This is destroyed by heavy machinery. Soil compaction can cut down plant growth and harvests; and increase the risk of floods, as water runs off the land and reaches waterways more quickly. Farm machinery today is now so heavy that it irreparably compacts soil below the first 20 cm, where it isn’t tilled.
Soil can only withstand so much pressure, writes The Conversation. Whether this is from compaction or other threats such as continual harvesting, erosion or pollution. Humans, so the authors conclude, must act to reduce pressures on soils.
Coming back to land
Until quite recently, agricultural production was stimulated by tractors and chemicals. This made possible the formidable population growth that we witnessed in the past two centuries. But now, soil degradation has reached a point where it cannot be compensated anymore, either by chemicals or machinery. The effects may be different from country to country. The Conversation notes that ‘in Australia, years of irrigation have turned soils saline and toxic to crops. In the UK, the drained peatland soils of the Fens, which produce the most high-grade foods, are disappearing at a rate of 2cm a year. Spain, a huge producer of fresh fruits and vegetables, is in danger of desertification due to increasing temperatures and droughts. In sub-Saharan Africa, a quarter of the land is degraded, while 20% of China’s soils are polluted. Across the world, soils have been pushed beyond their capacity to recover, and humanity’s ability to feed itself is now in danger.’
The diversity of these effects means that we will have to find adequate and diverse solutions for every habitat. We need locally appropriate action, as the IPCC notes. It stresses the importance of land rights and secure access, driving home the message that land and its peoples are indivisible.
What we need to do
We need to restore land and prevent existing land to degrade. We need to support bottom-up experimentation by farmers and land managers; helping them develop and share their expertise. Big buyers and farmers need to be aware of the problem. Regenerating land is a win-win, The Conversation concludes, for humans and their ecosystems; if only we dare to look beyond the immediate short-term horizon.
Interesting? Then also read:
Why didn’t decades of climate concern influence global emissions growth?
The myth of pristine nature
Productive soils as a carbon sink