Understanding the terminology around Carbon, Land Use, and Net Zero Goals

The total amount of greenhouse gases (GHGs), including CO₂, methane (CH4), and nitrous oxide (N₂O), emitted by human activities. It is typically measured in metric tons of CO₂ equivalent (CO_2e, a unit based on carbon dioxide’s global warming potential (GWP).

Achieving a balance between the amount of GHGs emitted into the atmosphere and the amount removed or offset. Achieving net zero is essential to limit global warming.

The amount of carbon emissions produced per unit of energy, product, or economic activity. Reducing carbon intensity is a key strategy for decreasing overall emissions.

Mechanisms that allow companies or individuals to compensate for their emissions by investing in projects that reduce or capture CO₂ elsewhere, such as reforestation or renewable energy projects.

A strategy where businesses invest in carbon reduction or sequestration projects within their own practices rather than relying on external offsets.

A way of tracking the balance between carbon emissions from operations, such as farming or forestry activities, and carbon sequestered through practices like soil management, reforestation, or crop growth. By managing this balance minimises net carbon output and contributes to sustainability goals.

These include CO₂, methane (CH₄), nitrous oxide (N₂O), and other gases that contribute to global warming. Different gases have varying impacts on the climate and remain in the atmosphere for different durations. The GWP is used to compare their effects over time. Below is a table from NASA (which describes the major greenhouse gas sources, their lifespans and possible added heat.

Major Greenhouse Gas Sources, Lifespans,and Possible Added Heat

This distinction is crucial when discussing carbon in soils. Soil carbon stocks refer to the amount of carbon stored in the soil, while carbon fl ows describe the rate of carbon entering or leaving the soil. Although soils can store large quantity of carbon, the rate at which they accumulate more is often slow and depends on many factors, including the soils’ existing levels and overall soil health. Generally, if the level of soil carbon is high, the rate at which new carbon can be incorporated is very low or static – the soil is in a steady state.. It’s important to know that soil carbon is usually measured in terms of mass. For example, 1 gigaton of carbon (GtC) refers to the weight of carbon molecules stored in the soil. When this carbon is released into the atmosphere, it combines with oxygen to form carbon dioxide (CO₂), a greenhouse gas. The weight of carbon dioxide is about 3.67 times heavier than the carbon alone. This is because the molecular weight of CO₂ includes both carbon and oxygen atoms (44 for CO₂ compared to 12 for carbon). So, when carbon leaves the soil and becomes CO₂, the overall impact on the atmosphere is greater in terms of weight.

Global Carbon Flux

A natural or artifi cial reservoir that absorbs and stores more carbon than it releases. Forests, oceans, and soils are the most signifi cant carbon sinks.

Different crops absorb and release carbon at varying rates, with perennial and deep-rooted crops typically sequestering more carbon in the soil over their lifespan than shallowrooted or annual crops.

Carbon levels in the soil fluctuate within and between years due to seasonal changes, weather patterns, and crop cycles, with higher rates of carbon uptake typically occurring during the growing season. For long-term net zero strategies, understanding these fluctuations is critical to accurately assessing carbon budgets and implementing practices that stabilize or increase sequestration over time. It’s important to understand that soil carbon is always in flux, i.e. it’s constantly being added to and released from the soil. How long carbon stays in the soil depends on how well it’s protected within undisturbed soil aggregates. These aggregates shield carbon from microbial decomposition and release it into the atmosphere as CO₂. This means that the structure of the soil plays a big role in how stable soil carbon is. Well structured soils, with strong aggregates, help keep carbon stored for longer periods, contributing to carbon sequestration.

Every soil has a maximum capacity to store carbon. This means that there is a limit to how much carbon can be added to the soil, depending on many factors including climate and the time period. This limit is known as the soil carbon sequestration potential, i.e. the maximum amount of carbon that the soil can hold under certain conditions. Once this limit is reached, soils won’t be able to store much more carbon, so managing soils to maintain their carbon levels is crucial for long-term carbon storage. The IPCC (Intergovernmental Panel on Climate Change) suggests that it can take about 20 years for soils to reach a new level of carbon storage, called equilibrium or saturation. However, this process doesn’t happen at a steady rate, it slows down over time. In fact, it can take 10 to 50 years or even longer for soils to reach their maximum carbon storage capacity. This means that while soil can absorb carbon, the rate of absorption decreases as it gets closer to its limit.

Carbon Credits and/or Verified Carbon are common units based on one tonne of carbon dioxide (CO₂). Agricultural practices that avoid, reduce, and/or remove one tonne of Greenhouse Gases (GHGs), including CO₂, out of the atmosphere can generate one Carbon Credit or one Verified Carbon Unit in the carbon market. One tonne of carbon is equal to 3.67 tonnes of CO₂.

The carbon market is a system where companies, governments, or organisations can buy and sell carbon credits to help reduce global carbon emissions. Companies that reduce their emissions can sell their unused carbon credits to others who need them. This creates an incentive to cut emissions because companies can make money by selling excess credits. It is important to mention that there are two main types of carbon markets:

1. Compliance markets, where companies are legally required to limit their emissions.
2. Voluntary markets, where companies or individuals choose to buy credits to offset their carbon footprint.

Carbon markets aim to lower overall emissions by putting a price on carbon, encouraging more sustainable practices.