Number 2: 10/03/2023
Changes in Global Land Use
In Number 1 of this series of diagrams and graphs, I showed that Greenhouse gases (GHG) come from three major sources; the release of CO2 from land clearance and agriculture; from the destruction of forests and woodlands; and from the burning of fossil fuels. The graphs below show that before the mid-19th century, the cause of most of the long term release of CO2 was from changes in land uses. However, today, they are less important sources than fossil fuels, which I will discuss later in this series.
Since humans first used fire in hunting and gathering foods from nature, GHG have been released. More importantly, the rate of emission of GHG has grown since land was cleared for agricultural fields or grazing at the expense of native forests and grasslands. As populations remained small, the expansions of agricultural lands grew relatively slowly. Also, as soil fertility lessened, farmers moved on clearing more land. Especially in recent times, wealthy people have wanted more meat and variety in their diets, further increasing pressure for clearing more land.
As agricultural land expanded, forested land decreased. Especially as population has increased in the last six decades, more and more forested land has been replaced by agricultural fields. (Note that the two diagrams are not directly comparable because different measures of forest and woodland were used.) That forests have decreased, and decreased very rapidly, however, is not at question.
Forests sequester (or absorb) and store carbon dioxide from the atmosphere, helping reduce greenhouse gas emissions. When deforestation occurs, much of the carbon stored by trees is released back into the atmosphere as carbon dioxide, which contributes to climate change. The most important driver of deforestation today is the global demand for agricultural commodities: agribusinesses clear huge tracts of forest and use the land to plant high-value cash crops like palm oil and soya, and for cattle ranching.
“Land use change, principally deforestation, contributes 12–20% of global greenhouse gas emissions. Forest degradation (changes that negatively affect a forest’s structure or function but that do not decrease its area), and the destruction of tropical peatlands, also contribute to these emissions. As a result of deforestation and degradation, some tropical forests now emit more carbon than they capture, turning them from a carbon ‘sink’ into a carbon source.” (Charles Palmer, Natalie Pearson and Georgina Kyriacou. The Grantham Research Institute and the Guardian, © The Guardian 2012)
https://upload.wikimedia.org/wikipedia/commons/thumb/a/af/Greenhouse_Gas_Emissions_by_Economic_Sector.svg/750px-Greenhouse_Gas_Emissions_by_Economic_Sector.svg.png?20210806180237
I will return to the other sources of greenhouse emissions in later postings. The next post will deal with the growth of the world population of humans and the decrease in the earth’s biodivesity.