People leave their “footprint” on the earth’s land through agriculture, clearing forests or new cities. These global land use changes now encompass around 32 percent of the earth’s surface, as a new mapping has now revealed. This means that the changes are about four times as great as previously assumed. The global forest areas have been reduced particularly sharply, while fields are much more common today.
Whether deforestation, urban growth or more intensive agriculture – humans are constantly changing the nature of the earth’s land. With enormous consequences: For example, intensive agriculture accelerates soil erosion, so that fertile soil is lost, agricultural productivity is reduced and global nutrition is endangered. In addition, in contrast to forest soils, the soils of fields emit more carbon dioxide into the atmosphere and, at the same time, the content of the carbon stored in them decreases, so that climate change is accelerated. In addition, land use is already changing many habitats in such a way that the biodiversity of the ecosystems is threatened.
How big are the land use changes?
But how big are the global land use changes currently? Scientists working with Karina Winkler from the Karlsruhe Institute of Technology (KIT) have now examined this in detail. So far, studies on these changes have mostly been limited in terms of space or time. Therefore, the research team now combined the results of land use statistics with high-resolution satellite data, whereby changes in urban areas, arable and pasture land, forest, cultivated grass and shrubland and areas with sparse and no vegetation were considered. “The main difficulty in our work lies in dealing with very different data sets,” explains Winkler. They first have to be standardized in a time-consuming process. The researchers succeeded in this and they created a high-resolution set of maps from the pattern of global land use changes between 1960 and 2019, the “Historic Land Dynamics Assessment +” (HILDA +).
The result: the land use changes are apparently greater than previously assumed. According to the new mapping, around 32 percent of the global land area – around 43 million square kilometers – has been affected over the past 60 years or so. “We estimate that land use change has affected almost a third of the global land area in just six decades, and is thus around four times as large as the previously estimated extent of long-term land changes,” the scientists report. This means that an area of land roughly twice the size of Germany has been changed every year since 1960.
Less in Europe, more in Asia
Above all, the significant changes in forest and arable land are new. “We see a global net loss of forest area of 0.8 million square kilometers, but an expansion of global agriculture of one or 0.9 million square kilometers,” explains the team. However, changes in land use do not show the same patterns all over the world. The researchers were able to determine that the land use changes differ, especially between regions in the north and south. Accordingly, in recent years in the global north, for example in Europe, the USA or Russia, the forests have expanded and the arable land has been reduced. In the global south, such as Brazil or Indonesia, on the other hand, the forest areas decreased and the arable and pasture areas increased.
In addition, the speed of land use changes has changed over time, according to Winkler and her colleagues. It was shown that a phase of accelerated land use change took place from 1960 to around 2005 and a phase of slowed down land use change from around 2006 to 2019. The first phase was particularly pronounced in the southern hemisphere, as in South America, Africa and Southeast Asia, where the production and export of crops increased, especially in the 2000s. “The trend reversal could be related to the increasing importance of global trade for agricultural production and to the global economic crisis in 2007 and 2008,” explains Winkler. Because at that time countries like Argentina or Indonesia, which before the crisis concentrated on the production of raw materials for the world market, no longer found buyers for their goods and reduced agricultural production and thus also the agricultural land. In addition to trade, extreme events triggered by climate change, droughts and floods could also have been a driver for the second phase, the researchers add.
Basis for environmental protection programs
The new land use data could in the future be an improved data basis for climate and earth system models – and thus also make a contribution to political debates about strategies for sustainable land use in the future. “In order to master the global challenges of our time, we have to better understand the extent of land use changes and their contribution to climate change, biodiversity and food production,” said Winkler. “Because land use also plays a decisive role in achieving the climate goals under the Paris Agreement.”
Source: Karlsruhe Institute of Technology, Article: Nature Communications, doi: 10.1038 / s41467-021-22702-2