Anthropogenic greenhouse gas emissions from land-use change have increased by a third over the past 30 years and could increase by another 40 percent by mid-century if current rates of development, plowing and logging do not slow. Meanwhile, emissions from land-use changes in agriculture have declined by four percent. Researchers believe this has been helped by the adoption of conservation practices. The study is published in the journal Global Change Biology.

Anthropogenic emissions of greenhouse gases enter the atmosphere not only through the direct combustion of fossil fuels, but also through land use. Following economic development, the map of the earth's surface is rapidly changing. Former forests can become pastures and high albedo deserts can become cities covered with dark, waterproof asphalt. To accurately assess and be able to manage the global balance of greenhouse gases, land-use changes are important to keep track of.

Researchers led by Lidong Li of the University of Nebraska-Lincoln investigated how different land-use practices affected greenhouse gas emissions in 191 countries from 1992 to 2020. They divided the land surface into five major land types - man-made surfaces, croplands, pastures, barren lands and forests. Data on emissions and land use types were taken from World Bank and FAO databases. Over the past 30 years, artificial surfaces have increased by 133 percent to 60 million hectares, while cropland has increased by six percent to 1.58 billion hectares. In contrast, pasture and forest areas decreased by four percent to 3.2 and 4.06 billion hectares in 2021, respectively. Greenhouse gas emissions associated with land use have risen from 31 to 46 billion tons of CO2 equivalent since 1992.

The authors of the study derived coefficients that can be used to predict how land use change will affect greenhouse gas emissions. Such an impact factor is 0.64 for man-made surfaces, 0.31 for cropland, 0.13 for pasture, 0.02 for barren land, and minus 0.9 for forests. In other words, if the area of a city increases by 10 percent, the total greenhouse gas emissions from that city will increase by 6.4 percent, and of all land surface types, only forests can be considered surface carbon dioxide sinks.

Although the total land area involved in agriculture (cropland and pasture) has increased since 1992, their annual greenhouse gas emissions have decreased 11.36 to 10.91 billion tons of CO2 equivalent, a four percent decrease. Their contribution to total anthropogenic greenhouse gas emissions has also decreased, from 37 percent to 24 percent. The authors attributed this to the introduction of new technologies and practices that mitigated climate impacts - livestock breeding, more efficient use of fertilizers and anaerobic digestion of manure. According to predictive modeling, by 2050, at current rates of land use change, annual anthropogenic emissions from land use could increase by 40 percent to 76±8 billion tons of CO2 equivalent. The only way to prevent such an increase in emissions is to conserve ecosystems and utilize conservation practices, as is already being done in agriculture.

Not only has agriculture been able to become less carbon-intensive, but it has not lost its yield. Contrary to popular beliefs, their conversion to calories (instead of the usual tons) has revealed not stagnation but steady growth over the past 60 years.