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The effects of human activity can be seen throughout the biosphere.

Rapid human population growth, combined with increasing resource consumption, has resulted in the widespread transformation of the Earth’s land cover. We use land to grow our crops, manage our livestock, and house our families. For example, between 1.5 and 1.8 billion hectares – an area about the size of South America – are used for crops. Even more land – roughly 3.2 to 3.6 billion hectares – is used for pasture and rangeland.

These worldwide changes in land cover may have profound impacts on environmental systems around the globe – including the linkages between land, water, and air.

SAGE scientists are working to document the patterns of land use and land cover change across the world. We also investigate how these changes modify complex earth processes at local, regional and global scales.

Documenting Worldwide Changes in Land Use and Land Cover

Scientists now recognize that land use is an important driver of worldwide environmental change. But we still do not know exactly how the land has been changing, or why. As a first step, we need to document the current land use practices across the globe, and estimate how these patterns have changed through recent history.

While landscapes are now routinely monitored from space, satellite images have only been available for the last two decades. To describe land cover changes of the last few centuries, we must also rely on other historical records such as census and tax records.

SAGE scientists have developed techniques for blending the spatial information from satellite images with historical information from census records. Using these techniques, we reconstruct global datasets of croplands and pastures.

While most of our work has focused on documenting the history of land use over the entire globe, we are paying particular attention to land use in the Amazon basin and the United States

Assessing Agricultural Lands and Food Security

Maintaining robust agricultural systems is central to the success of civilization.

Agricultural production critically depends on suitable climate and soil conditions, as well as direct human management. Although technology – including irrigation and fertilizer use – has extended the boundaries of cultivation, many large regions of the world are still unsuitable for crops.

We are assessing how agricultural production systems are distributed across the world today, and how these patterns may change in the future. Using land use datasets and ecological modeling tools, we examine the links between land use practices, agricultural production, and the underlying patterns of climate and soil quality.

Some of our initial results indicate a disturbing trend: the regions of the world with the least suitable agricultural lands are likely to be the ones hit hardest by increasing population and possible changes in climate.

Effects of Land Use on the Carbon Cycle

Changes in land use can directly affect the amount of carbon dioxide in the atmosphere. Destroying vegetation cover and degrading soils releases organic carbon into the atmosphere as CO2, while growing new vegetation and building up soil organic matter can remove CO2 from the air.

Along with the burning of fossil fuels, worldwide patterns of deforestation and soil degradation have released enormous amounts of CO2 into the atmosphere. In fact, until the 1950s, land use practices released more CO2 into the atmosphere than fossil fuel consumption.

As concerns about the greenhouse effect continue to mount, there has been increased discussion about the use of vegetation and soils to combat global warming. By planting trees, restoring degraded soils, and practicing different farming techniques, it might be possible to “sequester” carbon dioxide from the atmosphere, temporarily removing it from the pool of greenhouse gases. It is possible that carbon sequestration techniques could help ease our transition toward cleaner, more-efficient energy technologies.

This work has particular significance for the Kyoto Protocols, whereby countries have the option of offsetting their CO2 emissions by increasing carbon sequestration in ecosystems.

Scientists at SAGE are examining the role of land use and land cover change in the carbon cycle. Using our historical land use data and global ecosystem models, we are able to quantify current patterns of carbon uptake and release from ecosystems. We are also assessing the potential for carbon sequestration across the globe.