Land

Looking down from the cabin of a plane, it becomes abundantly clear that humans have drastically transformed the land surface of the planet.

Almost half of the planet’s land surface has been transformed by human actions. This has significant consequences for biodiversity, nutrient cycling, soil structure and climate.

Land-surface conditions – the temperature, the moisture – affect climate. Vegetation change also affects climate. Deforestation in the tropics is estimated to be responsible for 20% of all carbon emissions from human activities.

Changes on land


• In the last 150 years humankind has exhausted 40% of the known oil reserves that took several hundred million years to generate

• Nearly 50% of the land surface has been transformed by direct human action, with significant consequences for biodiversity, nutrient cycling, soil structure, soil biology, and climate

• More nitrogen is now fixed synthetically for fertilisers and through fossil fuel combustion than is fixed naturally in all terrestrial ecosystems

• More than half of all accessible freshwater is appropriated for human purposes, and underground water resources are being depleted rapidly in many areas



While the global population more than doubled in the second half of the last century, grain production tripled, energy consumption quadrupled, and economic activity quintupled.



Although much of this accelerating economic activity and energy consumption occurred in developed countries, the developing world is beginning to play a larger role in the global economy and hence is having increasing impacts on resources and environment.


Industrialisation has led to considerable air and water pollution associated with the extraction, production, consumption and disposal of goods.



Over the past three centuries, the amount of land used for agriculture has increased five-fold.



Furthermore, large areas of land area have been lost to degradation, due, for example, to soil erosion, chemical contamination and salinisation.



Biospheric Aspects of the Hydrological Cycle

One of IGBP’s first projects, the Biospheric Aspects of the Hydrological Cycle (BAHC) project, showed that land use and land cover strongly affect how water and energy move between land and atmosphere. The research demonstrates how land is an integral component of the climate system. Consequently, human-driven change in land cover is likely to result in significant regional and global climate change.

In turn, climate change affects terrestrial ecosystems at all spatial
and temporal scales. Potentially, these have destabilising effects on the vegetation of large regions, such as the Amazon rainforest.

Sinking deltas

Many of the world’s most important deltas are sinking. These fertile areas are densely populated and heavily farmed. But more and more land is being turned over to the ocean.

According to a recent report (2009) from IGBP’s chair James Syvitski and colleagues, humans are to blame for some of the problem. The vulnerability is a result of “sediment compaction from the removal of oil, gas and water from the delta's underlying sediments.” Reservoirs upstream are also a problem. They trap sediment preventing the deltas from replenishing sediment washed out to sea.

Syvitski and colleagues assessed 33 key deltas and found that in the past decade, 85% of the deltas experienced severe flooding, resulting in the temporary submergence of an area around the size of the United Kingdom (260,000 km2.

“We conservatively estimate that the delta surface area vulnerable to flooding could increase by 50% under the current projected values for sea-level rise in the twenty-first century,” the authors say. This figure could increase if the capture of sediment upstream persists and continues to prevent the growth and buffering of the deltas.

Sinking deltas due to human activities. Nature Geoscience 2, 681 - 686 (2009) 20 September 2009. doi:10.1038/ngeo629

Deforestation

Forests cover about 30% of Earth’s land, but large areas are lost each year. Significant efforts are now underway to halt acceleration of deforestation. These efforts, in Brazil at least, are beginning to bear fruit.

In 2012, the Brazilian government announced satellite observations were showing a decline in Amazonian deforestation 47.5% in a year. According to the journal Science, the statistic “is the largest decline since measurements began in 1988”. The measurements were undertaken by Brazil’s space agency, the Instituto Nacional de Pesquisas Espaciais (INPE).