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進入《TAIPEI TIMES》 Study shows vast extent of the repurposing of land
Earth is pictured in a photograph taken from the Apollo 10 spacecraft on May 18, 1969. Photo: AP
/ AFP, PARIS
Whether it is turning forests into cropland or savannah into pastures, people have repurposed land over the past 60 years equivalent in area to Africa and Europe combined, researchers said on Tuesday.
Counting all such transitions since 1960, it adds up to about 43 million square kilometers, four times more than previous estimates, a study in Nature Communications said.
“Since land use plays a central role for climate mitigation, biodiversity and food production, understanding its full dynamics is essential for sustainable land use strategies,” said lead author Karina Winkler, a physical geographer at Wageningen University & Research in the Netherlands.
Plants and soil — especially in tropical forests — soak up about 30 percent of anthropogenic carbon pollution, so large-scale landscape changes could spell success or failure in meeting Paris Agreement temperature targets.
The 2015 climate treaty enjoins nations to stop global heating at “well below” 2°C, and 1.5°C if possible.
Since 1960, Earth’s total forest cover has shrunk by nearly 1 million square kilometers, while areas covered by cropland and pastures have each increased by roughly the same extent, the study found.
However, the global figures obscure important regional differences.
Forest areas in the global north — Europe, Russia, East Asia and North America — have increased in the past 60 years, while forest loss in developing countries of the global south has been staggeringly high, the study showed.
Conversely, croplands have declined in the north and expanded in the south.
“Tropical deforestation has occurred for the production of beef, sugar cane and soybean in the Brazilian Amazon, oil palm in Southeast Asia, and cocoa in Nigeria and Cameroon,” Winkler said.
High oil prices — peaking at about US$145 per barrel of crude in 2008 — also fueled conversion of forests to bioenergy crops.
The study said that there has been rapid land use change — driven first by the green revolution in the 1960s and 1970s, and then by the expansion of globalized markets — up to 2005.
After a period of fluctuation in global markets, the pace at which land was repurposed slowed, it said.
“With the economic boom coming to an end during the Great Recession [of 2008], the global demand for commodities dropped,” the study said.
Earlier calculations of land use change since the middle of the 20th century have fallen short for a number of reasons, Winkler said.
Datasets were fragmented in space and time, and based as much on assumptions as concrete measurements, the study said.
The resolution of satellite data was coarse, and usually only distinguished between two or three categories of land, it said.
The study drew from long-term land use statistics compiled by the UN Food and Agriculture Organization, identifying urban areas, croplands, forests, grasslands, pastures and regions with sparse or no vegetation, such as deserts.
It also used a higher resolution of satellite images — 1 square kilometer.
About 17 percent of Earth’s land surface has switched categories at least once since 1960, the study showed, although sometimes the same piece of real estate changed more than once.
If all such transitions are taken into account, the total land surface affected was equivalent to 32 percent.
The Earth’s surface area is about 510 million square kilometers, about 70 percent of it water, mostly oceans. Of the remaining 149 million square kilometers, about 15 million square kilometers is permanently covered by ice, leaving 134 million square kilometers of ice-free land.
新聞來源：TAIPEI TIMES
