World land database charts troubling course

AMSTERDAM — Over the past 300 years, in an ever-accelerating process, humans have reshaped the terrestrial surface of the Earth. In doing so, humanity has scripted a scenario of global environmental change with impacts that promise to be at least as severe as global climate change, scientists reported here today, July 11.

Addressing an open science conference held under the auspices of the International Geosphere-Biosphere Programme, UW–Madison environmental scientist Navin Ramankutty and colleague Kees Klein Goldewijk of the Dutch National Institute of Public Health in Amsterdam, unveiled a historical global land-use inventory that chronicles the massive impact humans have had as they’ve remade the global landscape since the 17th century.

“We’re hitting a threshold of available global natural resources,” Ramankutty says. “We need to think about this issue before it’s too late. There is no substitute for natural resources.”

By far, the largest human influence on the global landscape is agriculture with 12 percent of the global land surface — an area equivalent to the surface area of all of South America — now under permanent cultivation, says Ramankutty.

Moreover, a global trend toward urbanization promises to “become one of the biggest consumers of land,” predicts Ramankutty. “Historically, we lost forest to crop land. Now we are losing crop land to urban areas.”

To take stock of how the Earth’s land resources have been influenced by people over the past 300 years, Ramankutty and Wisconsin climatologist Jonathan Foley embarked on a massive study of historical records, combining such things as agricultural land surveys, tax rolls and census data, to sketch a portrait of global landscape change that, for the most part, has gone unrecorded in any direct way by the world’s governments.

To augment the historical records, Ramankutty and Foley used growing repositories of satellite-derived land cover data sets that have recorded a broad spatial picture of human land-use and land-use change over the past 20 years. The resulting database, made available in Amsterdam in CD-ROM format along with a Dutch database, represents the first dynamic picture of global land use for the 300-year period between the beginning of the 18th century and today.

The database, says Ramankutty, is intended to provide a comprehensive picture of the growing dominance of human land use on global land-cover patterns. Data sets, he notes, could be used within global climate models and global ecosystem models to gain insight into the influence of land cover change on climate and biological and geochemical cycles.

In a related study, also presented by Ramankutty at the Amsterdam conference, it was shown that between 1860 and 1992, changes in land use contributed significantly to the build-up of atmospheric carbon dioxide, a major greenhouse gas.

These are key issues related to land use and there’s now a sense of urgency, says Ramankutty, as humans lock up the dwindling supply of the world’s natural resources and change the chemical makeup of the atmosphere. For example:

• Half of the world’s supply of fresh water is now appropriated by humans.
• Since 1700, nearly 20 percent of the world’s forests and woodlands have disappeared.
• Atmospheric carbon dioxide concentrations have risen by nearly a third since the industrial revolution.

“Knowing exactly what has changed and by how much, what are the historical patterns of change, and what are the consequences of change, are now key questions that we have to answer,” says Ramankutty.

The situation will worsen, he says, as world population continues to soar and the per capita consumption of goods and services derived from the natural resource base also continues to grow. Moreover, in some parts of the world intensive agriculture is exhausting the land, permanently removing acreage from production and the natural resource base.

The development of the global land-use database was supported by NASA and the Electric Power Research Institute.

The Amsterdam conference, “Challenges of a Changing Earth” is co-sponsored by three large international global change research programs: the International Geosphere-Biosphere Programme, the International Human Dimensions Programme and the World Climate Research Programme.