Dirt: The Erosion of Civilizations - Kootenay Local Agricultural Society

land was being exhausted. Although we use a little more than a tenth of
Earth’s land surface to grow crops, and another quarter of the world’s surface
for grazing, there is little unused land suitable for either. About the
only places left that could be used for agriculture are the tropical forests
where thin, highly erodible soils could only briefly support farming.
Because we are already farming about as much of the planet as can be
done sustainably, the potential for global warming to affect agricultural
systems is alarming. The direct effects of rising temperatures are worrisome
enough. A recent study published in the Proceedings of the National Academy
of Sciences reported that an average daily increase in the growing season’s
minimum temperature of just 1ºC results in a 10 percent reduction in
rice yields; similar projections hold for wheat and barley. Beyond the
immediate effects on crop yields, global warming scenarios that project
anywhere from a 1ºC to a 5ºC temperature rise over the next century carry
a far greater risk.
The world’s three great regions of loess soils—the American Midwest,
northern Europe, and northern China—produce most of the world’s
grain. The astounding productivity of modern agriculture depends on the
climate of these extensive areas of ideal agricultural soils remaining favorable
to crop production. The Canadian and American prairie is already
marginal as agricultural land in its western extent. Yet global warming is
predicted to increase the severity of droughts here in North America’s
heartland enough to make that of the Dust Bowl era seem relatively mild.
Given the projected doubling of humanity in this century, it is far from
certain that the world’s population will be able to feed itself.
Other places are predicted to become wetter as global warming leads to
a more vigorous hydrological cycle. More frequent high-intensity rainfall
events are predicted to substantially increase rainfall erosivity in New England,
the mid-Atlantic states, and the Southeast. Models of soil erosion
predict from 20 percent to almost 300 percent increases—depending upon
how farmers respond to changing rainfall patterns.
Global warming and accelerated erosion are not the only problems facing
agricultural land. Growing up in California’s Santa Clara Valley, I
watched the orchards and fields between Palo Alto and San Jose turn into
Silicon Valley. One of the more interesting things I learned from my first
job as a foundation inspector was that preparing a building site means carting
the topsoil off to a landfill. Sometimes the fine topsoil was sold as fill
for use in other projects. Completely paved, Silicon Valley won’t feed anyone
again for the foreseeable future.
dust blow 171