The discussion of human-induced climate change commonly revolves around indirect effects by humans. For example, we increase greenhouse gases, which leads to warming of the planet, which changes climate processes in myriad ways. But there are more direct effects by humans. Since I completed my post on human population (February 2, 2010) nearly 9 million people have been added to the planet—6.809 billion people total now. That is a lot of people to house, feed and transport around, and so requires lots of dirt to be moved. One interesting question is how does all the earth moving associated with human development compare to the amount of material moved by geologic processes, like mountain building, glaciation, and erosion by wind, waves and rivers?
Until 16 years ago most geologists would have thought that humans were no match for the Earth. But that all changed in 1994 when Dr. Roger Hooke, then a Professor at the University of Minnesota, published a paper in the Geological Society of America’s news magazine, GSA Today (see Hooke, R. LeB., 1994, On the efficacy of humans as geomorphic agents: GSA Today, v. 4, No. 9, p. 217, 224-225 and this link). In his article, Hooke did an elegant first-order analyses of resource and construction data along with geologic data that estimated humans moved about 45 billion tons of material a year (45 Gt/y), essentially equivalent to all the material moved by ricers, glaciers, waves, wind, and continental mountain building. Direct human actions moved as much material as all the geologic processes on Earth—phenomenal!
In his analyses, Hooke left out the material moved by agriculture. He included agriculture in another paper in 2000 (see Hooke, R.LeB., 2000, On the history of humans as geomorphic agents: Geology, v. 28, no 9, p. 843-846) and found that humans moved almost 2 times the material moved by geologic processes on the continents (80 Gt/y vs. 45 Gt/y). In the last 10 years more detailed and complete analyses by other geologists have found even higher “human erosions rates”. Dr. Bruce Wilkinson, from the University of Michigan, constructed a detailed historical time series of direct human movement of earth material (see Geology; March 2005; v. 33; no. 3; p. 161-164 ). He found that by approximately 1000 AD humans equaled geologic processes (see figure below). In 2000 AD, humans moved upwards of 40 times the geologic erosion rate. Wilkinson summed this up with this quote: “At these rates, this amount of material would fill the Grand Canyon in 50 yr.” To put this in perspective, it took geologic erosion about 6 million years to form the Grand Canyon—humans have become the largest geologic force on Earth’s continents, bar none. Phenomenal!