This study attempted to map the human footprint on the earth on a fine scale back in 2002.

The Human Footprint and the Last of the Wild

There is little debate in scientific circles about the importance of human influence on ecosystems. According to scientists’ reports, we appropriate over 40% of the net primary productivity (the green material) produced on Earth each year (Vitousek et al. 1986, Rojstaczer et al. 2001). We consume 35% of the productivity of the oceanic shelf (Pauly and Christensen 1995), and we use 60% of freshwater run-off (Postel et al. 1996). The unprecedented escalation in both human population and consumption in the 20th century has resulted in environmental crises never before encountered in the history of humankind and the world (McNeill 2000). E. O. Wilson (2002) claims it would now take four Earths to meet the consumption demands of the current human population, if every human consumed at the level of the average US inhabitant. The influence of human beings on the planet has become so pervasive that it is hard to find adults in any country who have not seen the environment around them reduced in natural values during their lifetimes—woodlots converted to agriculture, agricultural lands converted to suburban development, suburban development converted to urban areas. The cumulative effect of these many local changes is the global phenomenon of human influence on nature, a new geological epoch some call the “anthropocene” (Steffen and Tyson 2001). Human influence is arguably the most important factor affecting life of all kinds in today’s world (Lande 1998, Terborgh 1999, Pimm 2001, UNEP 2001).

Yet despite the broad consensus among biologists about the importance of human influence on nature, this phenomenon and its implications are not fully appreciated by the larger human community, which does not recognize them in its economic systems (Hall et al. 2001) or in most of its political decisions (Soulé and Terborgh 1999, Chapin et al. 2000). In part, this lack of appreciation may be due to scientists’ propensity to express themselves in terms like “appropriation of net primary productivity” or “exponential population growth,” abstractions that require some training to understand. It may be due to historical assumptions about and habits inherited from times when human beings, as a group, had dramatically less influence on the biosphere. Now the individual decisions of 6 billion people add up to a global phenomenon in a way unique to our time. What we need is a way to understand this influence that is global in extent and yet easy to grasp—what we need is a map.

Until recently, designing such a map was not possible, because detailed data on human activities at the global scale were unavailable. The fortunate confluence of several factors during the 1990s changed this situation. Rapid advances in earth observation, using satellite technology pioneered by NASA and other space agencies, meant that, for the first time, verifiable global maps of land use and land cover were available (Loveland et al. 2000). The thawing of the cold war and calls for efficiency in government meant that other sources of global geographic data, for example, on roads and railways, were released to the public by the US National Imagery and Mapping Agency (NIMA 1997). Improved reporting of population statistics at subnational levels enabled geographers to create global digital maps of human population density (CIESIN et al. 2000). Finally, advances in geographic information systems (GIS) have provided the integration technology necessary to combine these data in an efficient and reproducible manner. Although the datasets now available are imperfect instruments, they are of sufficient detail and completeness that scientists can map the influence of humans on the entire land’s surface.