How do human activities affect the natural environment?

Several centuries ago, Native Americans of the Hohokam tribe were able to create a civilization in the desert by building extensive irrigation canals. In the last two centuries, humans have found more and more efficient ways of making the desert livable for an increasing number of people. Technological advances, in the form of enormous dams, miles of water canals, and millions of air-conditioning units, have resulted in the desert becoming an extremely comfortable environment for cities, as well as for agriculture and grazing industries. However, these advances have had negative effects on the desert ecosystem. Increased grazing has degraded riparian zones and altered the desert plant community and agriculture and irrigation has altered streams, rivers, and canyons. Exotic and sometimes invasive species have been introduced that can quickly colonize and dominate the landscape. Increased visitors to parks and natural areas have effected the biotic soil crusts of even the most preserved areas. Finally, the growth of cities and ensuing suburban sprawl is replacing the once desert landscape with concrete, lawns, homes and picket fences. Source: http://www.earlham.edu/~biol/desert/impacts.htm