"Since 1800, the human population has increased from one billion to over six billion. In 2004, some 2.5 billion out of 6.3 billion people (39.7%) lived in urban areas, and this percentage is expected to continue to rise throughout the 21st century. In February 2008, the U.N. estimated that half the world's population will live in urban areas by the end of the year. Problems for humans living in cities include various forms of pollution and crime, especially in inner city an suburban slums.
Humans have had a dramatic effect on the environment. As humans are rarely preyed upon, they have been described as superpredators. Currently, through land development, combustion of fossil fuels and pollution, humans are thought to be the main contributor to global climate change. Human activity is believed to be a major contributor to the ongoing Holocene extinction event, which is a form of mass extinction. If this continues at its current rate it is predicted that it will wipe out half of all species over the next century."
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