One of the most pressing social issues of the 21st century, both in the United States and abroad, will be human population growth and its effect on global climate change. In 1995, the Intergovernmental Panel on Climate Change (IPCC) concluded that the observed increase in global average temperature over the last century "is unlikely to be entirely natural in origin" and that "the balance of evidence suggests that there is a discernible human influence on global climate." Much of the IPCC's research has been inspired by the dramatic increase in human population over the past 50 years. When there were few people, the dominant factors controlling the ecosystem were natural ones, but now that the human population has grown so large, there is concern that humans are becoming a significant influence on ecosystem dynamics. Because of the quadrupling of human population and more than tripling per capita carbon dioxide emissions in the 20th century, the human species now has a more significant impact on the earth's climate than ever before. In the following discussion I will address human behaviors and lifestyles contributing to global warming, disparities between developed and developing countries, population and climate change policies, the effect of global climate change on humans, and finally, what can be done to help the situation.