Anthropogenic refers to changes in nature caused by humans. Examples include air pollution, deforestation, the construction of roads and dams, the introduction of alien species, and the pollution of water bodies. Many of the anthropogenic changes are similar to natural changes except that they occur far more quickly and on a far larger scale. For example, some forests die naturally due to fires caused by lightening, small dams are commonly constructed by beavers, water bodies can become polluted by landslides, and air pollution can occur as a result of dust storms and volcanic eruptions.
The current period of rapid climate change is generally considered to be anthropogenic because of the huge increase in the burning of fossil fuels and massive deforestation during the past several centuries. However, the earth has also been in the midst of a much more gradual long-term warming that began during the last ice age. (Although there are various theories, the fundamental cause, or causes, of this natural warming are not known, just as the cause, or causes, of ice ages are not known.) Likewise, the current period of mass extinctions is anthropogenic, in contrast to the several earlier ones, which occurred millions of years ago and were the result of natural events such as meteor impacts, massive volcano eruptions and ice ages.