Soil degradation is the loss of land's production capacity in terms of loss of soil fertility, soil biodiversity, and degradation. Soil degradation causes include agricultural, industrial, and commercial pollution; loss of arable land due to urban expansion, overgrazing, and unsustainable agricultural practices; and long-term climatic changes. According to a recent report to the United Nations, almost one-third of the world's farmable land has disappeared in the last four decades. It was also reported that all of the World's topsoil could become unproductive within 60 years if current rates of loss continue. The issues of soil health and impacts on human well-being are discussed in detail in Chapter 27.