I = PAT that human population may stabilize at around 11.2 billion in 2100, the I=PAT equation will continue to be relevant for the increasing human impact on the environment in the short to mid-term future. Increased population increases humans' environmental impact in many ways, which include but are not limited to: The variable A, in the I=PAT equation stands for affluence. It represents the average consumption of each person in the population. As the consumption of each person increases, the total environmental impact increases as well. A common proxy for measuring consumption is through GDP per capita. While GDP per capita measures
Per capita income such as the euro or United States dollar, and is useful because it is widely known, is easily calculable from readily available gross domestic product (GDP) and population estimates, and produces a useful statistic for comparison of wealth between sovereign territories. This helps to ascertain a country's development status. It is one of the three measures for calculating the Human Development Index of a country. In the United States, it is defined by the U.S. Census Bureau as the following: "Per capita income is the mean money income received in the past 12 months computed for every man, woman, and