As international development has increased wealth across countries, and global warming has increase temperatures, global use of air conditioners has increased. By 2018 an estimated 1.6 billion air conditioning units were installed worldwide, with the International Energy Agency expecting this number to grow to 5.6 billion units by 2050. Between 1995 to 2004 the proportion of urban households in China with air conditioners increased from 8% to 70%. As of 2015, nearly 100 million homes or about 87% of US households had air conditioning systems. In 2019 it was estimated that 90% of new single-family homes constructed in the USA included air conditioning (ranging from 99% in the South to 62% in the West).