human overpopulation. The human carrying capacity of the Earth has been estimated to be 500 million, 1 billion or up to 12 billion. According to these studies, the human carrying capacity has already been exceeded or would be exceeded by the year 2100. The large variance in these studies’ estimates diminishes our confidence in them, as such estimates are very difficult to make with current data and methods. Possible negative effects The effects of a declining population can also be negative. As a country's population declines, GDP growth may grow even more slowly or may even decline. If the decline in total population is not matched by an equal or greater increase in productivity (GDP/capita), and if that condition continues from one calendar quarter to the next, it follows that a country would experience a decline in GDP, known as an economic recession. If these conditions become permanent, the country could find itself in a permanent recession. Other possible negative impacts of a declining population are: A rise in the dependency ratio which would increase the economic pressure on the workforce A loss of culture and the diminishment of trust among citizens A crisis in end-of-life care for the elderly because there are insufficient caregivers for them Difficulties in funding entitlement programs because there are fewer workers relative to retirees A decline in military strength A decline in innovation since change comes from the young A strain on mental health caused by permanent recession Deflation caused by the ageing population All these negative effects could be summarized under the heading of “Underpopulation”. Underpopulation is usually defined as a state in which a country's population has declined too much to support its current economic system. Population decline can cause internal population pressures that then lead to secondary effects such as ethnic conflict, forced refugee flows, and hyper-nationalism. This is particularly true in regions where different ethnic or racial groups have different growth rates. An example of this is white nationalism. White nationalists seek to ensure the survival of the white race, and the cultures of historically white nations. Many white nationalists believe that white people should therefore maintain a demographic majority and that mass immigration of non-whites and low birth rates among whites are threatening the white race. Low fertility rates that cause long-term population decline can also lead to population ageing, an imbalance in the population age structure. Population ageing