According to scientists from the University of Washington, the number of people in the world will reach the peak of 9.73 billion by the year 2064, and then begin gradually to decline, which has not happened in modern history. By the year 2100 the Earth will live for about 8.79 billion people, the researchers said. Potential cause of population decline, scientists believe the increasing availability of education and contraception.In a study published in the Lancet, scientists of the Medical Institute of the University of Washington has considered two possible scenarios of change of population of the 195 countries in the period up to 2100. Both scenarios take into account the level of fertility and mortality and migration. But the basic take into account the current growth rate of access to education and contraceptives, and the alternative assumes that all countries reach sustainable development goals set by the UN in matters of universal education and availability of contraceptives.Statistical modeling have allowed researchers come to the following conclusions. Under the baseline scenario, the world population will reach the peak of 9.73 billion, just to 2064 year and then will gradually decline and the end of the century will be 8.79 billion people. Alternative scenario implies that the peak is reached earlier, in 2045, but the maximum population in this case will be below the 8.79 billion, and by the end of the century it will fall to 6.29 billion scientists at the University of Washington disagree with the UN projections, which believes that by 2100 the Earth will live to 10.8 billion people.Scientists (under the baseline scenario), the total fertility rate in the world (that is, how much on average give birth to one female during the reproductive period), which in the year 2017, and $ 2.37, and in 1950 to 4.7, will steadily decline and by 2100 will reach 1.6. This is below the figure of 2.1 in which the natural population decline kompensiruet births.The fertility rates in different countries will in some cases radically diverge. So, in 23 countries, including Japan, Spain, Italy, Thailand, Portugal, South Korea, Ukraine and Poland, due to the declining birth rate the population by the end of the century will be reduced by half or more. In Japan will live to 60 million people (now 128 million) in Thailand — 35 million (71 million), Spain — 23 million (46 million), Ukraine — 17.6 million (44.4 million), etc. in 34 countries, the population can also be reduced by almost half, for example, in China — from the current 1.4 billion to 730 million people.But in African countries located South of the Sahara, the population will triple and will be about 3 billion people. At the same time on second place in the world by population will be Nigeria, where in 80 years, according to scientists, will live 800 million people. Still only two d��which regions of the world — North Africa and the middle East — the end of the century will live more people than now. As the most populated country in the world is India with 1.1 billion people.On the one hand, one would think that the reduction in population will impact positively on the environment. But it would be so, if it has not changed yet and the age structure of the population. If in 2017 the year there were 681 million, by the end of the century will only be 401 million Children and young people under the age of 20 years will be 1.7 billion the same trend will lead to the fact that more than a quarter of the world’s population of 2.37 billion will be aged over 65 years. The number of those over 80 years will grow from the current 140 million to 866 million by the end of the century. That is, old people will be more than two times more than children under the age of five years, and those over 65 years will be two times more than those who do not have 20 years.A direct result of fertility decline and population ageing in selected countries will be the reduction in the number of people of working age. According to scientists, will suffer the most from this is China, where instead of the current 950 million workers will be only 350 million people, able to work and provide for economic development of the country, and this reduction of 62%. But in Nigeria, where the population is expected to grow aggressively, able-bodied citizens to the end of the century will be over 450 million, whereas now there are only 86 million the Change in this indicator will entail changes in the GDP States. And if by 2050 China is expected to become the largest economy in the world, then by 2100 the US will regain the lead, pushing China into second place. On the third place by the end of the century will be India, which is now on the seventh. The top 5 will also include Japan and Germany, Nigeria will enter the top 10 and Russia will drop from the current 10-to 14-E. the study Authors noted that the negative effects of population decline for the economies can be partly compensated by migration. And will win in this case, States with liberal migration policies. Each of these options has its success stories. For example, in Sweden through programmes maternity support (paid maternity leave, guarantees of reinstatement, the system of preschool institutions, financial support) managed to increase the fertility rate from 1.5 in 1990 to the current of 1.9. And in Japan managed to increase the working-age population by labour of people aged 65-69 years.Commenting on these studies, one of its authors, Professor Christopher Murray, said: “this is very serious. Much of the world moves to a natural decline in the population. This is all very difficult to comprehend and acknowledge the extent of the problem, so it’s all very incomprehensible. We have to rebuild society.” According to him, ��legged now do not take such prospects seriously. “Some even laugh in response. They just can’t imagine that this is serious. They think that women would just want to have more children. But if we do not find solutions, then we as a species simply disappear. Although this will take a few centuries,” says the Professor.Alena Miklashevskaya