4 An increase in the elderly share of the total population is ageing. Explain.

declining fertility rates and rising life expectancy

Explanation:

Population ageing is an increasing median age in a population because of declining fertility rates and rising life expectancy. ... The number of people aged 60 years and over has tripled since 1950 and reached 600 million in 2000 and surpassed 700 million in 2006.

Explanation:

Population ageing is an increasing median age in a population because of declining fertility rates and rising life expectancy. Most countries have rising life expectancy and an ageing population, trends that emerged first in developed countries but are now seen in virtually all developing countries. That is the case for every country in the world except the 18 countries designated as "demographic outliers" by the United Nations. The aged population is currently at its highest level in human history.The UN predicts the rate of population ageing in the 21st century will exceed that of the previous century.The number of people aged 60 years and over has tripled since 1950 and reached 600 million in 2000 and surpassed 700 million in 2006. It is projected that the combined senior and geriatric population will reach 2.1 billion by 2050. Countries vary significantly in terms of the degree and pace of ageing, and the UN expects populations that began ageing later will have less time to adapt to its implications.

permafrost layer, it exists beneath a layer of soil, rock or sediment.

answer; elasticity of the lungs decreases;