Nonrenewable energy is the energy derived from sources with a very long regeneration period. The most common examples of nonrenewable energy sources are coal, petroleum, and natural gas (also known as fossil fuels). Since it takes millions of years for these resources to form, they are present in limited quantities. We have consumed these resources at a significant rate since the beginning of industrial age. In many cases, people have over-exploited these resources. Ultimately, these resources are going to run out.
It has been estimated that, if we maintain the rate of production of these resources at year 2011's levels, coal will run out after 126 years, oil will run out after 43 years and natural gas will run out after 64 years. However, if we include the current rate of growth of production, then these resources will run out after 46 years, 36 years, and 39 years, respectively.
These estimates are based on the assumption that we already know of all the reserves and no new reserves will be found.
Given this impending scarcity scenario, a lot of emphasis is being placed on renewable energy, such as solar power and wind energy.
Hope this helps.