Exponential growth occurs when anything is increasing at a fixed percentage, such as 1% or 7%.  Our global population has been growing exponentially.  As a result, we have been consuming resources such as food, water, coal, oil and natural gas at exponential rates.

Our current lifestyle absolutely depends on exponential growth of our economy.  In fact, the definition of an economic recession is when we experience more than three consecutive quarters without exponential growth.  But, we live on a finite planet and the exponential consumption of finite resources is not sustainable.