What energy growth rate per year would increase world energy use by 400% (2 doubling periods) in 80 years?

To calculate the energy growth rate per year that would increase world energy use by 400% (2 doubling periods) in 80 years, we can use the rule of 70. The rule of 70 is a way to estimate the number of years it takes for a certain variable to double.

Step 1: Understand the rule of 70 The rule of 70 states that to find the number of years required to double your money at a given interest rate, you just divide the interest rate into 70.

Step 2: Apply the rule of 70 to the problem In this case, we want to find the growth rate that would double the energy use twice (400% increase) in 80 years.

Since one doubling period is 70/growth rate, two doubling periods would be 2*(70/growth rate).

Step 3: Set up the equation and solve for the growth rate So, we set up the equation 2*(70/growth rate) = 80 years.

Solving for the growth rate gives us:

growth rate = 2*(70/80) = 1.75% per year

So, a growth rate of approximately 1.75% per year would increase world energy use by 400% in 80 years.