Describe how ecologists use the ecological footprint concept

The ecological footprint is defined as the biologically productive area needed to provide all the resources that a human population needs to survive. It is a measure that calculates the human demand on nature and can be used as an indicator of the human impact and dependency on Earth's ecosystem. The ecologists use the ecological footprint concept to estimate the earth's carrying capacity for humans. 

The process that fuels our sun and allows it to give off that much energy is called nuclear fusion.