The unit we typically use to define quantities of energy is the British Thermal Unit (Btu), which is a measurement of the heat content of fuels. According to the US Energy Information Agency (EIA), annual worldwide energy consumption exceeds 125 quadrillion Btu and is expected to grow to 138 quadrillion Btu by 2050. To put the enormity of these numbers into context, we can compare them to fossil fuel consumption in the world’s largest economy.