The blue line in this graph is not a statistical long - term trend or a 5 - year average - it's actual yearly data of total heat content. (skepticalscience.com)
But the accumulation of total heat energy over the earth is increasing at an astronomical rate, even though the temperature numbers look small locally — 0.8 degrees Celsius so far. (huffingtonpost.com)
It's a measure of total heat flow through a window or door from room air to outside air. (marvin.com)