Is waste heat produced by human activities important for the climate?

No. The sun provides almost 10,000 times as much energy to the Earth’s surface per time unit and unit area, namely 342 Wm-2, as we emit into the atmosphere or waters through industry, transport, housing, agriculture and other activities by using fossil fuels and the nuclear fuel uranium (0.03 Wm-2). The average heat flux of a human body, about 100 Joules per second (i.e. 100 Watts per person) represents only a few percent of the energy flux produced by our power supply systems in industrial countries. The human body’s heat flux is part of the natural energy budget, since the carbon contained in our food would be emitted as carbon dioxide by other creatures if not by ourselves. It is thus negligible. Compared to radiative forcing through greenhouse gas emissions which has already amounted to 3 Wm-2 and is supposed to steadily increase, we do not change global climate significantly through the heat we produce by using fossil fuels and the nuclear fuel uranium.