When fossil fuels are combusted, all the heat produced, used and wasted, ends up in the oceans, lakes, atmosphere and space. You may have noticed that weather temperatures near cities are warmer, because cities are ‘heat sinks’ of human activity, where waste heat is disposed of into the atmosphere.
The heat wasted into the air by cities, agriculture, livestock, transport and by evaporation from water storages is large. If you live near a thermal power station, where river, lake or ocean water is used for cooling, you may have noticed the water is warmed up and can even cause fog at night. Alternatively, heat could be wasted from a cooling tower.
You may have been at an airport and felt warm ‘jet wash’, exhaust gases from a plane manoeuvring.
There is evidence that human heat pollution is significant. By comparison with solar radiation received by Earth, the amount of thermal pollution is lower when the Sun is high, but at night thermal pollution contributes significantly to the daily heat balance, enough to cause global warming. I calculate that human-generated heat stays on Earth with an average residence time of 140 years.
Substitution of solar, wind and hydro for fossil fuel combustion would not reduce thermal pollution and could increase it, if electrical output efficiency is lower and more heat is wasted and replaced from the Sun.
The other theory, that global warming could be caused by heat entrapment by a tiny amount of carbon dioxide gas, is disputed in the literature, unnecessarily complex and without evidence. To reduce global warming, energy consumption must be reduced.
More information is in my book Animal Farm 2, on Amazon.
Earth’s heat balance is certainly complex, but higher temperatures could come from retention of increased heat from Earth sources, with solar radiation absorption and emission continuing as in the past. Modelling of changes to the world energy balance can account for global warming and the futility of the net zero concept.
Heat energy to warm Earth’s land, oceans and atmosphere, is emitted by respiration of living things, by combustion of vegetation and fossil fuels, by capture of renewable energy replenished by the Sun and by geothermal processes. Some heat produced is radiated into space, but my calculations indicate the remainder is sufficient to add to normal solar warming and cooling, causing warming noticeable near city heat sources.
Warming would not in the least be reduced by substituting for fossil fuels with solar, wind or hydro energy supplies. Warming in the environment is caused by spent inefficient energy consumed. Reduction to net zero could require cutting energy consumption and waste by human populations to a low level, until entropy increase is balanced if possible by removal in endothermic reactions, such as photosynthesis, which absorbs heat with light. Deindustrialisation may be necessary. The theory of warming by greenhouse gases is considered in my previous post here Greenhouse Gases Not To Blame.
My satirical book Animal Farm 2 explains paradigm-shifted climate science.