The climate of planet earth has heated and cooled in nested cycles for as long as we can determine. However, these cycles are not intrinsic, they are the result of physical and astronomical effects that can be studied, measured, and correlated with the changes in average earth surface temperatures. The study of the earth's climate over long periods of time is called climatology, in which I took an intermediate level course back in 1971 (that is a PhD in vdpphd.) At that time, the question of what drove the various cycles was a matter of great interest, as was the observation that a warming trend, without certain explanation at the time, was being measured, corresponding generally with the Industrial Revolution. A Nobel Prize-winning chemist, an expert in thermodynamics, by the name of Svante Arrhenius, had opined in the 1920s that dramatic increases in atmospheric concentrations of CO2 could cause dramatic increases in average earth surface temperatures. This contention was initially viewed with skepticism.
Since I took that course, hundreds of specific studies have been done, numerous cycles that drive the climate have been studied, and changes in average temperatures past and present have been correlated. The latest word is that there is a better than 90% certainty that the increase in average earth surface temperatures, about 1 degree centigrade so far since 1750, is due almost entirely to the doubling of the concentration of atmospheric carbon dioxide over that time period. The source of nearly all that extra carbon dioxide has been the combustion of coal, oil, and natural gas.
No fooling. Solid science. Ironclad math.