The climate has included variability throughout history. The period of Bayis Sheini (the “classical” period in European history) and the time of the Rishonim (the “high middle ages”) were warm, they were followed by cool periods (the goyim’s “Dark ages” and “Early modern periods”). While they didn’t have thermometers there are records of what crops grew where and when rivers froze. The climate scaremongers base their calculations on the end of the early modern period and therefore see rapid temperature increase. If they based it on the the high middle ages, they wouldn’t be upset.
One should also note, that in the past, the warm periods were generally times of greater prosperity and population growth (and note that a leading source of carbon emissions are people and animals exhaling). Cool periods usually resulted in a falling population and famines.