As numerous 'C3' articles on past warming has pointed out, our modern global warming is not so "unprecedented" as the scientifically illiterate alarmist doomers claim - here's looking at you, Greta Thunberg, know-nothing Hollywood celebrities, and mainstream mocking bird "journalists."
As this chart indicates, in the very distant past, temperatures were indeed at times warmer or match what we are currently experiencing.
Per the peer-reviewed study, across a span of 2,500 years researchers were able to reconstruct the bottom waters of a fjord.
"Asteman et al. first note that "the reconstructed temperature range (2.7-7.8 °C) is within the present-day annual variability, documented from instrumental temperature measurements in the fjord's deepest basin since 1890." Next, they point out that "the Gulmar Fjord winter bottom water temperature record shows both centennial and multidecadal variability and has a striking resemblance to climate periods historically known in northern Europe over the last 2500 years." Those periods include the Roman Warm Period (RWP), Dark Ages Cold Period (DACP), Medieval Warm Period (MWP), Little Ice Age (LIA) and Current Warm Period (CWP).
According to Asteman et al., temperatures during the RWP (prior to ~ AD 450) were approximately 2.5 °C higher than the 1961-1999 mean, encompassing a temperature range of 5.4-7.9 °C. During the DACP (~ AD 450-850), temperatures were more variable but stayed in the range of 4-8 °C. The MWP, which the authors say occurred around AD 850-1350, coincided with a grand solar maximum with water temperatures ranging between 5.4 and 7.6 °C. Thereafter, temperatures cooled once again during the LIA, with bottom water temperature averaging 2-3 °C lower than the instrumental 1961-1999 temperature mean and hovering between a range of 2.9 to 6.6 °C.Finally, at the end of the record, temperatures warmed up again. However, Asteman et al. report that the contemporary warming of the 20th century "does not stand out in the 2500-year perspective and is of the same magnitude as the Roman Warm Period and the Medieval Climate Anomaly."
Of course, all that past warming was due to normal climatic oscillations and fluctuations within various cycles. This past warming had nothing to do with CO2 and other emitted greenhouse gases.
And just as occurred in the past, it is highly likely that a major portion of the warming since the Little Ice Age is also natural.
Additional historical temperature charts.