As the preponderance of scientific studies and reports have proven, our current modern warming is not unprecedented. Significant warming has taken place quite often in the past, as well as climatic cooling.
"The 600-year reconstructed record -- dating back to AD 1392. As indicated, the record shows pronounced periods of subdecadal to multidecadal variability. Specifically, Elbert et al. note the presence of cold phases "during parts of the Little Ice Age (16th and 18th centuries) and in the beginning of the 20th century." In contrast, they state that warm phases persisted "in the 15th century, around AD 1600 and in the 19th century," the latter of which they characterized as the "most prominent" of the entire record."
Additional peer-reviewed postings.