Peer-reviewed studies, geologic records, and all the studies have shown that we have actually cooled since the Roman Warming Period, and likely since the Medieval Warming Period.
Claim that the Earth has cooled since Medieval or Roman times is contradicted by available data [...] A recent study1 analyzing a global database of paleoclimate records found that no previous warm or cool period in the last 2,000 years—including the Roman Warm Period and the Medieval Warm Period (also called the Medieval Climate Anomaly)—occurred globally and synchronously. But 20th Century temperatures were the warmest of the last 2,000 years for nearly the entire surface of the Earth. [...] 2) For the Northern Hemisphere (where we have much better proxy data and a better understanding of the uncertainties), we come to similar conclusions—in Wilson et al (2016)2 we find that the two warmest decades of our reconstruction (from 918 to 2004 CE) were 1994–2003 and 1946–1955. Coming in 3rd place is 1161–1170 CE. So, the latest in large-scale temperature reconstructions do NOT support a claim that temperatures either in the Medieval or Roman periods were warmer than today.