claim: But we do have other reliable indicators of temperatures before the late 1800s, and the evidence shows temperatures have been warmer than today for most of the past several thousand years, including warmer-than-present temperatures for most of the human civilization time period
evidence: For example, diverse geochemical and paleontological proxies indicate that at the maximum of global warmth the atmospheric carbon dioxide values were at 700–900 ppm while other proxies such as pedogenic ( soil building ) carbonate and marine boron isotopes indicate large changes of carbon dioxide of over 2,000 ppm over periods of time of less than 1 million years.