Read here. More scientific research, peer-reviewed, provides actual evidence that previous warming and cooling periods were far in excess of our modern temperatures. These intemperate periods, relative to ours, occurred at low levels of atmospheric CO2.
"...we have a situation where the Little Ice Age was found to have been the coldest period of the current interglacial [italics added], which suggests (once again) that 20th-century global warming could not have taken the earth into "uncharted" thermal territory, but only back to something similar to what prevailed prior to the Little Ice Age, like the Medieval Warm Period, which was merely a run-of-the-mill relatively warmer period that was still much colder than the several-millennia-long Holocene Thermal Maximum, which Briner et al. report "was several degrees warmer than today..."
