Read here. The paleo-climate empirical evidence continues to grow that documents the unequivocal, unprecedented warming of pre-industrial periods in many parts of the world. Thousands of researchers have now demonstrably proven that the recent IPCC Climategate science flim-flam and hockey-stick statistical bogosity claims, purporting to prove that higher levels of CO2 during industrial times have led to "unprecedented" warming, are without empirical merit.
The new Stewart et al. research clearly shows (click on image to enlarge) that the Lake Silvaplana, Switzerland region had robustly higher temperatures well prior to the modern industrial/consumer atmospheric levels of high CO2. During Roman and the pre-Roman iron age eras, peak summer temperatures would be considered unnaturally extreme by today's global warming alarmists.
"Working with a piston core that was extracted during the winter of 2005-2006 from Lake Silvaplana in the eastern Swiss Alps, the authors developed a June-July-August (JJA) temperature history of the surrounding region...report that "temperatures reconstructed from ca. 570 BC to AD 120 were warmer than today (AD 1950-2000; 9.8°C)," with the JJA temperatures of the warmest portion of this interval (ca. 570-351 BC) being approximately 11.2°C, after which they say they also "found moderately warm temperatures for the Roman Period (11°C, ca. 15 BC to AD 120)."...which yields a peak Current Warm Period temperature of 10.3°C. And thus we see that the peak temperature of the Roman Warm Period (11°C) was about 0.7°C warmer than the peak temperature of the Current Warm Period, while the peak temperature of the earlier 570-351 BC period (11.2°C) was approximately 0.9°C warmer than the peak temperature of the Current Warm Period." [Monique M. Stewart, Isabelle Larocque-Tobler, Martin Grosjean 2011: Journal of Quaternary]