BBC: The past 30 years in Europe have likely been the warmest in more than two millennia, according to new research. The study used tree ring records and historical documents to reconstruct yearly temperatures going back 2,100 years. Scientists say that past natural variability in temperatures was greater than previously thought. As a result, climate models may be underestimating the frequency and severity of heat waves in the future. According to the study, Europe has seen an increase in summer warming...