Temperature Fluctuations in Greenland and the Arctic

Abstract Greenland ice cores have generated a huge amount of climatic data. Ancient temperatures, measured using oxygen isotopes in the ice, can be accurately dated from annual dust layers in the ice dating back 100,000 years. The δ 18 O data clearly show remarkable swings in climate. In the past 500 years, Greenland temperatures have fluctuated back and forth between warming and cooling about 40 times, with changes every 25–30 years. Among the more prominent climate changes recorded in the ice cores are 8500 years of Holocene temperatures that were 2–5°F warmer than present; a 8200-year cold period in the early Holocene; the Minoan Warm Period (∼3300 years ago); the Roman Warm Period (250 BC to 400 AD); the Dark Ages Cold Period (∼400–900 AD); the Medieval Warm Period (900–1300 AD); the Little Ice Age (1300 AD to the 20th century); the Wolf Minimum Cold Period (∼1280–1350 AD); the Sporer Cold Period (1460–1550 AD); the Maunder Minimum Cold Period (1645–1710); the Dalton Cold Period (1790–1820); the 1880–1915 Cold Period; the 1915–1945 Warm Period; the 1945–1977 Cold Period; and the 1978–2000 Warm Period. Comparisons of the intensity and magnitude of past warming and cooling climate changes show that the global warming experienced during the past century pales into insignificance when compared to the magnitude of profound climate reversals over the past 25,000 years. At least three warming events were 20–24 times the magnitude of warming over the past century, and four were 6–9 times the magnitude of warming over the past century. The magnitude of the only modern warming that might possibly have been caused by CO 2 (1978–2000) is insignificant compared to the earlier periods of warming. Arctic temperatures have fluctuated repeatedly in step with Greenland and global climate changes. Historic records at many weather stations in the Arctic show that temperatures were higher in the 1930s and 1940s than during recent warming (1980–2000). Sea ice extent has expanded and contracted with temperature fluctuations and has sharply increased over the past several years.