May—July Temperature Variability Since 1801 Inferred from Tree Rings of Pinus tabulaeformis of Helan Mountains in China

Ninety newly measured tree-ring width and density series from Chinese Pines (Pinus tabulaeformis) from four sites in Helan Mountains are compiled. To remove non-climatic, age-related growth trends from the raw tree-ring width and density measurement series, while allowing lower frequency information above the mean segment length to be preserved, the program ARSTAN is used to detrend the ring width and density sequences using hugershoff growth curve and to average the standardized ring width and density sequences into the master chronologies. The correlating coefficient between earlywood density record and May—July maximum temperature of Yinchuan reaches up to 0.67 during 1951—2008. The May—July maximum temperature reconstruction (1801—2008) uses the earlywood density chronologies from the region. The explained variance of model is 44.9% (F=45.625, P < 0.0001). The mean temperature over the 1801—2008 periods is estimated to be 27.4 ℃. The reconstructed temperature has 3 warm periods, including 1801—1812, 1940—1953, and 1994—2008. The rising of temperature series in the 2000s is the fastest and indicates that temperature in the 2000s has been warmer than any other period since 1801. The reconstructed temperature during the last 208a has significant period cycles of 120 years (95%), 8.1 years (95%), 6.5 years (90%), 3.2 years (95%), 2.9 years (95%), and 2.1 years (99%). Many low density values are forced by volcanic eruptions. Comparison shows volcanic eruptions have no systematic relationship with this reconstruction data, but they are correlated with the regional characteristics of the temperature and forcing data. Detailed analysis, however, suggests a cooling of several years following primarily tropical events with a volcanic eruption index (VEI). Examples include Tambora in Indonesia (1815), Cosiguina in Nicaragua (1935), Chikurachki in Kurilels (1853), Sheveluch in Kamchatka (1854), Krakatu in Java (1883), Okataina in New Zealand (1886), Santa Maria in Guatemala (1902), Ksudach in Kamchatka (1907), Katmai in Alaska (1912), Bezymianny in Kamchatka (1956), Agung in Indonesia (1963), St Helens in US (1980), El Chichon in Mexico (1982), and Pinatubo in Philippines (1991). The mean of 28 low values after volcanic eruption in reconstructed temperature series is 26.9℃, which is 0.5℃ lower than the average over the 1801—2008. The earlywood density of Helan Mountains has good relations with the earlywood densities of Shimen Mountains and Changling Mountains in Gansu.