Temperature Variation Recorded By Tree Rings In Gaoligong Mountain And Its Response To Strong Volcanic Eruptions In Low Latitudes In Asia

The Gaoligong Mountain in the Northwest of Yunnan Province is the most important barrier for China ecological security construction.It is well known as the World Species Gene Bank because of its high forest coverage and extremely rich species distribution.Under the background of global change,as a water conservation area of many transboundary rivers in southwest China,the climate pattern in the region has been warm and dry.The natural landscape of the high altitude and cold area was degraded,which greatly threatens the protection of biodiversity and social security in this area.Changes in climate and natural environment makes the Gaoligong Mountain become a sensitive region onto global climate change in monsoon Asia.Strengthening the study of climate change and its driving mechanism in Gaoligong Mountain is an important decision-making basis for formulating the sustainable development strategy of natural economy and society.However,both meteorological data recorded by modern instruments or historical climate reconstruction data are relatively lacking,which limits our comprehensive understanding of climate change in Gaoligong Mountain.Tree-ring with high precision,strong continuity and wide distribution are perfect samples for quantitative reconstruction of paleoclimate.Based on the long tree age and climate sensitive Larix speciosa in Gaoligong Mountain area,this study carried out the historical climate reconstruction in the here.In this study,a 633-year regional tree-ring width chronology was successfully developed from 170 core samples collected from 91 Larix speciosa in five sampling sites in Gaoligong Mountain.The effective reconstruction period of the chronology was1420-2019.Through the correlation analysis with the meteorological data measured by the station instrument and the grid reanalysis data,it can be seen that temperature is the main promoting factor for the radial growth,while the restrictive effect of precipitation on the radial growth of Larix speciosa is weak.The developed regional chronology contains stable temperature signals.Based on the actual temperature records from 1948 to 2019 and the radial growth physiological process of Larix speciosa,the mean temperature in the warm season(May-September)of the past 600 years in Gaoligong Mountain was reconstructed on the basis of the linear regression model.The adjusted variance interpretation of the reconstructed model is 46.1%.leave-one-out crossvalidation test results shows that the regression model is stable and reliable,and can be used to transform the relationship between the annual tree-ring index of regional width chronology and the actual temperature in the warm season.The mean and standard deviation of the reconstructed warm season temperature for 600-years were 15.31 °C and 0.54 °C,respectively.There were eight warm and ten cold periods,104 warmer years(>15.85 °C)and 87 colder years(<14.76 °C).The frequency of warmer years since the 20 th century(n = 30)was significantly higher than that of colder years(n = 10).The mean temperature of the three years after 2016 was the highest temperature record in the past 600 years.The power spectrum and wavelet analysis results showed that the temperature in the warm season of the past 600-years have an obvious interannual and interdecadal periodic change.The actual temperature and reconstruction temperature have a highly correlated space field,where the highly correlated field are mainly concentrated in the 25-30° N and 95-100° E,which can characterize the temperature change in monsoon Asia.The main cold and warm periods revealed by the reconstructed warm season temperature series are well compared with other tree-ring temperature reconstruction sequences in the surrounding area.The corresponding relationship between the interannual and interdecadal is more than 99 %of the significant test,indicating the reliability of the reconstructed results.Solar activity,air-sea interaction and strong volcanic eruption in low latitudes of Asia are the possible driving factors for the interannual and interdecadal variations of temperature in the warm season of 600-years in Gaoligong Mountain.There were 8-14 years and 80 years of significant phase changes between the reconstructed temperature and the total number of sunspots,but the relationship was unstable.In 1850,the positive phase changed to the negative phase.The correlation between reconstructed temperature and sea surface temperature shows that ENSO and AMO\NAO are the internal factors that modulate the interannual and interdecadal variation of temperature in the warm season of Gaoligong Mountain.The combined analysis of low-temperature years and high-temperature years shows that the sea surface temperature,wind direction and wind speed change are opposite.The results of SEA analysis show that 21 strong volcanic eruptions at low latitudes in Asia in the past 600 years have caused a significant decrease in the mean temperature of the warm season in Gaoligong Mountain.In the year of eruption,the temperature decreased by 0.218 °C,and in the following two years,it decreased by 0.196 °C and 0.146 °C,respectively.The temperature returned to normal in the third year after eruption.The continuous cold period is accompanied by the evolution of historical civilizations such as the change of dynasties in South Asia and Southeast Asia,and the reconstruction of temperature change is related to human activities.If the sustainable development path and low forcing scenario(SSP1-2.6)are used,the temperature in Gaoligong Mountain area in the next 80 years can achieve the control of 1.5-2.0 °C temperature change,and avoid the serious consequences of ecosystem and natural landscape degradation caused by continuous warming.