PRELIMINARY STUDY ON SPATIOTEMPORAL PATTERN OF CLIMATE CHANGE OVER TIBET PLATEAU DURING PAST MILLENNIUM

Researching the change during past millennium over Tibet Plateau(TP) plays a vital role in the prediction of cryosphere change in such region and its far-reaching influence under future warming climate.By 15 high resolution paleoclimate series reflecting the evolution during past millennium over TP,this paper aims to further study the spatiotemporal pattern of change during past millennium over TP.The comprehensive reconstruction of temperature by these 15 series indicates that,generally,over the past millennium,TP has been characterized by a prominent Medieval Warm Period(MWP,the period before ~1450s),a moderate Little Ice Age(LIA,from ~1450s to 1870s),and the increase of temperature since then(the abrupt drop of temperature around 1920s and 1970s were evidently).By comparison,the warmth of MWP over TP shows a good agreement with that during the first half of 20th century,and that in other reconstructions of temperature over the Northern Hemisphere;the LIA over TP is relatively warmer than that over eastern China.Moreover,Empirical Orthogonal Function(EOF) analysis of these 15 series is carried out to explore the spatiotemporal pattern of change during past millennium over TP.It suggests that the three major climate anomalies during past millennium(MWP,LIA and post-industrial warming) have showed marked regional differences over sub-region of TP.The MWP lasts until ~1450s in Northeast TP and Northern TP and Western TP(the period during 1250—1300s was a cold epoch),~13th century in Karakoram region and Eastern TP;lots of materials in Southern TP revealed that the MWP would occur during 11—15th century(while the PC3 of EOF analysis,reflecting the information in Southern TP,indicated that the warmth of MWP was not evidently in this region).During LIA,there were three cold epochs(i.e.,1450—1520s,1650—1750s and 1780—1850s) in Northeast TP and Western TP,three cold epochs(i.e.,1450—1650s,1740—1780s and 1820—1850s) in Karakoram region,two cold epochs(i.e.,1580—1650s and 1740—1780s) in Southern TP and Eastern TP and Northern TP(the period during 1670—1730s would be a warm epoch which was also evidently in Karakoram region).Last but not least,few tree ring records in southern TP and Eastern TP have showed a decrease of summer temperature against the notable increasing of global temperature,possibly attributing to the inconsistency of temperature change in different seasons(i.e.,summer and winter) during global warming.