过去2000年气候变化的全球集成研究进展与展望

过去2000年是国际过去全球变化计划聚焦的一个主要时段，并专门设立了"过去2000年全球变化网络"（PAGES2k）进行全球集成研究。本文依据PAGES2k及相关团队发表的主要成果，梳理了过去2000年温度与干湿变化的全球集成研究进展，并简要分析了发展态势与研究难点。最新研究显示：1）尽管采用不同方法重建的过去2000年全球平均温度变幅各异，但均表明第一个千年较其后千年（除20世纪外）更暖；1850年以前存在显著降温趋势，之后则转为快速增暖；过去2000年的最暖10年、30年、50年均出现在20世纪后半叶。
2）过去2000年干湿变化的全球集成研究尚处于起步阶段；尽管已整编了全球范围的代用资料，研制了首套全球陆地区域的干湿变化格点数据集，但结果仍存在显著不确定性。3）现有研究仍大多主要依托年分辨率的树轮资料，未实现对不同分辨率资料的有效集成。未来PAGES2k将依托资料管理，融陆地、海洋和人类社会的代用记录及相关研究于一体，针对代用资料与模式理解、方法与不确定性、气候变率模态与机制等三大主题，重点开展代用指标气候指示意义的时空差异、代用证据的定年精度与多源证据校核、代用资料挖掘技术与多源数据融合、校准方法等难点问题研究。

State-of-art and perspective on global synthesis studies of climate change for the past 2000 years

The past 2000 years is a highlighted interval of the PAGES(Past Global Changes) project and PAGES initiates the 2k Network(PAGES2k) to coordinate and integrate studies over the world. This paper summarizes the recent advances, prospects and challenges about temperature and hydroclimate changes during the past 2000 years based on literatures related with PAGES2k. The results are as follows: (1) Although pronounced difference is shown for the amplitude of temperature changes over the past two millennia among the reconstructions of global mean surface temperature(GMST) produced by the different methods, all reconstructions show that the GMST during first millennium of the Common Era was warmer than that during the second millennium(except for the 20th century). All reconstructions show a significant cooling trend before 1850 A.D., followed by rapid industrial-era warming.
The warmest 10-year, 30-year and 50-year period of the past two millennia falls within the second half of the twentieth century. (2) The synthesis reconstruction for global hydroclimate is still at the initial stage. Although the proxy data for global hydroclimatic reconstructions over the Common Era was compiled and the first gridded hydroclimate dataset covering the global land area was presented, there existed uncertainties in the results mainly due to the lack of long-term and spatially resolved proxies. (3) The tree ring with annual resolution is a major proxy for current reconstructions, while other proxies with lower resolution are not well fused in the global synthesis so far. Based on the data stewardship, PAGES2k will synthesize the proxies derived from land, oceans and societies for further studies focused on the themes of proxy and model understanding, methods and uncertainties, and climate variability, modes and mechanisms. The major challenges include the interpretation of spatiotemporal difference for the significance of climate proxies, dating and cross-validation of multiple proxies, proxy data mining, and methods for proxy data assemble, calibration and assimilation.