Ensemble Estimation of Central Tropical Pacific Climate over the last 6,000 Years

围绕世界许多地区未来气候变化影响的重大不确定性，特别是关于热带降雨量及其极端情况的潜在变化。不确定性很大程度上源于对厄尔尼诺-南方涛动(ENSO)未来趋势的制约不力。厄尔尼诺-南方涛动(ENSO)是一种影响全球气温和降雨模式的自然气候循环，对热带地区的影响最大。ENSO的仪器记录太短，无法从统计上分离出强劲的趋势，因此本研究试图提供数百年来对过去ENSO变率的额外观测，以努力：1)量化这一全球相关气候周期的自然基线，以及2)评估最近的变化是否超出自然变率的范围。这项研究使用了一套来自热带太平洋中部的年代准确和高分辨率的珊瑚记录，将扩展ENSO记录和ENSO区域中心的更长期气候模式。因此，它将为未来对热带太平洋气候的预测提供信息，并限制整个热带和其他地区的区域降雨趋势。由于热带气候在年际到年代际时间尺度上的显著变异性，很难将热带太平洋气候趋势与气候的短暂工具记录分开。最近的古气候记录暗示，厄尔尼诺-南方涛动(ENSO)可能会因人为气候强迫而加剧，这意味着未来几十年热带极端降雨量可能会增加。这些记录还表明，自然的ENSO变率比之前认为的要大得多，需要进行大量的古重建来确定自然的ENSO变率，并将其与可能的人为信号区分开来。过去6000年是探索过去ENSO变化的一个特别重要的基线，因为全球气候模型表明，ENSO可能对这段时间内的一系列自然气候强迫很敏感。该项目涉及利用位于厄尔尼诺-南方涛动(ENSO)区域中心的圣诞岛(2°N，157°W)的数百个珊瑚化石记录，高度重复地重建过去6000年热带太平洋的平均气候和气候变异性。包括一名研究生在内的研究小组将把新的重建结果与热带太平洋古气候可变性的数值气候模型模拟进行比较，探索气候强迫、平均气候状态和ENSO可变性之间的关系。

Significant uncertainty surrounds future climate change impacts in many regions of the world, particularly regarding potential changes in tropical rainfall levels, and their extremes. Much of the uncertainty stems from poor constraints on future trends in the El Nino-Southern Oscillation (ENSO), a natural climate cycle that affects temperature and rainfall patterns around the globe, with its largest effects in the tropics. The instrumental record of ENSO is too short to isolate statistically robust trends, so this study seeks to provide hundreds of years worth of additional observations of past ENSO variability in an effort to: 1) quantify the natural baseline for this globally-relevant climate cycle, and 2) assess whether recent changes fall outside the range of natural variability. Using a suite of well-dated and high-resolution coral records from the central tropical Pacific, the study will extend the record of ENSO and longer-term climate patterns in the heart of the ENSO region. As such, it will inform future projections of tropical Pacific climate and constrain regional rainfall trends throughout the tropics and beyond. Tropical Pacific climate trends are difficult to isolate from the short instrumental record of climate, owing to significant tropical climate variability on interannual to decadal timescales. Recent paleoclimate records hint that the El Nino-Southern Oscillation (ENSO) may be intensifying in response to anthropogenic climate forcing, implying that tropical rainfall extremes may increase in coming decades. Such records also show that natural ENSO variability is much larger than previously thought, requiring a larger number of paleo-reconstruction to define natural ENSO variability and distinguish it from possible anthropogenic signals. The last 6,000 years is an particularly important baseline for probing past ENSO variability, as global climate models show that ENSO may be sensitive to a range of natural climate forcings over this period. This project involves generation of a highly-replicated reconstruction of both mean climate and climate variability in the tropical Pacific over the last 6,000 years using hundreds of fossil coral records from Christmas Island (2ºN, 157ºW), which lies in the heart of the El Niño-Southern Oscillation (ENSO) region. The research team, which includes a graduate student, will compare the new reconstructions to numerical climate model simulations of tropical Pacific paleoclimate variability, probing the relationships between climate forcing, mean climate state, and ENSO variability.