Climate Change in the Southern Hemisphere Extratropics

南半球温带气候变化

• 批准号: 0735056
• 负责人: Alexander Hall
• 金额: $ 37.13万
• 依托单位: University of California-Los Angeles
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0735056&HistoricalAwards=false
• 关键词: Climate; Change; Southern; Hemisphere; Extratropics

The region of the Southern Ocean is important for the global climate, because a large fraction of anthropogenic carbon dioxide is believed to enter the ocean in this region and because the growth or ablation of Antarctic ice sheets depends sensitively on the climate of the surrounding ocean. The climate dynamics of the Southern Ocean are distinguished by a high equilibrium sensitivity to greenhouse forcing, because of sea-ice feedbacks, a slow approach to equilibrium, because of the strong coupling to the deep ocean, and exceptionally strong internal variability associated with the Southern annular mode.Under prior support, Hall's group developed techniques for understanding the mechanisms for and constraining the strength of snow-albedo feedback in Northern Hemisphere land areas. Here they will apply similar methods to analyzing the climate feedbacks in the Southern Ocean as represented in global climate models (GCMs). The relevant feedbacks are those acting on the shortwave radiation budget, namely cloud and sea-ice albedo feedbacks, those acting on the long-wave radiation, and those associated with climate changes elsewhere on the planet. The ice-albedo feedback can be further decomposed into effects associated with changes in ice area and in ice thickness. The latter has the interesting property that a change in ice thickness during the cold season produces a change in surface temperature during the melting season.They will calculate the energy budgets over this region for a number of climate models, comparing present-day simulations with those of a future warmer climate. The results will be used to compute the various feedbacks and to relate the strengths of these feedbacks to differences in the climate sensitivity of the different models. The mechanisms involved in these feedbacks will be determined by analyzing the responses of sea-ice albedo to climate change as well as the changes in planetary albedo, due to changes in cloud cover, associated with changes in sea ice. Cloud behavior will be compared with observations obtained from satellite cloud climatologies. The validity of surface albedo feedbacks in the models will be determined by comparing observed and simulated ice-albedo feedbacks for the seasonal cycle. Additionally they will analyze the nature and mechanisms for internal variability in the Southern Ocean region and will use these results to attempt to determine whether recent climate trends in this region are consistent with internal variability. The results of the studies of equilibrium sensitivity and those of internal variability will be synthesized in an analysis of the transient climate change in the Southern Ocean region. The times at which different models exhibit the emergence of a clearly externally forced change will be determined, and the reasons for model differences in these emergence times will be studied. The results will be used to suggest the model improvements that are needed to produce more reliable projections of future climate in the Southern Ocean.Broader impacts of this work include its potential to narrow the spread among model projections of climate change and, therefore, to increase confidence in estimates of the ocean uptake of carbon dioxide and the risk of significant melting of the Antarctic ice sheets. Hall will teach a freshman seminar on the "Fate of the Antarctic Ice Sheet." The project will support the training of a postdoctoral fellow and a graduate student.

南大洋地区对于全球气候很重要，因为据信大量人为二氧化碳进入该地区的海洋，并且因为南极冰盖的生长或消融敏感地取决于周围海洋的气候。南大洋的气候动力学以对温室强迫的高平衡敏感性，因为海冰反馈的反馈，一种缓慢的平衡方法，由于与深海的强烈耦合，并且与南部的内部变异非常强烈在先前的支持下，霍尔的小组开发了了解北半球土地地区雪 - 阿尔贝托反馈强度的机制的技术。在这里，他们将采用类似的方法来分析全球气候模型（GCM）所代表的南大洋中的气候反馈。相关的反馈是那些以短波辐射预算作用的反馈，即云和海冰反映反馈，对长波辐射的作用，以及与地球其他地方的气候变化相关的反馈。冰 - 阿尔底多的反馈可以进一步分解为与冰面积变化和冰层厚度有关的影响。后者具有有趣的特性，即在寒冷季节的冰厚度变化会在熔化季节产生表面温度的变化。它们将计算许多气候模型的能源预算，将目前的模拟与这些模型进行比较未来温暖的气候。结果将用于计算各种反馈，并将这些反馈的优势与不同模型的气候灵敏度的差异联系起来。这些反馈所涉及的机制将通过分析海冰反照率对气候变化的反应以及随着云覆盖的变化，与海冰的变化相关，而行星反照率的变化则可以确定。将云行为与从卫星云气候获得的观察结果进行比较。模型中表面反照率反馈的有效性将通过比较季节周期的观察到和模拟的冰 - 艾尔底反馈来确定。此外，他们将分析南大洋地区内部变异性的性质和机制，并将使用这些结果来确定该地区最近的气候趋势是否与内部变异性一致。在分析南大洋地区的瞬时气候变化时，将合成平衡敏感性和内部变异性的研究结果。将确定不同模型表现出明显外部强迫变化的出现的时间，并将研究这些出现时间模型差异的原因。结果将用于提出所需的模型改进，这些改进是在南大洋中产生更可靠的未来气候的预测。这项工作的影响包括其潜力缩小气候变化模型预测之间的传播，因此增加对二氧化碳摄取的估计的信心以及南极冰盖融化的风险。霍尔将在“南极冰盖的命运”上教新生研讨会。该项目将支持博士后研究员和研究生的培训。