Collaborative Research: Closing the Gaps in Climate Models' Surface Albedo Schemes of Processes Driving the Darkening of the Greenland Ice Sheet

地表反照率是测量太阳辐射被介质反射的百分比。反照率越高（越低），介质吸收的太阳能量越低（越高）。反照率在格陵兰冰盖上起着至关重要的作用，在那里，吸收的太阳辐射是夏季地表融化的主要驱动力。格陵兰冰盖反照率的演变主要是由雪颗粒大小的变化、表面液态水的存在、裸露冰的暴露以及冰雪中吸收光的杂质的存在所驱动的。这些杂质包括烟灰、灰尘和细菌、藻类等生物成分。生物杂质与雪物理过程（如变质作用和熔体再分配）之间的相互作用是重要的，因为它们可以驱动正反馈，其中总熔体被放大。尽管这些过程很重要，但在用于模拟格陵兰对海平面上升贡献的当前估计和未来预测的模式中，这些与冰雪演变有关的生物成分的过程目前要么不存在，要么代表性不足。通过跨学科和协作的努力，该项目将把生物活动如何影响反照率的最新知识整合到气候模型中。这将有助于减少格陵兰对海平面上升贡献的不确定性，也将提高我们对冰盖与大气之间相互作用的理解。我们研究中应用的区域气候和地球系统模型是开源模型，例如社区地球系统模型（Community Earth System Model）。已经实现的模型改进将及时发布，供其他研究人员使用。该项目包括一名博士后的参与，从而培训年轻的研究人员通过跨学科的努力来解决复杂而关键的科学问题。该项目的结果将向媒体和公众传播，从而促进对影响格陵兰冰盖表面物质平衡的过程的更深入了解。

Surface albedo is a measure of the percentage of solar radiation that is reflected by a medium. The higher (lower) the albedo, the lower (higher) is the amount of solar energy absorbed by the medium. Albedo plays a critical role on the Greenland Ice Sheet, where absorbed solar radiation is the dominant driver of surface melt during summer. The evolution of albedo on the Greenland Ice Sheet is primarily driven by changes in snow grain size, the presence of liquid water on the surface, the exposure of bare ice, and the presence of light-absorbing impurities in the snow and ice. Such impurities include soot, dust, and biological constituents like bacteria and algae. Interactions between biological impurities and snow physical processes (e.g., metamorphism and melt redistribution) are important because they can drive positive feedbacks in which total melt is amplified. Despite their importance, these processes relating biological constituents to snow and ice evolution are currently either absent or poorly represented in models used to simulate current estimates and future projections of the contribution of Greenland to sea level rise. Through an interdisciplinary and collaborative effort, this project will integrate state of the art knowledge of how biological activity impacts albedo into climate models. This will help reduce uncertainties of the contribution of Greenland to sea level rise and will also improve our understanding of interactions between the ice sheet and the atmosphere.The regional climate and Earth System models that will be applied in our study are open-source models, such as e.g., the Community Earth System Model). Model improvements that are implemented will be released for use by other researchers in a timely way. The project includes the involvement of a postdoctoral fellow, and hence training of young investigators to address complex and yet crucial science questions through an interdisciplinary effort. Results from this project will be communicated to the media and public, thereby promoting deeper knowledge of the processes affecting the surface mass balance of the Greenland Ice Sheet.