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

表面反照率是衡量被介质反射的太阳辐射的百分比。反照率越高(低)，介质吸收的太阳能就越少(高)。反照率在格陵兰冰盖上起着关键作用，那里吸收的太阳辐射是夏季地表融化的主要驱动力。格陵兰冰盖上反照率的演变主要是由雪粒大小的变化、表面存在液态水、裸露的冰以及雪和冰中吸收光的杂质的存在所驱动的。这类杂质包括煤烟、灰尘以及细菌和藻类等生物成分。生物杂质与雪物理过程(例如，变质作用和熔体再分配)之间的相互作用很重要，因为它们可以驱动正反馈，放大总融化。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型中，这些将生物成分与冰雪演化联系起来的过程目前要么没有，要么表现得很差。通过跨学科和协作的努力，该项目将把关于生物活动如何影响反照率的最先进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和大气之间相互作用的理解。我们研究中将应用的区域气候和地球系统模型是开源模型，例如共同体地球系统模型)。已实施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研究员的参与，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。该项目的成果将传达给媒体和公众，从而促进对影响格陵兰冰盖表面物质平衡的过程有更深入的了解。

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.