Constraining carbon cycle processes over the last glacial cycle

人为气候变化是我们面临的最大的全球环境挑战之一。我们燃烧化石燃料产生的排放正在改变大气中温室气体的水平，并使地球气候变暖。这一点很清楚--然而，从长远来看，地球将如何应对这些排放仍存在相当大的不确定性。这种不确定性的主要来源之一是碳循环将如何应对更高水平的二氧化碳和不断变化的气候。气候模型是我们研究气候变化最重要的工具之一，然而，气候系统是复杂的，气候模型远远不是完美的。我们可以通过将气候模拟与过去气候和当前观测的重建进行比较来验证模拟的气候系统响应。从长期来看，一些最重要和最可靠的气候数据重建来自南极洲和格陵兰岛的冰芯。这些冰芯记录了几个冰川周期中温室气体和气候指标的变化。最近开发的复杂气候-碳循环模型和上一次冰川周期的数据重建为量化气候-碳循环反馈在很长时间尺度上的重要性提供了一个独特的机会。我的研究计划的一个关键目标是理解这些反馈，并评估它们在推动过去冰川形成方面的相对重要性。了解冰川周期气候变化背后的机制是一项重大的科学挑战。到目前为止，复杂的地球系统模型还无法模拟冰期-间冰期二氧化碳转变的全部规模和时间。尽管最初的作用力被认为主要来自地球轨道的变化，但之前用更简单的模型所做的工作表明，还有许多其他过程参与其中，各种碳循环反馈的重要性仍存在广泛争论。这项提案中概述的研究将利用唯一的加拿大模型，也是少数几个模型之一，能够模拟冰川周期中的碳循环。这项研究将利用最先进的陆地、海洋、冰盖和碳循环组件，在一致的建模框架内提供对碳循环反馈的系统评估。限制碳循环的反应将有助于减少气候系统对人为排放反应的不确定性，并将对气候政策制定者大有裨益。人为排放的长期后果，如生态系统的变化和冰盖融化导致的海平面上升，可能特别严重。至关重要的是，我们必须了解并量化过去的碳循环过程，以便更有信心预测未来的气候-碳循环反应。

Anthropogenic climate change is one of the greatest global environmental challenges we face. The emissions we generate from burning fossil fuels are changing the levels of greenhouse gases in the atmosphere and warming the Earth's climate. This is clear - yet there is still considerable uncertainty in how the Earth will react to these emissions over the longer term. One of the major sources of this uncertainty is how the carbon cycle will respond, both to higher levels of carbon dioxide and to the changing climate. Climate models are one of the most important tools we have for studying climate change, however, the climate system is complex and climate models are far from perfect. We can validate the modelled climate system response by comparing climate simulations to reconstructions of past climate and current observations. Over the long-term, some of the most important and reliable climate data reconstructions come from ice cores in Antarctica and Greenland. These ice cores record changes in greenhouse gases and proxies for climate over several glacial cycles. Recently developed complex climate-carbon cycle models and data reconstructions over the last glacial cycle provide a unique opportunity to quantify the importance of climate-carbon cycle feedbacks over very long time scales.******A key goal of my research program is to understand these feedbacks and assess their relative importance in forcing past glaciations. Understanding the mechanisms behind the climate variations over a glacial cycle is a major scientific challenge. Complex Earth System Models have not been able to simulate the full magnitude and timing of glacial-interglacial carbon dioxide transitions thus far. Although the initial forcing is thought to be primarily from variations in the Earth's orbit, previous work with simpler models suggests that many other processes are involved and the importance of various carbon-cycle feedbacks is still widely debated. Research outlined in this proposal will utilize the only Canadian model, and one of the few models anywhere, that is capable of simulating the carbon cycle over a glacial cycle. This research will provide a methodical evaluation of carbon cycle feedbacks within a consistent modelling framework, utilizing state of the art land, ocean, ice sheet and carbon cycle components. Constraining the response of the carbon cycle will help reduce the uncertainty of the climate system response to anthropogenic emissions and will be of great utility to climate policy decision makers. The long-term consequences of anthropogenic emissions, such as shifts in ecosystems and sea level rise from ice sheet melt, may be particular severe. It is critical that we understand and quantify past carbon cycle processes to give us more confidence in projecting any future climate-carbon cycle response.