Pliocene Gateways ('PlioGate')

随着二氧化碳(CO2)和甲烷等温室气体的增加，未来100年气候将如何演变？这个问题在科学家和政治家心中都是至高无上的。然而，尽管对气候敏感性进行了100多年的研究，但预计未来变暖的范围仍然令人震惊；1.5至6.1摄氏度意味着大气二氧化碳增加一倍。不同气候模型的预测之间的不一致导致了这种不确定性。由于必须在技术限制和我们对气候过程的知识之间达成妥协，气候模型必然是对现实的近似。因此，所有模型都在它们所代表的过程和它们运行的分辨率方面有所不同。这就是为什么气候模型会产生不同的结果，即使它们基于相同的数学原理。这也是为什么测试这些模型是至关重要的，以确保它们真的能够模拟地球的气候。由于没有对未来气候变化的观测，我们指望过去来评估气候模型。仪器记录提供了对该模型的一个这样的测试。然而，在我们工具记录的短暂持续时间内，与未来100年的预测变化相比，气候变化一直很小。这使得仪器记录不足以对模型进行权威性测试，我们还必须在其他时间段测试模型。上一次大气二氧化碳像今天这样高是在上新世晚期，特别是大约300万年前。显然，从很久以前就没有直接的观测到了，但来自上新世动植物化石遗骸的证据表明，一种依赖于气候的化学和生物信号，我们可以用来重建这些动植物生活的气候条件。这项工作的结论表明，气候比前工业化时代高出2至3摄氏度，其中北大西洋和格陵兰-冰岛-挪威海的升温幅度特别大。因此，上新世和未来情景之间的相似之处使上新世成为预测未来气候变化的模型的理想测试案例。到目前为止，这一时期的模型模拟已经能够模拟上新世的整体温暖，但无法再现北大西洋杜松子海的大范围温暖。最近，在国际PlioMIP项目的支持下，14个不同的最先进的气候模型在这一时期运行，但都未能再现北大西洋/GIN海变暖。我们认为，这种不匹配是上新世洋门不充分的征兆，而不是暖期气候模型的根本错误。布里斯托尔大学最近的研究表明，在现代气候模型中改变海洋门户的设置方式可以对区域气候产生5摄氏度或更高的影响。该提案将调查两个关键的海洋门户，即白令海峡和直布罗陀海峡的作用。没有人调查过它们交换的变化是否会对上新世气候产生影响，尽管有证据表明，这些门户是不同的，它们可以对气候产生重大影响。该项目的结果将对改善我们对上新世气候的理解以及气候模型是否适用于过去的温暖时段做出相当大的贡献。

In the wake of rising greenhouse gases, such as carbon dioxide (CO2) and methane, how will the climate evolve over the next 100 years? This question is paramount in the minds of scientists and politicians alike. However, despite over 100 years of research into climate sensitivity, the range of projected future warming remains startling wide; 1.5 to 6.1 degrees C for a doubling of atmospheric CO2. The disagreement between projections made by different climate models makes a considerable contribution to this uncertainty.Because a compromise must be reached between the limits of technology and our knowledge of climate processes, climate models are necessarily approximations of reality. As a result, all models differ in terms of the processes they represent and the resolution they run at. This is why climate models produce different results even though they are based on the same mathematical principles. It is also why it is crucial to test the models, to make sure that they really are capable of simulating Earth's climate.As there are no observations for future climate change, we look to the past to evaluate climate models. The instrumental record provides one such test of the model. However, throughout the short duration of our instrumental record, climate change has been small in comparison to projected changes for the next 100 years. This makes the instrumental record an inadequate definitive test of the models and we must test the models in other time periods too.The last time atmospheric CO2 was as high as today was during a period known as the late Pliocene, specifically around 3 million years ago. Obviously there are no direct observations from so long ago, but evidence from fossil-remains of Pliocene fauna and flora show a climate-dependent chemical and biological signal, which we can use to reconstruct the climate conditions that these fauna and flora lived in. The conclusions from this work suggest that climate was 2 to 3 degrees C warmer than the Pre-Industrial era, with particularly large amplitude warming in the N.Atlantic and Greenland-Iceland-Norwegian Sea. Therefore, the parallels between the Pliocene and future scenarios makes the Pliocene an ideal test case for models used to project future climate change.To date, model simulations for this period have been able to simulate the overall warmth of the Pliocene, but fail to reproduce the large amplitude warmth in the N.Atlantic GIN Sea. Recently, under the auspices of the international PlioMIP project, 14 different state-of-the-art climate models have been run for this period, but all have failed to reproduce the N.Atlantic/GIN Sea warming.We suggest that this mismatch is symptomatic of inadequate representation of ocean gateways during the Pliocene, rather than a fundamental error in climate models during warm periods. Recent work at the University of Bristol has showed that changing the way ocean gateways are set-up in a model of modern climate can impact regional climates by 5 degrees C or more. This proposal will investigate the role of two key ocean gateways, namely the Bering and Gibraltar Straits. Nobody has ever investigated whether changes in their exchange could have had an impact on Pliocene climate, despite the fact that there is evidence that the gateways were different and that they can have a big impact on climate. The results from the project will make a considerable contribution to improving our understanding of Pliocene climates and whether climate models work for past warm intervals.