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的心中都是最重要的。然而，尽管对气候敏感性进行了100多年的研究，预测未来变暖的范围仍然大得惊人；1.5到6.1摄氏度会使大气中的二氧化碳加倍。不同气候模式预估结果之间的差异对这种不确定性有很大的影响。由于必须在技术极限和我们对气候过程的认识之间达成妥协，气候模型必然是现实的近似值。因此，所有模型在它们所代表的过程和它们所运行的分辨率方面都是不同的。这就是为什么气候模型即使基于相同的数学原理也会得出不同的结果。这也是为什么测试这些模型至关重要，以确保它们确实能够模拟地球的气候。由于没有对未来气候变化的观测，我们依靠过去来评估气候模式。仪器记录为该模型提供了一个这样的测试。然而，在我们仪器记录的短时间内，与未来100年的预估变化相比，气候变化一直很小。这使得仪器记录成为模型的不充分的确定测试，我们也必须在其他时期测试模型。上一次大气中二氧化碳含量像今天这么高是在上新世晚期，具体来说是在300万年前。显然，这么久以前没有直接的观察结果，但是从上新世动植物的化石遗骸中得到的证据显示了一种依赖气候的化学和生物信号，我们可以利用它来重建这些动植物生活的气候条件。这项工作得出的结论表明，气候比工业化前时代升温2至3摄氏度，北大西洋和格陵兰-冰岛-挪威海的升温幅度尤其大。因此，上新世与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模式的理想测试案例。迄今为止，该时期的模式模拟已经能够模拟上新世的整体变暖，但未能重现北大西洋海的大幅度变暖。最近，在国际PlioMIP项目的主持下，对这一时期运行了14种不同的最先进的气候模型，但都未能重现北大西洋/印度洋海洋变暖。我们认为，这种不匹配是上新世期间海洋通道代表性不足的症状，而不是暖期气候模式的根本错误。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通道的设置方式可能会对区域气候产生5摄氏度或更多的影响。该提案将调查两个主要海洋门户的作用，即白令海峡和直布罗陀海峡。没有人调查过它们交换的变化是否会对上新世的气候产生影响，尽管有证据表明这些通道是不同的，它们会对气候产生重大影响。该项目的结果将对提高我们对上新世气候的理解以及气候模式是否适用于过去的温暖间隔做出重大贡献。

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.