Extratropical Climate Change in the Upper Troposphere and the Routing of Aircraft (EXTRA)

中纬度对流层上层是指高度在8-12公里左右的区域，包括急流、大风区域，这些区域与中纬度低压的强度和路径密切相关。气候变化预计将改变中纬度对流层上层的性质--气候模型表明，未来几十年，天气将变暖，相对湿度将增加，急流的强度和方向可能会改变，对流层和上面的平流层(对流层顶)之间的边界将高度增加。然而，当不同的气候模型被用来预测未来的气候变化时，它们产生的结果有很大的差异，这种差异的原因还不完全被理解。了解中纬度对流层上层的气候变化本身是重要的，但它具有更广泛的经济意义。商用飞机的巡航高度位于对流层上层，飞行时间会受到风力条件的强烈影响。最明显的是，(举个例子)伦敦和纽约之间的航班在向东飞行时，飞行时间通常要快一个多小时，因为飞机试图在急流中飞行，并受到额外的“推动”--相比之下，向西飞行的航班通常会试图避开急流，因为这会阻碍进度。然而，北大西洋天气条件的日复一日变化意味着，东行和西行航班的飞行时间可以相差长达100分钟，这主要取决于急流的强度和位置。由于燃料使用和二氧化碳排放与飞行时间密切相关，这种变化既有经济后果，也有气候后果。在我们最近的研究中，我们发现北大西洋对流层上层的天气可以分成不同的特征型(冬季5种，夏季3种)，它们的飞机路线是不同的。此外，我们亦发现飞机尾气排放的其他气候影响(例如氮氧化物排放所引起的尾迹和臭氧变化)很可能因这些天气模式而异。由於飞机的飞行路线视乎对流层上层的天气情况而定，因此自然会问气候变化会否影响飞机的飞行路线。关于航空对气候变化的影响，已经有很多研究，但令人惊讶的是，很少有人提出相反的问题：气候变化对航空的影响是什么？我们的建议旨在回答这个问题，同时提高对对流层上层气候变化的理解。由于航空业的目标是限制其二氧化碳排放，气候变化对航空航线的影响可能有助于或有悖于这些目标。我们将考虑北大西洋不同天气模式的频率变化可能如何影响个别飞机的航线，这些变化是由一些不同的气候模型预测的。我们将利用为政府间气候变化专门委员会目前正在编写的第五次评估报告制作的一系列世界领先的气候模型，利用最近对未来可能出现的气候变化进行的大量和容易获得的一组模拟。我们将评估气候模型在多大程度上再现了北大西洋目前的天气模式，然后看看这些模式如何在未来各种可能的气候中发生变化。然后，我们将看到这些天气模式对飞机航线的影响，并计算这种二氧化碳排放的影响。我们还将调查气候变化和航线改变对航空运输的其他气候影响的影响。我们将把这项工作扩展到北太平洋，预计在未来几十年，该地区的空中交通将大幅增加。

The upper troposphere in mid-latitudes is the region encompassing altitudes of around 8-12 km, which includes the jet streams, regions of very strong winds, which are closely related to strengths and paths of the mid-latitude depressions. Climate change is expected to change the nature of the upper troposphere at mid-latitudes - climate models indicate that over coming decades, it will warm, the relative humidity will increase and the strength and orientation of the jet stream might change, and the boundary between the troposphere and the overlying stratosphere (the tropopause) will increase in altitude. However, when different climate models are used to predict future climate change, there is a significant spread in the results they produce; the reasons for this spread are not fully understood.Understanding climate change in the mid-latitude upper troposphere is of importance in its own right, but it has a wider economic significance. The cruise altititude of commercial aircraft is in the upper troposphere and flight times can be strongly affected by the wind conditions. Most obviously, the duration of flights between (as an example) London and New York are normally more than an hour faster when going eastbound, as the aircraft attempt to fly in the jet stream and receive an extra "push" - by contrast, westbound flights normally try to avoid the jet stream as this would impede progress. However, day-to-day variations in weather conditions in the north Atlantic mean that flight durations of both eastbound and westbound flights can vary by up to 100 minutes, depending largely on the strength and position of the jet stream. Since fuel use, and hence carbon dioxide emissions, are closely related to the flight duration, there are both economic and climate consequences for this variation. In our recent research we have shown that the weather in the upper troposphere in the North Atlantic can be split into characeristic patterns (5 in winter and 3 in summer) for which the aircraft routes are distinct. In addition we have shown that other climate effects of aircraft emissions (for example, contrails and ozone change resulting from emissions of oxides of nitrogen) very likely vary between these weather patterns.Since aircraft routing is dependent on the weather situation in the upper troposphere, it is natural to ask whether climate change could impact on aircraft routing. There has been much research on the effect of aviation on climate change, but surprisingly little that asks the reverse question: what is the effect of climate change on aviation? Our proposal aims to answer this question, while at the same time improving understanding of upper tropospheric climate change. Since the aviation industry aims to put constraints on its carbon dioxide emissions, the effect of climate change on aviation routing could either assist or work against these aims. We will consider how the routes of individual aircraft may be affected by the changes in the frequency of different weather patterns in the North Atlantic, predicted by a number of different climate models. We will exploit a recent, large and easily available set of simulations of possible future climate change from a range of world-leading climate models that have been produced for the fifth assessment report of the Intergovernmental Panel on Climate Change, which is currently being written. We will assess how well the climate models reproduce the present-day weather patterns in the North Atlantic and then look at how these patterns change for various possible future climates. We will then see how aircraft routing is affected by these weather patterns and compute the impact of this carbon dioxide emissions. We will also investigate the impact of both the climate change and re-routing on the other climate impacts of aviation.We will extend this work to cover the North Pacific, which is expected to show a significant increase in air traffic over coming decades.