加拿大和美国西北部地区连日来受到高温热浪侵袭，多地气温直逼摄氏50度，打破历史最高温纪录。此次极端高温天气，主要是由一种名为热穹顶的天气现象导致的。这一现象几乎无法通过人为干预缓解，只能任由它持续一段时间，自己消失。下面我们通过几张图表来解释高温背后的原因。
US-Canada heatwave: Visual guide to the causes
A blistering heatwave hit Canada and parts of the US this week, sending temperatures to dangerous highs of nearly 50C (122F). Hundreds of people have died. Here's what we know about what is going on.
加拿大和美国西北部地区连日来受到高温热浪侵袭，多地气温直逼摄氏50度，突破过去的历史最高温纪录。持续高温造成数百人死亡。下面我们来解释此次极端高温天气的原因。
How bad is it?
情况有多糟糕？
Temperature records have been shattered across western Canada and the US Pacific Northwest. Canada broke its country temperature record for three straight days on Tuesday - 49.6C (121.3F) in the village of Lytton, British Columbia. Before Sunday, temperatures in the country had never passed 45C.
加拿大和美国西北太平洋地区这一波热浪带来的高温，已经打破了历史纪录。加拿大更是连续三天刷新该国历史最高温纪录，不列颠哥伦比亚省（British Columbia）的利顿（Lytton）出现摄氏49.6度的高温。在这次的极端高温热浪之前，加拿大以前气温从来没有超过摄氏45度。
The heat has been blamed for helping cause the deaths of hundreds in British Columbia. The US north-west has also seen record highs - and a number of fatalities. Portland, a city with a famously rainy climate, broke its all-time high temperature record for three days in a row.
加拿大不列颠哥伦比亚省过去几天以来已经有数百人死于与极端高温有关的症状。美国西北地区也出现历史最高温，数人死亡。以多雨天气闻名的美国波特兰也连续三天刷新当地最高温纪录。
The temperature at Portland International Airport peaked at 46.1C on Monday, going above the previous day's high of 44.4C and Saturday's 42.2C, according to the US National Weather Service. Dozens of deaths in Washington and Oregon are believed to be linked to the heatwave.
根据美国国家气象局（US National Weather Service）的数据，波特兰国家机场连续三天出现最高温纪录，分别是摄氏42.2度，44.4度，以及46.1度。在美国华盛顿州和俄勒冈州，至少有十多人死于和热浪有关的病症。
How have people been affected?
极端高温对人们有哪些影响？
The region's climate is typically mild, and many homes do not have air conditioning, which might help explain the sudden rise in deaths. Many have been forced to take refuge in cooling centres - air-conditioned buildings, such as stadiums, where residents can work and sleep.
加拿大和美国西北地区的气候一向温和，当地住宅大多没有冷气空调，突如其来的极端高温导致许多人丧命。许多居民被迫离开家里到体育馆等提供空调的降温中心避难，在那里休息和工作。
People and infrastructure in urban spaces, absorbing more heat than greener, rural areas, have been particularly affected by the high temperatures. The heat has been so intense it has melted power cables and buckled roads.
都市地区的人群和基础设施比相对绿色的农村地区更容易吸热，因此都市居民受到极端高温影响也更为严重。极端高温甚至融化了高压电缆，路面也热到变形。
In Vancouver, residents reported car windows cracking and melting, even when they were not parked in the sun. Vaccination centres were forced to close or relocate, schools shut their doors and some public transport was suspended - including the Portland Streetcar Service. Elsewhere, shops sold out of portable air conditioners, fans, ice and water. There are now fears of more devastating wildfires, such as that seen in Lytton, British Columbia.
在温哥华，有居民反映他们的车即使没有停放在太阳底下，高温也让车窗热到熔化爆裂。受到高温影响，疫苗中心被迫关闭，学校关门，包括波特兰有轨电车等公共交通也停摆。商店的便携式空调都卖断货，电扇、冰块和水也都被一扫而空。与此同时，人们更担心的是如同不列颠哥伦比亚省利顿市正在发生的山火一样更具破坏性的野火。
What is causing it?
极端高温产生的原因是什么？
The persistent high temperatures are the result of what is known as a "heat dome" - a mountain of warm air pressing down across a huge area.
连续多日的极端高温是所谓的“热穹顶现象”（heat dome）所造成的结果，大量热空气在这片地区上空被高气压向下推产生的高温现象。
As warm air tries to rise, this high pressure system above pushes the warm air back down to the surface. It becomes denser and hotter as it gets compressed. Experts say climate change is expected to increase the frequency of such extreme weather events, such as heatwaves. However, linking any single event to global warming is complicated.
由于热空气会往上升，然后又被上方的阻塞高气压往下推，被加压后到达地面，地表气温就变得更热。专家表示，气候变化预料将增加这种极端天气的发生频率，但是这次的单一事件也不能如此简单地全部归咎于全球变暖。
What is a heat dome?
什么是热穹顶现象？
The heat dome phenomena develops when there is a large poleward shift in the jet stream, which becomes wavy and elongated. When this happens, a high pressure system can get "stuck" in place, forming a heat dome.
当喷射气流大面积向极地方向移动，形成波浪状和拉长气流时，就会出现“热穹顶现象”。当这种情况发生时，高压气流可能会在某地盘桓，形成一个热穹顶。
The clockwise circulation of air associated with the area of high pressure can act "like a dome or cap, trapping heat at the surface and favoring the formation of a heat wave," the National Oceanic and Atmospheric Administration (NOAA) explained in a blog post.
美国国家海洋和大气管理局 (NOAA) 在一篇博文中解释说，与高压区域相关的空气顺时针循环可以“像一个圆顶或帽子，将热量困在表面并有利于热浪的形成” .
Heat domes can occur anywhere in high-latitude locations, including New England and southeastern Canada, Europe, Siberia and Australia.
热穹顶可能出现在高纬度地区的任何地方，包括新英格兰和加拿大东南部、欧洲、西伯利亚和澳大利亚。
Underneath of a heat dome, the air can become quite stagnant, leading to air quality concerns, especially when heat-fueled wildfires burn in a region.
在热穹顶下方，空气会变得异常停滞，导致空气质量问题，尤其是当一个地区发生野火时。
How long is it going to last?
还会热多久？
Temperatures have been easing in coastal areas of Canada and the north-west US but there has not been much respite for those living in inland regions. The weather system is now moving eastwards over Canada's Prairie provinces - Alberta and Saskatchewan and parts of Manitoba have been placed under heat warnings.
加拿大和美国西北部海岸地区的高温已经减缓，但是靠近内陆地区高温仍然持续。笼罩这片地方的高气压系统现在已经向东移动至加拿大草原地区省份，加拿大的阿尔伯塔省（Alberta），萨斯喀彻温省（Saskatchewan）和曼尼托巴省（Manitoba）部分地区已经发出高温警戒。
How can I keep cool in a heatwave?
如何降温散热？
You should cool off immediately if you have the following symptoms: headaches, feeling dizzy, loss of appetite, nausea, excessive sweating, cramps, fast breathing and intense thirst. If your body's temperature hits 40C (104F), heatstroke can set in, which requires urgent medical help. Danger signs include sweat stopping - the person may feel hot, but dry - and breathing difficulties.
医护人员建议，如果身体有头痛、昏眩、食欲不振、恶心、过度流汗、痉挛、气喘或极度口渴等情况发生，就要立即降温散热。如果体温超过40度就有可能会发生中暑，需要紧急医疗措施，中暑的征兆包括停止排汗和呼吸困难。
