Northern-hemisphere temperatures stayed flat from November to March
去年11月至今年3月,北半球的气温保持平稳

凛冬不至 Winter is not coming-书迷号 shumihao.com

THE MOST commonly cited risks of climate change are natural disasters: fiercer wildfires and hurricanes, bigger floods and longer droughts. But one of the most striking recent effects of global warming has been unusually mild weather in many parts of the world.
气候变化最常被提及的风险是自然灾害:野火和飓风变得更猛烈,洪水更汹涌,干旱持续更久。但是,全球变暖近期最显著的影响之一却是世界许多地方的天气异常温和。

The northern-hemisphere winter that ended on March 20th was the second-warmest since records began, and the warmest ever on land. The anomaly was biggest in Europe and Asia, where average temperatures from December to February were 3.2°C (5.8°F) and 3.1°C above the average from 1951-80, and 0.8°C and 0.7°C above those continents’ previous record highs. After a normal autumn, temperatures stayed close to their November levels for months. In Boston, where daily lows in January tend to hover around -6°C, the average minimum this January was 0°C; for Tokyo the figures were 0°C and 5°C. By local standards, the balmiest winter of all was in Russia. Moscow’s average daily low in January was -2°C, far from the customary -13°C.
北半球于3月20日结束的这个冬季是有记录以来气温第二高的冬天,也是陆地上有史以来最温暖的一个冬天。欧洲和亚洲气温异常的情况最显著,两地12月至2月的平均气温分别比1951到1980年的均温高出3.2℃和3.1℃,比各自之前的历史峰值高0.8℃和0.7℃。经过一个正常的秋天后,气温连续几个月与11月的水平相近。在波士顿,1月份的每日低温往年一般都在 – 6℃上下徘徊,而今年1月份的平均最低气温为0℃;东京的这两个数字分别是0℃和5℃。按地方标准衡量,俄罗斯的这个冬天最温暖。莫斯科1月份的日均低温为﹣2℃,远低于通常的﹣13℃。

The winter-that-wasn’t of 2019-20 is not yet a new normal. The main factor determining the severity of northern winters is the “Arctic oscillation”: the relative pressure of Arctic and sub-tropical air. When pressure is higher in the Arctic, cold air from the North Pole pushes south, bringing harsh, dry winters to many places. When pressure is higher towards the sub-tropics, warm air pushes northwards, hemming in cold air around the pole. These two patterns flip back and forth irregularly.
去年跨今年的“伪冬天”尚未成为一种新常态。决定北半球冬季寒冷程度的主要因素是“北极涛动”:北极和副热带空气间的相对压力。当北极的气压较高时,来自北极的冷空气会向南推进,给许多地方带来寒冷干燥的冬天。当副热带的气压较高时,温暖的空气会北上,围住极地周围的冷空气。这两种模式不规律地来回切换。

For reasons that are not yet clear, pressure in the sub-tropics this year was much stronger than in the Arctic. And researchers have not yet determined how rising temperatures affect the Arctic oscillation. Until a few years ago, climate models tended to show pressure in the Arctic strengthening, reducing the amount of warming during winter at temperate northern latitudes. The latest models find the reverse.
今年副热带的气压远高于北极,原因尚不清楚。而研究人员还没有确定气温上升会如何影响北极涛动。直到几年前,气候模型往往都还显示北极的气压在增强,从而降低北温带地区冬季变暖的程度。最新的模型得出的发现正相反。

However, climate change is still responsible for anomalies like this one. At the average global temperature in 1950, a winter this mild was all but impossible. In today’s climate, such reprieves from the cold should occur once every 11 years. And if global warming continues on its current trajectory, winters like this year’s could become standard within a few decades.
然而,气候变化仍与此次这样的气温异常脱不了干系。回到1950年那样的全球平均气温,像今年这样暖和的冬天几乎不可能出现。在如今的气候中,这种寒冬暂时缺席的情况应该会每11年发生一次。而如果全球变暖继续沿目前的轨迹发展,像今年这样的冬天可能会在几十年内变成常态。

Mild winters offer benefits. Heating is cheaper, flu seasons are shorter and fewer people die overall. But problems mount as well. Without hard frosts, pests can survive and multiply to attack crops more harshly. Warmer winters are usually wetter, changing snowfall patterns. This can shrink the snowpack that supplies rivers, and cause floods. Even people who bemoan frigid winters may miss them if they vanish. ■
暖冬有其益处。取暖费用降低,流感季节缩短,总体死亡人数减少。但问题也越来越多。没有严霜,害虫就会存活并繁殖,继而更猛烈地啃噬作物。更温暖的冬天通常也更潮湿,连带改变降雪模式。这可能会导致补充河流的积雪减少,并引发洪灾。如果冬季消失,即使那些在严冬叫苦连天的人恐怕也会想念这个季节。