国家地理:不再冻人的五大湖(7)

So, although one year may be warmer than the one before, some recent winters were icy cold. In 2013-14, the polar vortex carried frigid¹ air from the Arctic into the continental² U.S., and the cold stretched well south of the Great Lakes. Total ice cover on the Great Lakes spanned more than 90 percent, growing so thick in some places that the augers ice anglers used couldn't reach the water.

因此，尽管一年比一年的温度要高，但最近这些年的冬天还是很冰冷的。在2013-2014年，极地涡旋将寒冷的空气从北极带到了美国大陆，这种寒冷延伸到了五大湖以南。五大湖的总冰层覆盖面积超过90%，有些地方的冰层越来越厚，以至于冰钓人使用的螺丝钻都无法接触到水面。

The extra-tricky part is that the presence and growth of lake ice each winter create a complicated sequence of events.

特别棘手的是，每年冬天湖冰的存在和增加，会造成一系列复杂的情况。

Maybe it gets cold enough for ice to form early in the winter -- but if a stretch of bitter wind keeps the water's surface churning, ice will form later. Maybe the summer before was extra warm, zapping enough extra heat into the water that it takes it extra long to cool off and get to the point when it can start to freeze. Maybe a bunch of snow falls early in the season, insulating the ice from the top and, counterintuitively, keeping it from growing quickly through the cold temperatures.

比如说，在初冬时节，天气会变得很冷，从而形成冰，但是如果一股刺骨的寒风使水面保持翻腾，那么结冰就会晚一些。比如说，之前的夏天特别暖和，把足够多的热量注入水中，这样水就需要很长时间才能冷却下来、达到可以开始结冰的程度。再比如说，在初冬时节下得很大的雪，会使冰与顶部隔绝，而且，与我们的直觉相反的是，这会阻止冰在低温中迅速增加。

Some factors aren't so complicated. The air is getting warmer. So is the water, in many places faster than the air. In the Northern Hemisphere, nearly 15,000 lakes that used to freeze consistently now ice over intermittently³, if at all.

有些因素并不那么复杂。空气越来越暖和了。水也一样，在很多地区，其变暖的速度比空气还要快。在北半球，以前持续结冰的近15000个湖泊，现在只是间歇性地结冰了。

1 frigid   

adj.寒冷的，凛冽的；冷淡的；拘禁的

参考例句：

• The water was too frigid to allow him to remain submerged for long.水冰冷彻骨，他在下面呆不了太长时间。
• She returned his smile with a frigid glance.对他的微笑她报以冷冷的一瞥。

2 continental   

adj.大陆的，大陆性的，欧洲大陆的

参考例句：

• A continental climate is different from an insular one.大陆性气候不同于岛屿气候。
• The most ancient parts of the continental crust are 4000 million years old.大陆地壳最古老的部分有40亿年历史。

3 intermittently   

adv.间歇地；断断续续

参考例句：

• Winston could not intermittently remember why the pain was happening. 温斯顿只能断断续续地记得为什么这么痛。 来自英汉文学
• The resin moves intermittently down and out of the bed. 树脂周期地向下移动和移出床层。 来自辞典例句