原文已被隐藏，你可用 快捷键 - 或点击 显示原文 按钮来查看原文
第1段
1 .Listen to part of a lecture in an Earth Science class.
该句暂无译文！
2 .(male professor) Uh, getting back to climate patterns, let me point out that weather doesn’t always follow the usual pattern.
该句暂无译文！
3 . One of the classic cases of abnormal weather was the summer of 1816 in the northern hemisphere.
该句暂无译文！
4 .Actually, in the northeastern United States, 1816 is sometimes referred to as “the year there was no summer.”And the unusual cold was also felt that year in many other parts of the globe.
该句暂无译文！
5 . The funny thing is, in January and February, the temperatures in northeastern US weren’t all that much below the normal, no hint of what was to come.
该句暂无译文！
6 .That wasn’t seen until May when strong waves of cold are hit the region and covered it with ice and frost.
该句暂无译文！
7 .That’s pretty rare for some of those areas in May. And unfortunately, the cold snaps kept on coming.
该句暂无译文！
8 .There was widespread snowfall in June, followed by more cold spells in July and August.
该句暂无译文！
9 . Historians can point to a number of contemporary diaries from the northeast and beyond, including Jefferson’s, that’s Thomas Jefferson of course, a former president who had retired to his home down in Virginia, diaries that recorded and remarked on the extraordinarily cold temperatures that year.
该句暂无译文！
10 . To put it in perspective, the summer of 1816 was the coldest on record for some areas in nearly two hundred years of record keeping.
该句暂无译文！
11 . As a result, the corn crop finally harvested in some parts was less than ten percent of the usual yield, an economic disaster for many farmers.
该句暂无译文！
12 .So the summer of 1816, the summer that wasn’t, that’s more than just an interesting entry in the weather almanacs.
该句暂无译文！
13 . In fact, it led to a dramatic shift in agriculture with many farmers abandoning northeast US for the Midwest.
该句暂无译文！
14 . But what was the cause of all this? Just a variation in normal weather patterns, or was there something else going on here?
该句暂无译文！
15 . Well, there are a number of theories and several of them involved the Sun.
该句暂无译文！
16 . For example, in 1816, it happened that the Sun was in the middle of a period of low magnetic activity.
该句暂无译文！
17 .And it turns out that at this point in the cycle, when its magnetic activity is below normal, the Sun is slightly dimmer and the Earth gets less sunlight.
该句暂无译文！
18 .So, it’s no surprise that periods of low magnetic activity on the Sun have been associated with low temperatures here on Earth.
该句暂无译文！
19 .That’s a pattern observed over and over again and put forward by most authorities of the time to explain the extreme weather of 1816.
该句暂无译文！
20 .But the most widely held view among those of us in the field today is that the year with no summer was caused by several large volcanic eruptions just prior to 1816, particularly a volcano in Indonesia that erupted just a year before and by all the dust and gases thrown into the atmosphere as a result.
该句暂无译文！
21 .We’re talking huge amounts of dust and gases here, especially in the case of Tambora.
该句暂无译文！
22 . That’s the volcano in Indonesia.
该句暂无译文！
23 .Tambora is estimated to have thrown two hundred million tons of material into the atmosphere.
该句暂无译文！
24 .The idea is that a lot of the gas and dust that shot up from that volcano went clear up into an atmosphere layer called the stratosphere, about ten kilometers up.
该句暂无译文！
25 .Then winds in the stratosphere moved this enormous cloud of particles around the Earth.
该句暂无译文！
26 . And unlike the so-called greenhouse gases we’re producing so much of today, the particles in this enormous volcanic cloud up in the stratosphere primarily reflected sunlight back into space.
该句暂无译文！
27 . And that reduced the amount of sunlight reaching the Earth’s surface down below.
该句暂无译文！
28 . And less sunlight means a drop off in temperatures.
该句暂无译文！
29 .And even though a volcanic eruption may only last a few days, if it’s big enough, it can apparently impact the weather around the world for up to five years.
该句暂无译文！
30 .Incidentally, another way we can study the effects of volcanic eruptions besides reading contemporary reports is to use information from tree rings that grew over the last several centuries.
该句暂无译文！
31 .Remember, there’s a growth ring in a tree’s trunk for each year it’s alive.
该句暂无译文！
32 . And when the wood in the growth ring is very dense, for example, we’ve discovered this corresponds to a year that was particularly warm.
该句暂无译文！
33 .So a recent study was done where the growth rings of exceptionally old trees all over the northern hemisphere were analyzed.
该句暂无译文！
34 . Sure enough, the highest concentrations of low-density tree rings, which mean cold temperatures, they almost always follow major volcanic eruptions, including the eruption of Tambora.
该句暂无译文！