NARRATOR：

Now listen to part of a lecture on the topic you just read about.

MALE PROFESSOR：

Unfortunately the arguments of the reading passage are a little out of date.

Scientists now have new information that shows that none of the ideas the reading passage discusses could account for the Little Ice Age.

First, about the Gulf Stream.

Scientists now know that disrupting the Gulf Stream would cause cooling only in Europe and North America.

But the Little Ice Age also affected the Southern Hemisphere—in places like New Zealand and southern Africa, for example.

Since the disruption of the Gulf Stream cannot explain why these southern areas became colder, it cannot explain the Little Ice Age.

Second, the volcanoes theory.

It’s true that if volcano eruptions put enough dust into the atmosphere, the result can be a cooler climate.

But large amounts of volcanic dust in the atmosphere would have also produced striking visual effects that people would have noticed at the time.

For example, dramatically colorful sunsets, or snow being gray or brown instead of white.

But there are almost no reports of anything like that routinely happening during the Little Ice Age.

So it seems that the volcanic eruptions during that period were simply not strong enough to release the large amounts of dust needed to lower global temperatures.

Third, about forests on farm land stopping the warming greenhouse effect by removing carbon dioxide.

There just was not enough time for this effect to work.

The human population grew back to previous levels fairly quickly, which meant that forests were soon being cut down again to clear fields for the crops needed to feed the growing population.

As a result, we know that the forests mentioned in the reading pas sage were not there long enough to cause the long-term global cooling of the climate.