【英语时差8，16】全球变暖1

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D: Uhm, right . . .

Y: That's your cue¹, Don.

D: I know, Ya?l . . . but . . .

Y: What's wrong?

D: Well, we're a science program, right? And I know that the accepted scientific wisdom is that human activity is causing the Earth to get warmer. But I can't help but think that the melting of polar ice and everything else we're seeing is at least partly caused by natural warming. I mean, weather patterns do change naturally over time.

Y: Of course. And we know that the earth was going through heating and cooling cycles long before people started pumping carbon dioxide into the atmosphere. And, in fact, scientists have observed a strange weather pattern over the past twenty or so years. Normally, cold winds from the Arctic² blow south. But during the past few decades, warmer air and clouds from the south have blown north toward the Arctic. All that warm air is a big reason why so much Arctic ice has melted.

D: But warming caused by human activity still plays a role, right?

Y: A big role. Natural warming combined with man-made warming has melted so much Arctic ice that it's created a sort of feedback loop. Snow and ice reflect sunlight. But the darker ocean water absorbs light and heat, causing even more ice to melt.

D: So natural warming or man-made warming in isolation³ would cause some ice to melt...

Y: But not nearly as much as the two forces combined. That's what's really put us where we are today. 

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