英语听力：探索发现 科学新发现：我们的大气层-16（在线收听）

 The global average could be up 7 degrees F by the end of the century, wreaking havoc with weather patterns and habitats. We can't prevent climate change by preserving the air's delicate blend of gases, the unique mix that sets earth apart. And our planet is also marked by how this blend sets above the surface in a distinct layer structure. As we rise above the clouds and winds of lower altitudes, we enter a completely new zone---a world of extreme temperatures and ever thinning air, air that will kill us in seconds, but which shields us from deadly radiation. We live in a tiny sliver of earth atmosphere called the troposphere. Winds and clouds, rain and snow dominate this turbulent zone. But above it lie miles of freezing dry air. The conditions there will kill a human in seconds, but we desperately need the high atmosphere's weight and protection. Engineer John Powell's balloon team has spent 27 years exploring its layers, pushing further and further into this remote, dangerous world.