我怀着回报社会的想法，开始了教学生涯。然而，我得到的多于我付出的。这就引出了这次演讲的最后一篇乐章。首先我要讲一个了不起的科学发现，以及由此带来的新挑战。它是一个战斗的号令，到了做出改变的时候了。

　　So here is the movement.In the last several decades, our climate has been changing. Climate change is not new: the Earth went through six ice ages in the past 600,000 years. However, recent measurements show that the climate has begun to change rapidly. The size of the North Polar Ice Cap in the month of September is only half the size it was a mere 50 years ago. The sea level which been rising since direct measurements began in 1870 is now five times faster, at a rate now five times faster, than at the beginning of recorded measurements. Here’s the remarkable scientific discovery. For the first time in human history, science is now making predictions of how our actions will affect the world 50 and 100 years from now. These changes are due to an increase in carbon dioxide put into the atmosphere since the beginning of the Industrial Revolution. The Earth has warmed up by roughly 0.8 degreesCelsiussince the beginning of the Revolution. There is already approximately a 1 degree rise built into the system, even if we stop all greenhouse gas emissions today. Why? It will be decades to warm up the deep oceans before the temperature reaches a newequilibrium.

　　现在开始本次演讲的第一章。过去几十年中，我们的气候一直在发生变化。气候变化并不是现在才有的，过去60万年中地球就发生了6次冰河期。但是，最新的测量表明气候变化加速了。9月份，北极冰盖的覆盖面积只相当于50年前的一半。1870年起，人们开始测量海平面上升的速度，现在海平面上升的速度是那时的5倍。一个重大的科学发现就这样产生 了。科学第一次预测出我们的行为对50到100年后的世界有何影响。这些变化的原因是，从工业革命开始，人类排放到大气中的二氧化碳增加了。这使得地球的平均气温上升了0.8摄氏度。即使我们立刻停止所有温室气体的排放，气温仍然将比过去上升大约1度。为什么呢？因为在气温达到均衡前，海水温度的上升将持续几十年。

　　dilemma

　　n. 困境；进退两难

　　eg. So the real dilemma lies not in what handset you choose, but which network you opt for.

　　所以真正的困境不在于你选择什么手机，而在于你选择什么网络。

　　Celsius

　　adj. 摄氏的

　　eg. When water is cooled below 0 degrees Celsius, it freezes and becomes ice.

　　水冷却到0摄氏度以下时, 会冻结成冰。

　　equilibrium

　　n. 均衡

　　eg. He can't maintain enough equilibrium to ride a bike.

　　他骑自行车不能保持平衡