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I began teaching with the idea of giving back; I received more than I gave. This brings me to the final movement of this speech. It begins with a story about an extraordinary scientific discovery and a new dilemma that it poses. It’s a call to arms and about making a difference.
我怀着回报社会的想法，开始了教学生涯。我的一生中，得到的多于我付出的，所以我要回报社会。这就引出了这次演讲的最后一个乐章。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。
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 at a rate that is now five times faster than it was 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 degrees Celsius since 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 take decades to warm up the deep oceans before the temperature reaches a new equilibrium.
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60万年中就发生了6次冰河期。但是，现在的测量表明气候变化加速了。北极冰盖在9月份的大小，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。科学第一次在人类历史上，预测出我们的行为对50~100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。因为在气温达到均衡前，海水温度的上升将持续几十年。
If the world continues on a business-as-usual path, the Intergovernmental Panel on Climate Change predicts that there is a fifty-fifty chance the temperature will exceed 5 degrees by the end of this century. This increase may not sound like much, but let me remind you that during the last ice age, the world was only 6 degrees colder. During this time, most of Canada and the United States down to Ohio and Pennsylvania were covered year round by a glacier. A world 5 degrees warmer will be very different. The change will be so rapid that many species, including Humans, will have a hard time adapting. I’ve been told for example, that, in a much warmer world, insects were bigger. I wonder if this thing buzzing around is a precursor.
如果全世界保持现在的经济模式不变，联合国政府间气候变化专门委员会（IPCC）预测，本世纪末将有50%的可能，气温至少上升5度。这听起来好像不多，但是让我来提醒你，上一次的冰河期，地球的气温也仅仅只下降了6度。那时，俄亥俄州和宾夕法尼亚州以北的大部分美国和加拿大的土地，都终年被冰川覆盖。气温上升5度的地球，将是一个非常不同的地球。由于变化来得太快，包括人类在内的许多生物，都将很难适应。比如，有人告诉我，在更温暖的环境中，昆虫的个头将变大。我不知道现在身旁嗡嗡叫的这只大苍蝇，是不是就是前兆。
We also face the specter of nonlinear “tipping points” that may cause much more severe changes. An example of a tipping point is the thawing of the permafrost. The permafrost contains immense amounts of frozen organic matter that have been accumulating for millennia. If the soil melts, microbes will spring to life and cause this debris to rot. The difference in biological activity below freezing and above freezing is something we are all familiar with. Frozen food remains edible for a very long time in the freezer, but once thawed, it spoils quickly. How much methane and carbon dioxide might be released from the rotting permafrost? If even a fraction of the carbon is released, it could be greater than all the greenhouse gases we have released to since the beginning of the industrial revolution. Once started, a runaway effect could occur.
我们还面临另一个幽灵，那就是非线性的“气候引爆点”，这会带来许多严重得多的变化。“气候引爆点”的一个例子就是永久冻土层的融化。永久冻土层经 过千万年的累积形成，其中包含了巨量的冻僵的有机物。如果冻土融化，微生物就将广泛繁殖，使得冻土层中的有机物快速腐烂。冷冻后的生物和冷冻前的生物，它 们在生物学特性上的差异，我们都很熟悉。在冷库中，冷冻食品在经过长时间保存后，依然可以食用。但是，一旦解冻，食品很快就腐烂了。一个腐烂的永久冻土层，将释放出多少甲烷和二氧化碳？即使只有一部分的碳被释放出来，可能也比我们从工业革命开始释放出来的所有温室气体还要多。这种事情一旦发生，局势就失控了。
The climate problem is the unintended consequence of our success. We depend on fossil energy to keep our homes warm in the winter, cool in the summer, and lit at night; we use it to travel across town and across continents. Energy is a fundamental reason for the prosperity we enjoy, and we will not surrender this prosperity. The United States has 3 percent of the world population, and yet, we consume 25 percent of the energy. By contrast, there are 1.6 billion people who don’t have access to electricity. Hundreds of millions of people still cook with twigs or dung. The life we enjoy may not be within the reach of the developing world, but it is within sight, and they want what we have.
气候问题是我们的经济发展在无意中带来的后果。我们太依赖化石能源，冬天取暖，夏天制冷，夜间照明，长途旅行，环球观光。能源是经济繁荣的基础，我 们不可能放弃经济繁荣。美国人口占全世界的3%，但是我们消耗全世界25%的能源。与此形成对照，全世界还有16亿人没有电，数亿人依靠燃烧树枝和动物粪便来煮饭。发展中国家的人民享受不到我们的生活，但是他们都看在眼里，他们渴望拥有我们拥有的东西。
