My third piece of advice is as follows：As you begin this new stage of your lives, follow your passion. If you don"t have a passion, don"t be satisfi ed until you fi nd one. Life is too short to go through it without caring deeply about something. When I was your age, I was incredibly single-minded in my goal to be a physicist. After college, I spent eight years as a graduate student and postdoc at Berkeley, and then nine years at Bell Labs. During that time, my central focus and professional joy was physics.
Here is my fi nal piece of advice. Pursuing a personal passion is important, but it should not be your only goal. When you are old and gray and look back on your life, you will want to be proud of what you have done. The source of that pride won"t be the things you have acquired or the recognition you have received. It will be the lives you have touched and the difference you have made.
After nine years at Bell labs, I decided to leave that warm, cozy ivory tower for what I considered to be the"real world", a university. Bell Labs, to quote what was said about Mary Poppins, was"practically perfect in every way"，but I wanted to leave behind something more than scientifi c articles. I wanted to teach and give birth to my own set of scientifi c children.
Ted Geballe, a friend and distinguished colleague of mine at Stanford, who also went from Berkeley to Bell Labs to Stanford years earlier, described our motives best：
"The best part of working at a university is the students. They come in fresh, enthusiastic, open to ideas, unscarred by the battles of life. They don"t realize it, but they"re the recipients of the best our society can offer. If a mind is ever free to be creative, that"s the time. They come in believing textbooks are authoritative, but eventually they fi gure out that textbooks and professors don"t know everything, and then they start to think on their own. Then, I begin learning from them."
My students, post doctoral fellows, and the young researchers who worked with me at Bell Labs, Stanford, and Berkeley have been extraordinary. Over 30 former group members are now professors, many at the best research institutions in the world, including Harvard. I have learned much from them. Even now, in rare moments on weekends, the remaining members of my biophysics group meet with me in the ether world of cyberspace.
I began teaching with the idea of giving back；I received more than I gave. This brings me to the fi nal movement of this speech. It begins with a story about an extraordinary scientifi c discovery and a new dilemma that it poses. It"s a call to arms and about making a difference.
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 fi ve times faster than it was at the beginning of recorded measurements. Here"s the remarkable scientifi c discovery. For the fi rst 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. WhyIt will take decades to warm up the deep oceans before the temperature reaches a new equilibrium.
If the world continues on a business-as-usual path, the Intergovernmental Panel on Climate Change predicts that there is a fi fty-fi fty 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.
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 permafrostIf even a fraction of the carbon is released, it could be greater than all the greenhouse gases we have released since the beginning of the industrial revolution. Once started, a runaway effect could occur.
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.
