Category:

PROLOGUE

Climate 101

At the large university where I work, I teach a class about global warming that is listed in the course catalog as Climate 101. Every year, I begin my very first lecture with the same deceptively simple request:

"Please raise your hand if you can tell me why it gets cold at night," I ask and watch as nearly every hand in the lecture hall goes up.

I point to an eager student, who can hardly wait to answer this very elementary question. "Because the sun has set, and the Earth is no longer receiving its heat"—or words to that effect—the student invariably tells me.

The other students nod in agreement. This is their answer too. "Hmm," I say, pretending to consider how to evaluate this response. "For that incomplete answer, I will give you a B." Suddenly, all those confident faces appear puzzled.

Perhaps you are puzzled too. Perhaps you had formulated the same response in your head. In fact, wherever I ask this question—at dinner parties, with family, or in conversation with new friends—nearly everyone gives me the same answer as an enthusiastic college freshman. They aren't wrong; rather, they are making a good guess based on an empirical observation. When the sun is visible in the sky, they feel warm. When the sun disappears, it's time to pull out the blankets. But that's not the whole story, and the complete answer to this simple question can help us understand what climate is—and what is causing it to change.

As I tell my students, the sunset is certainly part of the answer. But to figure out why it is colder at night, we must remember that the Earth, like any other matter subject to the laws of physics, is constantly losing energy. Think of the way air in a room full of people grows warmer and warmer as all those human bodies radiate heat. The Earth does the same thing as those bodies. During the day, the sun provides a counterbalance to this energy loss, showering our planet with its warming rays. At night, the Earth continues to lose energy, and without the compensation of the sun, the temperature plummets.

On average, the Earth loses about 122,000 trillion watts of energy to space each year, which happens to be approximately equal to the amount of energy it receives from the sun. It is this balance—between outgoing and incoming energy—that determines the mean climate here on Earth. For nearly ten thousand years, the incoming and the outgoing energies were in such good balance that the global annual average temperature was a comfortable 14 degrees Celsius, making it possible for life to survive and humanity to thrive.

On Venus, this balance makes the annual average temperature 464 degrees Celsius. This isn't surprising, given that Venus is closer to the sun. But there is another big factor in addition to the energy a planet receives from the sun that influences climate: the chemical makeup of its atmosphere. On Venus, carbon dioxide accounts for 95 percent of the atmosphere. On Earth, our atmosphere is only about .04 percent carbon dioxide—or at least, it was.

In the past one hundred fifty years, humans chopped down many of Earth's carbon-sucking forests and began burning fossil fuels to heat their homes, power their factories, and propel their vehicles, releasing unprecedented amounts of CO2 into the atmosphere. Like the glass walls of a greenhouse, CO2 admits energy from the sun but prohibits energy from leaving the Earth. And so pretty quickly, our nicely balanced climate became imbalanced. In the past century, as the amount of CO2 in the atmosphere has increased, Earth's global mean surface temperature has ticked up from 14 to 15 degrees Celsius.

This is called climate change. Climate change due to human activities is now firmly established by the observed facts and the laws of physics. The consequences of the phenomenon are becoming self-evident, but so are, I'd argue, the capabilities of the new generation of scientists to find a way forward.

PART I

INITIAL CONDITIONS

CHAPTER ONE

We were a few hundred feet above the Bay of Bengal when the windshield cracked. From my window, I looked out at the black water below, roiling with foamy whitecaps. Gunmetal clouds obscured any trace of a horizon, and bullets of rain pelted the thin plexiglass that separated us from the storm. We had been aboard this Electra turboprop plane—a "hurricane hunter," as it was known in the business—every day for a week, flying directly into the most severe monsoon storms we could track down, but this was the first moment I had felt fear.