In Part I of this adventure, I recapped some of the wisdom about clouds that was conjured by the sages of antiquity and ended in 1802 when a young English chemist named Luke Howard created the first taxonomy of clouds.
In his day, Luke Howard’s sky-breaking essay “On the Modifications of Clouds” was as revolutionary to Enlightenment era scientists as E.O. Wilson’s work with ants has been to evolutionary biology a century and a half later. Howard broke clouds into three major groupings - cirrus, stratus, and cumulus – and subdivided each group into families of clouds with five and six siblings. That was the start of much bigger things to come. Along the way, Howard acquired the distinction of being named “the father of meteorology,” and the new field of atmospheric science that soon grew up around his work had some of the best and brightest minds trained on the heavens.
Within this new field of meteorology two distinct and very different disciplines coexist: the study of weather and the study of climate. As Mark Twain once quipped, weather is what’s falling on your head at any given moment. Climate is what happens to continents and oceans over decades. Thanks to an unlikely sequence of events that would have astonished Aristotle and Descartes and Luke Howard, the latter humble efforts to bring some scientific understanding to the self-ruining phenomena that float above our heads would eventually eclipse even astro- and nuclear physics in importance. The modern day-climatologist’s study of clouds, those silent messengers of weather that mesmerized the ancient Chaldeans and Chinese, had now morphed from the voodoo-like muse of poets into the most intense and important field of inquiry in modern-day science.
How did that happen? Well, that question can’t be answered in a blog, but suffice it to say that Howard’s scientific descendents in the field of climatology began asking some interesting questions about clouds in the 1970s. In many respects, they were the same kinds of questions asked by the ancient Chinese and Aristotle; only now, scientist had access to instruments (and planes and rockets and high altitude weather balloons) with which to actually venture aloft in search of answers. By the 1990s, when global climate change was becoming a very contentious topic in scientific and political circles around the world, the question that most intrigued climate scientists was simply this: What (if any) role do clouds play in the infinitely complex world of climate change?
Hot in pursuit of that answer were cloud physicists and climate modelers like NASA’s Anthony Del Genio, who works at the Goddard Space Institute at Columbia University in New York. What folks like Del Genio were soon to discover about clouds was nothing short – his words – of “amazing.”
The clouds Del Genio and his colleagues were most interested in were the cumulonimbus formations in the tropics. For one thing, these clouds are among Mother Nature’s most violent children, and for another, they completely dominate the skies in the tropical belt, that area on our planet that circles the globe 20 degrees north and south of the equator. It is here where weather is generated, so with that big question in mind: What role do these clouds play in driving the planet’s climate? NASA assembled more than three hundred scientists in Florida in the summer of 2002 for the largest experiment ever conducted on clouds.
CRYSTAL-FACE, as it is now known, was, in many respects, the culmination of thousands of years of human speculation about cumulonimbus formations. The experiment involved battalions of scientists, flocks of satellites, squadron’s of aircrafts, and oodles of money, $20 million and counting. What they discovered would have astonished Aristotle.
Cumulonimbus formations are those clouds that form in the early afternoon and quickly grow into towering giants. In fact, they flatten out on top, at about 55,000 feet, when they hit a warmer layer of air at the top of the troposphere. These are the classical anvil formations that have fascinated scientists for thousands of years – and for good reason. It turns out that one cumulonimbus cloud is so complex, says Del Genio, that NASA’s best computers cannot process all the data to properly model even one cloud. For example, that temperature at the base layer of one of these clouds is usually around 80 degrees Fahrenheit, but the temperature at the anvil is minus 100, a difference of 180 degrees. Inside the cloud, electrical charges are so intense and unstable that lightening discharged beneath the anvil, inside the cloud, can superheat the surrounding air to 50,000 degrees F, an imbalance that creates collumnar updrafts inside the cloud that move at hundreds of miles per hour.
Those updrafts, in turn, are encircled by downdrafts of cooler air moving just as fast! Along the way, these ferocious currents of air create violent outflows of air at various altitudes, and conversely, inflows at others. It is those entraining inflows that helped the scientists finally answer the big question.
CRYSTAL-FACE demonstrated that clouds of this size are entraining microscopic aerosol particles released into the atmosphere by man-made processes. Often, those aerosols, which can be tiny bits of sulfur discharged from coal burning power plants, can float thousands of miles through the atmosphere before becoming entrained, or pulled into, one of these clouds. Then, something remarkable happens. Each one of those tiny specks of dust or sulfur or carbon becomes the nucleus of a raindrop, and those billions of raindrops are then carried aloft to the top of the cloud by its hurricane force updrafts. At the top of the cloud, those gazillion drops freeze and become tiny mirrors, countless brilliant little mirrors that reflect solar radiation back into space and thereby help to cool the planet by deflecting heat causing radiation away from the planet.
Unfortunately, that cooling effect is being more than offset on the underside of the clouds, which are trapping enormous amounts of energy close to the ground. Scientists like Del Genio now believe that this may finally explain why our planet is experiencing a significant reduction in solar radiation, also know as solar dimming, at an unprecedented time of planetary warming.
So, thousands of years after the Greeks and Chinese first speculated on the nature of clouds, these latest discoveries would probably not come as a big surprise to the historical antecedents of modern scientists. Just as those ancients predicted, it turns out that some of the answers to the biggest ‘Why?’ and ‘How?’ of global climate may have been floating right above our heads all along.
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