Making Sense of Weather and Climate, by Mark Denny

MAKING SENSE of WEATHER and CLIMATE

The Science Behind the Forecasts

MARK DENNY

Forecast

It’s so dry the trees are bribing the dogs.

Charles Martin

The book that you hold in your hands will help you make sense of our weather. My aim in writing such a book is, as always, to provide transparent science that conveys the core ideas underpinning a complex physical system—in this case, the physics of our atmosphere. This book will also help you make sense of our climate (so extending the physics to our oceans) and how we model and predict climate and influence climate change. Loosely, climate is average weather, and thus shortterm climate prediction is a walk in the park compared with weather prediction. It is much easier to predict the average world temperature for next year, for example, than to predict the temperature at the bottom of your garden tomorrow morning. Even so, long-term climate predictions are far from easy, as we will see.1 Why did it rain today when the forecast said sun? More generally, why is it so hard for meteorologists to predict detailed weather accurately when the likely weather is so trivial to predict? (“The weather tomorrow will be the same as it is today” works about 70% of the time on average, depending on latitude.) Here are a few more questions that you may have asked yourself whenever the state of the weather

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intrudes on your thoughts. Why do thunderstorms happen? Weather is seasonal for obvious reasons, so why is the weather on my birthday not always the same? What is a weather front? If weather is so variable, why doesn’t the temperature ever go to –100° or +200°? Why are there weather patterns, and will they be the same when my grandchildren grow up? Why can I see through rain but not fog?

Climate questions may intrude at a different level—they are perhaps more important but less urgent. Why, like the atmosphere, is the globalwarming debate increasingly heated? Is human industry responsible for this global warming, and, if so, can we reverse the process? How much of climate change is natural and inevitable, whatever we do?

I answer these questions and many others in the chapters to follow. The explanations will be accessible to an intelligent reader with no background in meteorology or climatology, though the underlying physics is immensely complex. Concerning meteorology, I concentrate mostly on the weather you get in your backyard, not so much on the extremes that occasionally wreak havoc around the world.2 (You will, however, finish this book with a working knowledge of tornadoes, hurricanes, thunderstorms, droughts, and floods.) Each topic is presented with readable prose but no hype or agenda. Metaphorically, your forecast is for sunshine, not moonshine.3 One prosaic difference between weather and climate is politics, and politics does not mix well with rational debate or dispassionate analysis. So I will go to some effort to present you with the facts (“Just the facts, ma’am,” as Joe Friday would say) and eliminate the politics.

Except that this is impossible, when the subject is climate change.

I adopt the view of most (almost all) scientists that the accumulated data point to a changing climate and to human activity as the likely cause. The problem is that, merely by accepting these data and making the inference, I am declaring a political viewpoint even though I infer via rational scientific arguments and not from any political preconceptions. So be it: I follow where science leads, and if I end up in a political camp, then, from my perspective, I got there accidentally. Please try to do the same; readers will get more out of this book if they consider it to be what the writer considers it to be—an explanation of scientific phenomena, without any other agenda.

This is a good place to point out the position I hope that this book will occupy in the literature of popular weather and climate science.

Forecast

Few nonspecialist books attempt to explain both weather and climate, and many of those that do are rather superficial. They are, to quote the physicist David Derbes, “a mile wide and a millimeter deep.”4 Here we attain the breadth of coverage while penetrating deeper into key aspects of our subject. Coverage cannot be comprehensive but will be deep enough to give insight.

Our subject is inherently statistical, and most humans have poor intuition about statistical matters. Even though I am a scientist who is used to statistical data, it sounds odd to me when I hear the weather presenter talk about the highest temperature of the day as an average (“Today’s high was average for this time of year”), but it makes good sense. In chapter 6, I lead off my account of weather with a (light and readable, I hope) discussion of statistics and chaos in meteorology. Statistics as a subject may be drier than a summer day in Phoenix, but it doesn’t have to be presented that way, and it is essential to any insightful understanding of the subject.

“Lead off” in chapter 6? Yes, indeed. The first three chapters set the table for the feast, by providing necessary background about the basic weather-generating mechanism of heat transfer (chapter 1), about the star we circle and the planet we live on (chapter 2), and about the atmosphere we live under (chapter 3). Chapter 4 looks into the slow, dynamical effects that drive climate change without influencing dayto-day weather. Chapter 5 tees up the statistics of chapter 6 (which you think you will hate, but you’re wrong about that) by conveying to you the welter of data that feed our computer models of weather and climate. The remaining chapters build on these early foundations (our physical world is a complex system that takes a while to describe in a sensible way) and show you what we understand about weather and climate modeling and prediction.

I am not writing a textbook—there are already many meteorology and climatology texts out there. I am writing a solid account of weather physics and its slower sibling, climatology, that is aimed at the intelligent nonspecialist. You will need no more than high-school physics and math; there is a technical appendix with more math details for those of you who crave that sort of thing, but the main text is stand-alone. I want this book to be a breath of fresh air, not long winded. My approach is to explain key features of weather and climate physics with words and diagrams that get across the core ideas, backed

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up by more detailed examples set apart in boxes. One such example: hurricanes are an interesting and relevant phenomenon illustrating the Coriolis force, angular momentum, latent heat, and atmospheric instability, and so they merit such treatment.

Weather interests people for many reasons. It is one of the most relevant applications of science, affecting our daily lives. We don’t tune into local radio or television every morning to learn about the Higgs boson or to see the latest discoveries about slime molds, but we want to know what the weather is going to do today. Maybe we want to know this information simply so that we can decide what to wear, but likely there are more important reasons. Will there be ice on the road to work? Will the smog be bad? Transportation, agriculture, health care, safety, military operations—all are affected by weather. Thus freezing rain may bring out highway-maintenance trucks dispensing salt and grit, while flooding or fog may lead to traffic diversions. Crops may be watered (covered) if a dry spell (frost) is forecast. A heat wave can be fatal to unprepared retirees,5 while a storm at sea can be fatal to fishermen, and a tornado or wildfire fatal to anybody in its path. Military planners need to know about upcoming weather conditions in their area of operation (think of D-Day, or of air strikes in Bosnia). Taking the long view, if climate warming is real—and you will see that it is very real—then we need to know what its consequences will be. One of the important consequences is more extreme weather.

Our knowledge of weather physics, and especially our ability to predict weather, has greatly improved in recent decades; this is the subject of chapter 10. This trend will continue, though we will never be able to predict local weather accurately a month in advance (for reasons made crystal clear in chapter 6). My aims and hopes are twofold. First, having read this book, you will gain significant insight into the phenomena of weather and climate. Second, having read this book, you will better appreciate the considerable effort that is required to bring you the daily weather forecast.

6.125 × 9.25 SPINE: 0.875 FLAPS: 3.5

MAKING SENSE of WEATHER and CLIMATE

—SCOTT MANDIA, professor of physical sciences, Suffolk County Community College

MARK DENNY

received his Ph.D. in physics at the University of Edinburgh and worked in industry for 20 years before turning to his writing career. He is the author of Lights On! The Science of Power Generation (2013); The Science of Navigation: From Dead Reckoning to GPS (2012); Their Arrows Will Darken the Sun: The Evolution and Science of Ballistics (2011); Super Structures: The Science of Bridges, Buildings, Dams, and Other Feats of Engineering (2010); and Blip, Ping, and Buzz: Making Sense of Radar and Sonar (2007). These and his other popular-science books are outlined on his website, http://markdenny.shawwebspace.ca.

“Weather has always interested people and has always been societally relevant. Climate change is by now at a similar level of public interest and relevance. Making Sense of Weather and Climate delivers a popular overview of the physics of weather and climate, with a good amount of wit.

Denny’s approach to the subject from an applied-physics perspective is a real advantage: neither too technical nor too descriptive. This book is for anyone who wants to learn more about weather and climate.”

—THOMAS BIRNER, associate professor of atmospheric science, Colorado State University

“Making Sense of Weather and Climate is a beautifully written, lucid story of the science of climate and weather. It explores its subjects deeply but makes them accessible to the non-technical reader. The book captures the humanity of the scientific endeavor, and it describes how scientists observe weather, the statistical prism through which they must view the observations, and how they use them to construct models to render complex phenomena understandable.”

—EDMOND A. MATHEZ, author of Climate Change: The Science of Global Warming and Our Energy Future

COLUMBIA UNIVERSITY PRESS | NEW YORK Jacket design: Diane Luger Jacket images: Chemical glass flask (© Dollar Photo Club) Olexander, Sunset tornado (© Dollar Photo Club / James Thew) Author photo: © Jane Denny

MAKING SENSE of WEATHER and CLIMATE The Science Behind the Forecasts

“Making Sense of Weather and Climate is perfect for any individual who wants ‘textbook’ science delivered in a format that is easily digestible and exciting to read. The book fills a niche not only between popular and college-level science but also between the too-often separated topics of weather and climate change. Mark Denny makes clear that the two, frequently presented as separate issues, are in fact linked.”

DEN N Y

PRAISE FOR

MAKING SENSE of WEATHER and CLIMATE

The Science Behind the Forecasts

CUP.COLUMBIA.EDU ISBN: 978-0-231-17492-3

9 780231 174923 PRINTED IN THE U.S.A.

Columbia

MARK DENNY

H

ow do meteorologists design forecasts for the next day’s, the next week’s, or the next month’s weather?

Why are some forecasts more likely to be accurate than others? Noted physics author Mark Denny takes readers through key topics in atmospheric physics, presenting a cogent view of how weather relates to climate, particularly to climate change. Making Sense of Weather and Climate is the perfect book not only for amateur meteorologists but for anyone whose livelihood depends on navigating the weather’s twists and turns.

The book begins by explaining the essential mechanics and characteristics of the fascinating sciences of meteorology and climatology. Denny highlights the crucial differences between weather and climate, and then develops from this basic knowledge a sophisticated yet clear portrait of their relation. Throughout, he elaborates on the role of weather forecasting in guiding political, economic, and other aspects of human civilization. Denny’s exploration of the science of weather and the history of forecasting, both short term and long term, makes this book a unique companion for all who seek to understand the impact of weather and climate on individuals, society, and our planet.