Mark Serreze: The Value of Climate Science


Modern climate science is based on facts, physics and testable hypotheses. There is ample room for debate about what to do about climate change, but the underlying science is rock solid.

Modern climate science builds on a long track record of scientific inquiry on environmental and health issues that has benefited society. Through scientific analysis, it was discovered that DDT, widely used as a pesticide, was becoming concentrated in the food chain. As a result, laws were passed to curb its use. Tetraethyl lead was once added to gasoline to reduce engine knock. Through science, we learned that lead in the environment poses severe health hazards, so the use of lead in gasoline was consequently phased out. It was through science that we learned how CFCs were destroying stratosphere ozone. In turn, through many decades of research, we have developed a strong understanding of how the climate system works, how humans are affecting climate, and what is in store if society continues to follow its current path without taking corrective action.

Until the middle off the 20th century, climate science was pretty much a backwater. Climatologists, by and large, were bookkeepers, compiling records of temperature, precipitation and other variables. From these records, much effort was spent classifying climate types around the world, ranging from tropical rain forests to monsoons to semiarid steppes to deserts. Climate data certainly had value to farmers and the home gardener, civil and structural engineers and the military planning. But the focus was largely on statistics, with relatively little emphasis on climate dynamics – the processes that control the climate system and how it may evolve. There were notable exceptions, such as Svante Arrhenius, who, in the late 19th century, speculated on how rising concentrations of carbon dioxide would lead to warming, but for the most part, climatology was a largely descriptive and rather boring field of science.

The shift from simple bookkeeping to a more physically-based view of how the climate system works paralleled developments in meteorology—the science of weather prediction. The rapid advances in meteorology following the Second World War, in turn, largely paralleled the development of numerical computers. With computers, it became possible to translate the physical processes controlling weather systems into computer code. It was readily understood that the physics controlling weather were part of the broader set of physics that control climate, which led to the development of global climate models, or GCMs for short. GCMs were quickly seen as powerful tools to understand not just how the global climate system works, but how climate could change in response to things like brightening the sun or altering the level of greenhouse gases in the atmosphere.

Using early generation GCMs developed in the 1970, pioneers like Jim Hansen of NASA, and Suki Manabe of the Geophysical Fluid Dynamics Laboratory in Princeton confidently predicted that our planet was going to warm up, and that the Arctic would warm up the most, something that we now call Arctic amplification. But the more mundane chore of compiling climate records never stopped, and indeed, its value grew, for it was only with ever-lengthening climate records that it could be determined if things were actually changing. And as these records grew, it slowly became clear that the planet was indeed warming. From numerous GCM experiments, it also became clear that this warming, and all the things that go with it, such as the Arctic’s shrinking sea ice cover and Artic amplification, could only be explained as a response to rising levels of carbon dioxide in the atmosphere.

Climate scientists of today need to know:

  • The processes that can change how the earth absorbs and emits energy
  • How the atmosphere and weather systems work
  • How the atmosphere interacts with the oceans
  • How the atmosphere interacts with the land surface
  • And how the land interactions with the ocean.

But whatever our area of specialty, we all try and make contributions to our understanding, but those contributions are, to the best of our ability, based on facts, physics, and sound methodology. In science, there is no room for wishful thinking. As a society, need to get past partisan bickering, step back, and listen to what climate science is telling us: the climate is changing, we know why, and the implications must not be ignored. This is the value of climate science.

Mark C. Serreze is director of the National Snow and Ice Data Center, professor of geography, and a fellow of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. He is the coauthor of The Arctic Climate System. He lives in Boulder, Colorado.

Mark Serreze: Becoming A Scientist

In honor of Earth Day, Princeton University Press will be highlighting the contributions that scientists make to our understanding of the world around us through a series of blog posts written by some of our notable Earth Science authors. Keep a look out for this series all month long.

Mark Serreze, investigating the pressure ridges in the Arctic.

What is it that leads someone to become a scientist? It varies, but from what I’ve seen, it’s often a combination of nature and nurture. Just as some people seem to have an inherent knack for writing making music, or cooking, I think that some of us are wired to become scientists. In turn, there is often someone we can look back to—parents or perhaps a teacher—that encouraged or inspired us to pursue a science career.

I had an interest in science from when I was very young, and I was always full of questions about the natural world. The first book I ever owned is “The Golden Book of Science” 1963 edition—featuring 1-2 page essays on everything from geology to insects to the weather. Each night, at my insistence, my mother would read one of them to me. To this day, I still own the book.

When I wasn’t reading, I could spend hours outside marveling at the organized industriousness of ants as they built their anthills, or looking at colorful rocks with a magnifying glass. I was enthralled with the burgeoning manned space flight program, and, sitting beside my mother and staring at the black TV while she ironed clothes, watched in awe at the Project Gemini rocket launches.   

As for the nurture part, I had an advantage in that both of my parents were chemists with Master’s degrees. This was at a time it was quite unusual for women to hold advanced degrees. They met in the laboratory. Mom was a whiz when it came to thermodynamics, and Dad apparently knew everything there was to know about acrylic plastics. Ours was indeed an odd household. While my siblings and I chafed under a rather strict Catholic upbringing, at the same time we were very much free-range kids, and scientific experimentation of all sorts was quite acceptable.  

At one point, after getting a chemistry set for Christmas, I thought I might become a chemist myself. These were not the boring, defanged chemistry sets of today – back then, they included chemicals that, when properly mixed, yielded career-inspiring reactions. I later got heavily into model rocketry, astronomy, and civil engineering, building small dams across the stream running past our house to improve the habitat for the frogs. Included among the more foolish (albeit highly educational) endeavors was a scientifically-based experiment on the feasibility of riding ice floes down the Kennebunk River. Then there was the time when an experiment in pyrotechnics gone wrong ended up with a frantic call to the fire department to douse a five-acre conflagration in the neighbor’s field.

Years before I ever got into college I knew I was going to be a research scientists of some type, for, through nature and nurture, the roots were already there. As I talk about in my book, Brave New Arctic, a number decisions and events came together – mixed with some blind, dumb luck – to eventually steer me towards a career in climate science. What I could never have foreseen is how, through these events and decisions, and then through 35 years of research, I’d find myself in the position to tell the story about the dramatic transformation of the North.

Climate scientists, like myself, have to deal with an added challenge that climate change is a highly polarized subject. There are the frequent questions from the media: Will there be a new record low in Arctic sea ice extent this year? Why does it matter? Why is the Arctic behaving so differently than the Antarctic? It can be overwhelming at times. Then there are the emails, phone calls and tweets from those who simply want to rant. While I get a lot of emails from people fully on board with the reality that humans are changing the climate and want to get straight answers about something they’ve heard or read about, I also have a growing folder in my inbox labeled “Hate Mail”. Some very unflattering things have been said about me on social media and across the web. I’ve had to grow a thick skin.  

Making a career as a research scientist is not for everyone. Science is not the sort of thing that is easy to put aside at the end of the day. It gnaws at you. The hours are long, and seldom lead to monetary riches. It can also be a frustrating occupation, such as when realizing that, after months of research pursuing a lead, you’ve hit a dead end.

We chose to be scientists because it’s what we love to do. We live for those “aha” moments when the hard work pays off, and we discover something new that advances our understanding.

In writing this book I was forced to dig deeply to understand my own evolution as a scientist, and to document insights from other scientists who, like me, were there at the beginning when the Arctic still looked like the Arctic of old. It’s been an adventure, and when I someday retire (which is a very hard thing for scientists to do,) I hope to be able to look back and say that that this book opened some eyes, and inspired others to follow their own path to becoming a scientist.


Mark Serreze is director of the National Snow and Ice Data Center, professor of geography, and a fellow of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. He is the coauthor of The Arctic Climate System. He lives in Boulder, Colorado.

Mark C. Serreze: Approaching the March Sea Ice Maximum

Author Mark C. Serreze standing next to a snow machine in the Arctic.

The floating sea ice atop the Arctic Ocean waxes and wanes with the seasons. The maximum extent typically occurs around the second week of March, at which time ice has historically covered an area a bit less than twice the size of the contiguous United States. The term “Arctic sea ice extent” is actually a bit of a misnomer, for at or near the seasonal maximum, sea ice is found well south of the Arctic Circle, covering all of Hudson Bay and parts of the Bering Sea, the Sea of Okhotsk, the Baltic Sea and the Gulf of St. Lawrence.  With the start of spring, the ice cover begins to melt.  Initially, the growing warmth of spring slowly nibbles away at the southern edges of the ice pack.  The pace of melt picks up in May and June, and then gets underway in earnest in July.  As the sun gets lower in the sky in August, the melt slows.  The seasonal minimum in ice extent usually occurs in mid-September – at that time, the ice covers less than half of what it did in March, and ice is restricted to the Arctic Ocean proper.  As the sun then sets over the Arctic Ocean, the ice cover begins to grow again, renewing the cycle that has been going on for millions of years. 

But things are changing fast.  Earth observation satellites have been recording changes in Arctic sea ice extent since 1979.  These records show that sea ice extent is declining in all months, with the largest change in September, at the end of the melt season.  The downward trend for September is a whopping 13% per decade. The trends are by no means smooth – there are big ups and downs from month to month and year to year, but the pattern is clear. 

Scientists have long been at work to determine what sea ice conditions were like before the satellite era.  Data from shore observations, ship and aircraft reports, and before aviation, sources like logbook entries from whaling ships, extend the record back to 1850.  Paleoclimate reconstructions bring the record back a thousand years before today.  There is no evidence in any of these records for sea ice trends like we’ve seen over the past 40 years.  They are unprecedented.  The conclusion is inescapable – the Arctic Ocean is quickly losing its floating sea ice cover.  The summer ice cover may be gone 30 or 40 years from now.

At the University of Colorado National Snow and Ice Center (NSIDC), where I’ve been the director since 2009, we track the Arctic sea ice cover on a daily basis.  Every August, we start to brace ourselves for the inevitable tidal wave of questions from the media and interested public about what September will bring.  Questions like: Will there be a new record low in sea ice extent this year?  When will the Arctic completely lose its summer sea ice cover?  What will this mean for the rest of the planet?  We also get our share of flak from the skeptics, eager to tell us that this is all some sort of natural climate cycle, or that nothing is happening at all; we’re making it up and fudging the records.  We shrug this off and diligently continue processing the satellite data and report on what is happening. The data does not lie.

Until a few years ago, the March sea ice maximum went relatively unnoticed.  By comparison to September, the changes being seen in winter weren’t especially spectacular, and for good reason – even in a warming Arctic, it still gets cold and dark in winter and sea ice forms and covers a big area.  The ice that grows in autumn and winter is thinner than it used to be, but to the satellite sensors that we use to determine ice extent, thin ice looks pretty much the same as thick ice.

Things changed in 2015, when sea ice extent at the March maximum set a new record low.  Then the winter of 2015-2016 saw a mind-boggling heat wave over the Arctic Ocean.   At the end of December 2015, there was a brief period when the surface temperature at the North Pole rose to the melting point. In all my years of studying the Arctic, I’d never seen anything like it. It stayed warm and on March 24, when Arctic sea ice reached its seasonal maximum extent, it had bested the low mark set in 2015.  The winter of 2016/2017 was in many respects a repeat.   At the winter solstice on Dec. 22, temperatures near the North Pole were up 20 degrees Celsius (35 degrees Fahrenheit) above average.  When March 2017 rolled around, another new record low in extent had been set. The Arctic has gone crazy.

We’re still coming to grips with understanding these records lows in the winter ice cover. While the heat waves are clearly related to weather patterns bringing in warm air from the south, what’s the cause of these patterns?  While more ocean heat seems to be coming into the Arctic Ocean from the Pacific through the Bering Strait, why is this happening?  The inflow of ocean heat from the Atlantic has also changed in puzzling ways that inhibit winter ice formation in places like the Barents Sea.  

In short, while we know a great deal about what is happening to the Arctic and where it is headed, the emerging Brave New Arctic continues to challenge us.  Maybe we shouldn’t be all that surprised – after all, scientists have long known that, as the climate warms, the biggest changes would be seen the Arctic. That doesn’t mean that we can’t be amazed.


Mark C. Serreze is is director of the National Snow and Ice Data Center, professor of geography, and a fellow of the Cooperative Institute for Research in Environmental Sciences at the University of Colorado at Boulder. He lives in Boulder, Colorado.


Bender_Paleoclimate “Michael Bender, a giant in the field, fits the excitement, rigor, and deep insights of paleoclimatology into a succinct text suitable for a semester-long course introducing this indispensable branch of environmental science.”–Richard B. Alley, Pennsylvania State University

Michael L. Bender

In this book, Michael Bender, an internationally recognized authority on paleoclimate, provides a concise, comprehensive, and sophisticated introduction to the subject. After briefly describing the major periods in Earth history to provide geologic context, he discusses controls on climate and how the record of past climate is determined. The heart of the book then proceeds chronologically, introducing the history of climate changes over millions of years–its patterns and major transitions, and why average global temperature has varied so much. The book ends with a discussion of the Holocene (the past 10,000 years) and by putting manmade climate change in the context of paleoclimate.

The most up-to-date overview on the subject, Paleoclimate provides an ideal introduction to undergraduates, nonspecialist scientists, and general readers with a scientific background.


Watch Michael Bender discuss Paleoclimate at the Fundamentals of Climate Science Symposium at Princeton University

Request an examination copy.


Climate Dynamics

Cook_Climate_Dynamics “Climate change and its impacts are being embraced by a wider community than just earth scientists. A useful textbook, Climate Dynamics covers the basic science required to gain insights into what constitutes the climate system and how it behaves. While still being quantitative, the material is written in a lecture-note style that creates a simplified, but not simple, approach to teaching this complex subject.”–Chris E. Forest, Pennsylvania State University

Climate Dynamics
Kerry H. Cook

Climate Dynamics is an advanced undergraduate-level textbook that provides an essential foundation in the physical understanding of the earth’s climate system. The book assumes no background in atmospheric or ocean sciences and is appropriate for any science or engineering student who has completed two semesters of calculus and one semester of calculus-based physics.

  • Makes a physically based, quantitative understanding of climate change accessible to all science, engineering, and mathematics undergraduates
  • Explains how the climate system works and why the climate is changing
  • Reinforces, applies, and connects the basic ideas of calculus and physics
  • Emphasizes fundamental observations and understanding


Table of Contents

Sample this book:

Chapter 1 [PDF]

Request an examination copy.


New and Forthcoming Titles in Physics & Astrophysics

catalog coverIntroducing our new 2011 Physics and Astrophysics catalog at:

See page 2 for our new series, The Princeton Frontiers in Physics.  The series offers short introductions to some of today’s most exciting and dynamic research across the physical sciences.  Abraham Loeb’s How Did the First Stars and Galaxies Form? and Joshua S. Bloom’s What are Gamma-Ray Bursts? launch the series.  Great books for students, scientists, and scientifically minded general readers.

Additions to the Princeton Series in Astrophysics include Bruce T. Draine’s Physics of the Interstellar and Intergalactic Medium and Sara Seager’s Exoplanet Atmospheres. Professors, make sure to check out pages 3-5 for more textbooks.

The catalog is full of new titles by leading experts.  We invite you to browse and download the catalog.  If you’re at the American Astronomical Society meeting in Seattle, please stop by booth 301 and say hello.  Hope to see you there.