Earth's Changing Climate

Course No. 1219
Professor Richard Wolfson, Ph.D.
Middlebury College
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Course No. 1219
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Course Overview

In 2007 the Intergovernmental Panel on Climate Change concluded that "warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice, and rising global mean sea level." Representing a consensus of hundreds of scientists, the report went on to note that human activity is "very likely" the cause.

This course of 12 half-hour lectures reviews the most up-to-date research on climate change, explaining the concepts, tools, data, and analysis that have led an overwhelming number of climate scientists to conclude that Earth is warming and that we humans are in great part responsible.

Behind the Consensus

Whatever your views on climate change, it's important to understand how the current scientific consensus on global warming evolved out of basic physical principles and a broad range of observations. In a lucid presentation designed for nonscientists, you will learn about:

  • The difference between climate and weather
  • The concept of energy balance, which governs the natural warming of the planet by the Sun and is the key to a stable climate
  • The greenhouse effect, which makes Earth warmer and more hospitable than it would otherwise be due to naturally occurring gases in the atmosphere, such as carbon dioxide and water vapor
  • The carbon cycle, which controls the rate at which carbon dioxide released by fossil-fuel combustion accumulates in the atmosphere, and how long it remains to enhance the natural greenhouse effect.

Along with these and other concepts, you will investigate the "fingerprints" of global climate change, ranging from borehole temperatures to melting glaciers to the altered behavior of plant and animal species. These and other indicators show that Earth has been warming at an unprecedented rate in recent decades.

You will also explore the physical mechanisms behind these changes and their connections to the increasing concentration of greenhouse gases in the atmosphere since the start of the Industrial Revolution. And you will look at the techniques for projecting future climates, along with the options for switching to alternative energy technologies to avoid the most disruptive scenarios that now seem possible.

Your Personal Scientific Briefing

Earth's Changing Climate addresses only scientific issues and makes no policy recommendations. Instead, this course is designed to serve as your personal scientific briefing to equip you to engage knowledgeably in one of the most important environmental issues of our time. In Lectures 1–6 you will focus on the scientific basis of climate; then in Lectures 7–12 you will come to understand the human role in climate change and explore projections of future climate.

Professor Richard Wolfson is no stranger to this subject. A physicist who has written and taught extensively about climate change, in 1996 he taped an earlier course for The Teaching Company titled, Energy and Climate: Science for Citizens in the Age of Global Warming. Professor Wolfson's new course is completely updated and represents the latest research and analysis in this fast-changing field.

A master at making difficult concepts understandable, Dr. Wolfson's other Teaching Company courses are Physics in Your Life, hailed by Library Journal as "a wonderful series of lectures that make learning physics fun and interesting," and Einstein's Relativity and the Quantum Revolution, which one listener said was "as exciting as a suspense thriller!"

In Earth's Changing Climate, Dr. Wolfson brings these educational gifts to bear on a subject that, at times, can be complex and controversial. You will find his presentation clear, objective, engaging, and illustrated with fascinating examples and analogies.

The Evidence Mounts

Like many scientific problems, the gradual assembly of a detailed picture of past, present, and future climates has involved creative detective work. For example, scientists traditionally test their theories by changing different variables, but this has not been possible with theories about climate change on Earth for two reasons: It's unwise to transform the planet just to see what will happen, and there are not multiple Earths to serve as test subjects.

However, researchers have identified cases where nature has done the experiments for us:

  • Mars: Mars's atmosphere has only about 1 percent the density of Earth's and provides a test for the theory of the greenhouse effect—in this case, for a planet with a thin atmosphere. As theory predicts, Mars has negligible greenhouse warming.
  • Venus: Venus's atmosphere has 100 times the density of Earth's and is about 96 percent carbon dioxide. Here, the greenhouse effect has struck with a vengeance—just as theory forecasts—driving temperatures to 500°C, hot enough to melt lead.
  • Mt. Pinatubo: The eruption of the volcano Mt. Pinatubo in 1991 poured massive amounts of dust into the upper atmosphere and allowed scientists to test their climate models. The fall in average global temperature over the following few years was in close agreement with what the models predicted.
  • Ice Cores: Deep ice cores from Greenland and Antarctica preserve a nearly million-year-old record of Earth's past temperature and atmospheric composition, showing a correlation between temperature and carbon dioxide concentration.

Using such clues, scientists are able to connect the 0.65°C rise in average global temperature since the start of the 20th century with the increase in atmospheric carbon dioxide over the same period. Looking ahead, they project a global temperature rise in the range of 1.5°C to 4.5°C during the 21st century, depending on the extent of worldwide economic growth and the rate of fossil fuel consumption.

An increase of a few degrees may not seem serious, but Professor Wolfson stresses that this is a global average. The rise will be more substantial in certain areas—particularly in the polar regions and over almost all land. He further notes that about 6°C separates the present-day climate from the depths of an ice age. Thus, an increase of a few degrees in global temperature is climatologically significant and may lead to many more extreme events, such as heat waves, intense precipitation, droughts, and intense tropical storms. At the same time, the sea level will be rising due to the thermal expansion of the oceans and the melting of land-based glaciers and ice sheets.

Over the longer term, a cause for worry is "surprise" events that could be initiated by as-yet poorly understood processes. These include the sudden slipping of a large land-based ice sheet into the sea with a resulting surge in sea level, or a major upset in patterns of ocean circulation.

As the evidence mounts, scientists will continue to refine their picture of what the climate is doing and where it is heading, and society will continue to grapple with this problem. You can begin to address it yourself—intelligently and prudently—by investing six stimulating and rewarding hours with this course.

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12 lectures
 |  Average 30 minutes each
  • 1
    Is Earth Warming?
    The course begins with a look at Earth's average temperature over the past century and a half, which shows an overall warming trend. How do scientists take Earth's temperature, and how do they interpret the pattern of variation? x
  • 2
    Butterflies, Glaciers, and Hurricanes
    This lecture looks at more subtle indicators of climate change and shows how statistical analysis reveals clear "fingerprints" of change on a host of natural systems. x
  • 3
    Ice Ages and Beyond
    Thermometer-based temperature rec­ords go back only 150 years. This lecture explores techniques that scientists use to push the global temperature record back millions, even billions of years. x
  • 4
    In the Greenhouse
    Stable climate entails a balance between incoming sunlight and outgoing infrared radiation. Infrared-absorbing greenhouse gases in a planet's atmosphere alter the details of this balance, causing the planet's surface to warm. x
  • 5
    A Tale of Three Planets
    How do we know that greenhouse gases such as water vapor and carbon dioxide are associated with the warming of Earth's surface? Nature provides a climate "experiment" on neighbor planets Venus and Mars. x
  • 6
    Global Recycling
    Cycling of materials plays a role in climate, with the most important cycles being those of water and carbon. Carbon added to the system stays for centuries to millennia and adds to the atmospheric carbon content, enhancing the greenhouse effect. x
  • 7
    The Human Factor
    Fossil fuel burning by humans has in­creased the concentration of carbon di­ox­ide in the atmosphere by nearly 40 per­cent since the start of the Industrial Revolution—to levels the planet has not seen in at least a million years. x
  • 8
    Computing the Future
    Climate models are mathematical descriptions, exploring how climate be­haves in response to human-induced changes and natural factors. Most models pro­ject a global temperature rise of several de­grees Celsius over the next century. x
  • 9
    Impacts of Climate Change
    A temperature rise of only a few degrees will have significant effects. The rise will be more substantial particularly in the polar regions and over almost all land. x
  • 10
    Energy and Climate
    Energy use is the dominant reason for our increasing influence on Earth's climate. Per capita energy consumption in the United States is more than 100 times our own bodies' energy output, meaning that we have the equivalent of about 100 "energy servants" each. x
  • 11
    Energy—Resources and Alternatives
    The fossil fuels that supply most of the world's energy have many deleterious environmental impacts, one of which is the emission of climate-changing greenhouse gases. This lecture surveys alternative energy resources. x
  • 12
    Sustainable Futures?
    Avoiding disruptive climate change in the future probably means keeping atmospheric carbon dioxide to at most a doubling of its preindustrial level. This final lecture discusses several possible paths to a stable climate. x

Lecture Titles

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Course Guidebook Details:
  • 88-page printed course guidebook
  • Suggested readings
  • Questions to consider
  • Figures & data sources

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Your professor

Richard Wolfson

About Your Professor

Richard Wolfson, Ph.D.
Middlebury College
Dr. Richard Wolfson is the Benjamin F. Wissler Professor of Physics at Middlebury College, where he also teaches Climate Change in Middlebury's Environmental Studies Program. He completed his undergraduate work at MIT and Swarthmore College, graduating from Swarthmore with a double major in Physics and Philosophy. He holds a master's degree in Environmental Studies from the University of Michigan and a Ph.D. in Physics from...
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Earth's Changing Climate is rated 4.3 out of 5 by 105.
Rated 5 out of 5 by from Very well done! Kudos to Professor Wolfson for the thought and hard work that went into developing and delivering this excellent course. The only constructive comment I would suggest is to update the course to reflect advances in energy technologies since 2007. I would definitely add material on clean distributed energy resources and their assimilation into the new smart grid. Also, solar photovoltaic technology has progressed tremendously to the point that it is now a preferred technology for most utility companies around the world (due to national cost reduction goals being met in 2017 vs 2020). I was very happy to see the emphasis at the end of the course on the incredible roles that increased energy efficiency and energy conservation can and should play. Unfortunately, the current administration calls climate change a "hoax" and has made policy changes that has setback efforts to slow the growth in carbon emissions tremendously, including the decision to eliminate CAFE standards for vehicles (i.e., mileage requirements for new cars), which is one of the most irresponsible government decisions I've witnessed in my lifetime. Hopefully, new leaders can reverse this and other setbacks by climate deniers in years to come. Also, Professor Wolfson's concerns about the viability of carbon capture and sequestration are well founded, and were borne out by mining experts on a recent National Academies Committee. Great job by an excellent professor; I highly recommend this course.
Date published: 2020-09-11
Rated 4 out of 5 by from Informative and balanced I learned a great deal from this course and I recommend it. Dr. Wolfson is even-handed in his presentation of the science of climate change; he's very good in clarifying what is known and how we know it. If anything, he goes a bit too far in the describing the various ways that scientists assemble and interpret data. I would have liked some more detail about the ways the climate itself is changing and how it is affecting our world and our lives. He also crams a lot of content into his lectures: I found myself taking notes, consulting the course materials, and relistening a few times. This is not a weakness of the course.
Date published: 2020-06-24
Rated 3 out of 5 by from A bit of good, and a bit of bad Only 3 stars, because there is both good and bad. So many other reviewers gave information on the good, so I will concentrate on the bad. 1. In lecture one, Wolfson notes the correlation between temperature and CO2, and concludes increases in CO2 causes higher temperatures. He relates correlation with cause and effect, which is blatantly false. 2. Also in lecture one, he describes how temperature readings are collected. He notes the well documented "urban heat island" effect, and then dismisses it as having no impact on global warming. It may not have an impact on actual warming because urban areas comprise an extremely small per cent of the earths surface, but it can have a great impact on the temperature readings you get when a high per cent of your readings are from urban areas. 3. In lecture 8, he talk about climate modeling, but fails in one extremely important area; how accurate those models have been since those models have been introduced. The only accuracy discussion was concerning the volcanic eruption of Mt. Pinatubo. No mention of the accuracy of the models since they were developed in the 1980s. This should be extremely important if you are trying to predict the climate 30 years from now. 4. Lecture 11 is very dated. He mentions the very large amount of oil imports by the U.S. At the time the course was produced, hydraulic fracturing was long underway in the oil drilling industry and output was already dramatically increasing. At this time net oil imports are less than 10% of U.S. consumption. 5. He seems to want to make the Industrial Revolution the bad guy here and the U.S. the leading bad player. Without the Industrial Revolution, 95% of the world would still be living in huts, cutting down trees to warm our huts, dying from diseases at an early age, women having 8 to 10 children with most dying before reaching adulthood, and 50 years old being an old person. He failed to mention that the U.S. has been reducing it CO2 emissions pretty consistently, plus our oil consumption has remained level since 1980 despite an increasing population and increasing GDP. I give Professor Wolfson credit for his observation of the economic growth happening in China and India and their impact on greenhouse gas emissions.
Date published: 2019-11-15
Rated 2 out of 5 by from Not very informative The lecturer is constantly checking his notes and taaalking about other courses he has taught, both of which are annoying. The visuals are few and far between, and those in the first three lectures were static and not very informative.
Date published: 2019-10-23
Rated 5 out of 5 by from Excellent Scientific Foundations! Earth's Changing Climate was informative, easy to understand, and filled with charts and visuals that assisted understanding. I knew when I purchased it that the statistics included in the course would reflect the earth's situation over a decade ago. But in spite of the outdated data, the course provided clear trends and historical perspectives that have only intensified in the intervening years. I found the scientific foundations were excellent and increased my understanding of global warming, carbon emissions in the atmosphere, and the growing effects of human activity on our current climate crisis. I would recommend this course to everyone. The more people who view it and gain better understanding of climate disruption, the better chance we have of making a difference for the future.
Date published: 2019-10-22
Rated 4 out of 5 by from Great 30 min lessons in climate change. Covers the basics of climate change. The lectures are not arrogant or lecturing. Covers many of the planetary boundaries and possible thresholds and tipping points that once breached might reach a point of no return.
Date published: 2019-04-08
Rated 5 out of 5 by from Outstanding way to learn important science ideas I got this class to understand climate science in a way that I, a non-scientist, could handle. It was fantastic for doing that. This class is more than enough to be able to explain the basics of climatology to your friends and family. Professor Wolfson was remarkably patient and tried to steer clear of politics.
Date published: 2019-03-07
Rated 5 out of 5 by from This course is very informative. I did not know how much research is going on. Whether you believe in global warming or not, you should listen to these lectures.
Date published: 2019-02-19
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