Global Warming
Answer the following questions without looking up the answers:
1. Describe in your own words what global warming means.
2. How does the greenhouse effect fit into global warming?
3. You've seen that science can sometimes be misrepresented in the media. List some reasons why this can happen.
4. Do you think it's a problem when science is misrepresented in the media? Why or why not? Does your answer depend on what the consequences might be?
5. Before you proceed to the following lessons, write a brief paragraph explaining your thoughts on global warming. What did you know about it before you started this lesson? Do you feel you have good information? Where did you learn what you know? It's okay if you don't know much, that's important to write, too.
Global Warming Part 2: Climate Change
Lessons from the Past
As a detective investigating global warming, the first thing you'll set out to do is learn what it is you're really dealing with. What is global climate change, exactly? Without understanding how climate has changed on Earth over millennia, it's impossible to have any basis for comparison when trying to understand current climate patterns.
To truly understand climate change, you'll do what many scientists have already done and continue to do — find out all you can about the history of earth's climate. Does earth have natural fluctuations in its climate? If so, over what time span do these fluctuations occur? Without understanding how climate has changed on earth over millennia, it's impossible to have any basis for comparison when trying to understand current climate patterns.
Follow the link to “NOAA's Paleoclimatic Data Before 1000 Years Ago.” to find out about the earth's climate and climate change prior to 1000 years ago. Be sure to read the linked summaries to “commonly cited periods of warmth.”
Next find out about climate over the last 1000 years by following the link to “NOAA's Paleoclimatic Data of the Last 1000 Years.” Pay particular attention to the paragraphs and graphs below the “Summary of Studies” heading.
You'll use the information you've just read to answer the questions
NOAA's Paleoclimatic Data Before 1000 Years Ago
NOAA's Paleoclimatic Data of the Last 1000 Years
1. How do you go about estimating ancient temperatures? Is there more than one way?
2. How would you determine whether climate was changing (consider that the earth has different seasons, so how would you know whether climate was changing?)?
3. When estimating ancient temperatures, do different estimates tend to agree with each other, or disagree? In other words, for a given period in earth's history, do different researchers and different climate measures give similar results?do they agree with one another?
4. Is there evidence that the earth has warmed or cooled in the past 1000 years?
5. Is there evidence that it has warmed or cooled before 1000 years ago?
6. What are some explanations for why the earth's climate changed in the ancient past?
7. When the earth's climate shifted in the ancient past, do we know how long it took?
8. Why do scientists look at climate both prior to 1000 years ago, and over the last 1000 years? Does this level of scrutiny provide us a better grasp of how global climate works?
Comparing Current to Ancient Climate
Now that you've learned about earth's ancient climate patterns, you'll want to do some further sleuthing to understand more about current global climate patterns. How would decide whether climate has changed over the last 100 years. Also, how would you know whether recent climate change is fundamentally different than it was prior to the industrial revolution? In other words, what evidence would you need to show that humans might be having an impact on current climate patterns (HINT: would comparing the rate of climate change in the ancient past to present day help answer the question?)?
Find out more about relatively recent climate change (over about the last 140 years) by following the link to “NOAA's Instrumental Record of Past Global Temperatures”.
You'll use the information presented there and the information from what you've already read at “NOAA's Paleoclimatic Data of the Last 100 Years” to answer the questions.
NOAA's Instrumental Record of Past Global Temperatures
NOAA's Paleoclimatic Data of the Last 1000 Years
1. Do scientists use different methods to estimate climate over the last 100 years, than they do for measuring ancient climate patterns? If so, would this affect the reliability of the data in either scenario?
2. Do measurements using human-made instruments (like satellites and thermometers) suggest that global climate has been warming over the last century?
3. Is there anything different about warming over the last 100 years compared to ancient global climate change?
4. Does the rate of warming differ over the last 100 years compared to the rates of warming further in the past?
5. Even if warming has been dramatically different over the last 100 years, does that provide definitive evidence that human-related activities are the cause? (We'll discuss this question at more length in subsequent sessions. What other things would you need to know — besides temperature change — to be able to say whether humans are partly responsible for current warming trends?)
Global Warming Part 3: Nuts and Bolts
How the Science Gets Done
The next part of your detective work is to gain a working knowledge of how the science of studying climate change gets done. If you see exactly how and why scientists say what they do about climate, and if you understand the nuts and bolts behind how the science gets done, then you'll be a better equipped detective — you'll be far more confident about judging the validity of information you find regarding climate change.
Recall that some of the tools scientists use to examine past climate patterns include ice cores, tree rings, satellites, and thermometers. There are actually two main approaches to measuring climate. One way is through direct measurements. The other is by using indirect, or “proxy” measurements. Proxy measurements are critical to scientists interested in the earth's past climate record. Without proxies, we'd have no idea of what earth's climate was like in the past. Some tools are like time machines — they provide scientists surprisingly detailed views of what the earth's climate and atmospheric composition were like in the past. Can you think of some ways you could measure climate directly versus indirectly?
Weather Stations
Various instruments come under the umbrella heading of “weather station.” In fact, any weather station may or may not contain all of these instruments. If you have an outdoor thermometer that tracks temperature change, you have a sort of weather station. But for climate researchers, tracking these measurements must be a long-term project. Climate researchers keep records of temperature, humidity, barometric pressure, wind speed and velocity, cloud cover and rainfall from all over the world — from both land and sea. In addition, many sites have climate data that are archived for many years — so researchers can compare measurements from decades ago to current weather patterns. These measurements are mainly recent, however. The ability to measure weather patterns this way has only been around for the last couple of centuries.
Satellites
Satellites can measure the temperature of the earth's lower atmosphere (troposphere). These measurements have been recorded for only about the last twenty years. But the measurements of temperature in the troposphere tend to agree with the surface temperature recordings, though by a slightly lesser degree.
Greenhouse Gases
Special equipment can precisely measure the amount of different greenhouse gases currently in the atmosphere. The records for these kinds of measurements are, by necessity, recent — they only go back as far as when the technology became available to measure them. But scientists can see short-term changes in atmospheric gases like carbon dioxide, nitrates, methane, and others. And they can compare ice core measurements (see below) of some of these gases from the more distant past. For more information on measuring greenhouse gases follow the link to “EPA's Climate Change and Greenhouse Gases”.
http://web.archive.org/web/20130510201015/http://www.epa.gov/outreach/scientific.html
The Climate Change Toolbox
Proxy Measurements
Tree Rings
Chances are good you've had the chance to count tree rings — you look at a crosswise slab of wood and pick out the lines spanning from the center to the bark's edge. You can read much more than the age of a tree with these lines, however. Scientists who specialize in reading tree rings are called “dendrochronologists.” And they can look at changes to each ring and make accurate predictions about what the climate was like when they tree laid down a particular ring. That's because each ring corresponds to a year of growth, and good years with favorable temperature and precipitation correspond to relatively large rings. When the climate was less favorable for a particular tree's growth the rings are smaller — showing that the tree didn't grow as well in a given year. To use tree ring data, scientists have to have trees. They can look at tree rings from trees recently cut down, or they can use a bore to study rings from live trees without cutting them down. They can also use long dead trees from ancient structures or shipwrecks. Wood that has been well preserved over the centuries works particularly well.
Pollen
“Paleobotanists” are scientists who specialize in understanding ancient plant life and pollen. Pollen can provide very good evidence of what regional climate was like for a given area. To find pollen that corresponds with ancient times, scientists take cores from lakes and sediments. Then they analyze the pollen grains at different levels in the core that correspond to different time periods — the oldest pollen can be found at the bottom of the core, while the most recent is found near the top. For every species of pollen, there is a suite of habitat conditions that would have been necessary for that species to survive and thrive. So if certain pollen grains turn up in a sample, scientists can make accurate predictions about what regional climate conditions were probably like at the time.
Historical and Biological Records
Like pollen, other species of organism can yield clues to scientists about ancient climate patterns. For instance, entomologists (scientists who study insects) can determine what the regional climate was based on which insects show up in different areas of a sediment core. The same is true for marine animals. Tiny bivalves and crustaceans from sea sediment cores can yield clues about what the marine environment was like at a particular time in history.
Ice Cores
Ice cores are like a window to the past. When you drill a core of ice from a place it has lain untouched for thousands of years, you get not only frozen water, but also a frozen record of past atmospheric data. Ice cores contain dust, different concentrations of gases, different forms of oxygen, and other pieces of data — all of which help scientists to draw a very detailed picture of what climate was like for a give region in ancient history.
Here you'll take a few minutes to do a little more in-depth exploration of how ice forms, how cores are collected, why they are important to climate research. Though we don't have time to review all of the climate change tools in this depth (but see the list of references if you want to learn more about the other tools), it is helpful to you as a detective to learn more about at least one of these tools. And ice cores are particularly valuable to climate researchers. Let's find out why...
Take a few minutes to visit the link found at the bottom of this page, “Secrets of the Ice,” a Web site developed by the Museum of Science in Boston.
http://web.archive.org/web/20120621213010/http://www.mos.org/soti/
Ice Core Review Questions
Ice Formation and Flow
1. What is “firn?”
2. How is “pure ice” formed?
3. How long may it take for pure ice to form?
4. What happens to air trapped in the snow as it is transformed into pure ice?
5. The oldest ice is at the ______of the ice core.
6. What are some factors that scientists consider when deciding from what location they should try to remove an ice core?
7. About how long does it take to drill and remove about 200 feet of ice?
8. When the cores are brought to the surface, scientists try to place them into a general time frame. They look at the light and dark banding of the cores to estimate time — much like scientists use tree rings to count backwards in time. The light areas represent what? And the dark areas represent what?
9. What is insolation?
10. Milankovitch cycles can account for some changes in the earth's climate in the past. Why?
11. How does dust in the earth's atmosphere affect climate? Why do scientists who study ice cores look at calcium dust, in particular?
12. How do atmospheric gases get trapped in ice? Can scientists see what greenhouse gases were present in ancient times by examining ice cores?
Ice Cores: Interpreting the Data
Now that you've learned about ice cores, imagine that you're a scientist who's going to interpret some data from a recently removed hunk of ice. Follow the link at the bottom of the page to “Interpreting Ice Core Data” and complete the “Secrets of the Ice” activity.