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It’s a Small World: How Oceans and Climates Can Affect Wildland Fires Thousands of Miles Away

The scientists in this study were interested in three common periodic changes in sea surface temperatures, called oscillations. In particular, the scientists wanted to see how wildfires over the past 400 years aligned with the oscillations.

It’s a Small World: How Oceans and Climates Can Affect Wildland Fires Thousands of Miles Away

Meet the Scientists

Thomas Kitzberger

Biogeographer

Peter Brown

Biological Science | Dendrochronologist

Emily Heyerdahl

Biological Science | Dendrochronologist

Thomas Veblen

Physical Geographer

Thinking About Science

Sometimes it is hard to study the past. This is especially true if the past you want to study was hundreds or thousands of years ago. It is made more difficult if the past you want to study has no written records. Some scientists, such as archeologists and paleontologists, use items from the past as clues. Archeologists usually use human-made items, and paleontologists usually use natural clues. A dendrochronologist is a scientist who uses the natural clues found in tree rings (figure 1).

**Figure 1**. Dendrochronologists are able to date Native American historic and cultural sites using wood samples. Photo courtesy of Peter Brown.

In this study, the scientists used clues provided by old trees to help them understand the past. The scientists used information from tree rings. As a tree grows, it adds a layer of new growth on its trunk. For trees growing in dry areas, a lot of growth in a wet year shows up as a thick ring. In a dry year, the tree’s growth ring is thin. If something happens to the tree during a year, scientists can find clues in the tree’s growth ring for that year. For example, if there was a wildland fire and the tree was not burned up or killed, a scar may be evident in that year’s growth ring. Clues from a tree’s growth rings also help scientists determine the past climate of an area, as well as when and where wildland fires occurred (figure 2).

Tree ring examples and a graphic of scars on a tree cookie — **Figure 2**. Tree rings provide clues about a tree’s history. On the right, a fire scar was created when a surface fire burned near the tree. Photos courtesy of Emily K. Heyerdahl and the Forest Service.

Thinking About the Environment

You may have heard the expression, “It’s a small world.” It seems hard to believe, but many ecosystems on Earth are connected, even if they are located far apart. For example, glaciers in Arctic regions hold large amounts of fresh water when they are frozen and release that water when the temperature rises. This can cause changes in ocean temperatures and currents far from Earth’s Arctic regions. Another example is the Gulf Stream, which is a current of seawater moving up the eastern North American coast and finally eastward to northern Europe. Although Norway is located close to the Arctic region, the Gulf Stream keeps that country’s west coast free of ice all year.

The oceans, in particular, affect many climatic and weather events on land. You are probably aware of the formation of hurricanes and cyclones, which form over ocean waters and sometimes reach coastal areas. Scientists have discovered that oceans can even affect the occurrence of wildland fire.

The scientists in this study were interested in exploring the connection between ocean patterns, climate, and the timing of wildland fires in the Western United States.

What is dendrochronology?

Dendrochronology is the study of “tree time” and is also called tree-ring dating. Dendrochronology is a science based on the fact that every year a tree grows it adds a new layer of wood to its trunk; this process forms tree rings. Over a period of time, these rings form a series of light and dark circles that are visible on cross-sections of cut trees. A cross-section of a tree is when you cut a tree down and expose the middle of the tree (figure 3).

A scientist using a chain saw to cut a tree cookie. A graphic of a tree cookie showing the lines on the tree before and after being cut. — **Figure 3**. Dendrochronologists use chain saws to take samples from trees that are already dead, like these old stumps. Photo courtesy of James P. Riser, II, and Emily K. Heyerdahl.

Often trees are sampled using a hand drill, called an increment borer (figure 4). Neither of these techniques kills
the trees.

A scientist using a tree borer — **Figure 4**. Dendrochronologists do not have to kill trees to get information from tree rings. An increment borer allows scientists to pull a small sample of the tree’s rings. The hole created by the borer is then sealed to protect the tree. The sample is a long, thin cylinder of wood. Photo courtesy of Edward Cook and the National Oceanic and Atmospheric Administration (NOAA) Paleoclimatology Program, U.S. Department of Commerce.

Introduction

Scientists have identified a number of periodic changes in sea surface temperatures that affect climate over land. The scientists in this study were interested in three periodic changes, called oscillations, in sea surface temperatures that vary over different time scales (figure 5).

Figure 5. A comparison of El Niño-Southern Oscillation (ENSO), Pacific Decadal Oscillation (PDO), and Atlantic Multidecadal Oscillation (AMO).
Oscillation	Where?	How long?	Sea Surface Temperature?
ENSO	Tropical Pacific Ocean	2-7 years	Warm and Cool
PDO	North Pacific Ocean	20 years	Warm and Cool
AMO	Atlantic Ocean	60 years	Warm and Cool

The most rapid periodic sea surface temperature change is called the El Niño Southern Oscillation, or ENSO (figures 6a and 6b). ENSO changes every 2 to 7 years in the tropical Pacific Ocean. The change involves a warming or cooling of the water at the ocean’s surface. The warm phase of ENSO is called El Niño, and the cool phase is called La Niña.

A graphic of two globes showing the relationship between ocean temperature and rainfall during the 1997 el Nino — **Figure 6a**. These two globes show the relationship between ocean temperature and rainfall during the 1997 El Niño. On the left, the darkest streaks shows warmer ocean sea
surface temperatures. The warm water easily evaporates and storms are more likely to form. On the right, the darkest areas indicate heavy rainfall. You can see that heavy rain fell in the Pacific Ocean, along the coast of Northwestern South America and in the Southeastern United States. From the National Aeronautics and Space Administration (NASA) Earth Observatory.

A graphic of two globes showing the relationship between ocean temperature and rainfall during the 1998 La Nina — **Figure 6b**. These two globes show the
relationship between ocean temperature and rainfall during the 1998 La Niña. On the left, the darkest streaks show that sea surface temperatures were cool in the east Pacific off of the coast of South America. Since cool air is dense, it does not rise and storms are not likely to form. On the right, the darkest areas show places where drought (very low rainfall) occurred in Northwest South America and the Southeastern United States. The Southeastern
United States is the area in the United States most affected by ENSO. From NASA Earth Observatory.

A second sea surface temperature change is the Pacific Decadal Oscillation, or PDO. PDO changes like ENSO, but only about every 20 years, and it occurs in the North Pacific Ocean. The sea surface temperature pattern that changes the most slowly is the Atlantic Multidecadal Oscillation, or AMO. It occurs in the Atlantic Ocean and changes about every 60 years (figure 7).

Four maps of the U.S. showing different drought frequencies — **Figure 7**. PDO and AMO patterns affect drought conditions in the United States. Image adapted from the U.S. Geological Survey (USGS).

These periodic changes in sea surface temperature affect
climate on land. For example, during years when AMO is in its warm phase, the entire Western United States is generally warm and dry (figure 8). These warm, dry conditions mean wildfires are more likely.

A map of the U.S. with the western states highlighted — **Figure 8**. The Western United States.

ENSO and PDO affect climate in different parts of the Western United States in different ways. For example, during years when ENSO is in its warm phase, the Southwestern United States is generally cool and rainy whereas the Northwest is generally warm and dry. During these years, there is less chance of wildfires in the Southwest than in the
Northwest.

The scientists in this study were interested in the relationship between the phases of ENSO, PDO, and AMO and when wildfires occurred in the Western United States over a 400-year time span.

Reflection Section

Methods

The scientists studied the period of time between 1550 and 1924. They needed three kinds of information for the Western United States for each year of this 374-year period. First, they needed to know what the climate was like and how it differed across the area. For example, was it dry to the north but wet to the south or was it dry everywhere? Second, they needed to know the phase of each of the three oscillations. Finally, they needed to know when and where wildfires burned.

To get information about climate and sea surface temperatures, the scientists used information already collected by other scientists. From the ring widths of trees living during these 374 years, other scientists had identified which years were rainy and which were dry. Because sea surface temperature also affects climate, still other scientists had used ring widths from trees to identify sea surface temperature patterns. In other words, they identified which phases of ENSO, PDO, and AMO occurred each year.

To get information about when and where wildfires occurred, the scientists once again used data that had already been collected. They did not need to collect new data because a database is available that contains a history of wildfires recorded by tree rings. The database is like a fire history museum. Scientists from around the world give their tree-ring data to this database so anyone can use their data to study wildfires in the past. The scientists used information from the database that was collected from more than 4,700 trees whose rings had recorded 33,039 fire scars in the Western United States (figure 9).

A graphic showing the years of tree rings on a tree cookie — **Figure 9**. Scientists examined tree-ring fire scars from samples already collected. Photo courtesy of Peter Brown.

Once they had collected the three kinds of information, the scientists identified the climate and phase of each oscillation during years when many fires occurred all across the Western United States and when many fires occurred only in certain areas. They used a computer to help them with their analysis because there was so much information.

Wondering about wildfires

A tree on fire from this inside — **Figure 10**. Many trees can survive lots of fires. Fire scars are created when a surface fire burns near a tree. Photo courtesy of Michael G. Harrington.

You might be surprised to learn that fire is a natural part of the environment. Fire scars in tree rings show that in the past, fires burned in some forests every 10 to 20 years for many hundreds of years. Certain ecosystems depend on
wildland fires to be healthy and sustainable. Wildland fires
help plants grow by replacing nutrients into the ecosystem
from the fire’s ash. There are many different types of fires. Some wildfires burn at low temperatures and burn slowly (figure 10). By trying to eliminate wildfires in the past, we have actually encouraged more fires to burn in forests that
mostly had surface fires in the past. Now, forest managers
sometimes start small, controlled fires that burn the fuel that is close to the ground. These fires are called prescribed fires. For more information on wildfires, check out the Wildland Fire 1 and Wildland Fire 2 Editions!

Reflection Section

Findings

The scientists found that it really is a small world! They found that the location of wildfires was related to the phase of the oscillations during the 374-year period they studied. When ENSO and PDO were both in their warm phases, many wildfires burned in the Southwest where it was dry, but few burned in the Northwest where it was wet.

The opposite was also true. When ENSO and PDO were both in their cool phase, few wildfires burned in the Southwest but many burned in the Northwest. AMO had a different effect on wildfires. When AMO was in its warm phase, wildfires sometimes burned all across the Western United States because it was dry everywhere.

Scientists can only predict the weather a few days in the future. This is not enough to help us know if or where wildfires are likely to burn during the next summer wildfire season. Sea surface temperature patterns, however, change periodically in ways that scientists can predict months or even years ahead. Because these oscillations affect climate, scientists can use them to predict whether and where wildfires are likely to burn in upcoming wildfire seasons.

Reflection Section

Discussion

The scientists noted that the AMO pattern is now entering a warm phase. This will likely affect the occurrence of more wildfires in the Western United States. Global climate change, with rising temperatures, may cause even more warming in the Atlantic Ocean. This may increase the effect of the AMO even more.

With climate change, temperatures are likely to increase. These warming patterns may also increase the chance of wildfires in the Western United States. Larger and more frequent wildfires may occur as a result. If the patterns uncovered by the scientists continue and average temperatures continue to rise, people living in the Western United States should prepare for the possibility of more frequent wildfires in the future.

Reflection Section

What You Can Do: RECYCLE

You can recycle paper and cardboard in your classroom and
at home. Recycling helps keep the paper out of landfills and helps reduce the amount of carbon dioxide produced by burning the paper. You can also reduce the amount of paper you use by using both sides of the paper or by using paper as scrap paper once one side has been used.

Adapted from Kitzberger, T.; Brown, P.M.; Heyerdahl, E.K.; Swetnam, T.W.; Veblen, T.T. 2007. Contingent Pacific-Atlantic Ocean influence on multicentury wildfire synchrony over western North America. Proceedings of the National Academy of Sciences of the United States of America. 104:543–548. http://www.pnas.org/cgi/doi/10.1073/pnas.0606078104.

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Natural Inquirer - Vol. 14 No. 1

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Peter Brown

Biological Science | Dendrochronologist

My favorite science experience was certainly the earliest I can remember. I grew up on the Navajo Indian Reservation in northern Arizona. When I was in second grade, I rode...
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Emily Heyerdahl

Biological Science | Dendrochronologist

My favorite science experience is solving ecological puzzles about past wildland fires using tree rings. Just as when I was a young woman, I like being outside all summer collecting...
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Thomas Kitzberger

Biogeographer

My favorite science experience is scouting large unexplored areas in search of evidence of past fires from old trees. It is like time traveling to find an old tree with...
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Thomas Veblen

Physical Geographer

My favorite science experience is learning what tree rings can tell us about the history of insect outbreaks on trees.
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Standards addressed in this Article:

ESS2.A-M2
ESS2.C-M1
ESS2.C-M2
ESS2.C-M3
ESS2.C-M4
ESS2.D-M1
ESS2.D-M2
ESS2.D-M3
ESS3.B-M1
ESS3.D-M1
LS1.B-M4
LS2.A-M1
LS2.C-M1

What Is a Natural Inquirer Journal?

Three Natural Inquirer journal covers with NI bee

A Natural Inquirer journal is a collection of 4-8 articles on a related science topic. Journals are written for a middle school audience, but they can also be adapted for both high school students and advanced upper elementary students. Some journals are particularly suited to high school students; you can find our grade level recommendations in the tags on the product page or by filtering journals by grade level.

Journals include:

Four to eight articles based on published, peer-reviewed research papers; the articles keep the research paper format (see more below) but are written in language students can understand.
A FACTivity for each article, which is an activity to complete after reading the article. The FACTivity helps reinforce major science concepts from the article. These activities are designed to be easy to implement, with few material requirements and options for adapting them for your audience or available resources. Some articles in a journal may have two FACTivities.
A short “Welcome to the journal” article about key background information and science concepts that unify the articles included in the journal
A glossary of new terms for each article and the introductory materials.
A list of related Natural Inquirer publications for each article as well as outside references.
Standards correlations, including Next Generation Science Standards, addressed in the articles and the FACTivities.

Journals may also include additional essays (called spotlights), other activities (like crossword puzzles or vocabulary challenges), and more.

A screenshot of the article resource tile for "A Flame Changer" showing the three different format option buttons.

Reading Modes

Journals are available in three different formats:

Hard copies can be ordered from the website and shipped, all free of charge.
PDF versions of the printed journal can be downloaded free on the website. The PDF version directly replicates the content and layout of the printed version. You can also download individual articles as pdfs.
The “Read Distraction Free” option allows the individual articles to open in their own window, without the rest of the website being visible. These articles can be found under the “Articles” tab. This version allows readers to scroll to particular sections of the article using the sidebar menu on the left side of the screen. This version also has interactive Reflection Sections and Number Crunches. Students can enter their answers, submit them, and then receive the correct answers to double-check their work. Submitted answers are not saved on the website and will disappear once the window is closed.

What's in a Natural Inquirer Article?

Here, we'll go into more detail about the parts of a Natural Inquirer article and give you some ideas about how they can be used.

Meet the Scientists
This section introduces the scientists (and others) who worked on the study. In their own words, they each share a memorable science experience, a favorite research project, or something they learned during the course of their education or research.

Use this section to:
- Introduce kids to the variety of people who work in science
- Introduce kids to the variety of scientific fields and give brief descriptions of science-related jobs
- Explore ways that people interact with science every day
Next Generation Science Standards (NGSS) applications:
- Science and Engineering Practices
- Crosscutting Concepts: Influence of Science, Engineering, and Technology on Society and the Natural World
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Many of the scientists and engineers featured in this section are also featured on our collector cards. Learn more about their work, how they got interested in their fields, and interesting projects they worked on. Cards can be printed as posters, too.
Thinking About Science
This section briefly describes a concept about science or scientific research. This overview can touch on topics like
- study type (longitudinal study, quantitative vs. qualitative data),
- behaviors of scientists (conducting literature reviews, collaborating with other specialists, replicating earlier studies),
- the practice of science (the scientific method, engineering design, data collection, randomization, controls and variables),
- or other aspects of science (bias, correlation vs. causation).
Use this section to:
- Reinforce steps in the scientific method and the process of science
- Encourage students to think about the practice of science and what it can and cannot tell us
- Consider the many types of scientific study and what information each type can provide
Next Generation Science Standards applications:
- Science and Engineering Practices
- Life Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

You can use key words to search for other or related scientific topics on our website (e.g. “longitudinal study,” “bias,” or “sampling”).
Thinking About the Environment
This section provides a brief overview of a topic or concept in environmental/life science. The topic or concept is directly related to the research study that follows. Examples of topics include the carbon cycle, the water cycle, habitat fragmentation, phenology, biodiversity, and ecosystem services.

Use this section to:
- Provide important background information to help students understand the research study
- Serve as a quick reference during reading or class instruction
- Connect the research article with other activities or media on the same topic
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

You can use key words to search for more resources on life or earth science topics on our website (e.g. “habitat,” “carbon,” or “genetics”).
Introduction
This section begins the scientific article format. Much like the published, peer-reviewed study this article is based on, the introduction provides background information for the study – what is currently known and what remains unknown. The introduction culminates in the question(s) the study hopes to answer.

The introduction is also the first section with a Reflection Section. This section includes two or three questions to help kids reflect on what they’ve just learned in the Introduction. If they are using the online distraction-free reading mode, they can answer these questions directly on the website.

Use this section to:
- Review important background information that kids need to understand the study
- Connect the study to the concepts addressed in the Thinking About Science and Thinking About the Environment sections
- Understand research questions and hypotheses, including generating their own hypotheses given what they already know
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Use one of the guided reading lesson plans to help kids follow the format of a scientific paper.
Methods
This section is the nuts and bolts of the study design – the who, what, when, where, why, and how of the research. Contained within the Methods section are usually maps of the study location or the set-up of study plots, as well as details about what data was collected and how.

The Methods section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Show students how experiments and studies are designed and carried out
- Explore sampling methods and randomization
- Introduce various data collection tools (e.g. camera traps, surveys, insect collection tools, weather stations, etc.)
- Explain bias and how studies are designed to remove bias
- Help students gain experience with map reading
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Many Methods and Findings sections contain Number Crunches, which are simple math exercises designed to help students interact with the data from the study.
Findings
This section summarizes the data collected during the study. The Findings section usually includes data tables or graphs and highlights the significant data points from the study. This section often mentions statistical analysis or the use of computer programs to model or analyze the data, though these methods are only discussed generally.

The Findings section also ends with a Reflection Section – two or three questions to help students think through what they just read. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Have students practice reading and interpreting graphs and tables
- Compare results between variables and controls
- Explain the concept of statistical significance
- Discuss how no data or negative results still provide valuable information
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Search the website for “map” or “graph” to find activities where students can practice making and reading maps and graphs.
Discussion
This section concludes each article. In it, we summarize the main findings of the scientists’ study. Additionally, we present the scientists’ ideas about the limitations of their study, the big-picture impacts of their research, and the scientists’ plans for future study or action.

The Discussion section ends with a Reflection Section – two or three questions to help students think through what they just read, especially general take-aways from the study. These questions are interactive on the distraction-free reading mode.

Use this section to:
- Discuss what conclusions can and cannot be drawn from the available data
- Explain the difference between correlation and causation
- Explore study limitations and opportunities for further study
- Brainstorm ways the study findings could be applied to real-world situations
Next Generation Science Standards applications:
- Life Science and some Earth Science Disciplinary Core Ideas (depending on topic)
- Most Crosscutting Concepts (depending on topic)
Note that specific standards for this particular monograph are linked on this educator guide tab.

Other resources:

Use the “Designing Your Own Study” resource page for videos of scientists discussing their own research studies. The page also includes educator resources to help students plan their own scientific studies.

Additional Resources on the Website

A screenshot of the product tabs for an NI monograph On the website, we pair each journal with a variety of other resources, as well. Use the tabs on the product page to browse through the following:

Related activities, including the FACTivity for each article
An “About” essay that gives some larger context for the research the scientists conducted or more information about the science topic from the journal
A glossary of all boldfaced terms from the journal
A “Scientists and Collaborators” page that lists the people involved in the studies in the journal; click on a researcher to reach their bio page and see what other articles they might be featured in
A “Related Content” page that lists both Natural Inquirer resources about similar topics and also outside reference materials

Article Selection and Review

Natural Inquirer partners with the USDA Forest Service, so we source research studies by Forest Service scientists that have been peer-reviewed and published in reputable journals. Some of our articles have also been created in collaboration with scientists from other Federal agencies, such as U.S. Geological Survey and the United Nations Food and Agriculture Organization, universities, and other non-profits.

All journal articles are reviewed by scientists who conducted the original research study to verify scientific accuracy. Journals are also reviewed by student editorial review boards of middle or high school students before publication. Additionally, all journals are reviewed by the Forest Service and the U.S. Department of Agriculture before publication.

A screenshot of the citation for "Lights, Camera, Tracks" Every journal article includes a citation of its source study. Many educators pair the original research paper with our article to help more advanced students learn how to read formal research papers. The journal article then serves as adapted primary literature, bridging the two articles.

Lessons

Give each student or group a copy of the THIEVES chart reproduced at the end of the lesson plan PDF. You may either write the questions on the board, or...
Lesson Plan – THIEVES Chart Guided Reading
Give each student or group a copy of the THIEVES chart reproduced at the end of the lesson plan PDF. You may either write the questions on the board, or...
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Natural Inquirer - Vol. 14 No. 1
In this lesson plan, students will read a Natural Inquirer article and write a letter to the scientist, asking for clarification on at least four questions. Note: This lesson plan...
Lesson Plan – Write A Scientist
- 2-3 Classroom Periods
In this lesson plan, students will read a Natural Inquirer article and write a letter to the scientist, asking for clarification on at least four questions. Note: This lesson plan...
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The goal of this lesson plan is to help students identify key concepts and develop their own interpretations of what they read. It includes 42 open-ended questions for them to...
Lesson Plan – Questions Only
The goal of this lesson plan is to help students identify key concepts and develop their own interpretations of what they read. It includes 42 open-ended questions for them to...
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Education Files

Project Learning Tree

If you are a Project Learning Tree trained educator, you may use “Living with Fire” and “Our Changing World” as additional resources.

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Journals & Monographs

Collector Cards

Readers

Coloring and Activity Books

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FACTivity – It’s a Small World

Glossary

archaeology

climate

database

dendrochronologist

drought

forest manager

nutrient

oscillation

periodic

sample

sustainable

weather

wildland fire

Peter Brown

Emily Heyerdahl

Thomas Kitzberger

Thomas Veblen

Standards addressed in this Article:

What Is a Natural Inquirer Journal?

Reading Modes

What's in a Natural Inquirer Article?

Meet the Scientists

Thinking About Science

Thinking About the Environment

Introduction

Methods

Findings

Discussion

Additional Resources on the Website

Article Selection and Review

Lessons

Lesson Plan – THIEVES Chart Guided Reading

Lesson Plan – Write A Scientist

Lesson Plan – Questions Only

Education Files

Project Learning Tree

Additional Resources

NOAA's El Niño Animations & Graphics

What is El Niño? - NASA Space Place