Class 6, Climate modes

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This document provides an overview of the principles of dendroclimatology and climate reconstruction using tree rings. It discusses three key principles: 1) cross-dating, which is matching patterns in tree ring widths between trees to identify exact years of growth; 2) aggregate tree growth, which is using a statistical model to decompose tree ring widths into age-related growth trends, climate signals, and other environmental factors; and 3) ecological amplitude, which is that trees near their ecological limits are more sensitive recorders of climate variations. It also provides examples of cross-dating tree ring patterns and the statistical model of aggregate tree growth. Finally, it outlines the workload expectations for a class paper reviewing the climate history of a region over the Hol

Education

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“
The trees composing the forest rejoice and
lament with its successes and failures and
carry year by year something of its story in
their annual rings.”

A. E. Douglass
University of Arizona

The principle of cross-dating
The principle of aggregate tree growth
The principal of ecological amplitude

THE PRINCIPLE OF CROSS-DATING
Matching pa erns in tree-ring widths or other ring
characteristics (such as ring density) among several trees
allow the identiﬁcation of the exact year in which each ring
was formed.

Same environmental forcings

Similar
growth pa erns

THE PRINCIPLE OF CROSS-DATING

1900 1910 1920 1930

Two Douglas-ﬁr cores from Eldorado Canyon, CO

Graphic: Jeﬀ Lukas, INSTAAR

THE PRINCIPLE OF AGGREGATE TREE GROWTH
Any individual tree-growth series can be "decomposed" into
a set of environmental signals that aﬀected the tree’s growth
through its lifespan.

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et
tree growth in year ‘t’

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et
size-related growth trend
caused by physiological aging

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et
climate during year ‘t’

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et

disturbance within the forest

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et

disturbance from outside
the forest

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et

random processes
not accounted by other sources

THE PRINCIPLE OF AGGREGATE TREE GROWTH

Rt = At + Ct + δD1t + δD2t + Et

THE PRINCIPLE OF ECOLOGICAL AMPLITUDE
Ecological range limits are o en controlled by climate, and
trees growing near the limits of their range are o en more
sensitive to climatic ﬂuctuations than similar trees growing
under more suitable conditions.

Workload
A paper, not to exceed 10 pages of text plus ﬁgures
and references, which reviews the climate history of a
single region over a speciﬁc time period during the
Holocene (e.g., the mid-Holocene, the last 2ka or the
last 500 yr).

(at least 5)
Workload

>
A paper, not to exceed 10 pages of text plus ﬁgures
and references, which reviews the climate history of a
single region over a speciﬁc time period during the
Holocene (e.g., the mid-Holocene, the last 2ka or the
last 500 yr).

Focus questions

What are the most important features of the modern
climate in your region?

What proxies are available in your region, over the
time interval speciﬁed? How are they related to
climate?

How diﬀerent were past climates from modern
conditions? Why is that important?

NARROW AND FOCUSED

“How has the climate of Australia changed since A.D. 1000?”
OK

NARROW AND FOCUSED

“How has the climate of Australia changed since A.D. 1000?”
OK
“Was Western Austria drier during the Medieval Period,
compared to today?”
Better

Course schedule (current)
October 27, 2010
The human dimension of past climate change

November 3, 2010
Megadrought II / Natural hazards

November 10, 2010
Isotope paleoclimatology

November 17, 2010
Climate forcings

November 24, 2010
Climate models

December 1, 2010
Regional climate history I

December 8, 2010
Regional climate history II

December 15, 2010
No class - Fall meeting, American Geophysical Union

OPTIONS

Presentations ➜ Feedback ➜ Papers

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Papers ➜ Feedback ➜ Presentations

By November 3
[Tentative] list of 10 articles related to
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Strong variance at decadal and multidecadal timescales is a common feature of most tree-ring width records. But does this aspect of tree growth exhibit such long-memory behavior due to biology, climate, or some combination of the two factors? Understanding the origins of this behavior is crucial for efforts to evaluate the causes of decadal variability in the climate system. Presentation at Johann Gutenburg University (Mainz) on February 16, 2017.

Five Things You Can Do Right Now To Make Your Research Presentations Just A L...

Scott St. George

The ability to deliver effective and engaging oral presentations is a critical skill for all researchers. Unfortunately, despite the importance of clear communication, too many scientific presentations at conferences and workshops are confusing, abstract, and boring. In this short workshop, participants learn several key strategies and tips that will make their professional presentations just a little bit better than the rest. We discuss strategies for presentation planning, show how basic design principles can create more memorable slides, and point towards an outstanding set online tools and resources. Become a presentation superstar! Scott St. George is Associate Professor in the Department of Geography, Environment and Society at the University of Minnesota and a Resident Fellow at UMN's Institute on the Environment. Prior to joining the faculty at Minnesota, he was a research scientist with the Geological Survey of Canada. Scott shares some of his experiences ‘doing presentations differently’ at conferences, outreach opportunities, and the classroom.

Trees as flood sensors

Scott St. George

In many settings, trees growing on floodplains provide an important source of indirect evidence that may be used to infer the occurrence, extent, and magnitude of floods prior to direct observations. That evidence may take several forms, including external scars caused by abrasion or impact from floating debris, anatomical changes within the annual growth increment following prolonged stem or root inundation, or tilting or uprooting due to the hydraulic pressure of floodwaters. Likely the most useful characteristic of paleoflood studies based on floodplain trees is their relatively high temporal resolution and dating accuracy compared to most other methods. Dendrochronological methods can routinely date past floods to the year of their occurrence and, in rare cases, can estimate the timing of floods that occur during the growing season to within two weeks. This high degree of chronological control, which is surpassed only by that provided by direct observation or instrumentation, can be used to determine whether floods in separate watersheds were synchronous or offset by several years and test hypotheses that suppose linkages between extreme floods and specific forcing mechanisms. Furthermore, the wide geographic distribution of tree species with dateable rings combined with the broad suite of methods available to examine interconnections between floods and tree growth allow this style of paleoflood hydrology to be applied to many settings that are not suitable for techniques that depend on geological evidence. Future paleoflood research involving tree rings will need to strike a balance between improving our understanding of the biological and fluvial processes that link tree growth to past events, and providing answers to questions about flood dynamics and hazards that are needed to safeguard people and property from future floods.

Expanding the window - the past, present, and future of Minnesota's water

Scott St. George

Nearly all decisions about water in Minnesota relate either directly or indirectly to data collected by the state’s hydrological observing network. Because most gauges were installed in early 20th century, as a whole the network provides us with roughly a 100-year ‘window’ to estimate flood risks, develop worst-case scenarios for drought, and set maximum allowable withdrawals for aquifers. But when we rely exclusively on observations made during this relatively brief interval, we may inadvertently increase our exposure to hydrological ‘surprises’. In order to make sound decisions about water in Minnesota, we need to expand this window: into the past, drawing upon historical accounts and natural archives; and into the future, via projections from climate and hydrological models. By cultivating a broader perspective on hydrological variability and extremes across the state, we will be better prepared to ensure adequate water supplies and mitigate the impacts of future floods and droughts.

Making Climate Data Sing

Scott St. George

These visuals were prepared to support a string quartet performance and panel on climate change at Northwestern University in February 2106. A well-designed graphic can help audiences to quickly understand the main message embedded within a complex set of climate data and to retain those ideas longer than they would have if they were conveyed by words alone. But the visual aids used regularly by climate scientists also have their limitations: they are most easily understood by people who are already fluent in technical illustrations; they're usually static and sometimes do not tell an obvious story; and for many, they don't elicit a strong emotional response. Music, by contrast, is inherently narrative and is known to exert a powerful influence on human emotions. Because of this, sonification — the transformation of data into acoustic signals — may have considerable promise as a tool to enhance the communication of climate science. Daniel Crawford and Scott St. George report on a collaboration between scientists and artists that uses music to transmit the evidence of climate change in an engaging and visceral way.

Large-scale dendrochronology and low-frequency climate variability

Scott St. George

Large-scale low-frequency variability has emerged as a priority for climate research, but instrumental observations are not long enough to characterize this behavior or gage its impacts on dependent geophysical or ecological systems. As the leading source of high-resolution paleoclimate information in the middle- and high-latitudes, tree rings are essential to understand low-frequency variability prior to the instrumental period. But even though tree rings possess several advantages as climate proxies, like other natural archives they also have their own particular impediments. In this lecture, Dr. St. George will describe the structure and characteristics of the Northern Hemisphere tree-ring width network, and outline how the fingerprint of decadal and multidecadal climate variability encoded within ancient trees varies across the hemisphere.

Noah, Joseph, And High-Resolution Paleoclimatology

Scott St. George

In 1968, Benoit Mandelbrot and James Wallis published an article titled ‘Noah, Joseph, and operational Hydrology’ in the journal Water Resources Research. In it, they argued that hydrological models of the day were not able to estimate the true risk of extreme floods or prolonged drought, and that rare hydrological events were much more common than usually assumed. In this lecture, I’ll review how high-resolution paleoenvironmental archives can help us judge more accurately the risks posed by the ‘Noah’- and ‘Joseph’-style events described by Mandelbrot and Wallis. I’ll give particular emphasis to the environmental information recovered from the rings of ancient trees, and explain how dendrochronology (tree-ring research) has been used to redefine the ‘flood of record’, test potential avenues for long-lead climate predictions, and gage the performance of state-of-the-art climate models.

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1. GEOG5426 Climate modes

2. Compared to my other classes, I am working: 4 3 0 0 0 A lot less Less About average More A lot more

3. Compared to my other classes, I am learning: 4 2 1 0 0 A lot less Less About average More A lot more

4. PRINCIPLES OF Dendroclimatology

5. “ The trees composing the forest rejoice and lament with its successes and failures and carry year by year something of its story in their annual rings.” A. E. Douglass University of Arizona

6. The principle of cross-dating The principle of aggregate tree growth The principal of ecological amplitude

7. THE PRINCIPLE OF CROSS-DATING Matching pa erns in tree-ring widths or other ring characteristics (such as ring density) among several trees allow the identiﬁcation of the exact year in which each ring was formed.

8. Same environmental forcings Similar growth pa erns

10. THE PRINCIPLE OF CROSS-DATING 1900 1910 1920 1930 Two Douglas-ﬁr cores from Eldorado Canyon, CO Graphic: Jeﬀ Lukas, INSTAAR

11. THE PRINCIPLE OF CROSS-DATING 1900 1910 1920 1930 Two Douglas-ﬁr cores from Eldorado Canyon, CO Graphic: Jeﬀ Lukas, INSTAAR

12. Smith and Lewis, 2006

13. THE PRINCIPLE OF AGGREGATE TREE GROWTH Any individual tree-growth series can be "decomposed" into a set of environmental signals that aﬀected the tree’s growth through its lifespan.

14. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et tree growth in year ‘t’

15. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et size-related growth trend caused by physiological aging

16.

17. Ring width Tree age

18. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et climate during year ‘t’

19.

20. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et disturbance within the forest

21.

22. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et disturbance from outside the forest

23.

24. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et random processes not accounted by other sources

25. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et

26. THE PRINCIPLE OF ECOLOGICAL AMPLITUDE Ecological range limits are o en controlled by climate, and trees growing near the limits of their range are o en more sensitive to climatic ﬂuctuations than similar trees growing under more suitable conditions.

27.

28.

29.

30.

31.

32.

33. Ring-width index

34.

35.

36.

37.

38. Single-site reconstruction

39. never trust one tree

40.

41.

42.

43. Multiple-site reconstruction

44.

45.

46.

47.

48. Network reconstruction

49. THE PRINCIPLE OF AGGREGATE TREE GROWTH Rt = At + Ct + δD1t + δD2t + Et

50. GEOG5426 Climate modes

51.

52.

53. Workload A paper, not to exceed 10 pages of text plus ﬁgures and references, which reviews the climate history of a single region over a speciﬁc time period during the Holocene (e.g., the mid-Holocene, the last 2ka or the last 500 yr).

54. (at least 5) Workload > A paper, not to exceed 10 pages of text plus ﬁgures and references, which reviews the climate history of a single region over a speciﬁc time period during the Holocene (e.g., the mid-Holocene, the last 2ka or the last 500 yr).

55. Focus questions What are the most important features of the modern climate in your region? What proxies are available in your region, over the time interval speciﬁed? How are they related to climate? How diﬀerent were past climates from modern conditions? Why is that important?

56. NARROW AND FOCUSED

57. NARROW AND FOCUSED “How has the climate of Australia changed since A.D. 1000?” OK

58. NARROW AND FOCUSED “How has the climate of Australia changed since A.D. 1000?” OK “Was Western Austria drier during the Medieval Period, compared to today?” Better

59. Course schedule (current) October 27, 2010 The human dimension of past climate change November 3, 2010 Megadrought II / Natural hazards November 10, 2010 Isotope paleoclimatology November 17, 2010 Climate forcings November 24, 2010 Climate models December 1, 2010 Regional climate history I December 8, 2010 Regional climate history II December 15, 2010 No class - Fall meeting, American Geophysical Union

60. OPTIONS Presentations ➜ Feedback ➜ Papers OR Papers ➜ Feedback ➜ Presentations

61. By November 3 [Tentative] list of 10 articles related to your region and time period.

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