GEOG3839.13, Global temperature reconstructions

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This document discusses the use of tree ring data to reconstruct past climate conditions. It describes principal component analysis (PCA) which is used to group tree ring data into components representing different climate influences. Linear regression models are then used to relate the principal components to temperature. The document discusses several global temperature reconstructions produced using long tree ring records and how they indicate periods of warmth like the Medieval Warm Period and cooler periods like the Little Ice Age. It also describes the "divergence problem" where some tree ring data no longer correlate as strongly with modern temperatures.

Education

a.k.a. Empirical Orthogonal Function analysis

PRINCIPLE COMPONENTS
ANALYSIS

PC1 (group 1)

PC3 (group 3)

PC2 (group 2)

most sites

Source: St. George and Luckman, 2001

most sites

farthest
north

Source: St. George and Luckman, 2001

most sites

farthest
north

unusual
site

Source: St. George and Luckman, 2001

Tjj = 0.23PC1 + -0.23PC3t+1
+ 0.16PC2t+1 + -0.09PC1t+1
+ -0.46

“ Tree-ring-derived records have played a prominent role
in a empts to establish how climate has varied
”
in the recent past.
— Jones et al., The Holocene, 2009

G L O B A L T E M P E R AT U R E R E C O N S T R U C T I O N S

Photograph: Marianna

Long, temperature-sensitive tree-ring records have been used to estimate
average temperatures across the entire hemisphere or globe.

Source: Esper et al., Science, 2002

“ ...this study provides evidence for intervals of
signiﬁcant warmth in the [Northern Hemisphere]
within the so-called Medieval Warm Period and for
signiﬁcantly colder intervals during the so-called
”
Li le Ice Age period.
— Osborne and Briﬀa, 2006

Source: Intergovernmental Panel on Climate Change, 2007

“ Tree-rings also allow the reconstruction of large-scale
regional or global temperature pa erns deﬁned by
large networks of chronologies.
”— Brian Luckman

Source: Briﬀa et al., Global and Planetary Change, 2004

h p://www.cru.uea.ac.uk/cru/people/briﬀa/temmaps/

1883
“THE LOUDEST SOUND IN MODERN HISTORY”

Mount Tambora, Indonesia Its eruption in 1815 was the most explosive since AD 180

Source: Briﬀa et al., Global and Biological Change, 2004

“Trees are not thermometers or rain gagues.” Keith Briﬀa and colleagues

the ‘divergence problem’ is deﬁned as the tendency for
tree growth at some previously temperature-limited
northern sites to demonstrate a weakening in mean
temperature response in recent decades.

Source: D’Arrigo et al., 2008

“ It is important to stress that not all high-latitude regions
display this apparent decoupling between observed and
dendroclimatically estimated temperatures.
”
— Jones et al., The Holocene, 2009

SURFACE TEMPERATURE
RECONSTRUCTIONS
FOR T H E LAS T 2 , 00 0 Y E A R S

NATIONAL RESEARCH COUNCIL
OF THE NATIONAL ACADEMIES

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This document summarizes an interdisciplinary tree-ring research conference. It discusses the need for new theory in dendroclimatology, presentations on temperature and river flow reconstructions from tree rings, and principles of tree ring research site selection and replication. It also questions how to evaluate rare signals in tree growth and climate relationships and where remote teleconnections may be most evident in tree rings.

The societal value of historical and paleoflood research in Manitoba, Canada

Scott St. George

1) Shared knowledge of past natural disasters has a major impact on preparation for future hazards. The document discusses the historical floods along the Red River in Manitoba, Canada. 2) Winnipeg built a large flood diversion channel in the 1960s after experiencing major floods, including in 1826 and 1950, to protect the city from future flooding of the Red River. 3) American communities like Grand Forks and Fargo were more vulnerable to Red River flooding until recently because they did not have the same long historical memory of floods that informed Winnipeg's early investment in flood protection infrastructure.

Solar ghosts: Weighing the evidence for sunspot cycles in fossil trees

Scott St. George

In their study of tree rings from the Chemnitz Fossil Forest (Germany), Luthardt and Rößler (2017) claim to identify a regular near-11-yr cyclicity in growth, and present that pattern as evidence of the influence of the Schwabe solar cycle (Usokin and Mursula, 2003) on climate and forest productivity during the early Permian. If correctly interpreted, these fossil tree rings would indicate the sunspot cycle was the dominant influence on interannual variability in Earth’s climate during this period and that it has been a consistent aspect of our Sun’s behavior for at least the past 300 m.y. We argue the fossil tree-ring record from Chemnitz does not constitute reliable evidence of solar activity during the Permian because the individual tree-ring sequences are not correctly aligned (dendrochronologically dated) and, as a result, the mean ring-width composite is not a meaningful estimate of year-to-year variations in tree growth in this ancient forest.

Long droughts: Using natural climate archives to gage the risks of future “me...

Scott St. George

In the Biblical story of Joseph, following seven years of abundance, the Kingdom of Egypt was confronted by seven years of drought and famine. In the parlance of modern climate science, intervals with several consecutive extremely dry years are described as ‘“megadroughts”. In this short talk, I’ll describe how climate scientists combine clues from natural weather archives (including corals, tree rings, lake sediments, and many other sources) to reveal the history of ancient megadroughts across our planet. And I’ll highlight new research that combines these surrogate drought records with simulations from state-of-the-art climate models to help us better anticipate the risks of unusually persistent droughts during the coming century.

Expecting the unexpected: The relevance of old floods to modern hydrology

Scott St. George

This document discusses the importance of understanding past floods to properly assess modern flood risks. It provides examples of paleoflood research along rivers like the Red River of the North, which uncovered major floods in 1826 and around 700 years ago that exceeded any floods measured by modern instrumentation. Understanding a river's full history through both recorded data and geological evidence of past floods is essential for floodplain management, development planning, and infrastructure design to mitigate future flood risks.

What to expect when you’re expecting decadal variability in hydroclimatic pro...

Scott St. George

Decadal variability in tree rings

Scott St. George

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.

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GEOG3839.13, Global temperature reconstructions

1. Source: St. George and Luckman, 2001

2. Source: St. George and Luckman, 2001

3. Source: St. George and Luckman, 2001

4. a.k.a. Empirical Orthogonal Function analysis PRINCIPLE COMPONENTS ANALYSIS

7. PC1 (group 1) PC3 (group 3) PC2 (group 2)

8. Source: St. George and Luckman, 2001

9. Source: St. George and Luckman, 2001

10. most sites Source: St. George and Luckman, 2001

11. most sites farthest north Source: St. George and Luckman, 2001

12. most sites farthest north unusual site Source: St. George and Luckman, 2001

13. LINEAR REGRESSION

14. yt = axt + b + ε

15. Tjj = 0.23PC1 + -0.23PC3t+1 + 0.16PC2t+1 + -0.09PC1t+1 + -0.46

16. Source: St. George and Luckman, 2001

17. “ Tree-ring-derived records have played a prominent role in a empts to establish how climate has varied ” in the recent past. — Jones et al., The Holocene, 2009

18. G L O B A L T E M P E R AT U R E R E C O N S T R U C T I O N S Photograph: Marianna

19. Long, temperature-sensitive tree-ring records have been used to estimate average temperatures across the entire hemisphere or globe. Source: Esper et al., Science, 2002

20. Source: Esper et al., Science, 2002

21. Source: D’Arrigo et al., 2006

22. Source: D’Arrigo et al., 2006

23. Source: Osborne and Briﬀa, 2006

24. “ ...this study provides evidence for intervals of significant warmth in the [Northern Hemisphere] within the so-called Medieval Warm Period and for significantly colder intervals during the so-called ” Li le Ice Age period. — Osborne and Briffa, 2006

25. LINEAR REGRESSION

26. Source: Intergovernmental Panel on Climate Change, 2007

27. Photograph: Mark Anbinder

28. “ Tree-rings also allow the reconstruction of large-scale regional or global temperature pa erns deﬁned by large networks of chronologies. ”— Brian Luckman

29. Source: Briﬀa et al., Global and Planetary Change, 2004

30. h p://www.cru.uea.ac.uk/cru/people/briﬀa/temmaps/

31. 1883 “THE LOUDEST SOUND IN MODERN HISTORY”

32. Krakatau, Indonesia 1883

33. h p://www.cru.uea.ac.uk/cru/people/briﬀa/temmaps/

34. 1816 THE “YEAR WITHOUT A SUMMER”

35. Mount Tambora, Indonesia Its eruption in 1815 was the most explosive since AD 180

36. Source: Briﬀa et al., Global and Biological Change, 2004

37. h p://www.cru.uea.ac.uk/cru/people/briﬀa/temmaps/

38. Huaynaputina Peru

39. “Trees are not thermometers or rain gagues.” Keith Briﬀa and colleagues

40. THE DIVERGENCE PROBLEM

41. the ‘divergence problem’ is deﬁned as the tendency for tree growth at some previously temperature-limited northern sites to demonstrate a weakening in mean temperature response in recent decades. Source: D’Arrigo et al., 2008

42. Source: D’Arrigo et al., 2008

43. “ It is important to stress that not all high-latitude regions display this apparent decoupling between observed and dendroclimatically estimated temperatures. ” — Jones et al., The Holocene, 2009

44. Source: Briﬀa et al., Global and Biological Change, 2004

45. Source: D’Arrigo et al., 2008

46.

47. SURFACE TEMPERATURE RECONSTRUCTIONS FOR T H E LAS T 2 , 00 0 Y E A R S NATIONAL RESEARCH COUNCIL OF THE NATIONAL ACADEMIES

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