Dendroclimatology

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Dendroclimatology
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Tree-ring data are just one of type of many
proxies of past climate.
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Tree-ring data are extremely valuable for
evaluating past changes in temperature, for
example. Why is past information needed?
To better understand trends in future climate,
whether human-forced or natural.
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Trends in reconstructed Northern Hemisphere
temperatures.
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Trends in reconstructed precipitation for the
American Southwest.
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Recent research emphasizes relationships between
trends in tree-ring data and long-term climate
oscillations.
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• Which climate variables can we analyze from the
  tree-ring record?
• Precipitation
• Monthly
• Seasonal
• Water Year
• Temperature
• Monthly
• Seasonal

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• Palmer Drought Severity Index (PDSI)
• Monthly
• Seasonal
• Palmer Hydrological Drought Index (PHDI)
• Monthly
• Seasonal
• Where do these come from?
• National Climatic Data Center
• FTP site for monthly divisional
  dataftp//ftp.ncdc.noaa.gov/pub/data/cirs/

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• Climate Data Row Header
• Example 0101011895
• 0101011895

State code
Division number
Climate Type
Year
Climate Data Types 01 Precipitation 07
Z-Index 75 SP0902 Temperature 08
PMDI 76 SP1203 Heating Degree Days 71
SP01 77 SP2404 Cooling Degree Days 72
SP0205 PDSI 73 SP0306 PHDI 74 SP06
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• El Niño-Southern Oscillation
• Changes in pressure patterns, wind patterns, and
  oceanic circulation
• Mainly concentrated in the Pacific Ocean
• Measured using Southern Oscillation Index
• Differences in pressure observed in Tahiti and
  Darwin, Australia
• SOI 10 x ((average Tahiti MSLP for month) -
  (average Darwin MSLP for month) - long term
  average difference for month) / long term
  standard deviation of difference for month)
• Combined to form ENSO phenomenon
• Brings drastic changes in weather to affected
  areas

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Normal ocean temperatures
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The big slosh of warm ocean temps to the eastern
Pacific.
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Warm ocean temps where they should be.
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• Different El Niño-Southern Oscillation Indices
  based on region of the Pacific Ocean
• The Niño 3 Region is bounded by 90W-150W and
  5S- 5N. The Niño 3.4 Region is bounded by
  120W-170W and 5S- 5N.

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• The NINO 3.4 Index is the departure in monthly
  sea surface temperature from its long-term mean
  averaged over the NINO 3.4 region.
• In this method, an El Niño or La Niña event is
  identified if the 5-month running-average of the
  NINO 3.4 Index exceeds 0.4 C (for El Niño -0.4
  C for La Niña) for at least 6 consecutive
  months.

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• Where do the data for indices come from?
• NOAAs Earth System Research Laboratory, Physical
  Sciences Division
• http//www.esrl.noaa.gov/psd/data/climateindices/

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Pacific Decadal Oscillation

• Discovered late 1990s by salmon fisheries experts
• Long-lived El Niño-like pattern of Pacific
  climate variability
• Operates on longer 20 to 30 year periods
• Note when regime shifts occurred

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Pacific Decadal Oscillation
Warm phase PDO
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Pacific Decadal Oscillation
Cool phase PDO
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Climate during positive (warm) PDO phase
Mantua, N.J. 1999. The Pacific Decadal
Oscillation and climate forecasting for North
America. In Maryam Golnaraghi (ed), Climate Risk
Solutions 1(1) 10-13.
http//www.atmos.washington.edu/mantua/REPORTS/PD
O/PDO_cs.htm
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Climate during positive (warm) PDO phase

• Mechanisms
• Warm ocean waters in the eastern Pacific.
• These give rise to development of low pressure
  troughs.
• Jet stream allowed to track further south.
• Brings moisture to southern tier of U.S.,
  especially southwestern U.S.
• Causes dry, warm (drought) conditions in
  northwestern U.S.
• Note polar relationship between the two western
  regions.
• Fire weather enhanced in northwestern U.S. during
  PDO phase (fires tended to occur during El Niño
  and positive PDO years.)
• Wet, cool weather in southwest rapid growth of
  fuels
• La Niña phase causes drying of fuels fire
  weather in southwest.

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Table 1 Summary of North American climate anomalies associated with extreme phases of the PDO (from Mantua 1999) Table 1 Summary of North American climate anomalies associated with extreme phases of the PDO (from Mantua 1999) Table 1 Summary of North American climate anomalies associated with extreme phases of the PDO (from Mantua 1999)
Climate Anomalies Warm Phase PDO Cool Phase PDO
Ocean surface temperatures in the northeastern and tropical Pacific Above average Below average
October-March northwestern North American air temperatures Above average Below average
October-March Southeastern US air temperatures Below average Above average
October-March southern US/Northern Mexico precipitation Above average Below average
October-March Northwestern North America and Great Lakes precipitation Below average Above average
Northwestern North American spring time snow pack Below average Above average
Winter and spring time flood risk in the Pacific Northwest Below average Above average
Implications for climate predictions
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Pacific Decadal Oscillation
PDO reconstructed from tree-ring data.
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Pacific Decadal Oscillation
PDO reconstructed from tree-ring data.
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Pacific Decadal Oscillation
PDO-SOI reconstructed from tree-ring data.
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Although PDO exhibits several patterns of
behavior, the most significant one seems to be in
regime shifts between "warm" and "cool" patterns
which last 20 to 30 years. 1750 PDO displays an
unusually strong oscillation. 1905 After a
strong swing, PDO changed to a warm phase. 1946
PDO changed to a cool phase. 1977 PDO changed to
a warm phase. 1998 PDO index showed several
years of cool values, but did not remain in that
pattern. 2008 The early stages of a cool phase
of the PDO Current PDO appears to be
tansitioning! During the 1900s, PDO regime shifts
were related to many different environmental
changes in the Pacific Ocean.
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El Malpais National Monument climate
reconstruction
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We also observed that CPYs became more numerous
during the 20th century (beginning with the
severe drought year of 1924) after a long absence
of severe regional drought years between 1717 and
1923. This relationship possibly suggests that
the influence of the PDO was nonexistent or
minimal during the period 17171923, Paul
Knapp, Henri Grissino-Mayer, and Peter Soule,
2002, Quaternary Research).
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El Malpais trees recording PDO? What the ?
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North Atlantic Oscillation

• Large scale seesaw in atmospheric mass between
  the subtropical high and the polar low
• Dominant mode of winter climate variability in
  the North Atlantic region ranging from central
  North America to Europe
• Again, note where shifts occurred

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North Atlantic Oscillation
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North Atlantic Oscillation Positive
Phase Strong Atlantic pressure gradient
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North Atlantic Oscillation Negative Phase Weak
Atlantic Pressure Gradient
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North Atlantic Oscillation

• Positive Phase
• More frequent and stronger winter storms crossing
  Atlantic on a more northerly track
• Results in warm and wet winters in Europe and in
  cold and dry winters in northern Canada and
  Greenland
• Eastern US experiences mild and wet winter
  conditions
• Negative Phase
• Fewer and weaker storms on a more southerly track
• Brings moist air into the Mediterranean and cold
  air to northern Europe
• Eastern US experiences more cold air outbreaks
  and snowy weather conditions

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Cook, DArrigo, and M. Mann, 2002. A
well-verified, multiproxy reconstruction of the
winter North Atlantic Oscillation Index since
A.D. 1400. Journal of Climate 15 1754-1764.
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Figure 2. Correlation coefficients between the
shortleaf pine standard chronology and
precipitation, temperature, and PDSI ( p lt 0.05,
p lt 0.01, p lt 0.001).
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Figure 7. Correlation coefficients between the
shortleaf pine standard chronology and PDO, NAO,
and SSTA ( p lt 0.05, p lt 0.01, p lt
0.001).
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Atlantic Multidecadal Oscillation

• A multidecadal (20-40 yrs) pattern of North
  Atlantic sea surface temperature variability
  between the equator and Greenland.
• When the AMO is positive (warm Atlantic),
  rainfall is lower than average over most of the
  United States.
• During warm phases of the AMO, the numbers of
  tropical storms that mature into severe
  hurricanes is much greater than during cool
  phases.
• Since the mid-1990s, we have been in a warm
  phase.
• Appears related to the past occurrence of major
  droughts in the Midwest and the Southwest.
  Positive AMO more frequent and severe droughts,
  and vice-versa.
• Two of the most severe droughts of the 20th
  century occurred during the positive AMO between
  1925 and 1965 The Dust Bowl of the 1930s and the
  1950s drought.

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Atlantic Multidecadal Oscillation
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Atlantic Multidecadal Oscillation
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Atlantic Multidecadal Oscillation

• Rainfall in central and south Florida becomes
  more plentiful during a warm phase AMO, and
  droughts and wildfires are more frequent in the
  cool phase.

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Atlantic Multidecadal Oscillation

• 52 of drought variability in the lower U.S. can
  be attributed to the AMO and PDO!

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Atlantic Multidecadal Oscillation

• Much of the long-term predictability of drought
  frequency may reside in the multidecadal behavior
  of the North Atlantic Ocean.
• G.J. McCabe, M.A. Palecki, and J.L. Betancourt,
  2004. Pacific and Atlantic Ocean influences on
  multidecadal drought frequency in the United
  States. Proceedings of the National Academy of
  Sciences 101(12) 4136-4141.
• The AMO time series is calculated from the Kaplan
  Extended SST data set (available from the Earth
  System Research Laboratory)
• 5 latitude x 5 longitude global grid, from
  87.5S to 87.5N and 2.5E to 357.5E.
• Kaplan, A., M. Cane, Y. Kushnir, A. Clement, M.
  Blumenthal, and B. Rajagopalan, 1998. Analyses of
  global sea surface temperature 1856-1991. Journal
  of Geophysical Research 103 18,567-18,589.

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Atlantic Multidecadal Oscillation
Accumulated Cyclone Energy by Year
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Atlantic Multidecadal Oscillation
AMO reconstructed from tree-ring data.
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One final note on oscillations

• Some feature of the atmosphere can always be
  found that will oscillate in accordance with your
  hypothesis.
• Shortly after its discovery the oscillation will
  disappear.
• Peter B. Wright, 1971. Quasi-biennial
  oscillations in the atmosphere. Weather 26
  6976.