DendroclimatologyDendroclimatology

Tree-ring data are just one of type of many proxies of past Tree-ring data are just one of type of many proxies of past climate.climate.

Tree-ring data are extremely valuable for evaluating Tree-ring data are extremely valuable for evaluating past changes in temperature, for example. Why is past past changes in temperature, for example. Why is past information needed?information needed?

To better understand trends in future climate, whether To better understand trends in future climate, whether human-forced or natural.human-forced or natural.

Trends in reconstructed Northern Hemisphere Trends in reconstructed Northern Hemisphere temperatures.temperatures.

Trends in reconstructed precipitation for the American Trends in reconstructed precipitation for the American Southwest.Southwest.

Recent research emphasizes relationships between trends Recent research emphasizes relationships between trends in tree-ring data and long-term climate oscillations.in tree-ring data and long-term climate oscillations.

Which climate variables can we analyze from the Which climate variables can we analyze from the tree-ring record?tree-ring record?

Precipitation:Precipitation:

• MonthlyMonthly

• SeasonalSeasonal

• Water YearWater Year

Temperature:Temperature:

• MonthlyMonthly

• SeasonalSeasonal

Palmer Drought Severity Index (PDSI)Palmer Drought Severity Index (PDSI)

• MonthlyMonthly

• SeasonalSeasonal

Palmer Hydrological Drought Index (PHDI)Palmer Hydrological Drought Index (PHDI)

• MonthlyMonthly

• SeasonalSeasonal

Where do these come from?Where do these come from?

• National Climatic Data CenterNational Climatic Data Center

• FTP site for monthly divisional data:FTP site for monthly divisional data:ftp://ftp.ncdc.noaa.gov/pub/data/cirs/ftp://ftp.ncdc.noaa.gov/pub/data/cirs/

Climate Data Row Header:Climate Data Row Header:

• Example: 0101011895Example: 0101011895

01010118950101011895State code

Division number

Climate Type

Year

Climate Data Types:Climate Data Types:

01 = Precipitation01 = Precipitation 07 = Z-Index07 = Z-Index 75 = 75 = SP09SP0902 = Temperature02 = Temperature 08 = PMDI08 = PMDI 76 = SP1276 = SP1203 = Heating Degree Days03 = Heating Degree Days 71 = SP0171 = SP01 77 = 77 = SP24SP2404 = Cooling Degree Days04 = Cooling Degree Days 72 = SP0272 = SP0205 = PDSI05 = PDSI 73 = SP0373 = SP0306 = PHDI06 = PHDI 74 = SP0674 = SP06

• 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

Normal ocean temperatures

The big slosh of warm ocean temps to the eastern Pacific.

Warm ocean temps where they should be.

What changes in climate can be expected?

Much colder temps now in eastern Pacific.

Different El Niño-Southern Oscillation Indices based on region of the Pacific Ocean:

The Niño 3 Region is bounded by 90°W-150°W and 5°S- 5°N. The Niño 3.4 Region is bounded by 120°W-170°W and 5°S- 5°N.

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.

Where do the data for indices come from?Where do the data for indices come from?

• NOAA’s Earth System Research Laboratory, NOAA’s Earth System Research Laboratory, Physical Sciences DivisionPhysical Sciences Division

• http://www.esrl.noaa.gov/psd/data/http://www.esrl.noaa.gov/psd/data/climateindices/climateindices/

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…

Pacific Decadal Oscillation

Warm phase PDO

Pacific Decadal Oscillation

Cool phase PDO

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/PDO/PDO_cs.htm

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.

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

Pacific Decadal Oscillation

PDO reconstructed from tree-ring data.PDO reconstructed from tree-ring data.

Pacific Decadal Oscillation

PDO reconstructed from tree-ring data.PDO reconstructed from tree-ring data.

Pacific Decadal Oscillation

PDO-SOI reconstructed from tree-ring data.PDO-SOI reconstructed from tree-ring data.

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.

El Malpais National Monument climate reconstructionEl Malpais National Monument climate reconstruction

“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 1717–1923, ” – Paul Knapp, Henri Grissino-Mayer, and Peter Soule, 2002, Quaternary Research).

El Malpais trees recording PDO? What the… ?El Malpais trees recording PDO? What the… ?

North Atlantic OscillationNorth Atlantic Oscillation

• Large scale seesaw in Large scale seesaw in atmospheric mass atmospheric mass between the subtropical between the subtropical high and the polar lowhigh and the polar low

• Dominant mode of Dominant mode of winter winter climate variabilityclimate variability in the in the North Atlantic region North Atlantic region ranging from central ranging from central North America to Europe North America to Europe

• Again, note where shifts Again, note where shifts occurred…occurred…

North Atlantic OscillationNorth Atlantic Oscillation

North Atlantic Oscillation: Positive PhaseNorth Atlantic Oscillation: Positive Phase

Strong Atlantic pressure gradientStrong Atlantic pressure gradient

North Atlantic Oscillation: Negative PhaseNorth Atlantic Oscillation: Negative Phase

Weak Atlantic Pressure GradientWeak Atlantic Pressure Gradient

• Positive Phase:Positive Phase:

• More frequent and stronger winter storms More frequent and stronger winter storms crossing Atlantic on a more northerly trackcrossing Atlantic on a more northerly track

• Results in warm and wet winters in Europe and in Results in warm and wet winters in Europe and in cold and dry winters in northern Canada and cold and dry winters in northern Canada and GreenlandGreenland

• Eastern US experiences mild and wet winter Eastern US experiences mild and wet winter conditionsconditions

• Negative Phase:Negative Phase:

• Fewer and weaker storms on a more southerly Fewer and weaker storms on a more southerly tracktrack

• Brings moist air into the Mediterranean and cold Brings moist air into the Mediterranean and cold air to northern Europeair to northern Europe

• Eastern US experiences more cold air outbreaks Eastern US experiences more cold air outbreaks and snowy weather conditionsand snowy weather conditions

North Atlantic OscillationNorth Atlantic Oscillation

Cook, D’Arrigo, 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 < 0.05, ** p < 0.01, *** p < 0.001).

Figure 7. Correlation coefficients between the shortleaf pine standard chronology and PDO, NAO, and SSTA (* p < 0.05, ** p < 0.01, *** p < 0.001).

• A multidecadal (20-40 yrs) pattern of North Atlantic sea A multidecadal (20-40 yrs) pattern of North Atlantic sea surface temperature variability between the equator and surface temperature variability between the equator and Greenland.Greenland.

• When the AMO is positive (warm Atlantic), rainfall is lower When the AMO is positive (warm Atlantic), rainfall is lower than average over most of the United States.than average over most of the United States.

• During warm phases of the AMO, the numbers of tropical During warm phases of the AMO, the numbers of tropical storms that mature into severe hurricanes is much greater storms that mature into severe hurricanes is much greater than during cool phases.than during cool phases.

• Since the mid-1990s, we have been in a warm phase.Since the mid-1990s, we have been in a warm phase.

• Appears related to the past occurrence of major droughts in Appears related to the past occurrence of major droughts in the Midwest and the Southwest. Positive AMO = more the Midwest and the Southwest. Positive AMO = more frequent and severe droughts, and vice-versa.frequent and severe droughts, and vice-versa.

• Two of the most severe droughts of the 20th century Two of the most severe droughts of the 20th century occurred during the positive AMO between 1925 and 1965: occurred during the positive AMO between 1925 and 1965: The Dust Bowl of the 1930s and the 1950s drought.The Dust Bowl of the 1930s and the 1950s drought.

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

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

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation• 52% of drought variability in the lower U.S. can be 52% of drought variability in the lower U.S. can be

attributed to the AMO and PDO!attributed to the AMO and PDO!

• ““Much of the long-term predictability of drought Much of the long-term predictability of drought frequency may reside in the multidecadal behavior of the frequency may reside in the multidecadal behavior of the North Atlantic Ocean.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 87.5°S to 87.5°N and 2.5°E to 357.5°E.

• 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.

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

Atlantic Multidecadal OscillationAtlantic Multidecadal OscillationAccumulated Cyclone Energy by Year

Atlantic Multidecadal OscillationAtlantic Multidecadal Oscillation

AMO reconstructed from tree-ring data.AMO reconstructed from tree-ring data.

• “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: 69–76.

One final note on oscillations:One final note on oscillations: