broken hockey sticks, 1500 year cycles, and ocean cooling dr. craig loehle ncasi principal scientist...

Broken Hockey Sticks, 1500 Year Cycles, and Ocean Cooling

Dr. Craig LoehleNCASI Principal Scientist

552 S Washington St., Ste. 224Naperville, Illinois 60540

The Broken Hockey Stick

• Fundamental assumptions of tree ring reconstruction are untested

• In fact, they are violated• Ms published online in Climatic Change,

Sept. 08• “A Mathematical Analysis of the Divergence

Problem in Dendroclimatology”

Climate Reconstruction(based largely on tree ring data)

How is it Done?

• Assume linear model ring vs. temperature• Fit to temperature histories, 20th Century• Inverse function for past temperature from

ring width / density

Signs of Trouble

• Widespread observations of divergence– good fit up to 1960– more warming than predicted by tree rings after

1960– Explanations are speculative

• Individual trees– may not respond to temperature– may grow worse when warmer

• (PPT limits)

IF Linear Response, Perfect Fit

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

0 200 400 600 800 1000

Years

Tem

pera

ture

0.00

0.10

0.20

0.30

0.40

0 200 400 600 800 1000

Years

Rin

g W

idth

IF Nonlinear Response, Get Truncation (inversion)

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

-2 0 2 4

Temperature

Rin

g W

idth

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

0 200 400 600 800 1000

Years

Tem

pera

ture

Peaks become troughs!

IF Ramp Response (no PPT Limitation),Get Truncation

0.20

0.25

0.30

0.0 0.5 1.0 1.5 2.0

Temperature

Rin

g W

idth

-2.5

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

0 200 400 600 800 1000

Years

Tem

pera

ture

Ramp results from species maximum growth rate

Conclusions

• Linear growth response invalid• Nonlinear growth explains divergence• Consequence

– can’t guarantee detection of temperatures warmer than calibration period

• Flattens out timeseries; reduces mean, range, and maximum• Can’t evaluate MWP or how unusual recent decades are from

linear reconstructions• Can’t use nonlinear model because gives nonunique inverse

model

The 1500-Year Climate Cycle

• Dansgaard-Oschger events in ice core data• About 1500 years apart• Cause: solar or ocean oscillator (multi-state

system)• Did they continue?

Greenland Data AnalysisUpdated GICC05 ice core chronology

Years BP (Yr 0 = 2000 AD)

δ18O

Greenland Data AnalysisBest-fit model for 30,000 to 37,000 BP

(R2 = 0.36, period = 1486 yrs)

Years BP (Yr 0 = 2000 AD)

δ18O

(val

ues

cent

ered

for b

etter

esti

mati

on o

f cyc

les)

Greenland Data AnalysisBest-fit model for 40,000 to 46,000 BP

(R2 = 0.30, period = 1598 yrs)

Years BP (Yr 0 = 2000 AD)

δ18O

(val

ues

cent

ered

for b

etter

esti

mati

on o

f cyc

les)

Greenland Data AnalysisBest-fit model for the Holocene to 8000 BP

(R2 = 0.45, period = 1434 yrs)

Years BP (Yr 0 = 2000 AD)

δ18O

(val

ues

cent

ered

for b

etter

esti

mati

on o

f cyc

les)

Best-fit Model 1681- and 1470-Year CyclesCompared to Loehle Reconstruction (R2 = 0.68, 0.65 respectively)

(confidence intervals not shown)

Years BP (Yr 0 = 2000 AD)

Anom

aly

(°C)

1470-yr cycle

1681-yrcycle

Best-fit Model to Moberg Low-Frequency Data (1152-yr cycle, R2 = 0.69)

and Fit to 1470-yr cycle (R2 = 0.54)(confidence intervals not shown)

Years BP (Yr 0 = 2000 AD)

Anom

aly

(°C)

1470-yr cycle1152-yr cycle

Best-fit Model to North Iceland Sea Surface Temperature(1552-yr cycle, R2 = 0.20)

Data shown after linear cooling trend removal

Years BP (Yr 0 = 2000 AD)

Anom

aly

(°C)

Oxygen Isotope Data from Central Alps, past 9000 yrsBest-fit models for 2004 AD to 3500 BP and 6500 BP to 8996 BP

(1479-yr cycle, R2 = 0.27, peak-to-trough amplitude 0.33°C)

Years BP (Yr 0 = 2000 AD)

-del

ta O

-18

(%)

Temperature inferred from Japanese CedarBest-free-form-fit (1089-yr cycle, R2 = 0.28); Best-fit when

forced with 1470-yr cycle looks similar (R2 = 0.22)

Years BP (Yr 0 = 2000 AD)

Anom

aly

(°C)

1089-yr cycle

1470-yr cycle

Conclusions

• Mean period 1524 yr vs. 1470 yr hypothetical (3.7% off)

• Models, data strongly agree on timing of MWP, LIA

• Supports role for this cycle in recent warming

Ocean Temperatures:Recent Trends

• ARGOS float data• To 700 m depth• 4.5 years data• Global coverage

Ocean heat content

Calendar Year

Oce

an H

eat C

onte

nt (x

1022

J)

Ocean heat content smoothed with a 1-2-1 filterand overlaid with a best-fit linear plus sinusoidal

(seasonal) model (R2 = 0.85)

Calendar Year

Oce

an H

eat C

onte

nt (x

1022

J)

Ocean heat content smoothed with a 1-2-1 filterand overlaid with linear trend portion of best-fit

model (slope = -0.35 x 1022 J/yr)

Calendar Year

Oce

an H

eat C

onte

nt (x

1022

J)

Recent Temperature Downturn Evident in Hadley Data

Conclusions

• Cooling trend over past 4.5 years matches satellite, surface data

• Rate of cooling similar to rate of warming before 2003