Broken Hockey Sticks, 1500 Year Cycles, and Ocean Cooling Dr. Craig Loehle NCASI Principal Scientist 552 S Washington St., Ste. 224 Naperville, 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

IF Nonlinear Response, Get Truncation (inversion) Peaks become troughs!

IF Ramp Response (no PPT Limitation),Get Truncation 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 Analysis Updated GICC05 ice core chronology Years BP (Yr 0 = 2000 AD) δ 18 O

Greenland Data Analysis Best-fit model for 30,000 to 37,000 BP (R 2 = 0.36, period = 1486 yrs) Years BP (Yr 0 = 2000 AD) δ 18 O (values centered for better estimation of cycles)

Greenland Data Analysis Best-fit model for 40,000 to 46,000 BP (R 2 = 0.30, period = 1598 yrs) Years BP (Yr 0 = 2000 AD) δ 18 O (values centered for better estimation of cycles)

Greenland Data Analysis Best-fit model for the Holocene to 8000 BP (R 2 = 0.45, period = 1434 yrs) Years BP (Yr 0 = 2000 AD) δ 18 O (values centered for better estimation of cycles)

Best-fit Model and 1470-Year Cycles Compared to Loehle Reconstruction (R 2 = 0.68, 0.65 respectively) (confidence intervals not shown) Years BP (Yr 0 = 2000 AD) Anomaly (°C) 1470-yr cycle 1681-yr cycle

Best-fit Model to Moberg Low-Frequency Data (1152-yr cycle, R 2 = 0.69) a nd Fit to 1470-yr cycle (R 2 = 0.54) (confidence intervals not shown) Years BP (Yr 0 = 2000 AD) Anomaly (°C) 1470-yr cycle 1152-yr cycle

Best-fit Model to North Iceland Sea Surface Temperature (1552-yr cycle, R 2 = 0.20) Data shown after linear cooling trend removal Years BP (Yr 0 = 2000 AD) Anomaly (°C)

Oxygen Isotope Data from Central Alps, past 9000 yrs Best-fit models for 2004 AD to 3500 BP and 6500 BP to 8996 BP (1479-yr cycle, R 2 = 0.27, peak-to-trough amplitude 0.33°C) Years BP (Yr 0 = 2000 AD) -delta O-18 (%)

Temperature inferred from Japanese Cedar Best-free-form-fit (1089-yr cycle, R 2 = 0.28); Best-fit when forced with 1470-yr cycle looks similar (R 2 = 0.22) Years BP (Yr 0 = 2000 AD) Anomaly (°C) 1089-yr cycle 1470-yr cycle

Conclusions Mean period 1524 yr vs 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 Ocean Heat Content (x J)

Ocean heat content smoothed with a filter and overlaid with a best-fit linear plus sinusoidal (seasonal) model (R 2 = 0.85) Calendar Year Ocean Heat Content (x J)

Ocean heat content smoothed with a filter and overlaid with linear trend portion of best-fit model (slope = x J/yr) Calendar Year Ocean Heat Content (x 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