The Hockey Stick Model Daniela Domeisen, Josh Gellers, and Heather Raven W4400 December 5, 2006

The Hockey Stick from the 2001 IPCC Report

Consensus of the 2001 IPCC Report Global average temperature has been rising by 0.6 +/- 0.2 °C until 2001 compared to 30-year mean (0.17°C per decade during the last 30 years) Global average temperature has been rising by 0.6 +/- 0.2 °C until 2001 compared to 30-year mean (0.17°C per decade during the last 30 years) Most of the warming during the past 50 years attributed to humans: emission of CO 2, CH 4 etc. Most of the warming during the past 50 years attributed to humans: emission of CO 2, CH 4 etc. Earth will be warming by 1.4°C to 5.8°C by the end of the 21st century Earth will be warming by 1.4°C to 5.8°C by the end of the 21st century –depends on future development of emissions

Hockey Stick: Affirmative View Validity Claims Overblown Validity Claims Overblown - Modest title - Recognition of proxy limitations Scientific Consensus Scientific Consensus - Principle endorsement of NAS Conclusion: Uncertainties are stated and the model is undergoing continuous revision. The Hockey Stick model does provide an adequate resource for understanding the range of warming we may face in the future.

The “Hockey Stick”! Published by Mann, Bradley, Hughes (1998). Uses tree rings, ice cores, and coral to join historical data and thermometer readings into one temp projection.

Use the Model with Care… o Large errors in ‘blade’ of the graph o Some error bars span 2.5 °C (Scenario A1FI, IS92a) o Could put the estimate of temp departure, from the 1990 value, at only 1 °C instead of the exaggerated estimate at 5.7 °C o Substantial error in ‘stick’ of graph o Systematic uncertainties in climate records prior to 1600 o AD: Temp reconstructions only a 2 to 1 chance of being right (NAS committee) o Very little long-term info on SH and parts of the ocean (representative of ‘global’ warming?) o ‘Uncertainties prevent decisive conclusions’ for data collected prior to 1400 AD (Mann, Nature, 2006)

Use the Model with Care… o Uncertainties in statistical methods: o Based on insufficient data and flawed stat analysis (McKitrick and McIntyre, Wegman report) o Mann concludes that higher resolution data are needed before ‘more confident conclusions can be reached’ o With flaws in model corrected, curves in ‘stick’ reappear, recent temp changes no longer look extraordinary (Bob Tippee, Oil & Gas Journal; Jul 11, 2005)

Use the Model with Care…

Take Home Points Hockey stick provides an adequate resource for understanding the range of warming we may face in the future. Hockey stick provides an adequate resource for understanding the range of warming we may face in the future. Model indicates that we are currently experiencing the fastest rise in temperature in the past millennium Model indicates that we are currently experiencing the fastest rise in temperature in the past millennium The model is always improving: question the pros and cons of the Hockey Stick Model as it changes The model is always improving: question the pros and cons of the Hockey Stick Model as it changes