The Hockey Stick ModelThe Hockey Stick Model

Daniela Domeisen, Josh Gellers, and Heather RavenDaniela Domeisen, Josh Gellers, and Heather RavenW4400W4400

December 5, 2006December 5, 2006

The Hockey StickThe Hockey Stickfrom the 2001 IPCC Reportfrom the 2001 IPCC Report

Consensus of the 2001 IPCC Consensus of the 2001 IPCC ReportReport

Global average temperature has been Global average temperature has been rising by 0.6 +/- 0.2 °C until 2001 rising by 0.6 +/- 0.2 °C until 2001 compared to 30-year mean (0.17°C per compared to 30-year mean (0.17°C per decade during the last 30 years)decade during the last 30 years)

Most of the warming during the past 50 Most of the warming during the past 50 years attributed to humans: emission of years attributed to humans: emission of COCO22, CH, CH44 etc. etc.

Earth will be warming by 1.4°C to 5.8°C by Earth will be warming by 1.4°C to 5.8°C by the end of the 21st centurythe end of the 21st century– depends on future development of emissionsdepends on future development of emissions

Hockey Stick: Affirmative Hockey Stick: Affirmative ViewView

Validity Claims OverblownValidity Claims Overblown- Modest title- Modest title- Recognition of proxy limitations- Recognition of proxy limitations

Scientific ConsensusScientific Consensus- Principle endorsement of NAS- Principle endorsement of NAS

Conclusion: Conclusion: Uncertainties are stated Uncertainties are stated and the model is undergoing continuous and the model is undergoing continuous revision. revision. The Hockey Stick model does provide The Hockey Stick model does provide an adequate resource for understanding an adequate resource for understanding the range of warming we may face in the range of warming we may face in the future.the future.

The “Hockey Stick”!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…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 900-1600 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…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…Use the Model with Care…

Take Home PointsTake Home Points

Hockey stick provides an adequate Hockey stick provides an adequate resource for understanding the range resource for understanding the range of warming we may face in the future.of warming we may face in the future.

Model indicates that we are currently Model indicates that we are currently experiencing the fastest rise in experiencing the fastest rise in temperature in the past millennium temperature in the past millennium

The model is always improving: The model is always improving: question the pros and cons of the question the pros and cons of the Hockey Stick Model as it changesHockey Stick Model as it changes