Hockey Stick: A Controversial Climate Change Indicator

The 'Hockey Stick' graph, a reconstruction of global temperatures over the past millennium, featuring a sharp 20th-century rise that sparked intense debate in climate science.

The “Hockey Stick” graph refers to a reconstruction of global temperatures over the past 1,000 years that features a long, relatively flat handle indicating stable pre-industrial temperatures and a sharp, upward-tilting blade in the 20th century, which signifies recent global warming. This term gained prominence in the Intergovernmental Panel on Climate Change (IPCC) Third Assessment Report.

Historical Context

The graph was first introduced by Michael E. Mann and colleagues in a 1999 paper. It played a significant role in the 2001 IPCC Third Assessment Report, symbolizing the human impact on climate.

Key Events

• 1998-1999: Original publication of the hockey stick graph by Mann, Bradley, and Hughes.
• 2001: Inclusion in IPCC’s Third Assessment Report.
• 2003-2005: Criticism and scrutiny of the statistical methods used.
• 2006: North Report by the National Research Council supports but also critiques the graph.
• 2010: A. W. Montford’s book “The Hockey Stick Illusion” further challenges the graph’s validity.

Methodology

The graph was constructed using principal components analysis (PCA) of proxy data such as tree rings, ice cores, and coral reefs.

Mathematical Models

Principal Components Analysis (PCA)

PCA is a statistical procedure that uses orthogonal transformation to convert observations of possibly correlated variables into a set of values of linearly uncorrelated variables called principal components.

    graph LR
	    A(Data Collection) --> B(Proxy Data)
	    B --> C(PCA Application)
	    C --> D(Temperature Reconstruction)
	    D --> E(Hockey Stick Graph)

Importance and Applicability

• Climate Science: It highlighted the rapid increase in global temperatures, encouraging climate action.
• Policy Making: Used by policymakers to underscore the urgency of climate change mitigation.

Considerations

• Data Quality: Proxy data can have significant uncertainties.
• Statistical Techniques: PCA and other methodologies must be rigorously validated.
• Significance: Further studies have provided mixed evaluations of its accuracy.

Related Terms

• Climate Change: Long-term alteration of temperature and typical weather patterns in a place.
• Global Warming: The ongoing rise in global average temperature near Earth’s surface.

Comparisons

• Medieval Warm Period vs. Modern Warming: Unlike the smooth medieval period, the modern era shows a dramatic temperature increase.

Interesting Facts

• The “hockey stick” shape has become an iconic symbol in the climate change debate.

Inspirational Story

Michael E. Mann, despite facing significant personal and professional attacks, has remained an ardent advocate for climate science, emphasizing the importance of addressing global warming.

Famous Quotes

“Climate change is real. We are seeing devastating impacts in every corner of the globe.” - Michael E. Mann

Proverbs and Clichés

• “Where there’s smoke, there’s fire.” (Implying that the evidence, though debated, indicates a real problem)

Jargon and Slang

• Proxy Data: Indirect measurements that stand in for direct measurements (e.g., tree rings).
• PCA: Principal Components Analysis.

FAQs

What is the Hockey Stick graph?

A reconstruction of global temperatures over the past 1,000 years, showing a recent sharp increase.

Why is it called the 'Hockey Stick' graph?

Because it resembles the shape of a hockey stick, with a long handle and a sharp upward curve.

Has the Hockey Stick graph been discredited?

While it faced criticism, many aspects of its findings have been supported by subsequent research.

References

1. Mann, M. E., Bradley, R. S., & Hughes, M. K. (1999). Northern hemisphere temperatures during the past millennium: Inferences, uncertainties, and limitations. Geophysical Research Letters, 26(6), 759-762.
2. Intergovernmental Panel on Climate Change (IPCC). (2001). Climate Change 2001: The Scientific Basis.
3. Montford, A. W. (2010). The Hockey Stick Illusion: Climategate and the Corruption of Science.

Summary

The “Hockey Stick” graph is a pivotal yet controversial representation of climate change, illustrating a dramatic rise in global temperatures in recent centuries. Despite methodological criticisms, it has significantly influenced climate science and policy, highlighting the urgent need for climate action.