There is another hockey stick graph in the news right now. This one is from tree ring data. The idea is to show a sudden and recent rise in global temperatures in recent years.
A basic tenet of science is that unusual outcomes require unusual evidence. If a graph shows data going along pretty steady for hundreds of years and then takes a quick jump, something unusual is being noted. Before any conclusions are drawn, unusual evidence must be acquired to support them.
The search for unusual evidence starts with the data, the collection, and the measurements. Then the analysis methods need to be examined for any errors. Issues of precision and accuracy need to be addressed. This level of examination is where most of these climate change ‘hockey stick’ graphs suffer. In this case, it appears that the tree ring data was selected so that anomalous data was provided more weight than would be normally indicated by statistical evaluations.
Even if the first level examination did not find any problems, an unusual outcome is still suspect unless other paths to the same conclusion can be found. One of these paths is that of mechanism. The caveat here is the quality of that mechanism as using an hypothesis not well proven (such as anthropogenic global warming) is not as confirming as a more fundamental mechanism based on, for instance, widely established and used physical theories.
Another path for establishing unusual outcomes is a parallel data path, one that comes to the same destination. Global warming often suffers here in that the scale of actual changes in temperature are often quite at odds with the massive changes cited in such things as tree rings, glaciation, or severe weather statistics.
When there are ideologic or political belief systems behind a conclusion, bias can be a problem and that leads to stories such as The Sordid Story Of A Global (Warming) Con.
We are being asked to fork over trillions of dollars, cripple our economy and lose millions of jobs over the global warming scare. We have been told the Earth is doomed if we do not act. But the data shows that this is not the case. It is long past time the truth is found and real scientists debate using the scientific method as the basis of that debate.
It is up to all of us to apply appropriate skepticism to claims made about pending doom and disaster no matter if the subject is the natural sciences or basic policy issues. That means we all need to match the actual evidence against the extremity of the claims.