Worse than the lack of data is that the statistical method used to produce the "hockey-stick" is flawed. It turns out that no matter the input data, the result turns out to look like the "hockey-stick."
From this link:
Global Warming Bombshell: Climate change turns out to be an artifact of poor mathematics.
Now comes the real shocker. This improper normalization procedure tends to emphasize any data that do have the hockey stick shape, and to suppress all data that do not. To demonstrate this effect, McIntyre and McKitrick created some meaningless test data that had, on average, no trends. This method of generating random data is called Monte Carlo analysis, after the famous casino, and it is widely used in statistical analysis to test procedures. When McIntyre and McKitrick fed these random data into the Mann procedure, out popped a hockey stick shape!
The net result: the principal component will have a hockey stick shape even if most of the data do not.
I read somewhere that McIntyre and McKitrick got a “hockey stick graph” from the Mann algorithm, after feeding numbers out of the telephone book into the computer!