Global warming bombshell - hockey-stick plot used modified data

But now a shock: Canadian scientists Stephen McIntyre and Ross McKitrick have uncovered a fundamental mathematical flaw in the computer program that was used to produce the hockey-stick.

In his original publications of the stick, Mann purported to use a standard method known as principal component analysis, or PCA, to find the dominant features in a set of more than 70 different climate records.

But it wasn't so. McIntyre and McKitrick obtained part of the program that Mann used, and they found serious problems. Not only does the program not do conventional PCA, but it handles data normalisation in a way that can only be described as mistaken.

Now comes the real shocker. This improper normalisation procedure tends to emphasise any data that do have the hockey-stick shape, and to suppress all data that do not.