This remark has nothing to do with any "decline" in observed instrumental temperatures. The remark referred to a well-known observation, in a particular set of tree-ring data, that I had used in a figure to represent large-scale summer temperature changes over the last 600 years. The phrase 'hide the decline' was shorthand for providing a composite representation of long-term temperature changes made up of recent instrumental data and earlier tree-ring based evidence, where it was absolutely necessary to remove the incorrect impression given by the tree rings that temperatures between about 1960 and 1999 (when the email was written) were not rising, as our instrumental data clearly showed they were. This "divergence" is well known in the tree-ring literature and "trick" did not refer to any intention to deceive - but rather "a convenient way of achieving something", in this case joining the earlier valid part of the tree-ring record with the recent, more reliable instrumental record. I was justified in curtailing the tree-ring reconstruction in the mid-20th Century because these particular data were not valid after that time - an issue which was later directly discussed in the 2007 IPCC AR4 Report. The misinterpretation of the remark stems from its being quoted out of context. The 1999 WMO report wanted just the three curves, without the split between the proxy part of the reconstruction and the last few years of instrumental data that brought the series up to the end of 1999. Only one of the three curves was based solely on tree-ring data. The e-mail was sent to a few colleagues pointing out their data was being used in the WMO Annual Statement in 1999. I was pointing out to them how the lines were physically drawn. This e-mail was not written for a general audience. If it had been I would have explained what I had done in much more detail.