It's important that critics get things right, so as not to give the alarmists an easy out.
He was not writing in those emails about "hiding the decline" in actual measured temperatures. He was referring to a period (in the 1990's, IIRC) when measured temperatures were increasing.
The "decline" which had to be "hidden" was in the "proxy data" (from cores of long lived pine trees, again IIRC) which Jones and other alarmists favored as means of determining temperatures before measurements were available.
The "proxy" data indicated that temperatures were dropping at a time when they were actually rising. IOW, during the period when the "proxy" data could actually be compared with directly measured data, the proxy data DIDN'T FIT the measured data. Therefore the decline in the PROXY DATA had to be hidden least it become clear that the proxy data they were using (showing lower temperatures before the industrial revolution, and which also conveniently smoothed out, and all but eliminated, both the Medieval Warm Period and the Little Ice Age) were untrustworthy.
Thanks. I accept all you wrote. I should have been a bit more careful.