Likely he had hoped no one would notice while also giving the appearance that the "usual suspects" (i.e. Singer et al.) are not the only ones still doubting AGW.

It gives the illusion that the so-called "science" they are conducting is still new and evolving and being taken seriously by other scientists (who don't have a controversial reputation).

It is also the power in numbers argument - try to give the impression that there are a lot of people out there with authority who doubt AGW when in fact there are only a handful.

It seems a pretty desperate act and one would hope is a sign that the denial machine is crumbling fast - however, unfortunately the ridiculous antics of the denialists are nothing new.

to their credit, heartland did resist the urge to add drs hugh jarse and i p freely to their list....

KEvron

Perhaps it's me just having missed something, but has Dennis Avery or the Heartland Institute actually explained precisely how a dead scientist can Dennis become a co-author? Surely being a co-author implies some degree of active involvement, which would seem precluded somewhat by 'co-authors' being dead.

For a start, why did he not also include other famous scientists like Albert Einstein, Richard Feynman, Galileo Galilei, Aristotle,..,? The list is effectively almost endless.

Of course a competent author would have needed to consider carefully the facts and chronology of the discovery of climate change, but bearing in mind Avery's apparent strong tendency to display a Crightonesque approach to science, so perhaps not.

So is it an honest mistake? - Clearly no.
Is it deliberate dishonesty? - It definitely looks like it. Dennis Avery's apparent dishonesty, says a great deal about the accuracy of the 'science' that he was trumpeting.

From the Dictionary of Mendacity
Definition of 'Crightonesque'
A cavalier disregarding of facts in the utter determination to prove an ideologically predetermined conclusion that is entirely unsupported by any available or cited peer-reviewed scientific evidence.. Often involves citing as evidence, scientists' work that does not support the proposition.

Background
[Origin eponymous – after Michael Crichton, author of popular low fiction, often using pseudo-scientific and fallacy-ridden arguments to disseminate the author's political views, with a view to misleading the public into believing that climate science has been subverted by a world-wide conspiracy. The facts reveal there is a documented conspiracy to undermine climate science, but the evidence available shows that it is funded by the fossil fuel industry through think-tanks and intermediaries, who expect to lose-out through carbon taxes and diminishing sales.]