"the way this wholesale manipulation of the official temperature record – for reasons GHCN and Giss have never plausibly explained – has become the real elephant in the room of the greatest and most costly scare the world has known."
emphasis mine. To me this means that GHCN and Giss did put forward arguments as to why the data was modified, however instead of showing the reader these arguments (and why he believes them to be implausible) he simply dismisses them.
And frankly, the rest of the article is a devoid of information as the above. There is a whole lot of name-dropping, and name-calling ("James Hansen, the scientist (later turned fanatical climate activist)"), but no where does he put up any actual references or data to back-up his claims.
I do not have the time to dive into literature and dissect his points one by one (again, he does not offer any references or concrete data so that would be difficult anyway), however his song sounds very familiar. Scientists adjust their data to ignore known cyclical effects: they're manipulating the facts! Scientists don't adjust their data: they're ignoring history to suit their agenda!
And slightly off-topic, what are so many Americans doing in the comment section of a UK newspaper? And why are people ranting about Obamacare on an article about climate change?