OK but why is he referred to as a denialist or a sceptic as opposed to a scientist with an alternate view ?
Nothing wrong with the moniker "sceptic". Anyone who lays claim to being a scientist must also be a sceptic ie demand well founded evidence for assertions of truth.
The contrarians (with at most a handful of exceptions) are not sceptics. They are deniers because they refuse to examine the mountain of evidence that the climate is warming and that greenhouse gases emitted due to human activity are the main driver. Instead they fixate (at best) on a single scientific paper holding it to undermine decades of research by hundreds of scientists. Even when such papers are thoroughly debunked, the deniers still cling to them, not because of any intrinsic merit in the publication, but because they think they can use them to uphold their ideology.
In this way they are no different from those who deny the causative connection between HIV and AIDS.
how can you be so sure that the scientists or climatologists view that you agree with is emphatically correct ?
Because the evidence is overwhelming.
This assertion is well supported by the fact that 97% of scientists actively publishing climate related research agree with the proposition that the planet is warming and humans are responsible. Furthermore every national science academy, scientific society and professional association of international standing that has issued a public position asserts the reality of AGW. None dispute it. We could add to that list the World Meteorological Organization and most national met offices. And there are yet more. Australia's CSIRO (one of the oldest and largest research organizations in the world) also emphatically states that AGW is very real.
There has been myth foisted onto the public that there is a major scientific disagreement about the reality of AGW. There is not.
But don't take my word for it. Go and have a look at what the real science is saying:
http://www.skepticalscience.com/More-evidence-than-you-can-shake-a-hockey-stick-at.html
or the NOAA 2009 State of the Climate report compiled by 300 scientists from 48 countries:
http://www.noaanews.noaa.gov/stories2010/20100728_stateoftheclimate.html