The favorite argument of catastrophists in taking on skeptics is "all skeptics are funded by Exxon." Such ad hominem rebuttals to skeptics are common, such as…
…comments like those of James Wang of Environmental Defense, who says that scientists who publish results against the consensus are “mostly in the pocket of oil companies”; and those of the, yes, United Kingdom’s Royal Society that say that there “are some individuals and organisations, some of which are funded by the US oil industry, that seek to undermine the science of climate change and the work of the IPCC”
and even from the editor of Science magazine:
As data accumulate, denialists retreat to the safety of the Wall Street Journal op-ed page or seek social relaxation with old pals from the tobacco lobby from whom they first learned to "teach the controversy."
Here is my thought on this subject. There is nothing wrong with mentioning potential biases in your opponent as part of your argument. For example, it is OK to argue "My opponent has X and Y biases, which should make us suspicious of his study. Let’s remember these as we look into the details of his argument to see his errors…" In this case, pointing to potential biases is an acceptable first argument before taking on issues with the opponent’s arguments. Unfortunately, climate catastrophists use such charges as their last and only argument. The believe they can stick the "QED" in right after the mention of Exxon funding, and then not bother to actually deal with the details.
Postscript: William Briggs makes a nice point on the skeptic funding issue that I have made before:
The editors at Climate Resistance have written an interesting article about the “Well funded ‘Well-funded-Denial-Machine’ Denial Machine”, which details Greenpeace’s chagrin on finding that other organizations are lobbying as vigorously as they are, and that these counter-lobbyists actually have funding! For example, the Competitive Enterprise Institute, a think tank “advancing the principles of free enterprise and limited government”, got, Greenpeace claims, about 2 million dollars from Exxon Mobil from 1998 to 2005. The CEI has used some of this money to argue that punitive greenhouse laws aren’t needed. Greenpeace sees this oil money as ill-gotten and say that it taints all that touch it. But Greenpeace fails to point out that, over the same period, they got about 2 billion dollars! (Was any of that from Exxon, Greenpeace?)
So even though Greenpeace got 1000 times more than the CEI got, it helped CEI to effectively stop enlightenment and “was enough to stall worldwide action on climate change.” These “goats” have power!
Most skeptics are well aware that climate catastrophists themselves have strong financial incentives to continue to declare the sky is falling, but we don’t rely on this fact as 100% or even 10% of our "scientific" argument.