"Warming of the climate system is unequivocal." "Anthropogenic drivers...are extremely likely to have been the dominant cause of the observed warming since the mid-20th century." - IPCC, AR5, 2013-2014
But that doesn't stop internet trolls from denying the science. We've discussed here before how there are professional denialists (lobbyists, their front groups, and their spokespeople) and amateur denialists (mostly ideologically and willfully ignorant people). The professional deniers seed the internet with falsehoods and count on the amateur deniers to plagiarize ad nauseam, thus saturating the blogosphere with crap. Amateurs do this without employing any skepticism of their sources or veracity of what they plagiarize; they gladly accept whatever idea agrees with their predefined narratives no matter how obviously ludicrous the talking point.
Let's take a quick look at some of the tactics used by amateur deniers on social networking sites, in particular, Facebook.
1) Deny: Obviously. Just deny all the science. Deny 100+ years of well-understood basic physics. Deny 100,000+ peer-reviewed published papers. Deny millions of data points. Deny all the world's climate scientists know the science they study. Deny all of this has reached a burden of proof. Deny the consensus. Deny, well, you get the idea. Deny everything. Rinse, Repeat.
When someone simply denies all the evidence, they are a denier by definition.
2) Lie: The repetition of falsehood is a primary tactic of climate deniers. Lie about the "hockey stick." Lie about the "pause." Lie about what scientists say. Lie about "climategate." Lie about even the dates of the reports. Lie about what other commenters say. A variant of this is to ignore all evidence presented by commenters; simply make believe it wasn't said. Then repeat the falsehood already debunked. Lying can also take the form of generally commenting dishonesty, for example, creating a strawman and harassing other commenters over and over to answer the strawman.
When someone chooses to comment with such dishonesty, you can understand their self-deceit.
3) Spam: Many commenters will simply spam the post with dozens of comments. Any reply gets not one response, but a series. Spammers leave multiple comments even when no one is talking to them. Their goal is to saturate the blog such that honest commenters choose not to participate. It's also a form of violence; spamming multiple comments is like beating someone with a stick over and over. Spammers are easily recognizable not just by their multiple comments in a row, but by the fact that they quickly come back to spam again if their target leaves a response even a day later.
Besides being a form of violence and harassment, it's a sign of mental insecurity, and in some cases, mental instability. It's also a trolling strategy taught by the Koch lobbying organizations to disrupt online discussions.
4) Non-Awareness of Ignorance: There is nothing more embarrassing to see than someone who repeatedly shows their shortcomings.
Most amateur deniers don't even understand how little they understand. Ironically, they believe they understand more than the scientists who study the science.
5) Reliance on Lobbyist Sources: Invariably, amateur deniers will cite lobbyist sources instead of scientific sources (assuming they bother to cite any source at all). Amateurs have convinced themselves (and lobbyists have trained them to believe) that all scientists are corrupt and part of a multigenerational global conspiracy and "Al Gore!" (Deniers usually find a way to insert Al Gore into the discussion; the name is like a bell to Pavlov's dogs). So to replace 100+ years of science, deniers rely on a series of blogs funded, supported, and seeded by lobbyists, their front groups, their spokespeople, and other conspiracy, scam, or ideologically motivated non-scientists.
If someone is citing WUWT, Climate Depot, Heartland, Laframboise, JoNova, and a slew of other non-science, lobbyist-supported, propaganda blogs, you know they haven't bothered to learn about the science. Each of these, and all their offshoots, have been shown to be wrong. Every single time. Every article or post is easily debunked, and most are simply recycling of older talking points that have been debunked many many times before. Often these blogs are so egregiously wrong it is hard to understand how any sentient being would put any weight in anything they say. But this is who deniers rely on.
Meanwhile, these same deniers dismiss NASA, NOAA, IPCC, NSIDC, and every other scientific organization as somehow incapable of understanding the science they've been researching and publishing for decades. And yet when they find it convenient, deniers will claim they are citing NASA (two breaths after calling NASA corrupt) - except they don't really cite NASA, they cite a lobbyist blog that has manipulated NASA data and/or fabricated a conclusion that isn't supported by the evidence and is often the opposite of what NASA actually said. [See #2 Lying]
Mostly these deniers are trolls. They choose not to learn, and never will. Interacting with them is mostly a waste of time, with the only exception being that when they go into spamming mode they tend to reinforce Facebook's positive feedback algorithms (think in terms of climate science and you know what I mean).
So be aware of the tactics of climate deniers, both the professionals and the amateurs. But don't waste effort on them because they are there largely to convince themselves they aren't as inconsequential as they actually are. It's sad, but it's true.
The rest of us can focus on communicating the science to the public.