The United States is experiencing a golden era of conspiracy theories. From the "9/11 truthers" to the "Trig birthers" to the "Obama birthers" and, most recently, the "Bin Laden deathers", alternate theories of reality are alive and thriving on the American fringes, perhaps more so than ever in the age of digital media. As Hendrik Hertzberg recently wrote in a New Yorker comment article about Donald Trump's recent championing of birtherism:

The dismaying truth is that birtherism is part of a larger pattern of rejection of reality that has taken hold of intimidating segments of one of the two political parties that alternate in power in our governing institutions. It is akin to the view that global warming is a hoax, or that the budget can be balanced through spending cuts alone, or that contraception causes abortion, or that evolution is just another theory, on a par with the theory that the earth is six thousand years old.

One group of these conspiracy theorists, however, has escaped the label – and has even succeeded in bringing its theory into the mainstream. These are the people who deny that human activity is contributing to climate change, despite overwhelming evidence to the contrary – call them the "climate truthers", for lack of a better term.

First, the facts: the US and international scientific community overwhelmingly agree that carbon dioxide emissions are triggering a slate of harmful effects on the planet. "Climate change is occurring, is very likely caused primarily by the emission of greenhouse gases from human activities, and poses significant risks for a range of human and natural systems," declared a recent report by the US National Academy of Sciences. Of course, a small percentage of scientists disagree, as is the case with, say, evolution.

Yet, unlike their counterparts, climate truthers aren't merely an irrelevant group of rabble-rousers. On the contrary, the scientific consensus is denied by the leaders of one of America's two great political parties, as well as the majority of its ideological base. John Boehner, the most powerful Republican in the country, considers the notion that carbon emissions are harming the planet "comical". In recent years, this belief has become something of a GOP litmus test, and today, it's difficult to find Republicans who accept the scientific community's view.

Climate trutherism embodies the lynchpin of most conspiracy theories: the belief that a group of influential people is coordinating a wide-ranging cover-up to advance their interests by bamboozling the rest of us. Doubting human-caused climate change requires the same paranoid logic as, say, doubting that the 9/11 attacks caught Bush officials by surprise, or that President Obama's birth certificate is authentic. But rather than believing that we're being lied to by the Bush White House or Obama's mother and the state of Hawaii, you're required to believe that we're being lied to by nearly every scientist and scientific institution in the world.

Conspiracy theories are usually traceable back to some small grain of truth, blown way out of proportion. The thinking goes something like this: George W Bush really did use 9/11 to start an unnecessary war, so he must have had a hand in the attacks. Or, Barack Obama really does look different to other American presidents, so he must be foreign. And in this case, mitigating global warming really does require government intervention in the energy industry, so it must be a leftwing, "big government" plot. What binds all these conspiracy theorists together is the belief that their ideological opponents are evil masterminds engaged in a cabal: healthy scepticism turned pathological.

There exists a somewhat tamer brand of climate trutherism, which takes a different tack: rather than attack or challenge the science head-on, its proponents merely assert that the science is unsettled. This is simply obfuscation, designed to exploit misconceptions. It's akin to saying evolution is "unsettled", on the grounds that a handful of scientists still dissent from Darwin's findings. Science always has its share of dissenters, so that's an unreasonable standard. To wit, the scientific consensus is so strong that you must either believe manmade climate change is real or you have to believe there's a massive conspiracy going on. There's hardly a third option.

So why, then, aren't climate truthers relegated to the fringes, alongside their brethren? First, climate truthers have the support of a wealthy, powerful industry dedicated to mainstreaming their theory. Second, the Republican party's anti-regulation policy agenda is threatened by the realities of climate change, so it's better to deny there's something wrong than cede that argument to their adversaries. And third – and this is why it self-perpetuates – the media like to stay in good odour with powerful politicians, so often can't quite bring themselves to pronounce one side unequivocally wrong.

But as with all other conspiracy theories, it is the media's job to call them out as wrong and resist the urge to "split the difference". If not, we'd be living in a society where 9/11 truthers and Obama birthers were legitimate sceptics, rather than outlandish people unable to come to grips with reality. Yes, it takes more courage to call out climate truthers, because some of them are very influential. But that's why it's more important – because climate change is relevant to our lives and futures in a way that the baseless speculation about Trig Palin's birthmother is not.

• Editor's note: this article as originally published used the phrase "doubting … that President Obama's birth certificate is a forgery"; this was the opposite of the author's intended meaning, and "a forgery" was amended to "authentic". This correction was made on Tuesday 31 May at 3.30pm BST (10.30am EST).