He's bleeding from sores all across his body. His skin is a dark yellowy green. His hair is flaking off in chunks. He coughs and blood sprays out. He tells the doctor that every time he tries to go to the toilet he's conspitated and sometimes blood comes out. The doctor takes his temperature and it's a whopping 105F.
The doctor looks alarmed, and says "Honestly, I think you're very ill. Let's get you into the ER."
At that moment, a heroic skeptic bursts through the window.
"Hang on a minute doctor", he says, "how can you be sure that he's ill? Correlation does not mean causation. Just because he's burning up, bleeding, flaking, discoloured and limping does not mean he is necessarily ill."
"Well", says the doctor, "I am a doctor and that's my opinion so far, but it doesn't take a doctor to see this man needs to be treated as an emergency. I mean, just look at him."
"The arrogance of so-called professionals", opines the skeptic. "If you were a true scientist, you would prove it. And just because you are a doctor does not mean you are automatically right. This man may be a conman, and these symptoms may be entirely false."
The doctor has to admit this is technically true, and she was going to investigate it further anyway, so she takes the man away and performs a series of tests. She performs an MRI scan, CT scan, X-rays, a colonoscopy, a sigmoidoscopy, a few blood tests, urine and stool samples and checks the patient visually for any further symptoms. She passes the results to her team of 10 specialists who evaluate the output and provide a diagnosis.
The doctor returns to the skeptic. "We've had a look at the results and have concluded that we think he is indeed, Extremely Very Ill."
The skeptic is unconvinced. "But just a minute, what do you mean you think? You mean you don't know for sure?"
"Well we can never really be totally sure, and there was some disagreement, but that is our general consensus after all the test results from various equipment designed to measure this sort of thing."
"Ah", the skeptic smiles. "So in other words, you made assumptions? You didn't prove in your experiments that the machines also work, that they perform the exam accurately and conclusively? And further, your team didn't totally agree?"
"We disagree on particulars. For example I and 7 other of my colleagues give the patient 2 days if he doesn't get treatment immediately. A couple of my colleagues expect he'll live as much as a week. And there's that one guy who reckons it will probably clear up by itself. And we don't have time or the resources to prove these machines were correct, but they have always been correct before."
The skeptic leans back triumphantly. "So in other words, you really don't know for sure, there is no consensus, you haven't proven anything, and you're relying on past data to inform what is currently happening now. And finally one of your colleagues – as much a doctor as you are – thinks it's not a big deal?"
The skeptic turns to the man, "You can go home now. They don't have proof that you're ill."
The doctor, even more alarmed, jumps in. "Now listen, this is ridiculous. There's a very small chance that he's fine. And if he is fine, then the worst that will happen is he'll have to stay in hospital for a bit and get poked with needles. But if we're right, then if he walks out that door he's going to die. You can look at the charts! Just look at the charts! I'm a doctor for Christ's sake!"
"Doctor, I'm sorry but we're done here, and your intellectual elitism isn't helping. Your dubious data won't convince me of anything since you already admitted that you don't have a true consensus. But I tell you what – if he dies I'll concede that you happened to be correct."
And so now we all understand climate change scepticism.