* 1. Allege that there's a conspiracy. Claim that scientific consensus has arisen through collusion rather than the accumulation of evidence.
* 2. Use fake experts to support your story. "Denial always starts with a cadre of pseudo-experts with some credentials that create a facade of credibility," says Seth Kalichman of the University of Connecticut.
* 3. Cherry-pick the evidence: trumpet whatever appears to support your case and ignore or rubbish the rest. Carry on trotting out supportive evidence even after it has been discredited.
* 4. Create impossible standards for your opponents. Claim that the existing evidence is not good enough and demand more. If your opponent comes up with evidence you have demanded, move the goalposts.
* 5. Use logical fallacies. Hitler opposed smoking, so anti-smoking measures are Nazi. Deliberately misrepresent the scientific consensus and then knock down your straw man.
* 6. Manufacture doubt. Falsely portray scientists as so divided that basing policy on their advice would be premature. Insist "both sides" must be heard and cry censorship when "dissenting" arguments or experts are rejected.