My approach to denialists has long been a simple question:
What is the minimum evidence you require to accept that human activities are driving global warming?
This is a question that any person committed to scientific scepticism must ask herself.
However, no denialist has ever dared to answer this question.
One may conclude, therefore, that those declining to provide an answer to this simple question are not interested in, or perhaps feel threatened by, scientific thinking. Were denialists mere sceptics, they would answer these questions. Their refusal to answer these questions identifies them as denialists.
To be fair to denialists, I should provide the minimum evidence for me to cease to give credence to AGW:
1. That CO2 is not as potent a greenhouse gas as mainstream scientists have measured and have reported in refereed journals.
2. That human contribution to terrestrial CO2 concentrations are much less than has been measured by mainstream scientists, as reported in refereed journals.