This cognitive dissonance takes the form of ignoring most or even all of the empirical evidence for the causes of, and the very fact of, current planetary warming.
Climate change deniers are usually lay people with no scientific training or education, and yet they claim that their denial is itself scientific, and that thousands of the world's professional scientists somehow have it all wrong. This has led to frequent reference to their 'Denial Science', and the term 'Denial Silence' is a play on these words, as well as being a subtle reference to the fact that climate change deniers would like the scientific discussion of human impact on climate to be shut down, so that no action is taken to reduce activities that lead to carbon emissions.
The 'Silence' portion of the term 'Denial Silence' is also a reference to the 'Silence' in Dr Who - a race of aliens able to edit from a human's mind any memory of ever having seen, heard or encountered these aliens, as soon as the humans are no longer able to see them. Similarly, deniers of anthropogenic global warming appear to edit from their minds any knowledge/understanding of real science as soon as they hear, read, or are otherwise informed of actual climatological/physical fact.