First off, they failed to engage. Instead. they resorted to name calling by labeling skeptics as “deniers” or worse. Then there is their exaggeration of what they see as the dire consequences of climate change. These exaggerations have led them to falsely predict that New York City would be under water and that the polls would be ice free. When that did not happen people like Al Gore lost credibility.
Fundamentally their “scientific” projections have been deeply flawed grossly overestimating the consequences of increased CO2. One of the principals of projections is that when they failed to be realized it is because they relied on invalid assumptions. This is true of financial projections and scientific projections.
In the case of the projections of the consequences of climate change, I suspect that they are overestimating the impact of CO2 on global temperatures. One reason I believe that is because they struggle to explain why they got it wrong and they do not want to admit which of their assumptions is invalid.
There is also the hysteria on the left when their beliefs are rejected. It is almost like the response of radical Islamist to the rejection of Islam. They act like the rejection of their point of view is blasphemy rather than an argument to overcome.
I think there is also the suspicion that the real objective of the left is to institute control freak government and climate change is their latest excuse for doing so since communism has been rejected.
To be fair, “failure to engage” can occur for two reasons. It may be because those who don’t engage are wrong, or because they’re right and have forgotten what Eugenie Scott has said about discussing evolution: “We’re educating a parade”.
Yes, if you have the facts in order, you may have to keep teaching them to each next person. And if you throw a fit and refuse to teach, you run the risk of looking like you don’t have anything to teach.