EDIT: Be cause I wrote the above in anger
Scientists have been sounding the alarm for as long as I have lived. They have consistently used the most optimistic scenarios and we have constantly done worse than that. Climate Deniers want to deny because the reality is an inconvenience to their ways of life. The costs of climate denial are diffuse; they can't be directly traced back to me. The benefits are acute and wholly captured by me. Add on to this that contribution toward climate change is disproportionately done by wealthier people and you get the most powerful people, who benefit the most from climate denial, trying to get others to deny with them.