So how can people's hearts be failing them for fear while they're cheerfully and complacently saying, "Peace and safety?" That's how despair works, and how people's hearts fail them for fear. The symptom of this kind of heart failure is not despondency, in which at least you're facing the bad news. Real despair is expressed in denial. The heart truly fails, losing the power to face and think about the real problems despaired of.
Thus Christians are told not to grieve as those do that have no hope. And how do such people grieve? They cheerfully affirm that the one who died is in a better place, looking down on us from heaven, and all sorts of other happy dreck like that, even when there is no ground at all for such optimism.
This kind of cheerful despair is especially prevalent in supposedly Christian churches. So-called "positive thinking" is actually taught, the same positive thinking taught by the false prophets when the armies of Babylon were laying siege to Jerusalem in the days of Jeremiah - and we know how that positive thinking worked out.
For real faith, the issue is not positive or negative thinking. It's about receiving the love of the truth, and about being damned if you don't receive it, which is in fact the only way anybody is damned (2 Thessalonians 2:9-12).
So the denial of climate change, and people kidding themselves that the US is about to become energy-independent through things like oil shale, and that we can have an ever-expanding economy in a finite world - the pursuit of such fairy tales is despair. Their denial is simply their hearts failing, unable even to think about these things that need to be thought about - and prayed about too. Their unbelief shows up as brazen professions of "faith." I don't know how to cure this sickness, but I know that naming it is a start.