Why do they do this?

Al Gore--and indeed the entirety of human scientific endeavor--is alarmist:
This is the second doomsday scenario of recent decades, the first being the Club of Rome's prediction in 1972 that the world would soon run out of natural resources. Both are "scientific," but their structure is the same as that of the biblical story of the Flood: human wickedness (in today's case, unbridled materialism) triggers the disastrous sequence, which it may already be too late to avert. Like biblical prophecy, scientific doomsday stories seem impervious to refutation and are constantly repackaged to feed the hunger for catastrophe.

Scientists argue that the media and politicians are responsible for exaggerating their findings as promises of salvation or warnings of retribution. But scientists themselves are partly responsible, because they have hardened uncertainties into probabilities, treated disputable propositions as matters of fact, and attacked dissent as heresy.

Scientists are notoriously loath to jettison conclusions reached by approved scientific methods, however faulty. But their intolerance of dissent is hugely magnified when they see themselves as captains in the salvationist army, dedicated to purging the world of evil habits.
Therefore, we should fear this apocalyptic alarmism:
Today it is the West that foists an apocalyptic imagination on the rest of the world. The best antidote to the doom merchants is skepticism. We must be willing to take uncertainty seriously. Climate change is a fact. But apocalyptic thinking distorts the scientific debate and makes it harder to explain the causes and consequences of this fact, which in turn makes it harder to know how to deal with it.

The danger is that we become so infected with the apocalyptic virus that we end up creating a real catastrophe - the meltdown of our economies and lifestyles - in order to avoid an imaginary one. In short, while a religious attitude of mind deserves the highest respect, we should resist the re-conquest by religion of matters that should be the concern of science.
Doesn't anyone writing these articles realize it makes no sense to simultaneously impugn one set of predictions--climate change could really suck--as alarmist by invoking alarmist--the meltdown of our economies and lifestyles--predictions?