The 1970's were a time of many such catastrophic prophecies. Neo-Malthusian Paul Ehrlich predicted that a "population bomb" would overwhelm the planet within decades unless radical changes were made:
Nuclear power, once synonymous with military supremacy and clean energy, became a symbol of destruction and something to be feared. Carl Sagan wondered if self-annihilation was the fate of most technologically advanced species.
Against this backdrop, Hanso partnered with the DeGroots to construct the Dharma Initiative, a prototype community devoted to studying life in the aftermath of planetary catastrophe. Participants were quarantined in underground bunkers, and conditioned to perform certain tasks on faith. The plan may have been to include the "special" among them in a Platonic community of the future.
Several clues suggest a preoccupation with catastrophism. Some have speculated that the 108-minute countdown in Swan Hatch downloads information from an orbiting satellite about the Earth's magnetic fields . I think that's partly right -- there is no actual satellite but the countdown does condition occupants for a time when there might be.
Another clue is the print log Eko and Locke discovered in Pearl Hatch. Some have suggested that the print-log numbers imply a time range of close to 5,000 years. I don't think the countdown has been running that long, but I suspect the period itself is significant. Many believe that planetary catastrophes tend to occur cyclically about every 5,000 years.
One popular catastrophic scenario involves cometary bombardment. Many have noted that the first Hanso Foundation logo looked uncomfortably like a swastika. Carl Sagan speculated that this ancient symbol may originally have been inspired by a comet that approached earth so closely that "arms" of gas, bent by the comet's spin, were visible worldwide.
As proof, Sagan cites an ancient Chinese manuscript depicting various comet tails:
Interestingly, the swastika is linked with the Hanso Foundation's subsequent emblem of the yin yang. Both appear on the famous Falun Emblem, which is said to depict the universe in miniature.
And therein lies a possible clue to what happened to Dharma. The swastika represents the Buddha School, while the yin yang represents the Tao. I don't pretend to understand the difference, but it could suggest a change in outlook or philosophy on Hanso's part. My guess is he became increasingly preoccupied with playing Grand Inquisitor, and forging the master race, prompting and the Dharma scientists to have second thoughts.
ETA: I've edited to add a pic of Carl Sagan and a quote from Paul Ehrlich's book Population Bomb. Notice the similarity between the latter and the notation on the Blast Door Map that the cure is worse than the disease.